THE ANATOMY 



OF THE 



DOMESTIC ANIMALS 



10 



SEPTIMUS SISSON, S.B., V.S. 

PROFESSOR OF COMPARATIVE ANATOMY IN THE OHIO STATE UNIVERSITY, COLUMBUS. OHIO 

MEMBER OF THE AMERICAN ASSOCIATION OF ANATOMISTS 

FELLOW OF THE AMERICAN ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE 



WITH 725 ILLUSTRATIONS 
MANY IN COLORS 



SECOND EDITION, ENTIRELY RESET 



PHILADELPHIA AND LONDON 

W. B. SAUNDERS COMPANY 

1914 






Copyright, 1910, by W. B. Saunders Company 



Reprinted June, 1911 
Revised, Entirely Reset, Reprinted 

AND ReCOPYRIGHTED SEPTEMBER, 1914 



Copyright, 1914, by W. B. Saunders Company 



^ly^^ 



)GI.A;j794(j9 

SfP \2 1914 



TO 

MY WIFE 
KATHERINE OLDIL\M SISSON 

IN GRATEFUL RECOGNITION OF CONSTANT INSPIRATION 
AND ENCOURAGEMENT 



PREFACE 

This book supersedes the author's Text-book of Veterinary Anatomy. A 
comparison of the two will show the new title to be justified by the extent and 
character of the changes which have been made. 

The number of illustrations has been increased from 588 to 725. More than 
three hundred new and original figures have been prepared. Nearly all of these 
are reproductions of photographs, most of which were taken by the author. The 
preparation of the prints for reproduction has been executed by Mr. W. J. Norris 
with unusual care and skill. 

Continued observations of well-hardened material and frozen sections have led 
to a considerable number of modifications of statement. It is scarcely necessary 
to say that the recent literature, so far as available, has been utilized. 

Many changes in nomenclature have been made. Most of the synonyms have 
been dropped or relegated to foot-notes. Exceedingly few new names have been 
introduced. Nearly all eponyms have been eliminated, on the ground that they 
are not designative and are usually incorrect historically. The changes made in 
this respect are in conformity with the report of the Committee on Revision of 
Anatomical Nomenclature which was adopted by the American Veterinary Med- 
ical Association two years ago. Progress in the direction of a simplified and uni- 
form nomenclature is much impeded by the archaic terminology which persists to 
a large extent in clinical literature and instruction. 

The author is under special obligation to Professors Ellenberger, Baum, and 
Schmaltz, and to their publishers, for permission to use or to copj' figures from 
their excellent works. Their generosity in this matter has been of great value to 
those who arc unable to use the German literature. A few illustrations have been 
taken from other sources and credit has been given in each case. 

For hel]iful suggestions and for assistance in the reading of the proof-sheets 
the author is much indebted to his colleague, Dr. F. A. Lambert. 

Great credit is due the publishers for their determination to spare neither 
pains nor expense in attaining a high degree of typographical excellence. 

Septimus Sisson 
The Ohio State University, Columbus, Ohio. 
September, 1914. 



PREFACE TO THE FIRST EDITION 

The lack of a modern and well-illustrated liook on the structure of the princi- 
pal domestic animals has been acutely felt for a long time by teachers, students, 
and practitioners of veterinary medicine. The work here offered is the expression 
of a desire to close this gap in our literature. 

The study of frozen sections and of material which has been hardened bj^ intra- 
vascular injection of formalin has profoundly modified our views concerning the 
natural shape of many of the viscera and has rendered possible much greater pre- 
cision in topographic statements. The experience of the author during the last 
ten years, in which almost all of the material used for dissection and for frozen 
sections in the anatomical laborator.y of this University has been hardened with 
formalin, has demonstrated that many of the current descriptions of the organs in 
animals contain the same sort of errors as those which prevailed in regard to similar 
structures in man previous to the adoption of modern methods of preparation. 

While the method of treatment of the subject is essentially systematic, topog- 
raphy is not by any means neglected either in text or illustrations; it is hoped that 
this will render the book of value to the student in his cUnical courses and to 
the practitioner. Embryological and histological data have been almost entirely 
excluded, since it was desired to offer a text-book of convenient size for the student 
and a work of ready reference for the practitioner. It is believed that the use of 
black type for the names of important structures and of small print for certain 
details or matter of secondary importance will prove useful in this respect. 

Veterinary anatomical nomenclature is at present quite chaotic in English- 
speaking countries. In this work an attempt is made to eliminate some terms 
which do not appear to the author to fulfil any useful purpose, and others which are 
clearly erroneous or otherwise undesirable. In many cases the terms agreed upon 
by the Congres.ses at Baden and Stuttgart are adopted either in the original Latin 
or in anglicized form; otherwise these terms are added in parenthesis. The 
author favors the substantial adoption of this terminology, but considered it 
desirable to offer a sort of transitional stage at present. 

The original illustrations are chiefly reproductions of photographs, many of 
which were taken by Mr. F. H. Haskett. The preparation of the pictures for 
reproduction was carried out by Messrs. J. V. Alteneder and W. J. Xorris. The 
author takes pleasure in expressing his appreciation of the care and .skill exercised 
bj' these gentlemen in this often difficult task. 

The author is under great obligation to Professors Ellenberger and Baum in 
Dresden, to Professor Schmaltz in Berlin, and to their publishers for permission to 
use or to copy figures from their most excellent works. Their generosity in this 
matter has made it possible to supply this text with a larger number of high-class 
illustrations than is to be found in any other. A few figures have been taken from 
other sources, and proper credit has been given in each case. 

For checking over certain data and for assistance in the correction of the proofs 
the author is much indebted to his associate. Dr. F. B. Hadley. 

The author desires to express his high appreciation of the determination and 
constant effort of the publishers to do all in their power to render the book worthy 
of favorable reception by the profession for whom it is intended. 

Ohio State University, Columbus, Ohio Septimus Sisson. 



CONTENTS 



INTRODUCTION 

OSTEOLOGY page 

The Skeleton 20 

Structure of Bones 21 

Development and Growth of Bone 23 

Composition and Physical Properties of Bone 24 

Descriptive Terms 25 

The Vertebral Column 25 

The Ribs and Costal Cartilages 27 

Costal Cartilages 27 

The Sternum 28 

The Thorax 28 

The Skull 28 

Bones of the Thoracic Limb 29 

Bones of the Pelvic Limb 30 

Skeleton of the Horse 32 

Vertebral Column 33 

Ribs 45 

Sternum 48 

Bones of the Skull 49 

Cranium 49 

Face 63 

The SkuU as a Whole 73 

The Cranial Cavity 81 

The Nasal Cavity 82 

The Paranasal Sinuses 84 

Bones of the Thoracic Limb 86 

Bones of the Pelvic Limb 105 

Skeleton op the Ox 125 

Vertebral Column 125 

Ribs 130 

Sternum 131 

Bones of the Skull 131 

The Skull as a Whole 140 

Bones of the Thoracic Limb 145 

Bones of the Pelvic Limb 151 

Skeleton of the Sheep 156 

Vertebral Column 156 

Ribs 156 

Sternum 157 

Skull •. 157 

Bones of the Thoracic Limb 160 

Bones of the Pelvic Limb 160 

Skeleton op the Pig 161 

Vertebral Column 161 

Ribs 165 

Sternum 166 

Bones of the Skull 166 

The Skull as a Whole 173 

11 



12 CONTENTS 

PAGE 

Bones of the Thoracic Limb 176 

Bones of the Pelvic Limb 180 

Skeleton of the Dog 184 

Vertebral Column 184 

Ribs 188 

Sternum 188 

Bones of the SkuU 188 

The SkuU as a Whole 195 

Bones of the Thoracic Limb 197 

Bones of the Pelvic Limb 202 

ARTHROLOGY 
Synarthroses 207 

DiARTHROSES 208 

A.mphiarthroses 210 

Articulations of the Horse 211 

Joints and Ligaments of the Vertebra: 211 

Atlanto-occipital Articulation 214 

Costo-vertebral Articulations 215 

Costo-chondral Articulations 216 

Chondro-sternal Articulations 216 

Sternal Joints and Ligaments 217 

Articulations of the Skull 217 

Articulations of the Thoracic Limb 218 

Articulations of the Pelvic Limb 229 

Articulations of the Ox, Pig, and Dog 244 

MYOLOGY 

The Muscles and Accessory Structures 252 

Fasci.id and Muscles of the Horse 254 

Fasciae and Muscles of the Head 255 

Fasciae and Muscles of the Neck 266 

Fasciae and Muscles of the Back and Loins ;. 276 

Fasciae and Muscles of the Tail 279 

Muscles of the Thorax 281 

Abdominal Fasciae and Muscles 287 

Muscles of the Thoracic Limb 293 

Fascise and Muscles of the Pelvic Limb 317 

Muscles of the Ox 343 

Muscles of the Pig 359 

Muscles of the Dog 368 

SPLANCHNOLOGY 

Digestive System of the Horse 385 

The Mouth 385 

The Tongue 390 

The Teeth 394 

The Salivary Glands 404 

The Pharynx 405 

The (Esophagus 409 

The Abdominal Cavity 410 

The Peritoneum 411 

The Pelvic Cavity 412 

The Stomach 415 

The Small Intestine 419 

The Large Intestine 422 

The Pancreas 432 

The Liver 434 



13 



The Spleen 439 

The Peritoneum 441 

Digestive System of the Ox 444 

Digestive System op the Sheep 470 

Digestive Sy'stem of the Pig 477 

Digestive System of the Dog 491 

THE RESPIRATORY SYSTEM 

Respiratory System of the Horse 508 

The Nasal Cavity 508 

The Larynx 614 

The Trachea 523 

The Bronchi 525 

The Thoracic Cavity .■ 525 

The Pleura; , 526 

The Lungs ' 530 

The Thyroid Gland of the Horse 535 

The Thymus of the Horse 536 

Respiratory System of the Ox 537 

Respiratory System of the Pig 545 

Respiratory System of the Dog 548 

THE UROGENITAL SYSTEM 

Urinary Organs of the Horse 554 

The Kidneys 554 

The Ureters 561 

The Urinary Bladder 561 

The Adrenal Bodies ; ^ 563 

Urinary' Organs of the Ox 564 

LTrinary Organs of the Pig 567 

Urinary Organs of the Dog 569 

THE MALE GENITAL ORGANS 

Genital Organs of the Stallion 571 

The Testicles 571 

The Scrotum 574 

The Ductus Deferens 575 

The Spermatic Cord 575 

The Tunica Vaginalis 576 

Descent of the Testicles 577 

The Vesiculae Seminales 578 

The Prostate 578 

The Uterus MascuUnus 579 

The Bulbo-urethral Glands 579 

The Penis 580 

The Prepuce 582 

Genital Organs op the Bdll 586 

Genital Organs op the Boar 591 

Genital Organs op the Dog 593 

THE FEMALE GENITAL ORGANS 

Genital Organs of the Mare 596 

The Ovaries 596 

The Uterine or Fallopian Tubes 599 

The Uterus 599 

The Vagina 602 



14 CONTENTS 

FAOB 

The Vulva 603 

The Urethra 604 

The Mammary Glands 604 

Genital Organs of the Cow 605 

Genital Organs of the Ewe 609 

Genital Organs of the Sow 610 

Genital Organs of the Bitch 612 

ANGIOLOGY 

General Considerations 614 

The Organs of Circulation 614 

Blood-vasctilar System of the Horse 617 

The Pericardium 617 

The Heart 617 

The Puhnonary .\rtery 629 

The Systemic Arteries 629 

The Coronary Arteries 630 

Common Brachiocephalic Trunk 631 

Arteries of the Thoracic Limb 650 

Branches of the Thoracic Aorta 660 

Branches of the Abdominal Aorta 661 

Arteries of the Pelvic Limb 673 

The Veins 681 

The Pulmonary Veins 681 

Cardiac Veins 681 

The Anterior Vena Cava and its Tributaries 682 

The Posterior Vena Cava and its Tributaries 692 

The Lymphatic System 697 

The Thoracic Duct 697 

The Right Lymphatic Duct 698 

The Lymph Glands and Vessels of the Head and Neck 698 

The Lymph Glands and Vessels of the Thorax 700 

The Lymph Glands and Vessels of the Abdomen and Pelvis 701 

The Lymph Glands and Vessels of the Thoracic Limb 703 

The Lymph Glands and Vessels of the Pelvic Limb 703 

The Fcetal Circulation 704 

Blood-vascular System of the Ox 705 

The Pericardium and Heart 705 

The Arteries 706 

The Veins 719 

Lymphatic System of the Ox and Sheep 722 

Circulatory System of the Pig 734 

The Pericardium and Heart 734 

The Arteries 736 

The Veins 740 

Lymphatic System 740 

Circulatory System of the Dog 742 

The Pericardium and Heart 742 

The Arteries 744 

The Veins 754 

Lymphatic System 766 

NEUROLOGY.— THE NERVOUS SYSTEM 

General Considerations 760 

Nervous System of the Horse 764 

The Spinal Cord 764 

The Brain 768 



CONTENTS 15 

PAGE 

The Cranial Nerves 793 

The Spinal Nerves 810 

Sympathetic Nervous System op the Horse 829 

Nervous System op the Ox 834 

Nervous System of the Pig 843 

Nervous System of the Dog 847 

.ESTHESIOLOGY 

The Sense Organs and Common Integument of the Horse 857 

The Eye 857 

The Ear 870 

The Conimon Integument 884 

The Ergot and Chestnut 895 

The Olfactory and Gustatory Apparatus 895 

The Sense Organs and Common Integument of the Ox 896 

The Sense Organs and Common Integument op the Pig 900 

The Sense Organs and Common Integument of the Dog ■ 902 



Index 907 



THE ANATOMY OF THE DOMESTIC ANIMALS 



INTRODUCTION 

Anatomy is the branch of liiological science whicli deals with the form and 
structure of organisms, Ijoth animal and vegetal. It is therefore in close correlation 
with physiology, which treats of the functions of the body. 

Etymologically the word "anatomy" signifies the cutting apart or disassociat- 
ing of parts of the body. In the earlier phases of its development anatomy was 
necessarily a purely descriptive science, based on such observations as were possible 
with the unaided eye and simple dissecting instruments — the scalpel, forceps, and 
the like. At this time, therefore, the term adequately expressed the nature of the 
subject. But as the scope of the science extended and the body of anatomical 
knowledge grew, subdivisions became necessary and new terms were introduced to 
designate special fields and methods of work. With the introduction of the mi- 
croscope and its accessories it became possible to study the finer details of structui'e 
and minute organisms hitherto iniknown, and this fielil of inquiry rajiidly developed 
into the science of microscopic anatomy or histology as conventionally distingnislied 
from macroscopic or gross anatomy. In the same way the study of the changes 
which organisms untlergo tluring their development soon attained sufficient im- 
portance to be regartled on practical grounds as a separate branch kno^vn as 
embryology.' 

Comparative anatomy is the description and comparison of the structure of 
animals, and forms the basis for their classification. By this means — including 
extinct forms in the scope of inquiry — it has been possible to show the genetic 
relationship of various groups of animals and to elucidate the significance of many 
facts of structure which are otherwise quite obscure. The deductions concerning 
the general laws of form and structure derived from comjjarative anatomical 
studies constitute the science of morphology or philosophical anatomy. The 
morphologist, however, deals only with such anatomical data as are necessary to 
form a basis for his generalizations. The anatomical knowledge required in the 
practice of medicine and surgery is evidently of a different character and must 
include many details which are of no particular interest to the morphologist. 

Special anatomy is the description of the structure of a single type or species, 
e. g., anthropotonn', hippotomy. 

Veterinary anatomy is the branch which deals with the form and structure of 
the principal domesticated animals. It is usually pursued with regard to pro- 
fessional requirements, anil is therefore largely descriptive in character. As a 
matter of convenience, the horse is generally selected as the type to be studied in 
detail and to form a basis for comparison of the more essential diff'erential characters 
in the other animals. 

Two chief methods of study are employed — the systematic antl the topo- 
graphic. In the former the body is regarded as consisting of systems of organs or 

' This term is usually limited in its application to the earlier phases of development during 
which the tissues and organs are formed. The term ontogeny is used to designate the entire 
development of the individual. The ancestral history or phylogeny of the species is constituted 
by the evolutionary changes which it has undergone as disclosed by the geological record. 
2 17 



18 INTRODUCTION 

apparatus which are similar in origin and structure and are associated in the per- 
formance of certain functions. The divisions of systematic anatomy are: 

1. Osteology, the description of the Skeleton. 

2. Arthrology, the description of the Joints. 

3. Myology, the description of the Muscles and accessory structures. 

4. Splanchnology, the description of the Viscera. This includes the following 
subdivisions: 

(1) Digestive System 

(2) Respiratory System 

(3) Urogenital System 

(a) Urinary Organs 
(6) Genital Organs 

5. Angiology, the description of the Organs of Circulation 

6. Neurology, the description of the Nervous System 

7. iEsthesiology, the description of the Sense Organs and Common Integu- 

ment 

The term topographic anatomy designates the methods by which the relative 
positions of the various parts of the body are accurately determined. It presup- 
poses a fair working knowledge of systematic anatomy. 

Descriptive Terms. — In order to indicate precisely the position and direction 
of parts of the body, certain descriptive terms are employed, and must be under- 
stood at the outset. In the explanation of these terms it is assumed here that 
they ap]3ly to a quadruped such as the horse in the ordinary standing position. 
The surface directed toward the plane of sujiport (the ground) is termed ventral 
(or inferior) , and the opposite surface is dorsal (or superior) ; the relations of parts in 
this direction are named accordingly. The longitudinal median plane divides the 
body into similar halves. A structure or surface which is nearer than another to the 
median plane is medial (or internal) to it, and an object or surface which is further 
than another from the median plane is lateral (or external) to it. Planes parallel 
to the median jalane are sagittal. Transverse or segmental planes cut the long axis 
of the body perpendicular to the median plane, or an organ or limb at right angles 
to its long axis. A frontal plane is perpendicular to the median and transverse 
planes. The term is also used with reference to parts of the limbs or various organs 
in a similar sense. The head end of the body is termed anterior or cranial; and the 
tail end posterior or caudal; relations of structures with regard to the longitudinal 
axis of the bcxly are designated accordingly. With respect to parts of the head, 
the correspontling terms are oral and aboral. Certain terms are used in a special 
sense as applied to the limlis. Proximal and distal express relative distances of 
parts from the long axis of the Ijody. The anterior face of the thoracic limb from 
the elbow downward is termed dorsal, anfl the opposite face volar. In the corre- 
sponding part of the pelvic limlj the terms are dorsal and plantar respectively. In 
the same regions radial and ulnar (thoracic limb), tibial and fibular (pelvic limb), 
may be used to designate that side of the extremity on which the corresponding 
bone is situated ; they are therefore equivalent respectively to medial and lateral 
in the animals with which we are concerned. In the case of the limbs, a frontal 
plane is at right angles to the transverse plane and the long axis of the segment 
involved. 

It is evidently advantageous to employ terms which are as far as possible independent of 
the position of the body in space and capable of general application, e. g., dorsal, ventral, proximal, 
etc. It is also desirable that the terms internal and external be reserved to indicate relations of 
depth in cavities or organs, and nicdinl .■iml titmil Id designate relations to the median plane. 
Such terms are coming into more cxli'iisix c iisi' in Innnaii and veterinary anatomy, but the older 
nomenclature is very firmly establislici I and caniidt well be discarded at once and entirely. To 
facilitate the transition, a table of the older and more recent terms is given below; the recent 
terms are in the first column and the older equivalents in the second. 



INTRODUCTION 19 

A. Relating to Head, Neck, and Trunk: 

Dorsalis Superior 

Ventralis Inferior 

Medialis Internal 

Lateralis External 

Cranialis 
Oralis 
Caudalis 
Aboralis 

B. Relating to Limbs: 

Proximalis Superior 

Distalis Inferior 

Dorsalis Anterior 

Volaris 



Anterior 
Posterior 



Plantaris 



■ Posterior 



Radialis \ t. . i 

Tibialis ^ ^"**^™^' 

Ulnaris 
Fibularis 



. External 



The terms superficialis and profundus are useful to indicate relative distances of parts from 
the surface of the body. 



OSTEOLOGY 

THE SKELETON 
The term skeleton i.s a])plietl tu tlie framework of hartl structures which sup- 
ports and protects the soft tissues of animals. In the descriptive anatomy of the 
higher animals it is usually restricted to the bones and cartilages, although the 
ligaments which bind these together might well be included. 

In zoology the term is used in a much more comprehensive sense, and includes all the harder 
supporting and protecting structures. When the latter are situated externally, they form an 
exoskeleton, derived from the ectoderm. Examples of this are the shells and chitinous coverings 
of many invertebrates, the scales of fishes, the shields of turtles, and the feathers, hair, and hoofs 
of the higher vertebrates, llic endoskeleton {\\\\ h which we have to deal at present) is embedded 
in the soft tissues. It is deri\cd from the mesoderm, but includes the notochord or primitive 
axial skeleton, which is of entodermal origin. 

The skeleton may be divided primarily into three parts: (1) a.xial; (2) appen- 
dicular; (3) splanchnic. 

The axial skeleton comprises the vertebral column, ribs, sternum, and skull. 

The appendicular skeleton includes the bones of the limbs. 

The splanchnic ur visceral skeleton consists of certain bones developed in the 
substance of some of the viscera or soft organs, e. g., the os penis of the dog and the 
OS cordis of the ox. 

The number of the bones of the skeleton of an animal varies with age, owing 
to the fusion during growth of skeletal elements which are separate in the fcetus 
or the young subject. Even in adults of the same species numerical variations 
occur, e. g., the tarsus of the horse may consist of six or seven bones, and the carpus 
of seven or eight; in all the domestic mammals the number of coccygeal vertebrae 
varies considerably. 

The bones are commonly divided into four classes according to their shape 
and function.' 

(1) Long bones (Ossa longa) are typically of elongated cylindrical form w'ith 
enlarged extremities. They occur in the limbs, where they act as supporting 
columns and as levers. The cylindrical part, termed the shaft or body (Corpus), 
is tubular, and incloses the medullary cavity, which contains the medulla or marrow. 

(2) Flat bones (Ossa plana) are expanded in two directions. They furnish 
sufficient area for the attachment of muscles and afford protection to the organs 
which they cover. 

(3) Short bones (Ossa brevia), such as those of the carpus and tarsus, present 
somewhat similar dimensions in length, breadth, and thickness. Their chief func- 
tion appears to be that of diffusing concussion. Sesamoid bones, which are de- 
velojied in the capsules of some joints or in tendons, may be included in this group. 
They diminish friction or change the direction of tendons. 

(4) Irregular bones (Ossa irregularia). This group would include bones of 
irregular shape, such as the vertebrae and the bones of the cranial base; they are 
median and unpaired. Their functions are various and not so clearly specialized 
as those of the preceding classes. 

'This classification is not entirely satisfactory; some bones, e. g., the ribs, are not clearly 
provided for, and others might be variously placed. 

20 



STRUCTURE OF BONES 



21 



STRUCTURE OF BONES' 

Bones consist chiefly of bone tissue, but considered as organs they present 
also an enveloping membrane, termetl the periosteum, the marrow, vessels, and 
nerves. 

The architecture of bone can be studied best by means of longitudinal and 
transverse sections of specimens which have been macerated so as to remove most 
of the organic matter. These show that the bone 
consists of an external shell of dense compact sub- 
stance, within which is the more loosely arranged 
spongy substance. In typical long bones the shaft 
is hollowed to form the medullary cavity (C'avum 
medullare) . 

The compact substance (Substantia compacta) 
differs greatly in thickness in various situations, in 
conformity with the stresses and strains to which 
the lione is subjected. In the long l^ones it is 
thickest in or near the middle part of the shaft and 
thins out toward the extremities. On the latter the 
layer is very thin, and is especially dense and smooth 
on joint surfaces. 

The spongy substance (Substantia spongiosa) 
consists of delicate bony plates and spicules which 
run in various directions and intercross. These are 
tlefinitely arranged with regard to mechanical re- 
quirements, so that systems of pressure and tension 
]5lates can be recognized, in conformity with the 
lines of pressure and the pull of tendons and liga- 
ments respectively. The intervals between the 
])lates are occupied by marrow, and are termed 
marrow spaces (C'ellulse naedullares) . The spongy 
substance forms the bulk of short bones and of the 
extremities of long bones ; in the latter it is not con- 
fined to the ends, but extends a variable distance 
along the shaft also. Some bones contain air-spaces 
within the compact substance instead of spongy 
lione and marrow, and hence are called pneumatic 
bones (Ossa pneumatica). These cavities are termed 
sinuses, and are lined with mucous membrane; 
they communicate indirectly with the external air. 
In certain situations the two compact layers of flat 
l)ones are not separated by spongy bone, but fuse 
with each other; in some cases of this kind the bone 
is so thin as to be translucent, or may undergo 
absorption, producing an actual deficiency. 

The flat bones of the cranial vault and sides 
are composed of an outer layer of ordinary compact 
substance, the lamina externa, an inner layer of 

very dense bone, the lamina interna or tabula vitrea, and between these a variable 
amount of spongy bone, here termed diploe. 

The periosteum is the membrane which invests the outer surface of bone, 
except where it is covered with cartilage. It consists of an outer protective fibrous 

' Only the gross structure is discussed here. For the microscopic structure reference is to 
be made to histological works. 




FiQ. 1. — Sagittal Section of Large 
Metatarsal Bone of Horse 
(Right). 

S.C., Compact substance; 5.s., 
spongy substance: Cm., medullao' 
cavity; F.n., nutrient foramen. Note 
the greater thickness of the compact 
substance of the anterior part of the 
shaft. 



22 



OSTEOLOGY 



layer, and an inner cellular osteogenic layer. During active growth the osteogenic 
layer is well developed, but later it becomes much reduced. The fibrous layer 
varies much in thickness, being in general thickest in exposed situations. The 
adhesion of the periosteum to the bone also differs greatly in various places; it 
is usually very thin and easily detached where it is thickly covered with muscular 
tissue which has little or no attachment. The degree of vascularity conforms to 
the activity of the periosteum. 

The endosteum is a thin fibrous membrane which lines the medullary cavity 
and the larger Haversian canals. 

The marrow (Medulla ossium) occupies the interstices of the spongy bone and 
the medullary cavity of the long bones. There are two varieties in the adult — 
red and yellow. In the young subject there is only red marrow (jMeduUa ossiuni 
rubra), but later this is replaced in the medullary cavity by yellow marrow (Medulla 
ossium flava). The red marrow contains several types of characteristic cells and 
is a blood-forming substance, while the yellow is practically ordinary adipose tissue.' 

Vessels and Nerves. — It is customary to recognize two sets of arteries — the 
periosteal and the medullary. The former ramify in the periosteum and give off 





Pig. 3. — Ckoss-section of Distal Third of Shaft O! 

Left Humerus of Horse. 

Section passea through nutrient foramen and canal. 



innumerable small branches which enter minute openings (Volkmann's canals) on 
the surface and reach the Haversian canals of the compact substance. Other 
branches enter the extremities of the long bones and supply the spongy bone and 
marrow in them. In the case of the larger bones — and especially the long bones — 
the large nutrient or medullary artery (Arteria nutricia) enters at the so-called nu- 
trient foramen (Foramen nutricium), passes in a canal (Canalis nutricius) through 
the compact substance, and ramifies in the marrow; its branches anastomose with 
the central branches of the periosteal set. The larger veins of the spongy bone do 
not, as a rule, accompany the arteries, but emerge chiefly near the articular surfaces. 
Within the bone they are destitute of valves. The l5rmph-vessels exist as peri- 
vascular channels in the periosteum and the Haversian canals of the compact sub- 
stance. They also form a fine subperiosteal network, from which the larger vessels 
proceed, usually in company with veins. Lymph-spaces exist at the periphery of 
the marrow. 

The nerves appear to be distributed chiefly to the blood-vessels. Special nerve- 

' Since yellow marrow is formed by regressive changes in red marrow, including fatty infiltra- 
tion and degeneration of the characteristic cells, we find transitional forms or stages in the process. 
In aged or badly nourished subjects the marrow may undergo gelatinous degeneration, resulting 
in the formation of gelatinous marrow. 



DEVELOPMENT AND GROWTH OF BONE 



23 



endings (Vater-Pacini corpuscles) in tlie periosteum are to be regarded as sensory, 
and probably are concerned in mediating the muscle sense (kinesthesia) 



DEVELOPMENT AND GROWTH OF BONE' 

The primitive embryonal skeleton consists of cartilage and fibrous tissue, in 
which the bones develop. The process is termed ossification or osteogenesis, and 
is effected essentially by bone-producing cells, called osteoblasts. It is ciistomarj', 
therefore, to designate as membrane bones those which are developed in fibrous 
tissue, and as cartilage bones those which are preformed in cartilage. The princi- 
pal membrane bones are those of the roof and sides of the cranium and most of the 
bones of the face. The cartilage bones comprise, 
therefore, most of the skeleton. Correspondingly 
we distinguish intramembranous and endochondral 
ossification. 

In intramembranous ossification the process 
begins at a definite center of ossification (Punctum 
ossificationis) , where the osteol)lasts surrountl them- 
selves with a deposit of bone. The process extends 
from this center to the periphery of the future bone, 
thus producing a network of bony trabeculse. The 
trabecule rapidly thicken and coalesce, forming a 
bony plate which is separated from the adjacent 
bones by persistent fibrous tissue. The superficial 
part of the original tissue becomes periosteum, and 
on the deep face of this successive layers of perios- 
teal bone are formed by osteoblasts until the bone 
attains its definitive thickness. Increase in circum- 
ference takes place by ossification of the surround- 
ing fibrous tissue, which continues to grow imtil 
the bone has reached its definitive size. 

In endochondral ossification the process is 
fundamentally the same, but not quite so simple. 
Osteoblasts emigrate from the deep face of the peri- 
chondrium or primitive periosteum into the cartilage 
and cause calcification of the matrix or ground- 
substance of the latter. Vessels extend into the cal- 
cif3ang area, the cartilage cells shrink and disappear, 
forming primary marrow cavities which are occupied 
by processes of the osteogenic tissue. There is thus 
formed a sort of scaffolding of calcareous trabeculse 
on which the bone is constructed by the osteoblasts. 
At the same time perichondral bone is formed by 

the osteoblasts of the primitive periosteum. The calcified cartilage is broken do^Ti 
and absorbed through the agency of large cells called osteoclasts, and is replaced 
by bone deposited by the osteoblasts. The osteoclasts also cause absorption of the 
primitive bone, producing the marrow cavities; thus in the case of the long bones 
the primitive central spongy bone is largely absorbed to form the medullary cavity 
of the shaft, and persists chiefly in the extremities. Destruction of the central 
part and formation of subperiosteal bone continue until the shaft of the bone has 
completed its growth. 

A typical long bone is developed from three primary centers of ossification, 

' Only a brief general statement of osteogenesis can be made here; details must be sought 
in embryological literature. 




Fig. 4. — Left Femur 

Lateral View, 

visiox OF A Long Bone into 

Shaft (s) and Extremities. 

Proximal extremity consists of 
two parts, head (h) and trochanter 
major (^m.), which have separate 
centers of ossification. Distal extrem- 
ity consists of trochlea (0 and condyles 
(c); ej., epiphyseal cartilages: s./., 
supracondyloid fossa. 



24 OSTEOLOGY 

one, which appears first, for the cUaphysis or shaft and one for each epiphysis or 
extremity. Many bones have secondary centers from which processes or apophyses 
develop. 

The foregoing outhne accounts for the growth of bones except in regard to 
length. Increase in length may be explained briefly as follows: Provision for con- 
tinued ossification at either end of the diaphysis is made by a layer of actively 
growing cartilage — the epiphyseal cartilage — which intervenes between the diaph- 
ysis and the ejiiphysis. It is evident that so long as this cartilage persists and 
grows, new bone may continue to be formed at its expense, and increase of length 
is possible. When the epiphyseal cartilage ceases to grow, it unflergoes ossification, 
the bone is consolidated, and no further increase in length is possible. This fusion 
takes place at fairly definite periods in the various bones, and it is of value to know 
the usual times at which it occurs in the larger bones of the limbs at least. In the 
case of membrane bones, increase in circumference is provided for by the ossification 
and new formation of the surrounding fibrous tissue. 

After the bones have reached their full size, the periosteum becomes relatively reduced and 
inactive so far as its osteogenic layer is coiicerned; the bone-forming function may be stimulated 
by various causes, as is well seen in the healing of fractures and the occurrence of bony enlarge- 
ments. 

Profound changes occur in the skeleton after birth, and during the period of growth the bones 
are much more plastic than might be supposed. In the new-born foal, for example, it is evident 
that the metacarpal and metatarsal bones are relatively long and the scapula and humerus short; 
also that in general the shafts of the long bones are slender in comparison with the extremities. 
The various prominences are much less pronounced than in the adult, and most of the minor 
surface markings are absent, so that the bones have a relatively smooth apiiearance. The period 
of growth may be regarded as'terminating with the union of the extremities and shafts of the long 
bones and the fusion of the parts of other bones. During adult life the skeletal cluingi's jirocced 
more slowly; they comprise accentuation of the larger prominences ami depressions and the ap- 
pearance of smaller ones. These secondary markings are chiefly correlated with the attachments 
of muscles, tendons, and hgaments, or are produced by pressure exerted by various structures on 
the bones. Later in life ossification invades more or less extensively the cartilages and the at- 
tachments of tendons and ligaments. Senile changes in the bones, consisting of decrease of the 
organic matter and rarefaction of the bone tissue, render them brittle and liable to fracture. 



CHEMICAL COMPOSITION OF BONE 
Dried bone consists of organic and inorganic matter in the ratio of 1 : 2 ap- 
proximately. The animal matter gives toughness and elasticity, the mineral 
matter hardness, to the bone tissue. Removal of the organic matter by heat does 
not change the general form of a bone, but reduces the weight by about one-third, 
and makes it very fragile. Conversely, decalcification, while not aff'ecting the form 
and size of the bone, renders it soft and pliable. The organic matter (ossein) when 
boiled yields gelatin. The following table represents the composition in 100 parts 
of ox bone of average quality: 

Gelatin 33.30 

Phosphate of lime 57.35 

Carbonate of lime 3.85 

Phosphate of magnesia 2.05 

Carbonate and chlorid of sodium 3.45 

100.00 

PHYSICAL PROPERTIES OF BONE 

Fresh dead bone has a yellowish-white color; when macerated or boiled and 
bleached, it is white. The specific gravity of fresh compact bone is a little over 
1.93. It is very hard and resistant to pressure; a 5-millimeter cube of compact 
bone of the ox will resist pressure up to 852 pounds, if the pressure be applied in 
the line of the lamellae (Rauber). Its tensile strength is estunated to be nearly 
twice that of oak. 



THE VERTEBRAL COLUMN 25 



DESCRIPTIVE TERMS 



The surfaces of the bones present a great variety of eminences and depressions, 
as well as perforations. The prominences and cavities may be articular, or non- 
articular, furnishing attachment to muscles, tendons, ligaments, or fascia. A 
number of descriptive terms are used to designate these features, and the following 
are some of those in general use : 

Process (Processus) is a general term for a prominence. 

A tuberosity (Tuber, Tuberositas) is a large, rounded projection; a tubercle 
(Tuberculum) is a smaller one. 

The term trochanter is applied to a few prominences, e. g., the trochanters of 
the femur. 

A spine (Spina) or spinous process (Processus spinosus) is a pointetl projection. 

A crest (Crista) is a sharp ridge. 

A line (Linea) is a very small ridge. 

A head (Caput) is a rounded articular enlargement at the end of a bone; it 
may be joined to the shaft by a constricted part, the neck (Collum). 

A condyle (Condylus) is an articular eminence which is somewhat cylindrical; 
a non-articular projection in connection with a condyle may be termed an epi- 
condyle (Epicondylus). 

A trochlea is a pulley-like articular mass. 

A glenoid cavity (Cavitas glenoidalis) is a shallow articular depression, and a 
cotyloid cavity or acetabulum is a deeper one. 

The term facet is conunonly applied to articular surfaces of small extent, 
especially when they arc not strongly ccjncave or convex. 

The terms fossa, fovea, groove or sulcus, and impression are applied to various 
forms of depressions. 

A foramen is a perforation for the transmission of vessels, nerves, etc. 

A sinus is an air-cavity within a bone or bones; it is lined with mucous mem- 
brane and communicates with the exterior. 

Other terms, such as canal, fissure, notch, etc., require no explanation.' 



THE VERTEBRAL COLUMN 

The vertebral colimin (Columna vertebralis) is the fundamental part of the 
skeleton. It consists of a chain of median, unpaired, irregular bones which 
extends from the skull to the end of the tail. In the adult certain vertebrae have 
become fused to form a single bony mass with which the pelvic girdle articulates. 
Vertebrae so fused are termed fixed (or "false") vertebrae (Vertebris immobiles), as 
distinguished from the movable (or "true") vertebrae (^'crtebrse mobiles). 

The column is subdivided for description into five regions, which are named 
according to the part of the hotly in which the vertebra arc situated. Thus the 
vertebrae are designated as cervical, thoracic, lumbar, sacral, coccygeal (Vertebra 
cervicales, thoracales, lumbales, sacrales, coccygeae). The number of vertebra? in 
a given species is fairly constant in each region except the last, so that the verte- 
bral formula may be expressed (for the horse, for example) as follows: 

CrTisLcSjCyis.oi. 

The vertebrae in a given region have characters by which they may be dis- 
tinguished from those of other regions, and individual vertebra have special 
characters which are more or less clearly recognizable. All typical vertebrae have 

' As might be expected from the history of anatomy, a good many of these terms are more or 
less interchangeable; furthermore, a given skeletal feature may differ greatly in various species. 



26 



OSTEOLOGY 



^drh'^'Mrild. 



a common plan of structure, which must first be understood. The parts of which 
a vertebra consists are tlie body, tlie arch, and tlie processes. 

Tlie body (Corpus vertebrae) is the more or less cylindrical mass on which the 
other parts are constructed. The anterior and posterior extremities of the body 
are attached to the adjacent vertebrae by intervertebral fibro-cartilages, and are 
usually convex and concave respectively. The dorsal surface is flattened and enters 
into the formation of the vertebral canal, while the ventral aspect is rounded later- 
ally, and is in relation to various muscles and viscera. In the thoracic region the 
body presents two pairs of facets (Fovese costales) at the extremities for articula- 
tion with part of the heads of two pairs of ribs. 

The arch (Arcus vertebrae) is constructed on the dorsal aspect of the body. 
It consists originally of two lateral halves, each of which is considered to consist 
of a pedicle and a lamina. The pedicle (Radix arcus vertebra) forms the lateral 
part of the arch, and is cut into in front antl behind by the vertebral notches (In- 
cisura verteliralis cranialis, caudalis). The notches of two adjacent vertebrae form 
intervertebral foramina (Foramina intervertebralia) for the passage of the spinal 

nerves and vessels; in some vertebrae, how- 
ever, there are complete foramina instead 
of notches. The laminae are plates which 
complete the arch dorsally, uniting with each 
other medially at the root of the spinous 
process. 

The body and the arch form a bony 
ring which incloses the vertebral foramen 
(Foramen vertebrale); the series of verte- 
bral rings, together with the ligaments which 
unite them, inclose the vertebral canal 
(Canalis vertebralis), which contains the 
spinal cord and its coverings and vessels. 

The articular processes, two anterior 
and two posterior (Processus articulares 
craniales, caudales), project from the bor- 
ders of the arch. They present articular 
surfaces adapted to those of adjacent verte- 
brae, and the remaining surface is roughened 
for muscular and ligamentous attachment. 
The spinous process or spine (Processus 
spinosus) is single, and projects dorsally from the niitklle of the arch. It varies 
greatly in form, size, and direction in different vertebrae. It furnishes attachment 
to muscles and ligaments. 

The transverse processes (Processus transversi) are two in number and project 
laterally from the sides of the arch or from the junction of the arch and body. 
In the thoracic region each has a facet for articulation with the tubercle of a rib 
(Fovea costalis transversalis). They also give attachment to muscles and liga- 
ments. 

Some vertebrae have also a ventral spine or a haemal arch. 
Mammillary processes (Processus mamillares) are found in most animals on 
the last thoracic and anterior lumbar vertebrae, between the transverse and an- 
terior articular processes or on the latter. 

Accessory processes (Processus accessorii), when present, are situated between 
the transverse and posterior articular processes. 

Development. — The vertebrae are developed by ossification in the cartilage 
^\•hicll surrounds the notochord and forms the sides of the neural canal. There are 
three primary centers of ossification, one for the boch^ and one for each side of the 




Costal facef 



Fig. 5. — First Thoracic Vertebra op Horse. 
To illustrate plan of structure of vertebrse. 



THE COSTAL CARTILAGES 27 

arch. Secondary centers appear later for the summit of the spinous process 
(except in the cervical region), the extremities of the transverse processes, and the 
thin epiphyseal plates at the extremities of the body. 

Sometimes there are at first two centers for the body, which soon fuse. The process of ossifi- 
cation extends from the lateral centers to form, not only the corresponding part of the arch, but 
also the processes and a part of the body next to the root of the arch (Radix arcus). In the horse 
and ox the body and arch are fused at birth or unite very soon after, but the epiphyses do not 
fuse till growth is complete. In the pig, sheep, and dog the body and arch are united at birth 
by cartilage (neurocentral synchondrosis), but fuse in the first few months. 

THE RIBS 

The ribs (Costie) are elongated curved bones which form the skeleton of the 
lateral thoracic walls. They are arranged serially in pairs which correspond in 
number to the thoracic vertebrae. Each articulates dorsally with two vertebriB 
and is continued ventrally by a costal cartilage. Those which articulate with the 
sternum by means of their cartilages are termed sternal ribs (Costae sternales); 
the remainder are asternal ribs (Costse a.sternales) . Ribs at the end of the series 
which have their ventral ends free in the abdominal wall are named floating ribs 
(Costse fluctuantes). The intervals between the ribs are termed intercostal spaces 
(Spatia intercostalia). 

A typical rib' consists of a shaft and two extremities. The shaft (Corpus 
costae) is band-like and varies much in length, breadth, and curvature in different 
ribs. In the case of some rilis the curvature is not uniform, but is accentuated at a 
certain point, termed the angle of the rib (Angulus costse) ; this occurs at a variable 
distance from the vertebral end, and is usually marked by a rough ridge. The 
direction also varies; the first rib is usually almost vertical, while the remainder 
slope backward in increasing degree. The lateral surface (Facies lateralis) is con- 
vex, and the medial surface (Facies medialis) flattened from edge to edge; on the 
latter, close to the posterior border, is the costal groove (Sulcus costae), which fades 
out ventrally. It contains the intercostal vein. The anterior and posterior 
borders (Margo cranialis, caudalis) are thin and sharp on some ribs, rounded on 
others. 

The vertebral extremity (Extremitas vertebralis) consists of the head, neck, 
and tubercle. The head (Capitulum costae) is the actual end of the rib, and is 
roundetl and somewhat enlarged. It presents two facets (Facies articularis capituli 
costse) for articulation with the bodies of two adjacent thoracic vertebrae; these 
surfaces are separated by a groove in which the conjugal ligament is attached. 
The neck (Collum costse) joins the head to the shaft. It varies in length and 
diameter. Its lateral surface is rough, its medial smooth. The tubercle (Tuber- 
culum costae) projects backward at the junction of the neck and shaft. It has a 
facet (Facies articularis tuberculi costae) for articulation with the transverse process 
of the posterior vertebra of the two with which the head articulates. The tubercle 
gradually approaches the head in the posterior ribs, and eventually fuses with it. 

The sternal extremity (Extremitas sternalis) is commonly slightly enlarged, 
and is roughened at the junction with the costal cartilage. 

Development. — The ribs are ossified in cartilage from three centers — one each 
for the shaft (and sternal end), head, and tubercle; the third center is absent in 
some ribs at the terminal part of the series. 

THE COSTAL CARTILAGES 

These (Cartilagines costales) are bars of hyaline cartilage which continue the 
ribs. Those of the sternal ribs articulate with the sternum, while those of the 

' The term is employed here, as is usual in descriptive anatomy, to designate only the bony 
part of the rib (Os costale); morphologically it includes the cartilaginous part also. 



28 OSTEOLOGY 

asternal riljs overlap and are attached to each other to form the costal arch (Arcus 
costalis). The cartilages of floating ribs are not attached to those adjacent. 



THE STERNUM 

The sternum (or breast-bone) is a median segmental bone which completes the 
skeleton of the thorax ventrally, and articulates with the cartilages of the sternal 
ribs laterally. It consists of six to eight bony segments (SternebrEe) connected by 
intervening cartilage in the young subject. Its form varies with that of the thorax 
in general and with the development of the clavicles in animals in which these bones 
are present. Its anterior extremity, the manubrixun stemi or prestemiun, is 
specially affected by the latter factor, being broad and strong when the clavicles 
are well developed and articulate with it (as in man), relatively small and laterally 
compressed when thej^ are absent (as in the horse) or rudimentary (as in the dog). 
The cartilages of the first pair of ribs articulate with it. The body or mesostemum 
(Corpus stemi) presents laterally, at the junction of the segments, concave facets 
(Incisurae costales) for articidation with the cartilages of the sternal ril)s. The 
posterior extremity or metastemum presents the xiphoid cartilage (Processus 
xiphoideus) ; this is thin and wide, as in the horse and ox, or narrow and short, as 
in the dog. 

Development. — The cartilaginous sternum is formed by the fusion medially 
of two lat(n-al jjars which unite the ventral ends of the first eight or nine costal 
cartilages, and is primitively unsegmentcd. The manubrium ossifies from a single 
center, but the centers for the other segments appear to be primitively paired. 
The sternum never becomes completely ossified; details in regard to persisting 
cartilage will be given in the special descrijations. The layer of compact tissue is 
for the greater jDart very thin antl the spongy substance is open-meshed and very 
vascular. 

THE THORAX 

The skeleton of the thorax com]:)ris('s the thoracic vertebrEe dorsally, the ribs 
and costal cartilages laterally, and the sternum ventrally. The thoracic cavity 
(Cavum thoracis) resembles in shape an irregular truncated cone; it is compressed 
laterally, especially in front, and the dorsal wall or roof is much longer than the 
ventral wall or floor. The anterior aperture or inlet (Apertura thoracis cranialis) is 
bounded by the first thoracic vertebra dorsally, the first pair of ribs and costal 
cartilages laterally, and the manubrium sterni ventrall3^ The posterior aperture 
(Apertura thoracis caudalis) is bounded by the last thoracic vertebra, the last 
pair of ribs, the costal arches, and the anterior part of the xiphoid cartilage. 

It may be noted here that the iliaphragrn (which forms the partition between the thoracic 
and abdominal ea\aties) does not follow the (-(j.stal arches in its posterior attachment, so that the 
posterior ribs enter also into the formation (jf the alidominal wall. 



THE SKULL 

The term skull is usually understood to include all of the bones of the head. 
The head consists of the cranium and the face, and it is therefore convenient to 
divide the bones into cranial and facial groups. 

The cranial bones (Ossa cranii) inclose the brain with its membranes and 
vessels and the essential organs of hearing. They concur with the facial bones in 
forming the orbital and nasal cavities, in which the peripheral organs of sight and 
of smell are situated. 

The facial bones (Ossa faciei) form the skeleton of the oral and nasal cavities, 
and also support the pharynx, the larynx, and the root of the tongue. 



THE BONES OF THE THORACIC LIMB 29 

Most of the bones of the skull are flat bones, developed in membrane; those 
of the cranial base may be classed as irregular, and are developed in cartilage. Only 
two form permanent movable joints with other parts of the skull. The mandible 
(or lower jaw-bone) forms diarthrodial joints with the temporal bones, and the 
hyoid bone is attached to the latter by bars of cartilage. The other bones form 
immovable joints, most of which disappear with age. 

In order to study the separate bones, skulls of young subjects are necessary, since later most 
of the lines of demarcation become effaced. The relations of each bone to its surroundings should 
be specially noted, since the final object is to understand the skull as a whole. In the descriptions 
which follow the skull is considered with its long axis horizontal, and that of the horse will serve 
as a type. 

THE BONES OF THE THORACIC LIMB 

The thoracic limb (Extremitas thoracalis) consists of four chief segments, viz., 
the shoulder girdle, the arm, the forearm, and the manus. 

The shoulder girdle (Cinguliun extremitatis thoracalis), when full>' developed, 
consists of three bones — the scapula (or shoulder-blade), the coracoid, and the 
clavicle (or collar-bone). In the domesticated mammals only the scapula, a large, 
flat bone, is well developed, and the small coracoid element has fusetl with it, while 
the clavicle is either absent or is a small rudiment embedded in the Ijrachiocephali- 
cus muscle. There is therefore no articulation of the shoulder with the a.xial 
skeleton. 

The shoulder girdle is fully developed in birds and the lower mammals (monotremata). In 
the higher mammals the coracoid is reduced to the coracoid process of the scapula, and the develop- 
ment of the clavicle is in conformity with the function of the Umlj. Thus in typical quadrupeds, 
such as the horse and ox, in which the foreUmbs are used only for support and locomotion, the 
cla\'icle is absent. Other animals which use these limbs for grasping, burrowing, climbing, etc. 
(('. g., man, apes, moles), have well-developed clavicles wliich connect tlie scapula with the sternum. 

Tlie arm (Brachiimi) contains a single long bone, the humerus (or arm bone). 

In the forearm (Antibrachium) are two bones, the radius and ulna. These 
vary in relative size and mobility. In the horse and ox the two bones are fused, 
and the distal part of the limb is fixed in the position of pronation. The radius is 
placed in front and supports the weight. The ulna is well developed only in its 
])roximal part, wliich forms a lever for the extensor muscles of the elbow. In the 
])ig the ulna is the larger and longer of the two bones, but is closely attached to 
the back of the radius. In the dog the ulna is also well developed and a small 
amount of movement is possible between the two bones. 

The manus,^ the homologue of the hand in man, consists of three subdivi- 
sions, viz., the carpus, metacarpus, and digit or digits. 

The carpus, popularly termed the "knee" in animals, and homologous 'with 
the wrist of man, contains a group of short bones, the ossa carpi.'- These are tyjjic- 
ally eight in nmnber and are arranged in two transverse rows — a proximal or anti- 
brachial, and a distal or metacarpal. The bones of the proximal row, named from 
the radial to the ulnar side {i. e., from within outward), are the radial, intermediate, 
ulnar, and. accessory carpal bones. The bones of the distal row are designated 
nmnerically, in the same direction, as first, second, third, and fourth carpal bones. 

This nomenclature, introduced by Gegenbaur, and now used largely by comparative anat- 
omists, seems decidedly preferable to the variety of terms borrowed from human anatomy and 
based on the form of the bones in man. The following table of synonyms in common use is ap- 
pended for comparison. The Latin terms and abbreviated notations are given in parentheses. 

1 It is unfortunate that there is no popular name for this part of the limb. The term "fore- 
foot" is sometimes apphed to it, but this leads to confusion, since the word "foot" has long been 
used in a different sense. 

^ The term "knee" as applied to this region is unfortimate, but tlie usage is very firmly 
established and there is no other popular name. 



30 OSTEOLOGY 

The central carpal bone (Os carpi centrale) is omitted, since it is not a separate element in the 
animals under consideration here. 

Radial (Os carpi radiale, Cr) Scaphoid 

Intermediate (Os carpi intermedium, Ci) Semilunar 

Ulnar (Os carpi ulnare, Cu) Cuneiform 

Accessory (Os carpi accessorium, Ca) Pisiform 

First carpal (Os carpale primum, CI) Trapezium 

Second carpal (Os carpale secundum, C2) Trapezoid 

Third carpal (Os carpale tertium, C3) Os magnum 

Fourth carpal (Os carpale quartum, C4) Unciform 

The metacarpus contains typically five metacarpal bones (Ossa metacarpalia 
I-V), one for each digit; they are long bones and are designated numerically from 
the radial to the ulnar side {i. e., from within outward). This arrangement occurs 
in the dog, although the first metacarpal is much smaller than the others, and the 
second and fifth are somewhat reduced. Further reduction has taken place in the 
other animals, resulting in the perissodactyl and artiodactyl forms. In the horse 
the first and fifth metacarpals are absent, the third is the large supporting meta- 
carpal bone and carries the single digit, while the second and fourth are much re- 
duced. In artiodactyls (e. g., ox, sheep, pig) the third and fourth are the chief 
metacarpals and carry the well developed digits; they are fused in the ox and sheep. 
The others are variously reduced or absent, as noted in the special descriptions to 
follow. 

The fossil remains of the ancestors of the existing Equidse illustrate in a most complete man- 
ner the reduction which has occurred in this respect. The earUest known ancestor of the horse, 
Eohippus of the Lower Eocene, had four well developed metacarpal bones, each of which carried 
a ftigit; the first metacarpal bone was small. Intermediate forms show the gradual evolution of 
the race from this primitive animal, which was about the size of the domestic cat. There is reason 
to beUeve that earlier forms had five digits. 

The digits (Digiti manus) are homologous with the fingers of man, and are 
typically five in number. They are designated numerically from the radial to 
the ulnar side, in correspondence with the metacarpus. The full number is present 
in the dog. In the ox and pig the third and fourth are well developed and support 
the weight, while the second and fifth are reduced. The existing horse has a single 
digit, the third of his pentadactyl ancestors. The skeleton of each fully developed 
digit consists of three phalanges and certain sesamoid bones. The first phalanx 
(Phalanx prima) articulates with the corresponding metacarpal bone above and 
with the second phalanx (Phalanx secunda) below. The third phalanx (Phalanx 
tei'tia) is inclosed in the hoof or claw, and is modified to conform to the latter. The 
sesamoid bones (Ossa sesamoidea) are developed along the course of tendons or in 
the joint capsules at points where there is increasetl j^ressure. Two proximal 
sesamoids (Ossa sesamoidea phalangis primse) occur at the flexor side of the meta- 
carpo-phalangeal joint and form a pulley for the flexor tendon. The distal sesa- 
moid (Os sesamoideum phalangis tertiae) is similarly placed between the deep 
flexor tendon and the joint between the second and third phalanx; it is absent in 
the dog, which has a small sesamoid on the extensor side of the metacarpo-phalan- 
geal joint, and often at the proximal interphalangeal joint also. 

Numerous ca.ses are recorded of the occurrence of supernumerary digits (hyperdactylism) 
in the horse and other animals. In some pigs, on the other hand, the two chief digits are fused, 
and the condition (syndactyhsm) appears to be inherited. 



THE BONES OF THE PELVIC LIMB 

The pelvic limb (Extremitas pelvina), like the thoracic, consists of four seg- 
ments, viz., the pelvic girdle, thigh, leg, and the pes; the last is subdivided into 
tarsus, metatarsus, and digits. 

The pelvic girdle (Cingulum extreniitatis pelvinse) consists of the os coxae (or 



THE BONES OF THE PELVIC LIMB 31 

hip bone), which joins its fellow of the opposite side ventrally at the symphysis 
pelvis, and articulates very firmly with the sacrum dorsally. The two coxal bones, 
together with the sacrum and the first three or more coccygeal vertebrse, constitute 
the bony pelvis. The os coxae consists originally of three flat bones, the ilium, 
ischium, and pubis, which meet at the acetaljulum, a large cotyloid cavity with 
which the heatl of the femur articulates. These three parts are fused before growth 
is complete, but are considered separately for convenience of description. The 
ilium (Os ilium) is situated in the lateral wall of the pelvis, the pubis (Os pubis) in 
the anterior part, and the ischiimi (Os ischii) in the posterior part of the ventral 
wall. 

The thigh (Femur), like the arm, contains a single long l)one, the femur (or 
thigh bone) (Os femoris). This articulates with the acetabulum above and the 
tibia and patella below. 

The skeleton of the leg (Crus) comprises three bones (Ossa cruris), viz., the 
tibia, fibula, and patella. The tibia is a large, prismatic long bone which supports 
the weight, and articulates distally with the tibial tarsal bone. The fibula is 
situated along the lateral border of the tibia, from which it is separated by the 
interosseous space of the leg. It is much more slender than the tibia and tloes not 
articulate with the femur. In the pig and dog it has a complete shaft and two 
extremities, but in the horse and ox it is nmch reduced and otherwise modified. 
The patella (or "knee-cap") is a short bone which articulates with the trochlea of 
the distal end of the femur; it is to be regarded as a large sesamoid bone intercalated 
in the tendon of the quadriceps femoris muscle. 

The tarsus (or "hock") consists of a group of short bones, the ossa tarsi, 
numbering five to seven in the different animals. The proximal or crural row con- 
sists of two bones, the tibial and fibular tarsals ; the former is situatetl at the tibial 
side, and has a trochlea for articulation with the distal end of the tibia; the latter, 
situated at the filiular side, has a process, the tuber calcis, which projects upward 
and backward and constitutes a lever for the muscles which extend the hock joint. 
The distal or metatarsal row consists of four bones when seven tarsal elements are 
jiresent, as in the pig and dog. They are best designated nmnerically as first tarsal, 
second tarsal, etc. The central tarsal is interposed between the rows. 

The preceding terms are anglicized abbre\'iations of those introduced by Gegenbaur into 
comparative anatomy. The Latin names and synonyms are given in the following table: 

Tibial (Os tarsi tibiale, Tt.) Astragalus or Talus 

Fibular (Os tarsi fibulare, Tf.) Calcaneus or Os calcis 

Central (Os tarsi centrale, Tc.) Scaphoid or Na\icular 

First Tarsal (Os tarsale primum, Tl) First or internal cuneiform 

Second Tarsal (Os tarsale secundum, T2) Second or middle cuneiform 

Third Tarsal (Os tarsale tertium, T3) Third or external cuneiform 

Fourth Tarsal (Os tarsale quartum, T4) Cuboid 

The metatarsal and digital bones resemble in general those of the corresponding 
regions of the thoracic limb; the differential features will be noted in the special 
descriptions. 



32 



THE SKELETON OF THE HORSE 



THE SKELETON OF THE HORSE 

The skeleton of the horse consists of 205 bones, as shown in the following table : 

Vertebral column 54 

Rilis 36 

Sternum 1 ^ 

Skull (including auditory ossicles) 34 

Thoracic limbs 40 

PeU-ic limbs 40 



205 

In this onvimeration the average number of coccygeal vertebra? is taken to be 18, the tem- 
poral and OS coxa; are not divided into parts, the usual number of carpal and tarsal elements is 
taken, and the sesamoids are included. 




Fig. 6. — Skeleton of Horse, with Outline of Contour of Body. 
I.H., Atlas; 7.//., seventh cervical vertebra; I.R., first thoracic vertebra; 17. R., seventeenth thoracic vertebra: 
I.L., first lumbar vertebra; e.L., sixth lumbar vertebra; K, sacrum; I.S., first coccygeal vertebra; le.S., sixteenth 
coccygeal vertebra; 6. R., sixth rib; 6. K., costal cartilage; /S.iS., last rib; 1, scapula; 1', cartilage of scapula; 2, spine 
of scapula; 4, humerus; 4' lateral epicondyle of humerus; 5, lateral tuberosity of humerus; 6, deltoid tuberosity; 
7, shaft of ulna ; 8, olecranon; 9, radius; 10, carpus; 11. accessory carpal bone; 12, metacarpus; 13. digit; 14, sternum, 
14", xiphoid cartilage; 1.5, ilium; 16, 16', angles of ilium; 17, ischium; 18, femur (shaft) ; 19, trochanter major; 20, 
patella; 21. tibia (shaft); 21', lateral condyle of tibia; 23, fibula; 22, tarsus; 24, tuber calcis4 25, metatarsus; 
26, digit; 27, trochanter minor of femur; 28, trochanter tertius of femur. (After Ellenberger-Baum, Anat. fur 
Kiinstler.) 



THE VERTEBRA.L COLUMN 



,33 



The Vertebral Column 

The vertebral formula of the horse is CjTisLeSsCyis-oi 




Fig. 7. — Cervical Vertebr.e of Horse; Dorsal View. Fig. 8. — Cervical Vkrtebr.e op Horse; Ventral 

a, Articular processes; b, transverse processes; 1, View. 

dorsal arch of atlas; ^, wing of atlas; 3, intervertebral a, Transverse processes; 1, ventral tubercle of atlas; 

foramen of atlas; 4, sl\q.t foramen of atlas; 6, foramen 3, anterior articular cavities of atlas; S, fossa atlantis; 

transversarium of atlas; 6, dens of axis; 7, intervertebral 4, alar foramen; 6, foramen trans versarium; 6, ventral 

foramen of axis; S, foramen transversarium of axis; 9, spines, 
spinous processes. 

3 



34 



THE SKELETON OF THE HORSE 



Vertebral foramen 




Fig. 9. — Sixth Ce 



Head 

K-AL Vertebra of Horse 



Anterior View. 



THE CERVICAL VERTEBRE 

The cervical verteljrae (Vertebrae cervicales) are seven in number. 
The first and second cervical vertebrae are highly modified in conformity with 

the special functions of support 
and movements of the head. 
The sixth and seventh present 
special characters, but do not 
differ greatly from the type. 
With the exception of the first, 
they are quadrangular, mass- 
ive, and longer than the ver- 
tebrae of other regions; they 
decrease in length from the 
second to the last. The third, 
fourth, and fifth have the fol- 
lowing characters: 

1. The body is long as 
compared with those of other 
vertebrae. The ventral surface 
presents a median ventral 
spine, which becomes more 
prominent as it is traced back- 
ward, and is tuberculate at its 
posterior end ; it separates two 
concave areas. The dorsal sur- 
face has a flat central area which is narrow in the middle of the vertebrae, and ^^^de 
at either end ; it gives attachment to the dorsal longitudinal ligament. On either 
side of this area there is a groove which lodges the longitudinal spinal vein. These 
lateral grooves are connected about the middle of the surface by a transverse furrow, 
in which there are several for- 
amina through which veins 
emerge from the spongy sub- 
stance of the body. The an- 
terior extremity or head (Ca- 
put vertebrae) has an oval 
articular surface which faces 
forward and downward; it is 
strongly convex, and wider 
above than below. The pos- 
terior extremity is larger and 
has a nearly circular cotyloid 
cavity (Fossa vertebrae). 

2. The arch is large and 
strong. It is perforated on 
either side by a foramen which 
commimicates with the for- 
amen transversarium. The 
vertebral notches are large. 

3. The articular processes 
are large. Their articular sur- 
faces are extensive, oval in outline, and slightly concave; the anterior ones are 
directed dorso-medially; the posterior, ventro-laterally. The remaining surface is 
mainly roughened for ligamentous and muscular attachment. A crest connects 



Spinous process 

Vertebral 

foramen Articu, 



^/j 


z 


x\ 


Head 
OF Horse 


kfej • Trnns- 


Fig. 10. 


-Seven 


Veiitrnl spine 
TH Cervical Vertebra 


process 
Anterior View 



THE ATLAS 



35 



The spinous 



the articular processes of the same side on the fourth and fifth; on the third it does 
not reach the anterior process. 

4. The transverse processes are large and plate-like. Each arises by two 
roots, one from the arch and one from the body; between these is the foramen 
transversarium, through which the vertebral vessels and a nerve pass. The aggre- 
gate of these foramina constitutes the canalis transversarius. The process divides 
laterally into anterior and posterior branches, which are thickened and rough for 
muscular attachment. 

5. The spinous process has the form of a low crest (Crista spinosa), which 
widens behind, and is connected by ridges with the posterior articular processes. 

The sixth cervical vertebra has the following distinctive features: It is shorter 
and wider than the fifth. The arch is large, especially posteriorly. The posterior 
articular processes are shorter, thicker, and further apart; each is connectetl with 
the corresponding anterior one by a thick ridge. The spinous process is less rudi- 
mentary; it is half an inch or more (ca. 1.5 cm.) in height. The transverse proc- 
esses have three branches; the third part is a thick, almost sagittal plate, which 
forms with its fellow and the body a wide ventral groove; the other branches 
correspond to those of the typical vertebra, but are short and thicker.^ The fora- 
men transversarium is large; below its posterior end there is a fossa. The 
ventral spine is small and is less prominent posteriorly. 

The seventh cervical vertebra is readily distinguished liy the following charac- 
ters: It is shorter and wider than the others. The body is flattened dorso-ventrally 
and wide, especially behind; here it has a facet on each side for articulation with 
part of the head of the first rib. The arch and its notches are large. The anterior 
articular processes are wider and longer than the posterior pair. 
process is an inch or more (ca. 3 cm.) 
in height. The transverse process is 
undivided, and has no foramen trans- 
versarium.- The ventral crest is re- 
placed by a pair of tubercles. 

The Atlas 

This vertebra is decidedly atypi- 
cal in form and structure. The body 
and spinous process are absent. It 
has the form of a strong ring, from 
which two curved plates, the wings, 
project laterally. The ring incloses a 
verjf large vertebral foramen, and con- 
sists of two lateral masses connected 
by dorsal and ventral arches. 

The lateral masses (Massae later- 
ales) present two deep oval anterior 
articular cavities (Fovese articulares 

craniales) which receive the occipital condyles; they are separated by a wide notch 
above and a narrow one below. The lateral margin is also notched, and a trian- 
gular non-articular depression cuts into the medial part of each cavity. The pos- 
terior articular surfaces (Facies articulares caudales) are somewhat saddle-shaped; 
they are confluent on the ventral arch, but are widely separated dorsally, and do 
not conform in shape to the corresponding surfaces of the axis. 

' The third branch of the transverse process and the fossa are sometimes absent or reduced 
on one side. 

^ In some specimens a large foramen transversarium is present on one side or (rarely) on 
both sides. 




Fig. IL— Atla 



' AFTER Removal 



Horse. Dorsal Vi 
OF Dorsal Arch. 
1, Anterior articular cavities; 2, 2' 
surfaces: 5, articular surface of ventral arcli for dens of 
axis; 4> transverse ridge; 5, 5', alar foramina; G, 6\ foram- 
ina transversaria. 



poste 



articular 



36 



THE SKELETON OF THE HORSE 



The dorsal arch (Arcus dorsalis) presents a median dorsal tubercle (Tuljer- 
culum dorsale) and is concave ventralh'. It is perforated on either side near its 
anterior margin by the intervertebral foramen (Foramen invertcbrale). The an- 
terior border is deeply notched, and the posterior is thin and concave. 

The ventral arch. (Arcus ventralis) is thiclccr, narrower, and less curved than 
the dorsal. On its lower surface is the ventral tubercle (Tuberculum ventrale), 
into which the terminal tendon of the longus colli muscle is inserted. The upper 
face has posteriorly a transversely concave articular surface, the fovea dentis, on 
which the dens or odontoid process of the axis rests. In front of this is a transverse 
rough excavation and a ridge for the attachment of the ligamentum dentis. 

The wings or alse are modified transverse processes. They are extensive 
curved plates which project ventro-laterally and backward from the lateral masses. 
The dorsal surface is concave. Between the ventral aspect of the wing antl the 
lateral mass is a cavity, the fossa atlantis; in this there is a foramen which opens 
into the vertebral canal. The border is thick and rough; its position can be recog- 
nized in the living animal. Two foramina jierf orate each wing. The anterior one, 
the foramen alare, is connected with the intervertebral foramen by a short groove. 
The i)osterior one is the foramen transversarium. 

Development. — The atlas ossifies from four centers, two for the ventral arch, 
and one on either side for each lateral mass, wing, and half of the dorsal arch. At 
birth the bone consists of three pieces — the ventral arch and two lateral parts, 
which are separated by a layer of cartilage in the dorsal median line and by two 
ventro-lateral layers. These parts are usually fused at about six months. 

The Axis 

The axis (Axis s. Epistropheus) is the longest of the vertebrte, and is character- 
ized by the presence of the dens or oilontoid process, which projects from the an- 
terior part of the body. 

The anterior extremity of the body presents centrally the dens or odontoid 



Spinous ijroci'ss 



Dens 



Anterior articular process 




Body 

Fig. 12. — Axis op Hor.se, Left View. 
ch; 2, intervertebral foramen; 3, notch; .{. foraine 



Posti liar articular process 



Transverse process 



process (Dens axis) ; this has a convex articular surface ventrallj^ for articulation 
with the ventral arch of the atlas, and two rough depressions for the attachment of 
the ligamentum dentis dorsally. Flanking this on either side are the modified 
anterior articular processes, which have saddle-shaped articular surfaces confluent 



THE THORACIC VERTEBRA 



37 



ventrally with that of the dens. The posterior extremity has the usual cavity. 
The ventral spine reseniljles that of the typical vertebra. 

The arch presents in the young subject a notch on each side of its anterior 
border; this is converteil into a foramen by a ligament which ossifies later. The 
posterior border has the usual notches. 

The posterior articular processes are typical. 

The transverse processes are small, single, and project backward. The 
foramen transversarium is small. 

The spinous process is very large and strong. Its free border is rough, thickens 
posteriorly, and is continued to the articular processes by two ridges. The lateral 
surfaces are concave and rough for muscular attachment. 

Development. — The axis has six or seven centers of ossification. In addition 
to the usual five, one or two appear for the dens, which is regarded as the displaced 
body of the atlas. A nucleus behind the dens, which remains distinct to three or 
four years of age, is considered to be the head of the axis. 



THE THORACIC VERTEBRA 
The thoracic vertebrae (Vertebrae thoracales) are usually eighteen in number in 
the horse, but there are sometimes nineteen, rarely seventeen. As regional char- 
acters we note the surfaces for articulation with the ribs and the length and form of 
the spinous processes. Those in the 
middle of the series are the most 
topical and present the following fea- 
tures: 

1. The bodies are short anil con- 
stricted in the middle. The ends are 
expanded and have articular surfaces 
which are not strongly curved ; the an- 
terior surface is convex, the posterior 
concave. On the upper part of each 
side are anterior and posterior costal 
facets (Fovea costalis cranialis, cau- 
dalis), which, with those of adjacent 
vertebrae and the intervening fibro-car- 
tilages, form sockets for the heads of 
the ribs. 

2. The arches are small. Their 
posterior notches are relatively large 
and are often converted into foram- 



Spinous 
jjroccss 




Facet for tubercle 
of rib 



Body 



-Seventh Thoracic Vert 
TERioR View. 



3. The articular processes are 

small. The anterior processes are in 
fact represented only by two oval facets f 
on the anterior part of the arch which 
face almost directly upward. The pos- 
terior processes spring from the base of the spinous process; their facets face 
almost directly tlownward. 

4. The transverse processes are short, thick, and tubei-ous at the free end. 
Each has a facet (Fovea transversaria) for articulation with the tubercle of the 
rib which has the same serial number. 

5. The spinous process is lai'ge, narrow, and slopes upward and backward. 
The anterior border is thin, the posterior wider and furrowed. The summit is 
expanded and rough. 



38 



THE SKELETON OF THE HORSE 



The first thoracic vertebra has the following specific characters: The body is 
wide ami flattened dorso-ventrally. In front it has a head like the cervical verte- 



Spinous "prncess 
Articular processes 



Arch — i 



Facet for tubercle of first rib 

Facet for head of first ril 
Fig. 14. — First Thoracic Verteb 




Transverse process 
■odij 



brse, and behind a cavity somewhat deeper than any other thoracic vertebra. Two 
large costal facets are found on either side, and a well-marked spine ventrally. 




Fig. 1.5. — Last Three Thor.acic Vertebr.e of Horse, Left View. 
It Body; 2, 2, facets for head of rib; S, facet for tubercle of rib; 4, 4' f articular processes; 5, 
6, mammillary process; 7, spinous process. 



ntervertebral foramen; 



The arch is large and strong, and has large notches. The articular processes are 
much larger than those of other thoracic vertelirje, and resemljle a good deal those 
of the seventh cervical. The transverse processes are short and thick, and each 



THE LUMBAR VERTEBRA 39 

has on its ventral aspect a large concave facet for articulation with the tubercle of 
the first rib. The spinous process is curved backward and tapers to a point. Its 
length is usually about three or four inches (ca. 8 to 10 cm.). This vertebra may be 
mistaken at first glance for the last cervical, but is promptly identified bj^ the three 
costal facets on each side and the length of the spine. 

The last thoracic vertebra is distinguishetl by the absence of the posterior pair 
of costal facets, antl the confluence of the anterior pair with those on the transverse 
processes. 

The serial position of others may be determined at least approximately by the 
following data: (1) The bodies gradually diminish in length and width to the 
middle of the region and then increase slightly. Their costal facets become smaller 
and less concave from first to last. The ventral crest is distinct on three or four 
vertebriB at either end of the region. (2) The transverse processes iliminish in 
size and are placed lower down as they are traced backward. Their costal facets 
become smaller and lower in position; on the last (and sometimes on its predecessor 
also) it fuses with the costal facet of the body. The upper non-articular part of 
the process gradually l^ecomes more sharjjly defined, and in the last four or five 
forms a distinct mammillary process, (3) The spinous processes increase in length 
to the third and fourth, and then gradually diminish to the fifteenth, beyond which 
they have about the same length. The backward inclination is most pronomiced 
in the second, the sixteenth is vertical, and the last two are directed a little forward. 
The longest spines {i. e., those of the withers) are the thickest and have expanded 
summits which remain more or less cartilaginous; the others are more plate-like, 
and are surmounted by a thick lip. The second spine is more than twice as large 
as the first. The summits of the fourth and fifth usually form the highest point 
of the withers. 

Development. — There are six or seven centers of ossification, three for the 
body, two for the arch, and one for the spinous process; some of the latter have an 
additional center for the summit. 



THE LUMBAR VERTEBRS: 

The hmibar vertebrfe (Vertebrse lumbales) are usually six in number in the 
horse. They are characterized by the size and form of their transverse processes. 

The bodies of the first three are semi-elliptical on cross-section, and present a 
distinct ventral crest. From the fourth backward they become wider and flatter 
and the ventral crest subsides. 

The arches of the first three are about equal in size and similar to that of the 
last thoracic; behind this they increase in breadth and height. The posterior 
notches are much deeper than the anterior ones. 

The anterior articular processes are fused with the mammillary processes, and 
present dorsally concave surfaces for articulation with the posterior pair of the 
preceding vertebra. The posterior articular processes project distinctly from the 
arch at the base of the spinous process, and have vcntrally convex articular surfaces, 
which fit into the concave surfaces of the anterior pair of the next vertebra. 

The transverse processes are elongated plates, flattened dorso-ventrally, which 
project outward and usually curve slightly downward; their length increases to 
the third or fourth, and then diminishes to the last, which is the shortest. The 
first one or two usually curve somewhat backward, the last two decidedly forward. 
Those of the fifth have an oval concave facet on the medial part of the posterior 
border for articulation with the sixth process; the latter has a corresponding con- 
vex facet on the anterior border, and a larger concave surface on the posterior border 
for articulation with the wing of the sacrum. Sometimes the fifth process has a 
small surface for articulation with the fourth. The medial part of the sixth process 



40 



THE SKELETON OF THE HORSE 



is thick, the lateral part thinner, narrower, and curved forward. The medial part 
of the fifth is also somewhat thickened. Medial to the articular surfaces the edges 
of the transverse processes are cut into by notches, which form foramina by apposi- 
tion with each other and the sacrum. 

The spinous processes resemble those of the last two thoracic vertebrae. 



Spinous process 

Mammillary process 
Articular process 




Ventral spine 
Fig. 16. — Second Lumbar Vertebra, of Horse; Posterior View. 

They are usually about equal in height, l:)ut minor differences are common, and the 
width diminishes in the last three. 

Development. — This is similar to that of the thoracic vertebrae. The extremi- 
ties of the transverse processes remain cartilaginous for some time after ossification 
is otherwise complete. 

The transverse processes of this region are considered equivalent to the proper transver.se 
process + the costal element, and hence the distinctive term processus lateralis (s. costarius) 



Spinous process 




Notch 



FiG. 17. — Last Lumb 



Ro(h/ 



Articular surface for 
wing of sacrum 
of Horse; Posterior View. 



has been proposed. The occurrence of a rib in connection with the transverse process of the first 
lumbar vertebra is common. Reduction of the number to Hve has been observed frequently, and 
may or may not be compensated by an additional thoracic vertebra. Very few cases are recorded 
of seven lumbar vertebrae — especially with the normal thoracic number. An anomalous \-ertebra 
with mixed thoracic and lumbar characters sometimes occurs at the junction of the two regions. 



THE SACRUM 



41 



THE SACRUM 

The sacrum (Os sacrum) is formed by the fusion of five vertebrae, and is con- 
veniently described as a single bone. It is triangular in form and is wedged in 
between the ilia, with which it articulates very firmly on each side. Its long axis 
is gently curved and slightly oblique, so that the posterior end is a little higher 
than the anterior. It presents two surfaces, two borders, a base, and an apex. 

The dorsal surface (Facies dorsalis) presents centrally the five sacral spines 
(Processus sijinosi), which are directed upward and backward, and have (with the 
exception of the first) tuberous summits which are sometimes bifid. 




Fig. is. — Sacrum of Ho 
I~V, Spinous processes; I-4, dorsal sacral foramina; 
with transverse processes of last lumbar vertebra; / 
canal. 



;se: Dorso-lateral View. 

, -5', articular processes; 6, surfaces of wings for articulation 
body of first sacral vertebra. Arrows point into sacral 



Tlie first spine is relatively thin and narrow, anil is not so high .as the s.aer.al angle of the 
ilium. The second is the longest and highest, and the length and height diminish to the last. 
The bases of the spines are often fused in old subjects. 

On either side of the spines there is a groove, in which are the four dorsal sacral 
foramina (Foramina sacralia dorsalia); the dorsal branches of the sacral nerves 
emerge through them. 

The pelvic surface (Facies pelvina) is concave in its length, witle in front, 
narrow behind. The curvature is variable and is more pronoimced in the mare 
than in the stallion. It is marked by four more or less distinct transverse lines 
(Linece transversae) , which indicate the demarcation of the l)odies of the vertebriE. 
At the ends of these lines are the ventral sacral foramina (Foramina sacralia ven- 



42 



THE SKELETON OF THE HORSE 



tralia), which are larger than the dorsal series and diminish in size from first to 
last; they transmit the ventral divisions of the sacral nerves. 

The dorsal and ventral foramina communicate with the sacral canal and are 
together equivalent to the usual intervertebral foramina. 

The lateral borders are rough, thick in front, thin behind. 

The base (Basis ossis sacri) is directed forward, and is relatively very wide. 
It presents centrally the body of the first sacral segment, which is wide transversely, 
flattened dorso-ventrally, and has a rounded surface which articulates with the 
last lumbar vertebra through the medium of an intervertebral fibro-cartilage. 
The ventral margin projects slightly, forming the promontory (Promontorium). On 




Fig. 19. — Sacrum of Horse; Ventral View. 
I-V, Bodiea of original five vertebrae, marked off by transverse lines; I-4, ventral sacral foramina; S, articular 
surface of body of first vertebra ; 6^6, notches ; 7, 7, surfaces of wings for articulation with transverse processes of last 
lumbar vertebra; 5, 5, wings; 9, auricular surface: iO, lateral border; li, transverse process; 13, posterior orifice 
of sacral canal; 13, last spinotis process. 



either side of the body there is a smooth notch, which, with one on the last lumbar 
vertebra, forms a large foramen for the passage of the ventral branch of the last 
lumbar nerve. Above the body is the entrance to the sacral canal, flanked by a 
pair of articular processes, which project upward and forward from the arch, and 
have concave surfaces medially for articulation with those of the last lumbar 
vertebra. Lateral to each of these is a smooth notch which is converted into a 
foramen by apposition ^vith the last lumbar vertebra. The lateral parts of the base, 
the alae or wings (Alae sacrales), are strong prismatic masses with pointed ends. 
Each has in front a large, oval, slightly convex surface for articulation with the 
transverse process of the last lumbar verteljra. Posteriorly there is an elongated 
oval area which faces dorso-laterally; this is the auricular surface (Facies auricu- 



THE COCCYGEAL VERTEBRA 43 

laris), which articulates with the iUum; it is shghtly concave in its length, and 
somewhat rough and irregular. The rest of the dorsal surface of the wing is rough- 
ened for ligamentous attachment, while the ventral surface is smooth. 

The apex (Apex ossis sacri) is the posterior aspect of the last sacral vertebra 
and is quite small. It presents the elliptical flattened surface of the body, above 
which is the triangular posterior opening of the sacral canal, surmounted by the 
last sacral spine. There is a pair of narrow notches between the arch and body, 
above which rudiments of articular processes may occur. 

The name sacral canal (Canalis sacralis) is applied to that part of the vertebral 
canal which traverses the sacruni. Its anterior part is large and has the form of 
a triangle with the angles rounded off; its width is nearly twice its height. Traced 
backward it is seen to diminish in size rapidly, and the posterior opening is small 
and triangular. 

The term lateral part (Pars lateralis) designates the portion lateral to the 
foramina, which results froni the fusion of the transverse processes. 

Development. — The several sacral vertebrae ossify in the typical manner. 
Separate centers for costal elements in the lateral parts have not yet been found in 
the domesticated animals. Fusion begins in front, and is usually not complete 
till adult age.^ The lateral parts unite before the bodies. It is rather curious 
that the epiphyseal plates of adjacent segments unite with each other before they 
fuse with the main portion of the bodies. 



THE COCCYGEAL VERTEBRA 
The coccygeal vertebra (Vertebra coccygeae) vary considerably in number, but 
eighteen may be taken as an average. From first to last they become reduced 
in size and, with the exception of a few at the beginning of the series, consist of 



r~ 





spinous process Spinous process 

Vertebral foramen Vertebral forainm 

, , Arch 

Arch 

Transverse process 

Transverse proc- 
ess 



Body Body 



Fig. 20. — First CoccygEAL Vertebra of Horse; Fig. 21. — Secont> Coccygeal Vertebra op Horse; 

Posterior View. Posterior View. 

Leader to arch points to rudimentary articular process. 

bodies only. The first three have bodies which are somewhat flattened dorso- 
ventrally, constricted in the middle, and have at the ends convex, elliptical, artic- 
ular surfaces. The ventral surface has a median groove (Sulcus vasculosus) for 
the coccygeal artery. The arch is small and triangular; it is formed of two flat 
plates which are prolonged to form a short spinous process with a thickened and 
often double summit. The anterior notches are absent. Functional articular 
processes are not present, but small rudiments of the anterior pair commonly occur. 
The transverse processes are relatively large plates which project horizontally 
outward. Further back the arch becomes incomplete dorsally, and soon disap- 
pears; the transverse processes gradually fade out, and the vertebra are reduced 
to cylindrical rods of diminishing size. The last one has a pointed end. 

' It is not rare to find fusion of some of the bodies incomplete even in adult subjects. 



M 



THE SKELETON OF THE HORSE 



Variations. — The number is said by good observers to vary between fourteen and twenty- 
one. In old age the first is often fused with the sacrum, and sometimes with the second. The 
arch of the third may he open. 



THE VERTEBRAL COLUMN AS A WHOLE 

In the mid-dorsal line is the series of spinous processes, which are low ridges 
in the cervical region with the exception of the secontl and seventh, reach their 
nnaxinium height at the fourth and fifth thoracic vertebrie, antl diminish to the 
fifteenth or sixteentli thoracic. Behintl this they are about equal in lieight as far 
as the last lumbar and first sacral, which are somewhat lower. The second sacral 
spine is about as high as the middle lumbar; behind this they diminish rather 
rapidly in height and fade out about the third coccygeal. Their inclination back- 
ward is most decided at the second thoracic and diminishes from the sixth or seventh 
to the six-teenth thoracic, which is vertical and is termed the anticlinal or dia- 
phragmatic vertebra. Behind this they are inclined a little forward until the 
sacrum is reached; here there is an abrupt change to the backward inclination, so 
that a considerable interspinous angle is formetl. 

On either side of the spinous processes is a vertebral groove which contains the 
deep muscles of the spine. The floor of the groove is formed l)y the arches and 
articular processes. It is wide in the neck and narrows progressively in the back. 

Viewed from the side, the column presents a series of curves. When the head 
and neck are in the ordinary neutral position, the anterior part of the cervical spine 
forms a gentle curve, concave ventrally. The posterior cervical and first thoracic 
vertebra form a more pronounced curve in the opposite direction. At the junction 
of the cervical and thoracic regions there is a marked change of direction, forming a 
ventral projection or angle. At the second thoracic vertebra a gentle curve, con- 
cave ventrally, begins. This is continued to the lumbo-sacral junction, where 
there is a change of direction, and hence a promontory. The sacrum has a variable, 
but never very pronounced, ventral concave curvature, which is continued in a 
much accentuated form in the coccygeal region. It shoukl be noted that a line 
through the sunimits of the spines does not correspond to these curves formed by 
the bodies. 

The vertebral canal corresponds in its curvature to that of the bodies. Its 
caliber varies greatly at different points. The greatest diameter is in the atlas, 
where it contains the dens of the axis in addition to the spinal cord, and provision 
must be made for extensive movement. It is very much smaller in the axis. It 
widens considerably at the junction of the cervical and thoracic regions to accom- 
modate the cervical enlargement of the spinal cord. Beyond this it diminishes, 
and is smaller in the middle of the back than at any preceding point; this is corre- 
lated with the small size of the spinal cortl and the very limited movement of the 
spine here. Bej-ond the middle of the lumbar region it again enlarges considerably 
to contain the lumbar enlargement of the spinal cord. The caliber diminishes very 
rapidly from the second sacral segment backward, and the canal ceases to be com- 
plete at the fourth coccygeal vertebra. 

The transverse and vertical diameters of the vertebral canal at various points are given 
in the annexed table. The measurements were made on a horse of medium size; they represent 
the maximum width and height in the middle of the vertebra and are expressed in centimeters. 



Vertebra 


CI 


C2 


C4 


C7 


TIO 


L3 


LO 


SI 


So 




5.2 
4.2 


2.6 
2.5 


2.6 
2.1 


3.5 
2.5 


2.3 
1.7 


2.4 
1.8 


4.0 
2.5 


4.0 
2.1 


1.8 


Vertical 


1.5 



The articular processes are very large anrl wide apart in the neck, greatly 



THE RIBS 45 

reduced and much closer together in the back, larger and interlocking in the lumbar 
region. 

The transverse processes are large and outstanding in the neck, where they 
form the lateral boundary of a ventral groove occupied bj' the longus colli muscle. 
In the l^ack they are short and stout, and are characterized by the facets for the 
tubercles of the ribs. On the first thoracic vertebra this facet is large, deeply con- 
cave, and situated almost directly outward from the cavity for the head of the rib ; 
traced backward it becomes smaller and flatter, and gradually comes to lie behind 
the cavity for the head of the rib, with which it is fused on the last and often also on 
the next to the last thoracic vertebra. The processes in the lumbar region have a 
characteristic elongated plate-like form. In the sacral region they are fused to 
form the wings and lateral parts of the sacrum. In the coccygeal region they are 
at first of considerable size relatively, but undergo rapid reduction, and disappear 
at the fifth or sixth vertebra. 

The cavities for the heads of the ribs diminish progressive!}- in size and depth 
from first to last. 

The mammillary processes are usually distinct on the fourteenth to the seven- 
teenth thoracic vertelirie. In front of these they blend with the traniBverse, behind 
with the anterior articular, processes. 

The length of the vertebral column (including the intervertebral fibro-cartilages) in a horse 
of medium size is about nine feet (ca. 2.7 meters). The relative lengths of the various regions ap>- 
pear to vary most in the neck and back. The following average lengths of the several regions 
were obtained by measurement of several subjects: Cervical, 70 cm.; thoracic, 86 cm.; lumbar, 
34 cm.; sacral, 20 cm.; coccygeal, 60 cm. The percentage values are approximately 26, 32, 12.5 
7.5, 22. 



The Ribs 

There are usually eighteen pairs of ribs in the horse, Ijut a nineteenth ril) on 
one side or both is not at all rare. Eight are sternal ribs, the remainder asternal. 
Ribs from different parts of the series vary much in length, curvature, and other 
characters. We will therefore consider as a t3'pe a rib from the middle of the series 
first, and afterward note the chief serial cUfferences; such a rib has the following 
characters: 

The shaft or body (Corpus costs) is elongated, relatively very narrow, and 
strongly curved; the curvature is most pronounced in the dorsal third, and the 
ventral part is twisted and inclined inward, so that when a rib is laid wth its lateral 
surface on the table, the sternal end is raised. The lateral surface is convex in 
its length and also transversely; its anterior part is, however, grooved longitudin- 
ally. A distinct angle, i. e., a point at which the curve of the rib changes rather 
suddenly, as in man, can scarcely be said to exist in the horse. The term is some- 
times applied, however, to a corresponding rough elevation which gives attachment 
to the longissimus muscle. The medial surface is smooth, concave in its length, 
and rounded from side to side; the costal groove (Sulcus costs) , situated posteriorly, 
is very distinct above and fades out about the middle; it contains the intercostal 
vein. The anterior border is concave, the posterior convex. 

The vertebral extremity (Ext.remitas vertebralis) consists of the head, neck, 
and tubercle. The head (C'apitulum costs) has an articular surface (Fades 
articularis capituli costs) which is composed of two convex facets, anterior and 
posterior, separated by a groove (Sulcus capituli) for the attachment of the con- 
jugal ligament. It articulates with the cavity formed Ijy facets on the bodies of 
two adjacent thoracic vertebrs and the intervertebral filiro-cartilage. The neck 
(Collum costs) is roughened above and in front. The tubercle (Tuberculum costs) 
is placed above and behind the junction of neck and shaft; it has an oval surface 



46 



THE SKELETON OF THE HORSE 



(Facies articularis tuberculi costse) for articulation with the transverse process of 
the corresponding thoracic vertebra. 

The sternal extremity (Extremitas sternalis) is slightly enlarged, and is united 
with the costal cartilage. 

The first rib is easily distinguished. It is shortest and the shaft widens greatly 
toward the sternal end. At the lower part of the anterior border there is a smooth 



Head Neck Tubercle 
Groove 



Costal groove 




Head 



Anterior border 




1^ 
Sternal extremity 

22. — Left Eighth Rib of Hoese; Lat- 
eral View. 




Sternal extremity of costal cartilage 



-Right Eighth Rib and Costal Caetilagb 
Horse: Medial View. 



impression where the brachial vein curves around it; above this there is commonly 
a small tubercle (Tuberculum scaleni) which indicates the lower limit of the in- 
sertion of the scalenus muscle. The costal groove is absent. The head is large and 
has two facets of unequal extent, which meet at an acute angle in front ; the smaller 
one faces forward and articulates with the last cervical vertebra; the larger one is 
directed medially and articulates with the first thoracic vertebra. The neck is 
thick and very short. The tubercle is larger than that of any other rib and has an 



THE COSTAL CARTILAGES 



47 



extensive articular surface which is convex in its length. The sternal end is larger 
than that of any other rib; it is thick and very wide, and is turned a little forward. 

The last rib is the most slender and regularly curved. It is usually but little 
longer than the second. The facet on the tubercle is confluent with that of the head. 
(This feature, however, is common on the seventeenth also, and may occur on the 
sixteenth.) 

The serial position of the other ribs may be determined approximately by the fol- 
lowing considerations : The length increases from the first to the tenth and eleventh 
and then diminishes. The width increases somewhat to the sixth and then diminishes. 
The anterior border is thin and sharp from the 
second to the eighth, and behind this becomes thick 
and rounded. The groove of the lateral surface is 
distinct on the fourth to the eighth inclusive. The 
curvature increases in degree rapitlly from the second 
to the seventh, remains about the same to the six- 
teenth, and then decreases very noticeably. In re- 
gard to ilorso-ventral direction, the first rib inclines 
a little forward, the second is about vertical, while 
behind this they slope backward in increasing de- 
gree, so that a transverse plane tangent to the ventral 
ends of the last pair cuts the third lumbar vertebra. 
The head and tubercle diminish in size from first to 
last. Their relative positions change, in that the 
tubercle of the first rib is almost directly lateral to 
the head, while further Ijack it gradually comes to 
lie behind it. The neck is longest on the longest 
ribs, and is absent on the last two or three. A 
costo-transverse foramen (Foramen costo-transver- 
sarium) is formed between the neck and the trans- 
verse process. 

Development. — The ribs ossify in cartilage from 
three centers, one each for the shaft, head, and 
tuliercle; tiie third center is absent in some of the 
posterior ribs. 

Cartilage 




Fig. 24. — Left First Rib of Horse; 
Medial View. 



Variations. — A nineteenth rib on one side or both is not 
at all rare. It is usually imperfectly developed and quite vari- 
able. In many cases it is a mere strip of cartilage connected 
by ligament with the first lumbar transverse process; in other 
cases it is well developed, and may be fused with the process; 
in others again it is connected with a vertebra which may be thoracic or lumbar or ambiguous 
in character. It is commonly floating, but may be attached to the eighteenth costal cartilage. 
Reduction in number is uncommon. In rare cases the first rib is imperfectly developed and does 
not reach to the sternum. Partial fusion of adjacent ribs and other anomaUes occur. 



THE COSTAL CARTILAGES 

The first costal cartilage is an inch or more (2.5 to 3 cm.) in length. The 
dorsal end is very wide and thick. The sternal end is small. The two articulate 
with each other as well as with the sternum. The cartilages of the other sternal 
ribs increase progressively in length and become more rotmded. The sternal end 
is enlarged and has an elliptical convex facet for articulation with the sternum. 
The cartilages of the asternal ribs are long, slender, and pointed. The ninth is 
very firmly attached to the eighth; it and the next two are the longest and behind 
this they diminish progressively in size. The cartilages of the asternal ribs overlap 
and are attached to each other by elastic tissue, forming the costal arch (Arcus 



THE SKELETON OF THE HORSE 



costarum). Except in the case of the first, the cartilage does not continue the 
direction of the rib, but forms with the latter an angle which is open in front, and 
increases from second to last. More or less extensive ossification is to be regarded 
as a normal occurrence, especially in the cartilages of the sternal ribs. 



Ventral 
border 



The Sternum 

The sternum of the horse is shaped somewhat like a canoe; it is compressed 

laterally, except in its posterior part, which is flattened dorso-ventrally. It is 

inclined obliquely so that the posterior end 
is about six to eight inches (15 to 20 cm.) 
lower than the ant(>rior. 

The dorsal surface (Facies dorsalis) has 
the form of a very narrow isosceles triangle 
with the apex in front. It is concave longi- 
tudinally, flattened transversely. 

The lateral surfaces (Facies laterales) 
are convex above, slightly concave below, and 
diminish in extent Ijehind. Each presents on 
its upper part seven costal cavities (Fovese 
costales), with which the sternal ends of the 
second to the eighth costal cartilages inclu- 
sive articulate. These cavities are situated 
in series at the intersternebral junctions. 
The first four are elliptical in outline with 
the long diameter vertical, and are sepa- 
rated by considerable regular intervals. 
The others are progressively smaller, more 
circular, and closer together. The area 

below these cavities gives attachment to the pectoral muscles. 

The dorso-lateral borders separate the dorsal and lateral surfaces. They give 

attachment to the lateral branches of the sternal ligament. 

The ventral border forms the prominent keel-like crest of the sternum (Crista 

sterni) which may be felt in the living animal; it fades out behind. 




Xiphoid cartilage 



Fig. 25. — Sternum and Costal Cartilages oi 
Horse; Ventral View, (.\fter EUenberger 
Baum, Anat. f. Kiinstler.) 




r a. I 

Fig. 26.— Stebnom of Horse; Lateral View. 
The aternebrae are designated by Roman numerals and the costal facets by ordinary figures. 



The anterior extremity or manubrium stemi^ can he distinctly' felt in the 
central furrow of the l:)reast. It consists largely of a laterally compressed cartil- 
aginous prolongation, commonly called the cariniform cartilage. Its lateral sur- 
faces are flat and furnish attachment to muscles of the breast and neck. The 

• The manubrium sterni of man is equivalent, strictly speaking, to the cariniform cartilage 
+ the first osseous segment of the horse. 



THE THORAX — THE OCCIPITAL BONE 



49 



ventral border is rounded, and is continuetl backward on the body of the bone. 
The dorsal border is concave ami has an articular cavity for the first pair of costal 
cartilages. 

The posterior extremity is formed by the xiphoid cartilage (Processus xiphoideus). 
This is a tliin plate, connected in front with the last hony segment by a relatively 
thick, narrow neck, and expanding in nearly circular form behind and laterally. 
Its dorsal surface is concave, and gives attachment to the diaphragm. The ventral 
surface is convex and furnishes attachment to the transversus abdominis and the 
linea allm. The free margin is very thin. 

Development. — At birth the sternum of the horse consists of seven bony seg- 
ments termed sternebris, which are united by in- 
tersternebral cartilages. The last two sternebrae 
fuse in the second month, but the others do not 
usually unite completely even in old age. The 
sternebrte consist of very vascular spongy bone 
covered by a very thin layer of compact sub- 
stance. The adult sternum thus consists to a />-^'^WL Jj Ifcr" ^'''^^ 
very considerable extent of persisting cartilage, ri^^jp '^ ^Mk^T^X '''"'"'!"'" 
viz., the intersternebral cartilages, the ventral *"^ 
keel, and the extremities; in old age these under- 
go partial ossification. 

First rib 



THE THORAX 

The bony thorax of the horse is rcmarkal.)ly 
compressed laterally in its anterior part, but 
widens greatly behind. The anterior aperture 
(Apertura thoracis cranialis) is oval and very 
narrow below; in a horse of medium size its 
greatest width is about 4 inches (10 cm.), and its 
height 7 to 8 inches (ca. 18-20 cm.). The ventral 
wall (3r floor is about 16 inches (40 cm.) long, and 
the dorsal wall or roof about 38 to 40 inches 
(95-100 cm.) long. The height from the last seg- 
ment of the sternum to the seventh or eighth 
thoracic vertebra is about twice that of the anterior 
aiDerture; this is due to the olsliquity and diver- 
gence of the roof and floor. The greatest width of 
the posterior aperture is about 20 to 24 inches 

(50-60 cm.). The intercostal spaces (Spatia intercostalia) increase in width from 
the first to the seventh or eighth, and then diminish. Their average width is 
about lj<i to 13^ inches (3-3.5 cm.). 




', — Anterior Aperture of Tho- 
s OF Horse, (.\fter Schmaltz. Atlas 
Anat. d. Pferdes.) 



The Bones of the Skull 

(A) BONES OF the CRANroM 
The bones of the cranium (Ossa cranii) are the occipital, sphenoid, ethmoid, 
interparietal, parietal, frontal, and temporal. The first three are single, the others 
paired. 

The Occipital Bone 

The occipital bone (Os occipitale) is situated at the posterior part of the cra- 
nium, of which it forms the posterior wall and part of the ventral wall or base.' 
1 The long axis of the skull is considered to be horizontal in these descriptions. 



50 



THE SKELETON OF THE HORSE 



Its lower part is perforated centrally by a large, almost circular opening, the 
foramen magnum (Foramen occipitale magnum), at which the cranial cavity and 
vertebral canal join. The foramen is bounded laterally and dorsally by the lateral 
parts of the bone, antl ventrally by the basilar part. Above the lateral parts — 
but not entering into the formation of the foramen magnum — is the squamous part. 

The lateral parts (Partes laterales)^ bear the occipital condyles (Condyli oc- 
cipitales), which articulate with the atlas. The condyles are obliquely placed, 
wide apart dorsally, and separated ventrally by a small interval (Incisura inter- 
condyloidea). The articular surface is curved so sharply in the dorso-ventral 



Occipital Parietal Squamous temporal 

^_ 

Frotital 




i. Occipital condyle; ^, paramastoid procuss; J, mastuid pruccss; -^, posterior process of 
S, external acoustic process; 6, zygomatic process of temporal bone: 7, postglenoid process; S, g 
temporal bone; 9, condyle of same; 10, supraorbital process of frontal bone; 11, temporal 
orbital part of frontal bone; i3, fossa sacci lacrimalis; 7^, orbital surf ace of lacrimal bone; 
zygomatic process of malar bone; 17, maxillary tuberosity; IS, facial crest; 19, infraorbital 
lary notch; £1, body of premaxilla; £l', nasal process of same; S2, body of mandible; B3, 
horizontal and vertical parts of ramus of mandible; B6, condyle of mandible; 27, coronoid 
angle of mandible; 29, vascular impression; 30, interalveolar margin; 31, incisor teeth; S& 
bone (great cornu). 



squamous temporal bone 
lenoid cavity of squamous 
part of frontal bone; i^i 
IS, lacrimal tubercle; 16, 
foramen; SO, naso-maxil- 
mental foramen; 24, 2.5 
process of mandible; 2S. 
f, canine teeth; 33, hyoid 



direction as to form a blunt ridge. The cranial surface is concave and smooth. 
Lateral to the condyle is the paramastoid process (Processus paramastoideus),^ a 
strong plate of bone which projects downward and backward; its lateral surface is 
convex and roughened for muscular attachment; its medial surface is concave from 
end to end. Between the root of this process and the condyle is a smooth depres- 
sion, the condyloid fossa (Fossa condyloidea ventralis) ; in this is the hypoglossal 
foramen (Foramen hypoglossi), which transmits the nerve of like name. 

The basilar part (Pars basilaris)^ is a strong, somewhat prismatic bar, which 

^ Also known as the exoccipitals. ^ w^q known as the styloid or jugular process. 

^ Also termed the basi-occipital or basilar process. 



THE OCCIPITAL BONE 



51 



extends forward from the ventral margin of the foramen magnum. It is wide and 
flattened behind, narrower and thicker in front. The ventral surface is rounded. 
The cranial surface is concave and smooth ; its posterior part supports the medulla 
oblongata, and its anterior j^art has a shallow cavity on which the pons rests. The 
lateral borders are thin and sharp, and form the medial margin of the foramen 
lacerum. The anterior end has, in the young subject, a semicircular, flat, pitted 
surface which is attached to the body of the sphenoid bone by a laj'er of cartilage ; 
in the adult there is complete fusion. On the ventral aspect of the junction are the 
basilar tubercles (Tubercula basilaria) for the attachment of the ventral straight 
muscles of the head. 

The squamous part (Squama occipitalis)' is the somewhat quadrilateral mass 




Fig. 29. — Occipital Bone of 
ly Depression of squamous part for cerebellum: ^. foramer 
a, squamous part; 6, lateral part; r, basilar part; d, junction ^ 
/, junction with petro-mastoid part of temporal bone. 



Colt; Front View. 

magnum; 3, paramastoid process; .$, condyloid fossa; 

nth interparietal bone; e, junction with parietal bone; 



situated dorsal to the lateral parts, from which it remains distinct till the second 
year. The external surface is crossed by a very prominent ridge, the nuchal crest 
(Crista nuchalis) ; the middle part of this is thick, transverse in direction, and forms 
the highest point of the skull when the head is in the ordinary position; laterally it 
becomes thinner and runs downward and forward to join the temporal crest.- The 
crest divides the surface into two very unecjual parts ; the small dorsal area ( Planum 
parietale) presents a median ridge which is the posterior part of the external parietal 
crest (Crista sagittalis externa); the large ar(>a ventral to the crest (Planum nu- 
chale) has a central eminence, the external occipital protuberance, on which the funic- 
ular part of the ligamentum nucha; is attached. The internal surface is concave 

• .\lso known as the supraoceipital. 

- The nuchal crest of this description is equivalent to the external occipital protuberance 
and superior nuchal line of man; it has been commonly termed the occipital crest, but is not the 
equivalent of that feature of the human skull. A curved line a little lower down, which is con- 
tinued on the paramastoid process, represents the inferior nuchal line of man. 



52 



THE SKELETON OF THE HORSE 



and presents a deep central depression and two shallower lateral ones which adapt 
it to the surface of the cerebellum. 

The parietal border (Marg;o iiariotalis) is united by suture with the parietal 
and interparietal. The mastoid border (Margo mastoideus) joins the petro- 
mastoid part of the temporal l>one. The basilar part is connected by cartilage (in 
the young subject) with the body of the sphenoid. The conilyles articulate with 
the atlas. 

Development. — The occipital bone ossifies in cartilage from four centers, and 
consists at birth of four pieces as described above. The lateral parts unite with the 




Fig. 3(1.- 

A, B, C, .Squamous, lateral, and basilar parts sf occipital bone; D, interp-nrietal bone: E, parietal bone; F, squa- 
mous temporal bone: G, petro-mastoid part of temporal bone; 1, external occipital protuberance; 2, 2, depresstons iu 
which complexus tendons are attached; 3, sutural (prcinterparietal?) bone; 4, supraorbital process; 5, zygomatic 
process of temporal bone; 6, postglenoid process; 7, posterior process of squamous temporal bone; 8, mastoid process; 
9, paramastoid process; 10, occipital condj-le; 11, arrow in foramen magnum. 



basilar part at three to four months, and with the squama in the second year, when 
the bone is consolidated. 

The parieto-occipital suture and the spheno-occipital synchondrosis are ob- 
literated about the fifth year usually. The occipito-mastoid suture partially ossifies 
in old subjects. 

The Sphenoid Bone 

The sphenoid bone (Os sphenoidale) is situated in the base of the cranium, its 
central part lying in front of the basilar part of the occipital. It consists of the 
body, two pairs of wings, and two pterygoid processes. 

The body (Corpus) is situated medially; it is cylindrical, but flattened dorso- 
ventrally, and wider in front than behind. Its ventral surface (Facies externa) is 
convex in the transverse direction, and its anterior ]iart is concealed to a large extent 
by the vomer and pterygoid bones. The cerebral surface (Facies cerebralis) 
presents the following features: (1) In front there is a raised, flattened part (Jugum 
sphenoidale) which is partially subdivided by a median elevation into two slightly 
concave lateral areas; this part has a posterior, thin, free margin (Limbus sphe- 



THE SPHENOID BONE 



53 



noidalis), which overhes the entrance to the optic foramina. The median ridge is 
termed the ethmoidal spine, since it fits into a notch of tlie crilsriform plate of the 
ethmoid bone and joins the crista galli. (2) Just l^ehind this and at a lower level 
is a smooth transverse depression, the optic groove (Sulcus chiasmatis), on which 
the optic chiasma rests. (3) From each end of this groove the optic foramen 
(Foramen opticum) passes forward antl outward to terminate in the posterior part 
of the orbital fossa.' (4) Near the posterior end is a central depression, the hypo- 
physeal or pituitary fossa (Fossa hypophyseos), which lodges the hypophysis cerebri 
or pituitary botly. On each side of this is a shallow groove for the internal carotid 
artery and the cavernous sinus. The anterior end is ex]3anded, anil joins the eth- 
moid and palatine bones; it is excavated to form the sphenoidal sinuses. These 
cavities extend back as far as the optic 
groove, and are usually continuous in front 
with the cavities in the vertical parts of the 
palate bones;- they are separated by a com- 
plete septum which is not always median. 
The posterior end is flat and is joined to 
the basilar part of the occipital ; at the line 
of junction there is dorsally a slight trans- 
verse elevation, the spheno-occipital crest 
(Crista spheno-occipitalis). 

The orbital wings (Ahe orbit ales) curve 
dorso-laterally from the sitles of the b(jdy of 
the presphenoid. Their cerebral surface is 
concave, and is marked by digital impres- 
sions (Impressiones digitatse) for the gj-ri 
of the cerebrum. The lateral surface is con- 
vex and is largely concealed by the overlap- 
ping temporal wing and the squamous tem- 
poral and frontal bones ; a narrow part of it 
(Facies orbitalis) is uncovered on the medial 
wall of the orbital cavity at the sphenoidal 
notch of the frontal bone. The dorsal bor- 
der unites with the frontal lione at the 
spheno-frontal suture. The anterior border 
joins the ethmoid at the spheno-ethmoidal 
suture; at its lower part it concurs with the 
ethmoid and frontal in the formation of the 
ethmoidal foramen (Foramen ethmoidale).' 
The posterior border is overlapped by the 
temporal wing and the squamous temporal. 
The root of the wing is perforated by the 
optic foramen (Foramen opticum) . Immedi- 
ately below and behind the latter (i. e., beneath the root) is the foramen orbitale. 
Below this, and separated from it usually by a thin and often incomplete plate, is a 
larger opening, the foramen rotundum, which is bounded externally by the root of 
the pterygoid process. 

The temporal wings (Alae temporales) extend outward and somewhat upward 
from the body of the postsphenoid; they are smaller than the orbital wings and 




Fig. 31. — Sphenoid Bone and Basil 
Occipital Bone of New-born Fc 
View. 

C, Body of presphenoid; C, body of postsphe- 
noid: B.O., basilar part of occipital bone; .4.0., orbital 
wing of sphenoid bone: A.t., temporal wing of sphe- 
noid bone; 1, 1, optic foramina: 2, optic groove; 3, 
hypophyseal fossa; 4. 5, grooves; 6, ethmoidal 
notch; 7, ethmoidal spine; 8, junction with crib- 
riform plate of ethmoid bone; 9, junction with 
frontal bone; 10, junction with squamous temporal 
bone; 11, margin of foramen lacerum an terius; 12, 
spheno-occipital crest; 13, junction of basilar part 
of occipital bone with lateral part. 



1 This foramen might well l)e called a canal, since it is an inch or more in length. 

- The cavity so formed may be termed the sphenopalatine sinus. The sphenoidal sinus may 
be a separate ca\'ity which communicates only with the ventral ethmoidal meatuses; this arrange- 
ment exists in about a third of the cases according to PaulU. 

' Also called the internal orbital foramen. 



54 THE SKELETON OF THE HORSE 

are irregularly quadrilateral in outline. The temporal surface (Facies temporalis) 
enters into the formation of the infratemporal fossa, and Ijears the pterygoid process 
on its anterior part; at the junction with the body there is a small groove which 
leads forward to the pterygoid canal. The cerebral surface (Facies cerebralis) 
presents, at the junction with the body, two longitudinal grooves (Sulci nervorum). 
The lateral groove is the larger, and leads forward to the foramen rotundum; it 
contains the maxillary nerve. The medial groove conducts to the foramen orbitale, 
and contains the cavernous sinus of the dura mater. The outer groove is bounded 
laterally by a thin overhanging crest, on which is a small groove for the fourth nerve. 
The remaintler of the surface is concave and supports the pyriform lol^e of the brain. 
The dorsal border joins the squamous temporal at the spheno-squamous suture. 
The anterior border joins the orbital wing alcove; below this it is free and forms the 
pterygoid crest (Crista pterygoidea). The crest is continued on the pterygoid 
process; on or under its upper part there is usually a small opening, the trochlear 
foramen (Foramen trochleare). Just behind the crest is the foramen alare parvum/ 
through which the anterior deep temporal artery emerges from the alar canal of 
the pterygoid process. The posterior border forms the anterior boundary of the 
foramen lacerum; it presents three notches, which are, from within outward, the 
carotid, oval, and spinous (Incisura carotica, ovalis, spinosa). The angle of junc- 
tion of the dorsal and posterior l:)orders articulates with the parietal bone. 

The pterygoid processes (Processus pterygoidei) arise from the temporal wings 
and the body. They project downward and forward, and curve outward at the 
lower part. The root is perforated by the alar canal (Canalis alaris) ,- which trans- 
mits the internal maxillary artery. From this canal a branch leads upward and 
forward to open at the foramen alare parvum. The lateral siuface is concave, and 
is marked by lines for muscular attachment. The medial surface is convex; it is 
largely concealed by the overlapping palate and pterygoid bones. 

The pterygoid canal (Canalis pter.ygoideus)^ continues the groove noted on the 
ventral surface of the temporal wing at its junction with the body. It extends for- 
ward and upward between the root of the pterygoid process, the presphenoid, and 
the pterygoid bone, and opens in the posterior part of the pterygo-palatine fossa. 
It transmits the nerve of the pterygoid canal. 

Development. — The sphenoid is ossified in cartilage, and consists in early life 
of two distinct parts, the presphenoid and postsphenoid. The former develops 
from two centers, one in each wing; the latter has three centers, one for the body 
and one for each wing. The pterygoid processes ossify from the centers of the 
temporal wings. 

In the new-born foal the unossified dorsal part of the orbital wing fits into a hiatus of the 
frontal bone; in some cases it comes to the surface through a defect in the frontal bone at the place 
where the horn process is situatM in animals which have frontal horns. 

The Ethmoid Bone 

The ethmoid bone (Os ethmoidale) lies in front of the body and orbital wings 
of the sphenoid. It projects forward between the orbital parts of the frontal bones 
and enters into the formation of the cranial, nasal, and paranasal cavities.'' It 
consists of four parts — the cribriform plate, two lateral masses, and the perpen- 
dicular plate. 

The cribriform plate (Lamina cribrosa) is a sieve-like partition between the 

' Also termed the temporal foramen. 

' This is also called the subsphenoidal canal or pterygoid foramen. 

' Also known as the Vidian canal. 

■* On account of its deep situation and the fact that it cannot be separated from its surround- 
ings, the ethmoid must be studied by means of appropriate sagittal and transverse sections of the 
skull. 



THE ETHMOID BONE 



55 



cranial and nasal cavities. Its margin joins the orbital wings of the sphenoid 
laterally, the body of the sphenoid ventrally, and the cranial plate of the frontal 
bones dorsally. Its cerebral surface is divided into two parts by a median ridge, 
the crista galli, which may be regarded as the intracranial projection of the perpen- 
dicular plate. Each half forms a deep oval cavity, the ethmoidal fossa, which 
lodges the olfactory bulb. The plate is perforated by numerous small foramina for 
the passage of the olfactory nerve filaments, and on either side is the much larger 
ethmoidal foramen. The nasal surface is convex, and has the lateral masses 
attached to it. 

Each lateral mass or labyrinth (Labyrinthus ethmoidalis) is conical in shape and 
its base is attached to the cribriform plate. It projects forward into the posterior 




Votner 



Fig. 32. — Cross-section of Cr.\nh:m of Horse. The Section Passes Through the M 
IS Viewed from In Front. 
1, Lateral mass of ethmoid bone; 2, perpendicular plate of same; 3, common nasal meatus; 
sinus: 5, perpendicular part of palatine bone; 6, zygomatic process of temporal bone; 7, zygomati 
part of frontal bone. 



OF the Orbits ; 



sphenopalatine 
.rch; S, orbital 



part of the nasal cavity. The medial surface is separated by a narrow space from the 
perpendicular plate. The lateral surface is convex and faces chiefly into the frontal 
and maxillary sinuses, but is attached behind to the inner wall of the orbital cavity; 
it is covered by a very thin layer of bone, the lamina lateralis. The mass consists 
of a large number of delicate, scroll-like plates of bone, tenned ethmo-turbinates.^ 
These are attached to the lamina lateralis, and are separated by narrow intervals 
termed ethmoidal meatuses, which communicate with the nasal cavity. In the 
fresh state the ethmo-turbinates are covered with mucous membrane. 

The lateral mass is a very complex structure, the arrangement of which may be understood 
by examination of cross-sections. Each mass consists of six turbinates which extend almost to the 

'The term "ethmoid cell," borrowed from human anatomy, should not be retained, since 
it connotes an entirely erroneous conception of these structures in macrosmatic animals, such as 
those under consideration. 



56 



THE SKELETON OF THE HORSE 



perpendicular plate and are termed endoturbinates. These diminish in size from above down- 
ward; the largest is attached to the nasal bone, and is hence usually called the dorsal or nasal 
turbinate; the second is much smaller, and is very commonly termed the great ethmoid cell. 
The cavity enclosed by this communicates laterally with the maxillary sinus, but not directly 
with the nasal cavity. Between the endoturbinates are twenty-one small ectoturbinates, and 
all are beset with secondary and tertiary coiled lamellse. 

The perpendicular plate (Lamina perpendicularis) i.s median, and forms the 
posterior part of the septum nasi. Its lateral surfaces are nearly plane, but are 
marked below Ijy some grooves and ridges; they are covered by the nasal mucous 
membrane. The anterior border is irregular and is continuous with the septal 
cartilage. The posterior border projects into the cranial cavity as a ridge, the 

Frontal Posterior end Supraorbital 

suture of frontal sinus process 

(sawn off) 



Frontal hone (temporal part} 
Orbital wing of sphenoid 




Foramen orhitale 
Foramen rotundum 
Alar canal 



of sphenoid Pterygoid process 



Fig 33. — Cross-section of Cranium or Horse. The Section is Cut Just in Fro.nt of the Tf.mpor.\l Condyle 

AND Is Viewed from Behind. 
1, Internal plate of frontal bone; 2, crista galli; 3. cribriform plate; 4. ethmoidal foramen; 5, ethmoidal spine of 

phenoidbone; 6. optic foramina. 



crista galli. The dorsal border joins the frontal bones at their line of junction. 
The ventral border is received into the groove of the vomer. 

Development. — The ethmoid develops in cartilage from five centers, two for 
each lateral mass, and one for the perpendicular plate; from the latter ossification 
extends into the cribriform plate. At birth the perpendicular and crilsriform plates 
are cartilaginous. By the time ossification is complete the ethmoid has united 
with surrounding bones to such an extent that it cannot be separated intact for 
study. 

The Interparietal Bone 
This bone (Os interparietale) is centrally placed between the squamous part 
of the occipital and the parietal bones. It is usually described as a single bone, 
although it ossifies from two chief lateral centers, and is often distinctly paired in 
skulls of young foals. 



THE PARIETAL BONES 



57 



The external, parietal surface (Facies parietalis) is quadrilateral and is flat and 
smooth in the very j'oung foal ; later it presents the parietal crest. 

The internal, cerebral surface (Facies cerebralis) presents the internal occipital 
protuberance, a three-sided process which projects downward and forward into tlie 
cranial cavity between the cerebral hemispheres and the cerebellum; it has three 
concave surfaces, and three. sharp borders which form part of the tentorium osseum. 
Behind the base of the protuberance there is a transverse groove for the sinus com- 
municans of the dura mater. 

The posterior border is thick; it joins the scjuamous part of the occipital 
bone. The lateral and anterior borders are 
united with the parietal bones. Squamous pari of 

Development.— The interparietal ossi- ocdpital bone 

ties in membrane from two chief lateral cen- 
ters.^ It fuses first with the parietals, some- 
what later with the occipital, but the period />•*'' 
at which this union takes place is quite 
variable. 

The Parietal Bones 

The two parietal bones (Ossa parie- 
talia) form the greater part of the roof of 
the cranium; they unite in the median line, 
forming the parietal suture. Each is quadri- 
lateral in outline and has two surfaces and 
four borders. 

The external, parietal surface (Facies 
parietalis) is convex, and is marked by a 
more or less prominent curved line, the ex- 
ternal parietal crest; this is median in its 
posterior part, and is continuous with the 
crest of like name on the interparietal and 
occipital; in front it curves outward and is 
continuous with the frontal crest. The sur- 
face lateral to the crest (Planum temporale) 
enters into the formation of the temporal 
fossa, and is roughened for the attachment 
of the temporal muscle. 

The internal, cerebral surface (Facies 
cerel^ralis) is concave. It jjresents numerous 
digital impressions (Impressiones digitatse) 

which correspond to the gyri, and ridges (Juga cerebralia) which correspond to the 
sulci, of the cerebrum. There are also furrows (Sulci vasculosi) for the meningeal 
arteries. Along the medial border there is a sagittal groove (Sulcus sagittalis) for 
the superior longitudinal sinus. 

The anterior border joins the frontal bone at the parieto-frontal suture (Sutura 
parieto-f rontalis) . 

The posterior border meets the occipital bone at the parieto-occipital suture. 
Below this junction it curves inward and concurs with the temporal lione in the 
formation of the temporal canal (Meatus temporalis). A transverse groove (Sulcus 
transversus) connects this canal with the sagittal sulcus. 

The medial border is thick and serrated. It joins its fellow in great part at the 
parietal suture, but (in the young subject) meets the interparietal at its posterior 

' According to Martin, there are originally four centers, two anterior and two posterior 
(smaller) ones, which fuse in a variable manner. 




Squamous Part of 
-BORN Foal; Ven- 



1, Junction of interparietal with squamous 
part of occipital bone; 2, interparietal suture; 3, 
internal occipital protuberance; 4, transverse groove 
for sinus; 5, depression for vermis cerebelli; 6, de- 
pression for hemisphere of cerebellum; 7, junction 
of squamous part with lateral part of occipital 
bone; 8, junction of occipital with petro-mastoid; 
9, 9, junction of interparietal with parietal. 



58 



THE SKELETON OF THE HORSE 



part. The line of junction of the two parietal bones is marked internally by the 
internal parietal crest (Crista parietalis interna). 

The lateral border is beveled and is overlapped by the squamous temporal 




Fig. 35. — Right Parietal Bone of New-born Foal; Dorso-lateral View. 

1, Junction with opposite bone; 2, junction with interparietal; 3, junction with occipital; 4, junction with squamoua 

temporal; 5, junction witji frontal, 

bone, forming the squamous suture (Sutura squamosa). The angle of junction of 
the lateral and posterior borders articulates with the posterior angle of the temporal 
wing of the sphenoid. 

Development. — Each parietal bone ossifies in membrane from a single center. 




Fig. 36. — Right Parietal Bome of New-born Foal. Cerebral Surface. 

1, Junction with opposite bone; 2, junction with interparietal; 3, junction with occipital; 4, junction with squamous 

temporal; 5, junction with frontal; 6, edge which concurs with temporal bone in formation of temporal canal. 



In the young foal the central part of the bone is more convex than in the adult and 
forms a prominence similar to the pronounced tuber parietale of the young child; 
the external parietal crest is not present, and the external surface is smooth. The 



THE FRONTAL BONES 



59 



parietal suture is usually closed at four years, the parieto-occipital at five j^ears, and 
the squamous at twelve to fifteen j'ears. 

The Frontal Bones 

The frontal bones (Ossa frontalia) are situated on the limits of the cranium 
and face, between the parietals behind and the nasal bones in front. Each is 
irregularly quadrilateral, and consists of naso-frontal, orbital, and temporal parts. 

The naso-frontal part (Pars naso-frontalis) forms the basis of the forehead. 
Its external or frontal surface (Fades frontalis) is nearly flat, and is smooth and 
suljcutaneous; it is separated from the temporal part by the external frontal crest 
(Crista frontalis externa). At the junction with the orbital part the supraorbital 
or zygomatic process (Proc. zygomaticus) curves outward and dowiiward to join 
the zygomatic arch. The process partially separates the orbit from the temporal 
fossa; its root is perforated by the supraorbital foramen (Foramen supraorbitale), 
or presents instead a notch on its anterior l)order; its uj^per surface is convex, while 
the orbital surface is concave and smooth, forming a shallow fossa for the lacrimal 




Fig. 37. — Left Frontal Bone of New-borx Foal; Vextro-medial View. 
A, Cerebral surface; B, B, orbital part; C, temporal part; D, nasal surface; 1, surface of junction with opposite 
bone; 2, frontal sinus; 3, ridge to which cribriform plate of ethmoid bone is attached; 5, fissure into which orbital wing 
of sphenoid bone fits; 6, sphenoidal notch; 7, supraorbital process; S, junction with nasal bone; 9, junction with pari- 
etal bone; 10, junction with squamous temporal bone. 



gland (Fossa glandulse lacrimalis). The internal surface enters into the formation 
of the cranial and nasal cavities. The two plates of the l)one separate and diverge 
in front, and thus inclose a large air-space which is part of the frontal sinus. The 
internal plate curves downwaril and forward and joins the criln-iform jjlate of the 
ethmoid. Bej'ond this it inclines upward and joins the external plate at the naso- 
frontal suture. The cerebral surface jjresents digital impressions for the cerebral 
gyri. The nasal surface is longitudinally grooved. The external plate extends 
forward and joins tlie nasal and lacrimal bones. 

The orbital part (Pars orbitalis) forms the major part of the medial wall of the 
orbital cavity. It is separated from the naso-frontal part l^y a prominent ridge 
which is part of the orbital margin. Its orbital surface (Facies orbitalis) is concave 
and smooth, and presents superiorly a small depression (Fovea trochlearis), which 
is Ijridged by a small bar of cartilage, around which the superior oblique muscle of 
the eye is reflected. The lower border concurs ^\^th the orl)ital wing of the sphenoid 
in the formation of the ethmoidal foramen. The nasal surface faces into the 
frontal sinus and is to a small extent united with the lateral mass of the ethmoid. 

The temporal part (Pars temporalis) is separated from the orbital part by the 



60 THE SKELETON OF THE HORSE 

deep sphenoidal notch (Incisura sphenoidalis), which is closed by the orbital wing 
of the sphenoid. Its lateral surface forms part of the inner wall of the temporal 
fossa. The medial surface is largely covered by the orbital wing of the sphenoid 
in the young subject, but later forms part of the wall of the frontal sinus. 

The principal connections of the frontal bone are as follows: (1) The medial 
border joins its fellow at the frontal suture. (2) The anterior liorder meets the 
nasal and lacrimal at the naso-froijtal antl fronto-lacrimal sutiu^es. (3) Laterally 
it forms the spheno-frontal suture with the ortjital wing of the sphenoid, antl also 
joins the palatine bone and maxilla at the fronto-palatine and fronto-maxillary 
sutures. (4) Posteriorly it meets the parietal at the parieto-frontal suture, and 
articulates below this with the squamous temporal at the squamous suture. 
(5) The extremity of the supraorbital process unites with the zygomatic process 
of the temporal bone. 

Development. — Each ossifies in membrane from one center which appears in 
the root of the supraorbital process. In the new-born foal there is a slit between 
the cranial plate and the orbital and temporal plates which receives the unossified 
dorsal part of the orbital wing of the sphenoid. 

The TEMPOBfAL Bones 

The temporal bone (Os temporale) forms the greater part of the lateral wall 
of the cranium. It is situated between the occipital behind, the parietal dorsally, 
the frontal in front, and the sphenoid ventrally. It consists in the horse of two 
distinct parts, squamous and petrous. 

1. The squamous temporal bone (Squama temporalis) is a shell-Hke plate 
which has two siu'faces antl four borders. 

The cerebral surface (Facies cerebralis) is concave and is largely overlapped 
by the surrounding bones, but its central part is free antl presents digital impres- 
sions and vascular grooves. 

The temporal surface (Facies temporalis) is convex, antl enters into the forma- 
tion of the temporal fossa. From its ventral part there springs the zygomatic 
process (Processus zygomaticus), which forms the lateral boundary of the tem- 
poral fossa. The process is at first directed outwartl, antl is wide and flattened 
dorso-ventrally. It then turns forwartl, becomes narrower, and is twisted so that 
its surfaces are medial and lateral. Its anterior entl is pointed and joins the zygo- 
matic process of the malar bone, with which it forms the zygomatic arch (Arcus 
zygomaticus). The narrow anterior part has a convex lateral surface and a concave 
medial one. Its dorsal border has a rough area for articulation with the supra- 
orbital process of the frontal. Its ventral bortler is wide and rough. The wide 
posterior part presents on its ventral face a surface for articulation with the condyle 
of the mantiible. This surface consists of a transversely elongatetl condyle (Condy- 
lus temporalis), behind which is the glenoid cavity. The fossa is limited behintl by 
the postglenoid process (Processus postglenoidalis), the anterior surface of which 
is articular. Behind this process there is a fossa, in which is the postglenoid fora- 
men (F. postglenoitlale) , the external opening of the temporal canal. The dorsal 
surface is concave and forms the lateral boundary of the temporal fossa. The 
dorsal border is sinuous and is continuous behind with the temporal crest. 

The posterior process (Processus aboralis) springs from the posterior part of 
the squama. Its lateral surface bears the temporal crest, which forms here the 
lateral limit of the temporal fossa. The medial surface forms the outer boundary 
of the temporal canal, and is elsewhere applied to the petrous portion. It divides 
into two branches, upper and lower; the upper branch unites with the occipital 
bone, while the lower one curves downward behind the external acoustic process 
and overlaps the mastoitl process. 

The dorsal border of the squamous temporal articulates with the parietal, 



THE TEMPORAL BONES 



61 



forming the squamous suture. The ventral border joins the temporal wing of the 
sphenoid at the spheno-squamous suture. The anterior border unites with the 
frontal lione at the sc|uamo-frontal suture, and the posterior with the occipital and 
petrous temporal l)oncs. 

2. The petrous temporal bone (Os petrosum) is placed between the occipital 




Fig. 38. — Right Squamous Temporal Bone of New-born Foal; Lateral View. 
1, Zygomatic process; 2, glenoid cavity; 3, condyle; 4, postglenoid process; 5, notch; 6, posterior process; 7, 
temporal crest; 8, junction with parietal: 9. junction with frontal; 10, junction with supraorbital process; 11, junction 
with zygomatic process of malar; 12. junction with sphenoid; 13, junction with petro-mastoid; 14, junction with oc- 
cipital. 

behind and the parietal in front, and is largely overlapped l)y the squamous tem- 
poral. It has the form of a four-sided pyramid, the l^ase of which is ventral. 

The lateral surface is mainly concealed by tlie sciuamous temi^oral, but two 
features are visiljle. A short tube of bone, the external acoustic process (Processus 
acusticus externus) , protrudes from the lowest part through the notch of the squa- 
mous temporal. The process is directed outward, upward, and a little forward. 




3 

Fig. 39. — Right Squamous Temporal Bone of New-born Foal; Medial View. 
Cerebral surface; 1, zygomatic process; 2, junction with parietal; 3, junction with temporal wing of sphenoid; 
4, posterior process (overlaps petro-mastoid). 



It gives attachment to the annular cartilage of the ear. Its lumen, the external 
acoustic meatus (Meatus acusticus externus) , conducts to the cavity of the middle 
ear (tympanum) in the dry skull, but is separated from it by the tympanic mem- 
Ijrane in the natural state. The mastoid process (Processus mastoideus) projects 
ventrally in tlie interval lietween the posterior process of the squamous temporal 



62 



THE SKELETON OF THE HORSE 



and the root of the paramastoid process of the occipital bone. It is crossed by a 
groove which leads to the mastoid foramen (Foramen mastoideum), from which a 
canal extends forward to the temporal canal. 

The medial surface faces into the cerebellar fossa of the cranium. It is con- 
cave and smooth, Ijut irregular. In its ventral part is the entrance to a short canal, 
the internal acoustic meatus (Meatus acusticus internus), which transmits the 
seventh and eighth cranial nerves. 

The entrance to the meatus is termed the porus acusticus internus. The fundus of the 
meatus is divided by a crest into two fossae. In the superior one is the origin of the facial canal, 
which curves through the bone and opens externally at the stylo-mastoid foramen; it transmits 
the facial (seventh cranial) nerve. The inferior fossa presents small foramina for the passage of 
fibers of the acoustic (eighth cranial) nerve. 

Behind the meatus and near the posterior margin of the surface is the slit-like 
external opening of the aquseductus vestibuli (Apertura externa aquaeductus ves- 




FiG. 40. — Left Petrous Tempor.^] 
Lateral View. 
1, External acoustic meatus; 2, mastoid process; 3, 
hyoid process; 4, muscular process; 5, petrosal crest; 6, 
groove which concurs in formation of temporal canal; 
7, groove for posterior meningeal artery. 



: OF Horse; 



Bone of Horse; Fig. 41. — Left Petrous Temporal Bo.v 

Postero-medial View. 
1, Mastoid process: 2, notch which 
occipital bone in formation of mastoid foramen; 3, apex; 
4, opening of aquseductus vestibuH ; 5, medial surface; 
6, petrosal crest; 7, internal acoustic meatus; 8, mus- 
cular process; 9, bullaossea; 10, stylo-mastoid foramen; 
A.c, opening of aquseductus cochleae. 

tibuli), covered by a scale of bone. Below this there is a narrow fissure, the 
orifice of the aquseductus cochleae (Apertura externa aquseductus cochlea). 

The anterior surface looks upward antl forward. The greater part articulates 
with the parietal bone, l)ut a small medial part faces into the cerebral fossa of the 
cranium. A sharp border, the petrosal crest (Crista petrosa), separates this sur- 
face from the medial one. 

The posterior surface is slightly concave and is attached to the lateral part of 
the occipital bone. 

The base forms the lateral boundary of the foramen lacerum. It is very 
irregular and presents a number of important features. The hyoid process (Pro- 
cessus hyoideus) is a short rod which projects downward and forward below the 
base of the external acoustic process, inclosed in a bony tiil le ; it is connected by a 
bar of cartilage with the hyoid bone. The stylo-mastoid foramen (F. stylo- 
mastoideum) is situated between the hyoid process and the mastoid process; it is 



BONES OF THE FACE THE MAXILLA 63 

the external opening of the facial canal, through which the facial nerve emerges. The 
bulla ossea is a considerable eminence situated centrally; it is thin walled and 
incloses a cavity which is part of the tympanum. The muscular process (Processus 
muscularis)^ is a sharp spine which projects downward and forward from the an- 
terior part of the base; it gives origin to the tensor and levator palati muscles. 
Lateral to the root of the preceding is the small petrotympanic fissure (Fissura 
petrotympanica) for the passage of the chorda tympani nerve. The osseous 
auditory or Eustachian tube (Tuba auditiva ossea) is a semicanal at the medial 
side of the root of tlie muscular process; it leads to the tympanum. At the medial 
side of the preceding is the slit-like orifice of the petrosal canal, which commvmi- 
cates with the facial canal. 

The apex projects upward and backward between the squamous temporal and 
the occipital bone. 

Development. — The squamous temporal develops in membrane. The pe- 
trous temporal may be regarded as consisting of petro-mastoid and tympanic parts. 
The latter includes the external acoustic process, the bulla ossea, and the muscu- 
lar process; it is developed in membrane. The petro-mastoid is developed in the 
cartilaginous ear capsule. Its petrous part consists of very dense bone which con- 
tains the labyrinth or internal ear and forms the medial wall of the tympanum. 

The auditory ossicles and the interior of the petrous temporal bone are described in the 
section on the organ of hearing. 

The temporal canal (Meatus temporalis)- is a continuation of the transverse 
groove which extends laterally from the base of the tentorium osseum. It is 
directed downward, forward, and somewhat outward, and opens externally in front 
of the root of the acoustic process. It is bounded by the squamous temporal 
laterally, the petrous behind, and the parietal in front and medially. Several 
foramina open from it into the temporal fossa. It contains a large vein (Vena 
cerebralis dorsalis), the continuation of the transverse sinus of the dura mater. 

The foramen lacenmi (basis cranii) is a large, irregular opening in the cranial 
base, bounded metliall.\'" by the 1 )asilar part of the occipital bone, laterally by the 
petrous temporal, and in front jjy the temporal wing of the sphenoid. It consists 
of a large anterior part (Foramen lacerum anterius), and a narrow posterior part 
(Foramen lacerum posterius). It transmits the internal carotid artery, the middle 
meningeal artery, the mandibular, ninth, tenth, and eleventh cranial nerves, and 
the ventral cerebral vein. 

In the fresh state the foramen is occupied by a dense fibrous membrane which is perforated 
by apertures for the various structures transmitted. Thus there are three openings in front for 
the internal carotid artery, the mandibular nerve, and the middle meningeal artery; these are 
named (from within outward) the foramen caroticum, ovale, spinosum. 



(B) BONES OF THE FACE 

The bones of the face (Ossa faciei) are the maxilla, premaxilla, palatine, 
pterygoid, nasal, lacrimal, malar, dorsal turbinate, ventral turbinate, vomer, mandi- 
ble, and hyoid. The last three are single, the others paired. 

The Maxh-Lje 
The maxillae are the principal bones of the upper jaw and carry the upper 
cheek teeth. They are situated on the lateral aspect of the face, and articulate 
with almost all of the facial bones and the frontal and temporal also. For descrip- 
tion each may l^e divided into a body and two processes. 

' This has been termed the styloid process. It is not the homologue of the styloid proc- 
ess of man. 

' This is also known as the parieto-temporal canal. 



64 



THE SKELETON OF THE HORSE 



The body (Corpus maxillae) presents two surfaces, two borders, and two ex- 
tremities. The lateral surface (Facies lateralis) is somewhat concave in front and 
convex behind.' On its posterior part there is a horizontal ridge, the facial crest 
(Crista facialis) ; in a skull of medium size its anterior end is about an inch and a 
half (3 to 4 cm.) above the third or fourth cheek tooth, and it is continued behind 
on the malar bone. About two inches (.5 cm.) above and a little in front of the 
anterior end of the crest is the infraorbital foramen (Foramen infraorbitals) ; this 
is the external opening of the infraorbital canal. 

The medial or nasal surface (Facies nasalis) is concave dor.so-ventrally; it 
forms the greater part of the lateral wall of the nasal cavity. Its upper part is 
crossed obliquely forward and downward by the shallow lacrimal groove (Sulcus 
lacrimalis), which contains the naso-lacrimal duct; in the adult the posterior part 
of the groove is converted into a canal, which is continuous with that on the inner 
surface of the lacrimal bone. Below the groove is the ventral turbinate crest 
(Crista turbinata ventralis), to which the ventral turl)inate bone is attached. 
Lower down and parallel with the turbinate crest is the palatine process, which 




Fig. 42. — Right Maxilla of New-bohn Foal; Medial View. 
1, Lacrimal groove; 2, ventral turbinate crest; 3, palatine process; 4, maxillary sinus; .5, .5, area of articulation 
with palatine bone; 6, groove which concurs with one on the palatine bone to form the pjalatine canal; 7, zygomatic 
process; 8, maxillary tuberosity; 9, junction with nasal bone; 10, junction with nasal process of premaxilla. 



projects horizontally like a shelf. Behind this the surface is rough for articulation 
with the palatine bone; this area is crossed by a groove which concurs with one on 
the palatine bone in the formation of the palatine canal (Canalis palatinus). The 
posterior part of the bone is excavated to form part of the maxillary sinus. 

The dorsal border is irregular and scaly. Its anterior part is grooved and 
its po.sterior part beveled for articulation with the nasal process of the premaxilla 
and the nasal and lacrimal bones. 

The ventral or alveolar border (Processus alveolaris) is in its greater part thick, 
and presents six large cavities, the dental alveoli, for the cheek teeth. The alveoli 
are separated by transverse interalveolar septa. There is often a small alveolus 
for the first premolar ("wolf tooth") close to the first large one. At the bottom 
of the alveoli there are small openings (Foramina alveolaria) for the passage of 
vessels and nerves. Further forward the border is narrow and forms part of the 
interalveolar or interdental space (Margo interalveolaris). Behind the last alve- 
olus is a rough area, the alveolar tuberosity (Tuber alveolare). 

The anterior extremity is pointed. It joins the premaxilla, and forms with it 
the alveolus for the canine tooth. 

- In the young horse the anterior part of the surface is convex over the embedded parts of the 
teeth. As the latter are extrudeil the surface flattens and becomes concave in old subjects. 
The form of the underlying teeth may be indicated by ridges (Juga alveolaria), and sometimes in 
young horses there may be defects in the bone over the teeth. 



THE PREMAXILL^ 65 

The posterior extremity forms a rounded prominence, the maxillary tuberosity 
(Tuber niaxillare). Medial to the tuberosity is a deep recess (Recessus maxillaris), 
in which are three foramina. The upper one, the maxillary foramen (Foramen 
maxillare), leads into the infraorbital canal. The lower one, the posterior palatine 
foramen (Foramen palatinum aborale), is the entrance to the palatine canal. The 
sphenopalatine foramen (Foramen sphenopalatinum) perforates the inner wall of 
the depression and opens into the nasal cavity. 

The zygomatic process (Processus zygomaticus) projects backward, dorso- 
lateral to the tulierosity; it is overlapped by the corresponding part of the malar 
and also articulates with the zygomatic process of the temporal. A small curved 
plate (Processus temporalis) extends medially from it and joins the frontal and 
palatine bones, forming part of the floor of the orbit. 

The palatine process (Processus palatinus) is a horizontal plate which projects 
from the lower part of the medial surface of the body. It forms the greater 
part of the basis of the hard palate. Its nasal surface is smooth and is con- 
cave transversely; on its anterior part, close to the medial border, there is a 
shallow groove in which the vomero-nasal organ (of Jacobson) is situated. The 
palatine surface is slightly concave from side to side, and presents along its lateral 
part the palatine groove (Sulcus palatinus) ; this is continuous at the anterior 
palatine foramen (Foramen palatinum orale) with the palatine canal, and con- 
tains the palatine vessels and nerve. The medial border unites with its fellow to 
form the median palatine suture; its nasal aspect bears the nasal crest (Crista 
nasalis), which forms, with that of the opposite process, a groove for the vomer. 
The posterior border unites with the horizontal part of the palatine bone at the 
transverse palatine suture. Variable accessory palatine foramina perforate the 
process. 

The infraorbital canal (Canalis infraorbitalis)' extends almost horizontally 
from the maxillarj' foramen to the infraorbital foramen. It is placed at the upijer 
edge of the inner plate of the maxilla, and traverses the maxillary sinus. Near the 
infraorbital foramen it gives off a small canal (Canalis alveolaris incisivus) which 
lies above the roots of the premolars and extends also into the premaxilla, carrying 
vessels and nerves to the teeth there. 

Development. — The maxilla ossifies in membrane ventral and lateral to the 
cartilaginous nasal capsule. It has one chief center and a supplementary one in 
the region of the deciduous canine tooth (Martin). 

The PREMAX1LL.E 

The premaxillae (Ossa incisiva) form the anterior part of the upper jaw and 
carry the incisor teeth. Each consists of a body, a nasal process, and a palatine 
process. 

The body (Corpus) is the thick anterior part which carries the incisor teeth. 
Its labial surface (Facies labialis) is convex anil smooth, and is related to the upper 
lip. The palatine surface (Facies palatina) is concave and often presents a foramen 
a little behind its middle.- The medial surface (Facialis medialis) is rough, and 
joins the opposite bone; it is marked by a curved groove, which forms, with that on 
the opposed surface, the foramen incisivum. The alveolar border (Limbus alveo- 
laris) separates the palatine and labial surfaces; it is curved and thick, and presents 
three deep alveoli for the incisor teeth ; behind the third alveolus it is free, forming 
part of the interalveolar space. 

The nasal process (Processus nasalis) projects backward and upward from the 
body, forming here the lateral wall of the nasal cavity. The two surfaces, facial 

' This is also known as the superior dental canal. 

- This foramen is somewhat variable in position, but is commonly opposite the corner in- 
cisor. Smaller inconstant foramina are often present. 
5 



66 



THE SKELETON OF THE HORSE 



and nasal, are smooth and rounded. The dorsal border is free, thick, and smooth; 
it concurs with the free margin of the nasal bone in forming the naso-maxillary 
notch (Incisura nasomaxillaris). The ventral border is dentated and joins the 
maxilla; at its anterior end it forms with the latter the alveolus for the permanent 

canine tooth.' The posterior ex- 
tremity fits into the interval be- 
tween the nasal bone and the 
maxilla. 

The palatine process (Pro- 
cessus palatinus) is a thin plate 
which forms the anterior part of 
the basis of the hard palate. Its 
nasal surface (Facies nasalis) has 
a longitudinal ridge which forms 
with that of the other side a groove 
for the septal cartilage; lateral to 
the ridge there is a groove for the 
vomero-nasal organ. The palatine 
surface (Facies palatina) is flat. 
The medial border is serrated and 
meets its fellow at the median pala- 
tine suture. The lateral border is 
separated from the maxilla and the 
nasal process by the palatine fis- 
sure (Fissura palatina). The pos- 
terior extremity fits into the inter- 
val Ijetwecn the vomer and the 
palatine process of the maxilla. 

Development. — The premax- 
illa ossifies from a single center. 
Fusion of the two bones is com- 
plete at the end of the third or 
the beginning of the fourth year. 

The Palatine Bones 
The palatine bones (Ossa pala- 
tina) are situated on either side of 
the choanse or posterior nares, and 
form the posterior margin of the 
hard palate. Each is twisted so as 
to form a horizontal and a perpen- 
dicular part. 

The horizontal part (Pars hori- 
zontalis) is a narrow plate which 
forms the posterior part of the 
hard palate. It presents smooth 
nasal and palatine surfaces (Facies 
nasalis, palatina). The medial border meets its fellow at the median palatine 
suture, on the nasal aspect of which is the nasal crest. The anterior border joins 
the palatine process of the maxilla at the transverse palatine suture, and forms with 
it the anterior palatine foramen (Foramen palatinum anterius). The posterior 
border is concave and free; it gives attachment to the aponeurosis of the soft palate. 

' The alveolus for the temporary canine is commonly formed in the maxilla alone. 




OF Horse About Four 



Fig. 43. — Upper 



1, 1, Choanffi or posterior nares; 2, vomer; 3, horizontal 
part of palatine bone; 4, anteriorpalatine foramen; 5, palatine 
groove: 6, transverse palatine suture; 7, median palatine .suture; 
8, palatine process of maxilla; 9, palatine process of premaxilla; 
10, foramen incisivum; 11, malar bone; 12, maxilla; 13, anterior 
end of facial crest; 14, interalveolar space; I. 7-3, incisor teeth; 
C, canine tooth; P.l, first premolar or "wolf" tooth. The 
opening lateral to 9 is the palatine fissure. 



THE PTERYGOID BONES — THE NASAL BONES 67 

The perpendicular part (Pars perpenclicularis) is more extensive and forms 
most of the lateral wall of the choanae or posterior nares. The nasal surface (Facies 
nasalis) is in the greater part of its extent concave and smooth, but presents a 
narrow rough area to which the pterygoid bone is attached. Below this the bone 
curves outward, forming the pterygoid process. The maxillary surface (Facies 
maxillaris) presents three areas for consideration. The largest articulates with the 
maxilla; it is rough and is crossed by a groove which concurs with one on the max- 
illa in the formation of the palatine canal. Behind this is a smooth part which 
assists in forming the pterygo-palatine fossa (Fossa pterygopalatina) . The rough 
area below this is overlapped b}^ the pti>rygoid process of the sphenoid bone. The 
dorsal border is perforated by the sphenopalatine foramen. Behind the foramen 
the two plates of the bone separate to inclose part of the sphenopalatine sinus. 
The inner plate curves medially to articulate with the vomer. The outer ])late 
joins the maxilla and frontal and the orbital wing of the sphenoid; it may join the 
lacrimal Ijone also. 

Development. — The palatine bone ossifies in membrane from a single center. 

The Pterygoid Bones 

The pterygoid bones (Ossa pterygoidea) are narrow, thin, bent plates, situated 
on either side of the jjosterior nares. Each has two surfaces and two extremities. 
The medial surface is smooth, and forms part of the wall of the posterior nares. 
The lateral surface articulates with the palatine, vomer, and sphenoid, concurring 
with the last in the formation of the pterygoid canal. The ventral extremity is 
free, turned slightly outward, and forms the hamulus pterygoideus ; this is grooved 
externally and forms a pulley around which the tendon of the tensor palati muscle 
is reflected. 

Development. — The pterygoid ossifies in membrane from a single center. 

The Nasal Bones 

The nasal bones (Ossa nasalia) are situated in front of the frontal bones and 
form the greater jjart of the roof of the nasal cavity. They have an elongated 
triangular outline, wide behind, pointed in front. Each presents two surfaces, two 
borders, and two extremities. 

The facial surface is smooth and is convex transversely; the profile contour is 
usually slightly wav.y, with a depression about its middle and a variably prominent 
area in front. 

The nasal surface is smooth and concave from side to side. About in its 
middle it presents the dorsal turbinate crest (Crista turbinata dorsalis), which is 
parallel with the medical border, and has the dorsal turbinate bone attached to it. 
Most of this surface faces into the nasal cavity, but its posterior part, external to 
the turbinate crest, enters into the formation of the frontal sinus; the latter area is 
marked off by an oblique ridge which corresponds to the septmn between the an- 
terior and posterior ]iarts of the dorsal turbinate bone. 

The medial border is straight, and meets the opposite bone at the nasal suture. 

The lateral border is irregular. Its anterior third is free and conciu's with 
the nasal process of the premaxilla in forming the naso-maxillary notch (Incisura 
naso-maxillaris). Behind this it joins the end of the nasal process, the maxilla, 
and the lacrimal, forming the naso-maxillary and naso-lacrimal sutures. 

The greater part of the edge is beveled and fits into a groove on the upper Ijorder of the 
nasal process, the maxilla, and the lacrimal bone. 

The posterior extremity or base is beveled and overlaps the frontal bone, 
forming the naso-frontal suture. 

The anterior extremity or apex is pointed and thin. 



bo THE SKELETON OF THE HORSE 

Development. — Each nasal bone ossifies in membrane from a single center. 
The nasal suture does not close completely even in old age. In some cases the two 
plates separate to inclose a small air-space (nasal sinus) in the posterior part. 

The Lacrimal Bones 

The lacrimal bones (Ossa lacrimalia) are situated at the anterior part of the 
orbit, and extend forward on the face to the posterior border of the maxilla. Each 
presents three surfaces and a circumference. 

The lateral face is clearl}' divided into orbital and facial parts by the orbital 
margin. The orbital surface (Facies orbitalis) is triangular in outline, smooth and 
concave ; it forms jjart of the medial and front wall of the orbit. Near the orbital 
margin it presents a funnel-like fossa (Fossa sacci lacrimalis), which is the entrance 
to the lacrimal canal; the fossa is occupied by the lacrimal sac, which is the dilated 
origin of the naso-lacrimal duct. Behind this is a depression in which the inferior 
oblique muscle of the eye takes origin. The facial surface (Facies facialis) is more 
extensive, and has the form of an irregular pentagon. It is slightly convex and 
smooth in the foal, flattened in the adult. It usually bears the small lacrimal 
tubercle, which is situated nearly an inch (ca. 2 cm.) from the orbital margin. 
The orbital margin (Margo orbitalis) is concave, rough above, smooth below. 

The nasal surface (Facies nasalis) faces into the frontal and maxillary sinuses. 
It is concave and very irregular, and is crossed almost horizontally by the osseous 
lacrimal canal (Canalis lacrimalis osseus). 

The circumference articulates dorsally with the frontal and nasal bones, 
ventrally with the malar and maxilla, in front with the maxilla, and behind with 
the frontal. The various sutures so formed are designated by comtjinations of the 
names of the bones. 

Development. — Each ossifies in membrane from a single center. 

The Malar Bones 

The malar or zygomatic bones (Ossa zygomatica) are placed between the lac- 
rimal al)ove and the maxilla below and in front. Each is irregularly triangular in 
outline and presents tliree surfaces, three borders, and a process. 

The facial surface (Facies facialis) is smooth, slightly convex, wide in front, 
and narrow behind. At its lower part it presents the facial crest, which is continu- 
ous in front with the similar ridge on the maxilla and l)eliintl with the zygomatic 
process of the temporal; the crest is rough below, where the masseter muscle is 
attached to it. 

The orbital surface is much smaller than the facial surface, from which it is 
separateil Ijy the concave orbital margin (Margo orbitalis). It is concave and 
smooth, and forms jDart of the lower and front wall of the orbit. 

The nasal surface is concave and faces into the maxillary sinus. In the .young 
foal a consitlcrable iiart of it articulates with the maxilla. 

The dorsal border articulates with the lacrimal chiefly, but to a small extent 
behind with the maxilla also. 

The ventral and anterior borders articulate with the maxilla. 

The posterior extremity is formed by the zygomatic process, which is beveled 
above and is overlapped by the zygomatic process of the temporal bone. 

Development. — Each ossifies in membrane from one or two centers. 

The Turbinate Bones 

These (Ossa turbinata) are delicate, scroll-like bones, four in number, which 
are attached to the lateral walls of the nasal cavity. They project into the cavity 
and greatly diminish its extent. Each is composed of a very thin lamina, cribri- 



THE TURBINATE BONES 



69 



form in many places, and covered on both sides witli mucous membrane in the fresh 
state. They are arranged in two pairs, dorsal and ventral. 

The dorsal turbinate bone (Os turlsinatum dorsale)' is somewhat cylindrical in 
form, but is flattened from side to side and tapers at each end. It is attached to 
the turbinate crest of tlie nasal bone and the nasal plate of the frontal bone. The 
anterior part is rolled like a scroll one and a half times, thus inclosing a cavity which 
communicates with the middle meatus nasi. The arrangement is best seen on a 
cross-section (Fig. 55). The posterior part is not rolled, but its ventral border is 
attached to the lateral nasal wall, thus helping to inclose a large space which is part 
of the frontal sinus. This cavity is separated from that of the scroll-like part by a 
transverse septum. The medial surface is flattened, and is separated from the sep- 
tum nasi by a narrow interval, the common meatus (Meatus nasi communis). 
Another narrow passage, the dorsal meatus (Meatus nasi dorsalis), separates the 
dorsal surface from the roof of the nasal cavity. The space between the ventral 
surface and the ventral turbinate is the middle meatus (Meatus nasi medius). The 



Nasal 
sinus 



Frontal 
sititis 



Nasal 




Fig. 44. — Part of Sagittal Section of Skull of Horse. 
1, Perpendicular plate of ethmoid bone; 2, great ethmo-turbinate; 3. tlorsal turbinate; 4, ventral turbinate; 5, 
vomer; 6, middle nasal meatus; 7. ventral nasal meatus; S, perpendicular part of palatine bone; 9, palatine process of 
maxilla; 10, body of premaxilla; 11, nasal process of premaxilla; 12. palatine process of premaxilla; 13, pterygoid proc- 
ess of palatine bone. Dotted lines indicate septa. 



anterior extremity is prolonged toward the nostril by two small bars of cartilage. 
The posterior extremity is small, and joins the cribriform plate and lateral mass of 
the ethmoid. 

The ventral turbinate bone (Os turbinatum ventrale)^ is shorter and smaller 
than the upper one. It is attached to the ventral turbinate crest, and consists, 
like the upper one, of an anterior coiled and a posterior uncoiled portion. 

To express briefly the mode of coiling of the two bones of the same side we may saj' that 
they are rolled toward the septum and each other. 

The ventral and posterior borders of the posterior part are attached to the 
maxilla, thus helping to inclose a cavity which is part of the maxillary sinus. The 
lower surface is separated from the floor of the nasal cavity by the ventral meatus 
(Meatus nasi ventralis), which is much larger than the other nasal passages. The 
anterior extremity is prolonged toward the nostril by a curved bar of cartilage. 

Development. — Each ossifies in cartilage from a single center. 

' This bone is also termed the naso-turbinal; it is really a greatly developed first ethmo- 
turbinate. 

^ This is also called the maxillo-turbinal. 



70 THE SKELETON OF THE HORSE 



The Vomer 

The vomer is a median bone, which assists in forming the ventral part of the 
septum nasi. It is composed of a thin lamina which is bent (except in its posterior 
part) so as to form a narrow groove (Sulcus vomeris) , in which the lower part of the 
perpentlicular plate of the ethmoid bone and the septal cartilage are received. The 
lateral surfaces, right and left, are highest near the posterior end and diminish 
gradually to the anterior end; they are slightly convex dorso-ventrally, and are 
covered by the nasal mucous membrane during life. The ventral border is thin 
and free in its posterior third, and divides the choanse or posterior nares medi- 
ally; in the remainder of its extent it is wider and is attached to the nasal crest. 
The anterior extremity lies above the ends of the palatine processes of the premax- 
illse. The posterior extremity consists of two wings (AIjb vomeris) which extend 
outward below the body of the presphenoid; posteriorly they form a notch (In- 
cisura vomeris), and laterally join the palatine and pterygoid bones. 

Development. — The vomer is primitively double, and ossifies from a center on 
either side in the membrane covering the cartilaginous septum nasi; the two 
lamina; then fuse below and form a groove. 

The Mandible 

The mandible (Mandibula),' or lower jaw bone, is the largest bone of the 
face. The two halves of which it consists at birth unite during the second or third 
month, and it is usually described as a single bone. It carries the lower teeth, and 
articulates by its condyles with the squamous temporal on either side. It consists 
of a body and two rami." 

The body (Corpus mandiljiulte) is the thick anterior part which Ijears the incisor 
teeth. It presents two surfaces and a border. The lingual surface (Facies lin- 
gualis) is smooth and slightly concave; during life it is covered by mucous mem- 
brane, and the tip of the tongue overlies it. The mental surface (Facies mentalis) 
is convex and is related to the lower lip. It is marked by a median furrow which 
indicates the position of the primitive symphysis mandibulse. The curved alveolar 
border (Limbus alveolaris) presents six alveoli for the incisor teeth, and a little 
further back two alveoli for the canine teeth in the male; in the mare the latter are 
usually absent or small. 

The rami (Rami mandibulse) extend backward from the boclj' and diverge to 
inclose the mandibular (or submaxillary) space (Spatium mandibulare). Each 
ramus is bent so as to consist of a horizontal part (Pars molaris) which l^ears the 
lower cheek teeth, and a vertical part (Ramus mandibulse [S. N. A.]) which is ex- 
panded and furnishes attachment to powerful muscles; the term angle is applied 
to the most prominent part of the curve. The ramus presents two surfaces, two 
borders, and two extremities. The lateral surface is smooth and slightlj^ convex 
fi-om edge to edge on the horizontal part; at the junction with the body it presents 
the mental foramen (Foramen mentale), which is the external opening of the man- 
dibular canal. On the vertical part it is somewhat concave and presents a numljer 
of rough lines for the attachment of the masseter muscle. The medial surface of 
the horizontal part is smooth, and presents a shallow longitudinal ilepression in its 
midtUe; above this there is often a faint mylo-hyoid line (Linea mylohyoidea) for 
the attachment of the muscle of like name. At the lower part of the junction with 
the body there is a small fossa for the attachment of the genio-hyoid and genio- 

' This bone is also commonly called the inferior maxilla. 

- In the Stuttgart Anatomical Nomenclature (S. N. A.) the body (Corpus) is the part which 
bears the teeth, and is divided into a pars incisiva and a pars molaris. The ramus is the rest of 
the bone. This mode of description is copied from the Basel Nomina Anatomica. It does not 
seem to the author to be well adapted to comparative purposes. 



THE MANDIBLE 71 

glossus muscles. On the vertical part the surface is concave, and is marked in its 
lower and posterior part by rough lines for the attachment of the medial pterj'goid 
nmscle. In front of its middle is the mandibular foramen (Foramen mantlibulare)/ 
which is the posterior orifice of the mandibular canal (Canalis mandibulge).'- The 
canal curves downward and passes forward below the cheek teeth, opening exter- 
nally at the mental foramen; it is continued into the body of the bone as a small 
canal (Canalis alveolaris incisivus), which carries the vessels and nerves to the 
incisor teeth. The dorsal or alveolar border (Limbus alveolaris) forms anteriorly 
part of the interalveolar space; here it is thin. Behind this it is thick and is ex- 
cavated by six alveoli for the lower cheek teeth. Behind the last alveolus it curves 
sharply upward and is narrow and rough. In the young foal there is commonly a 
small alveolus for the vestige of the first premolar ("wolf tooth") close to the first 
large one. The ventral border of the horizontal part is nearly straight; it is thick 
and rounded in the j'oung horse, becoming narrower and sharp in old subjects. At 





Fig. 45. — Left Half of Mandible of Horse; Medial View, 
1, Body of mandible (median section): 2, 2', horizontal and vertical parts of ramus; 3, interalveolar border; 4, 
depression for attachment of genio-hyoideus muscle; 5, mandibular foramen; 6, vascular impression: 7, angle; 8, 
condyle; 9, coronoid process; 10, mandibular notch; 11, incisor teeth; 12, canine tooth; 13, cheek teeth. 

its posterior part there is a smooth impression (Incisura vasorum) where the facial 
vessels and parotid duct turn round the bone. Behind this point the border curves 
sharply upward, forming the angle of the mandible ( Angulus mandibulse) ; this part 
is thick and has two roughened lips, separated by a considerable intermediate space; 
near the condyle it becomes narrower. The anterior extremity joins the body. 
The articular extremity comprises the coronoid process in front and the condyle 
behind, the two being separated by the mandibular notch (Incisura mandibulie), 
through which the nerve to the masseter muscl(> passes. The coronoid process 
(Processus coronoideus) is thin transversely and curved slightly medially and 
backward. It projects upward in the temporal fossa and furnishes insertion to 
the temporal muscle. The condyle of the mandible (Condylus mandibulse) lies at 
a much lower level than the end of the coronoid process. It is elongated trans- 
versely and articulates with the squamous temporal through the medium of an 

' This is also commonly called the inferior maxillary foramen. 
^ This is also termed the inferior dental canal. 



72 



THE SKELETON OF THE HORSE 



articular disc. The part below the condyle is usually termed the neck of the 
mandible (Collum mandibulffi) ; on its antero-medial part is a depression, the fovea 
pterygoidea, in which the lateral pterygoid muscle is attached. The middle of the 
vertical part of the ramus consists to a large extent of a single plate of compact 
substance which may be so thin in places as to be translucent. 

Development. — The mandible develops from two chief centers in the connec- 
tive tissue which overlies the paired Meckel's cartilages. At birth it consists of 
two synmietrical halves which meet at the median symphysis mandibulae. Fusion 
usually occurs in the second or third month. 

Age Changes. — These are associated largely with the growth, and later with the reduction, 
of the teeth. In the young horse, in which Ihc teeth are long and are in great part einbeddecl 
in the bone, the body is thick and strongly cur\cd, and the horizontal part of the ramus is also 
thick. Later, as the teeth are extruded from the bone, the body becomes flattened and narrower, 
and the horizontal part of the ramus is thinner, especially in its lower part. In the old subject 
the angle, the vascular impres.sion in front of it, and the lines for the attachment of tendinous 
layers of the masseter and pterygoid muscles are more pronounced. 




The Hyoid Bone 

The hyoid bone (Os hyoideum) is situated chiefly between the vertical parts 
of the rami of the mandible, but its upper part extends somewhat further back. 
It is attached to the petrous temporal bones by rods of cartilage, and supports the 

root of the tongue, the pharynx, and the 
larynx. It consists of a body, a lingual 
process, and three pairs of cornua. 

The body or basihyoid (Corpus ossis 
hyoidei) is a short transverse bar, com- 
pressed dorso-ventrally. The dorsal sur- 
face is concave and smooth in its middle, 
and presents at each end a convex facet 
or tubercle for articulation with the small 
cornu. The ventral surface is flattened 
and is slightly roughened for muscular 
attachment. The anterior border carries 
medially the lingual process. The pos- 
terior border is concave and smooth in its 
middle, and carries on either side the thy- 
roid cornu. The body, the lingual proc- 
ess, and the thyroid cornua are fused 
and may be compared to a spur or a fork 
with a ver\' short handle. 

The lingual process (Processus lingu- 

alis) projects forward metlially from the 

body, and is embedded in the root of the 

tongue during life. It is compressed laterally and has a blunt-pointed free end. 

The lateral surfaces are slightly concave. The dorsal border is thin and irregular, 

and the ventral border is thick and rough. 

The thyroid cornua or thyrohyoids (Cornua thyreoidea)' extend backward and 
upward from the lateral parts of the l:)0(ly. They are compressed laterally (except 
at their junction with the body), and the posterior end has a short cartilaginous 
prolongation which is connected with the anterior cornu of the thyroid cartilage 
of the larynx. 

The small cornua or keratohyoids (Cornua minora) are short rods which are 
directed upward and forward from either end of the body. Each is somewhat 
constricted in its middle part and has slightly enlarged ends. The ventral end has 
• These correspond to the great cornua of man. 



Fig. 46. — HvoiD Bone op House, Vieweb toom the 
Side and Somewhat prom in Front. 
a. Body; b. Ungual process; c, thyroid cornu; c', 
cartilage of c,- d, small cornu; e, middle cornu; /.great 
cornu; /', muscular angle of great cornu; g, cartilage 
of great cornu. (Ellenberger-Baum, Anat. d. Haus- 
tiere.) 



THE SKULL AS A WHOLE 73 

a small concave facet which articulates with the body. The dorsal end articulates 
with the great cornu, or with the middle cornu when present. 

The great comua or stylohyoids are much the largest parts of the bone. They 
are directed dorsally and backward, and are connected above with the base of the 
petrous temporal bones. Each is a thin plate, seven or eight inches (ca. 18 to 20 
cm.) long, which is slightly curved in its length, so that the lateral surface is con- 
cave antl the medial surface is convex; both are smooth. The borders are thin. 
The dorsal extremity is large and forms two angles; the articular angle is connected 
by a rod of cartilage with the hyoid process of the petrous temporal bone; the 
muscular angle is somewhat thickened and rough for muscular attachment. The 
ventral extremity is small, and articulates with the small or the miildle cornu. 

The middle comua or epihyoids are small, wedge-shaped pieces or nodules 
interposed between the small and great cornua. They are usually transitory, and 
unite with the great cornua in the adult. 

Development. — The hyoid ossifies in the cartilages of the second and third 
visceral arches. Each part has a separate center, except the lingual process, which 
ossifies by extension from the body. In the foal there is a separate nucleus at each 
end of the body which intervenes between the latter and the thyroid cornu; it 
articulates with the small cornu. The anterior part of the lingual process may be 
a separate piece. 



THE SKULL AS A WHOLE 

The skull of the horse has, as a whole, the form of a long, four-sided pyramid, 
the base of which is posterior. It is convenient, however, to exclude the mandible 
and hyoid from present consideration. The division between the cranium (Cra- 
nium cerebrale) and the face (Cranium viscerale) may be indicated approxi- 
mately by a transverse plane through the anterior margins of the orbits. 

The dorsal or frontal surface (Norma frontalis) is formed by the squamous 
part of the occipital, interparietal, parietal, frontal, nasal, and premaxil- 
lary bones. It may be divided into parietal, frontal, nasal, and premaxillary 
regions. The parietal region extentls from the nuchal crest to the parieto-frontal 
suture. It is marked medially lay the external parietal crest, which bifurcates in 
front, the branches becoming continuous with the frontal crests. The latter curve 
outward on either side to the root of the supraorbital process. The frontal region 
is the widest part of the surface, and is smooth and almost fiat. It is lioimded in 
front by the naso-frontal suture. On either side of it is the root of the supraorbital 
process, pierced by the supraorbital foramen. The nasal region is convex from 
side to siile, wide behind, narr(.)w in front. Its profile is in some cases nearly 
straight; in others it is umlulating, with a variabl\' marked depression about its 
micklle and at the anterior end. The premaxillary region presents the osseous 
nasal aperture (Ajiertura nasalis ossea) and the foramen incisivimi. 

The lateral surface (Norma lateralis) (Fig. 28) may be divided into cranial, 
orbital, antl preorbital or maxillary regions. 

The cranial region presents the temporal fossa, the zygomatic arch, and the 
outer part of tlie jietrous temporal bone. The temporal fossa is bound medially 
by the parietal and frontal crests, laterally by the temporal crest and the zygomatic 
arch, and behind by the nuchal crest. Its upper and middle parts are rough for 
the attachment of the temporal muscle. In its lower posterior part are several 
foramina wliich communicate with the temporal canal. The fossa is continuous 
in front with the orbital cavity. The zygomatic arch is formed by the zygomatic 
])rocesses of the tem]5oral, malar, and maxilla. Its ventral face presents the con- 
dyle and glenoid cavity for articulation with the lower jaw, through the medium 
of the articular disc. Behind the glenoid cavity is the postglenoid process. The 



74 



THE SKELETON OF THE HORSE 



external acoustic process projects outward through a deep notch in the ventral 
margin of the squamous temporal below the temporal crest. A little further back 
is the mastoid process, crossed in its upper part by a groove for the posterior 
meningeal artery. 

The orbital region comprises the orbit and the pterygo-palatine fossa. Tlie 



OccipiUil 
Interparietal 

Parietal 
Squamous tempi 



FrunUd 




Nasal process of preniaxilla 



•nral fossa 
■III crest 

( 'iirnnoid process 
Zygomatic arch 

Siipraorlnlal process 
Si( praorbital foramen 

Orbit 
Facial crest 



I iifraorhilal foramen 



Foramen incisivum 
Fig. 47. — Skull of Horse; Dorsal View. 
1, Parieto-occipital suture; 2, squamous suture; 3, parietal suture; 4, parieto-frontal suture; 5, frontal suture; 
6, naso-frontal suture; 7, naso-lacriraal suture; S, lacrimo-malar suture; 9, lacrimo-maxillary suture; 10, maxillo- 
malar suture; 11, naso-maxillary suture; 12, nasal suture. 



orbit is a cavity which incloses the eyeball, with the muscles, ves.sels, antl nerves 
associated with it. It is not separated in the skeleton from the temporal fossa. 
The axis of the orbit (Axis orbitse), taken from the optic foramen to the middle of 
the inlet, is directed forward, outward, and slightly upward. The medial wall 
(Paries medialis) is complete and extensive. It is concave and smooth, and is 
formed by the frontal and lacrimal and the orbital wing of the sphenoid. In its 



THE SKULL AS A WHOLE 



75 



extreme anterior part is the fossa for the lacrimal sac. Behind this there is a small 
depression in which the inferior obliciue muscle of the eye arises; here the plate 
which separates the orbit from the maxillary sinus is very thin. The dorsal wall 
(Paries dorsalis) is formed by the frontal and to a small extent by the lacrimal bone. 
It presents the supraorbital foramen, which perforates the root of the supraorbital 
process. The ventral wall (Paries ventralis) is very incomplete, and is formed by 
the malar, the zygomatic process of the temporal, and to a small extent by the max- 
illa. The lateral wall (Paries lateralis) is the supraorl)ital process. At the extreme 
posterior part is the orbital group of foramina. Four are situated in front of the 
pterygoid crest. Of these, the uppermost is the ethmoidal foramen, which trans- 




FiG. 4S. 



Zygom 



t Supra- 



\L AND Orbital Regions of Skull of Horse: Lateral View. 
ORBITAL Process Have Been Sawn Off. 
5. o.. Squamous part of occipital; P, parietal; S, squamous temporal; S.o., basilar part of occipital; B.s., body of 
sphenoid; .4./., temporal wing of sphenoid; .4.0., orbital wing of sphenoid; /*(. p., pterygoid process of sphenoid; P.p., 
perpendicular part of palate bone ; F, F', facial and orbital parts of frontal bone; L, L', orbital and facial parts of lacri- 
mal bone; M, facial part of malar bone; A/.x., maxilla; a, parieto-occipital suture; b, squamous suture; c, d, spheno- 
squamous suture; e, fronto-palatine suture; /, fronto-lacrimal suture. 1, Occipital condyle; 2, condyloid fossa; 3, 
paramastoid process; 4, nuchal crest; 5, external occipital protuberance; 6, external acoustic meatus; 7, mastoid 
process; 8, hyoid process; 9, stylomastoid foramen; 10, muscular process; 11, foramen lacerum; 12, postglenoid 
process; 13, glenoid cavity; 14, temporal condyle; 15, pterygoid groove; 16, alar canal of pterygoid process incUcated 
by arrow; 17, alar foramen; 18, ethmoidal foramen; 19, optic foramen; 20, foramen orbitale; 21, maxillary fora- 
men; 22, sphenopalatine foramen; 23, posterior palatine foramen; 24, supraorbital foramen (opened); 25, fossa for 
lacrimal sac; 26, depression for origin of obliquus oculi inferior; 27, facial crest; 28, maxillary tuberosity; 29, alveolar 
tuberosity; 30, hamulus of pterygoid bone. 



mits the ethmoidal vessels and nerve. The optic foramen is .situated a little lower 
anil further back; it transmits the optic nerve. Immediately below the optic is 
the foramen orbitale, which transmits the ophthalmic, third, sixth, and sometimes 
the fourtli nerve; commonly there is a very small trochlear foramen in the crest 
for the last-named nerve. The foramen rotimdum is below the foramen orbitale, 
from which it is separated by a tliin iilate; it transmits the maxillary nerve. The 
alar canal opens in common with the foramen rotundum, and the anterior opening 
of the pterygoid canal is also found here. Tlie foramen alare parvum is just be- 
hind the pterygoid crest and on a level with the foramen orbitale. It is the upper 
opening of a canal which leads from the alar canal, and through it the anterior deep 



76 



THE SKELETON OF THE HORSE 



temporal artery emerges. The inlet of the orbital cavity (Aditus orbitae) is cir- 
cumscribed by a complete bony ring, which is nearly circular. Its infraorbital 
margin (Margo infraorbitalis) is smooth and rounded; the supraorl)ital margin 
(Margo supraorbitalis) is rough and irregularly notched. During life the cavity is 
completed by the periorl^ita, a conical filsrous membrane, the apex of which is at- 
tached around the ojjtic foramen. Ventral to the orbital cavity is the pterygo- 
palatine fossa. Its wall is formed by the pterygoid process, the perpendicular 
part of the palate bone, and the tuber maxillaro. Its deep anterior recess contains 
three foramina. The upper one, the maxillary foramen, is the entrance to the in- 



Nuchal crest 

Dorsal border of 

for. magnum 

Foramen magnum 

H 1/ poglossal foramen 

For. Incerum posterius - 
Stylomastoid foramen -■ 

Hyoid process — ^ 
Muscular process -y 
For. lacerum anterius -- 
Basilar tubercles 



Alar canal 

Pterygoid process 
of sphenoid 
Pterygoid bone 

Vomer {alee) 
Pterygoid process of 
palatine bone 

Palalliii' hour ( pvr- .. 

pn.ln.h.r i,„rl) 
Atiriilnr InlurosUy -- 

Posterior nares -- 
Last molar tooth 




External occipital pro- 
tuberance 

Occipital condyle 

Paramastoid process 

Corulyloid fossa 

Mastoid process 



Postglenoid process 

Glenoid cavity 

Temporal condyle 
Zygomatic process 
Infratemporal fossa 
Zygomatic process of 
malar 

Pterygo-palatine fossa 
Maxillary recess 
Maxillary tuberosity 
Facial crest 
Hamulus of pterygoid 
Vmner 

Palatine bone (hori- 
zontal part) 
Ant. palnline foramen 

Palatine groove 

Palatine process of 
maxilla 

Fig. 49. — Line Drawing of Postekior Half of Base of Skull of Horse, Without Mandible. (Key to Fig. 50.) 
.4, Basilar part of occipital; B. body of sphenoid: C, temporal wing of sphenoid; D, squamous temporal bone; 
S, petrous temporal bone; F, orbital part of frontal bone, i, Incisura carotica; .3, incisura ovalis; ^, incisura spinosa; 
4, external orifice of temporal canal; 5, o.sseous auditory or Eustachian tube; 6, petro-tympanic fissure; 7, external 
acoustic process; 5, hyoid process; 5, pterygoid groove ; 10, supraorbital process. 



fraorbital canal, which transmits the infraorbital nerve and vessels. The spheno- 
palatine foramen perforates the medial wall of the recess and transmits vessels and 
nerves of like name to the nasal cavity. The lower foramen, the posterior palatine, 
transmits the palatine artery and nerve to the palatine canal. The upi)cr part of 
the fossa is smooth, and is crossed by the internal maxillary artery and the maxillary 
nerve. The lower part is chiefly roughened for the attachment of the lateral 
pterygoid muscle, but is crossed in front by a smooth groove in which the palatine 
vein lies. In its extreme posterior part is the small opening of the pterygoid 
canal. 

The preorbital or maxillary region is formed chiefl\' l>y the maxilla, I)ut also by 



THE SKULL AS A WHOLE 



77 



the premaxilla, and the facial parts of the lacrimal and malar bones. Its contour 
is approximately triangular, the base being posterior. It offers two principal 
features. The facial crest extends forward from the ventral margin of the orbit, 
and ends abrui)tly at a point about an inch and a cjuarter (ca. 3 to 3.5 cm.) above the 




The skull 13 inclined slightly 



third or fourth cheek tooth;' its ventral aspect is rough for the attachment of the 
masseter muscle. The infraorbital foramen is situated in a transverse plane about 
an inch (ca. 2 to 3 cm.) in front of the end of the crest and about two inches (5 cm.) 

1 This relation varies with age. In the new-born foal the posterior part of the second tooth, 
in the young horse the posterior part of the third tooth, in the older subject the fourth, lies below 
the end of the crest. 



78 THE SKELETON OF THE HORSE 

above it. The foramen opens forward, and through it the infraorbital artery and 
nerve emerge. The surface over the premolar teeth varies greatly with age, in 
conformity with the size of the embedded parts of the teeth. In the young horse 
the surface here is strongly convex, the outer plate of bone is thin and even defective 
sometimes in places, and the form of the teeth is indicated by eminences (Juga 
alveolaria). In the old animal the surface is concave on account of the extrusion 
of the teeth from the bone. The downward curve of the premaxilla is pronounced 
in the young subject, very slight in the aged. 

In some skulls there is a distinct depression a short distance in front of the orbit; here the 
levator labii superioris proprius arises. 

The ventral or basal surface (Norma basalis), exclusive of the mandible, 
consists of cranial, guttural, and palatine regions. 

The cranial region (Basis cranii externa) extends forward to the vomer and 
pterygoid processes (Fig. 50). At its posterior end is the foramen magnum, flanked 
by the occipital condyles. Lateral to these is the condyloid fossa, in which is the 
hypoglossal foramen, which transmits the hypoglossal nerve and the condyloid 
vein. Further outward are the paramastoid processes (Processus jugulares) 
of the occipital bone. Extending forward centrally is a prismatic bar, formed 
by the basilar part of the occipital and the body of the sphenoid bone; at the 
junction of these parts are tubercles for the attachment of the ventral straight 
muscles of the head. On either side of the basilar part of the occipital bone is the 
foramen lacerum (basis cranii), bounded laterally by the base of the petrous tem- 
poral bone. In front of these the region becomes very wide on account of the lateral 
extension of the zygomatic processes, which present ventrally the condyle and 
glenoid cavity for articulation with the mandible. Beyond this the process turns 
forward and joins the zygomatic process of the malar, completing the zygomatic 
arch and the surface for the attachment of the masseter muscle. On either side of 
the body of the sphenoid is the infratemporal fossa, formed by the temporal wing 
and the root of the pterygoid process of the sphenoid bone. It is bounded in front 
by the pterygoid crest, which separates it from the orbit and the pterygo-palatine 
fossa. In it is the alar canal, which transmits the internal maxillary artery. A 
little lower is the entrance to the pterygoid canal. 

The guttural region presents the pharyngeal orifice of the nasal cavity. This is 
elli])tical and is divided in its depth medially by the vomer into two choanae or 
posterior nares. It is bounded in front and laterally by the palate and pterygoid 
bones, behind by the vomer. It is flanked by the hamular process of the pterygoid 
bone. The plane of the opening is nearly horizontal, and the length is about 
twice the width. 

The palatine region comprises a little more than half of the entire length 
of the base of the skull (Fig. 43). The hard palate (Palatum durum) is concave 
from side to side, and in its length also in the anterior part. It is formed by the 
palatine processes of the premaxilliB antl maxillse, and the horizontal parts of the 
palatine bones. It is circumscribed in front and laterally by the alveolar parts of 
the maxilla and premaxilla. The interalveolar space (Alargo interalveolaris) is that 
part of the arch in which alveoli are not present. Behind the last alveolus is the 
alveolar tuberosity, and medial to this is a groove for the palatine vein. In the 
middle line is the median palatine suture (Sutura palatina mediana). In the line 
of the suture, a little behind the central incisors, is the foramen incisivum, through 
which the palato-labial artery passes. On either side, parallel with the alveolar 
part of the maxilla, is the palatine groove (Sulcus palatinus), which contains the 
palatine vessels and nerve. It is continuous at the anterior palatine foramen with 
the palatine canal, which is situated between the maxilla and the palatine bone. 
The palatine fissure is the narrow interval along the lateral margin of the palatine 



THE SKULL AS A WHOLE 



79 



process of the premaxilla; it is closed in the fresh state by a process of the cartilage 
of the septum nasi. Scattered along each side of the palate are several accessory- 
foramina. The transverse palatine suture (Sutura palatina transversa) is about 
half an inch from the jjosterior border. The latter is opposite to the fifth cheek 
tooth in the adult, antl is concave and free. 

The nuchal or occipital surface (Norma occipitalis) is formed by the occipital 



Nuchal crest 



Neck of mandible 




Posterior View. The Hyoid Bone Has Been Removed. 
2, curved line: 3, forameii magnum; 4, occipital condyle; 5, paramastoid 



Angle of mandible . 

Fig. 51. — Skull of Horse 
1, External occipital protuberance; 
process: 6, basilar part of occipital; 7, mastoid foramen; S, mastoid process; 9, postglenoid process; 10, muscular 
process of petrous temporal: 11, alar canal; 12, pterygoid process of sphenoid; 13, bod.v of sphenoid; 14, vomer; 15, 
15', perpendicular and horizontal parts of palatine bone; IG. 16, posterior nares or choanae; 17, hamulus of pterygoid 
bone: 18, maxillary tuberosity: 19, palatine process of maxilla: 20, palatine process of premaxilla; 21, palatine fissure; 
22, accessory palatine foramina; 23, body of mandible. 



bone. It is trapezoidal in outline, wider below than above, concave dorso-ventrally, 
convex transversely. It is separated from the dorsal surface l;)y the nuchal crest. 
Below the crest are two rough areas for that attachment of the complexus muscles. 
A little lower is a central eminence, the external occipital protuberance, on which the 
ligamentum nuchas is attached. At the lowest part centrally is the foramen mag- 
num. This is bounded laterally by the occipital condyle, lateral to which is the 
paramastoid process. 



80 



THE SKELETON OF THE HORSE 





THE CRANIAL CAVITY 



81 



The apex of the skull is formed by the bodies of the premaxillse and mandible, 
carr3'ing the incisor teeth. 

THE CRANIAL CAVITY 

This cavitj^ (Cavum cranii) incloses the brain, with its membranes and vessels. 
It is relatively small and is ovoid in shape. 

The dorsal wall or roof (Calvaria) (Fig. 52) is formed by the supraoccijiital, 
interparietal, parietal, and frontal bones. In the middle line is the internal parietal 
crest, which joins the crista galli in front, and furnishes attachment to the falx 
cerebri. Posteriorly the crest is continued by the sharp anterior margin of the 




Pdramastiiid Orcipilil hour Splienuid bone 
process (basilar pari) {I'l'dy) 



Fig. 54. — Sagittal Section of Cranium op Horse. 
1, Lateral wall of foramen magnum; 2, hypoglossal foramen; 3, foramen laocrum posterius; 4, 5, 6. carotid, oval, 
and spinous notches; 7, floccular fossa; 8, internal acoustic meatus; 9, petrosal crest; 10, hypophyseal or pituitary 
fossa; 11, groove for maxillary nerve; 12, groove for cavernous sinus; 13, optic foramen; 14, 14, sphenoidal sinus; 
15, crista galli; 16, perpendicular plate of ethmoid bone; 17, vomer; IS, septum between frontal sinuses: 19, orbital 
wing of sphenoid; 20, temporal wing of sphenoid; 21, internal occipital protuberance; 22, canalis transversus; 23, de- 
pression for vermis cerebelli. 



tentorium osseum, which projects downward and forward into the cavity, and gives 
attachment to the tentorium cerebelli by its sharp lateral edges. Behind this the 
roof is grooved centrally for the middle lobe or vermis of the cerebellum. Trans- 
verse grooves pass from the base of the tentorium osseum to the temporal canals. 
The anterior part of the roof is hollowed by the frontai sinus. The occipital part 
is very thick and strong. i 

The lateral wall (Fig. 54) is formed chiefly bj' the temporal and frontal bones 

and the orbital wing of the sphenoid. It is crossed obliquely by the petrosal crest, 

which concurs with the projecting margin of the parietal bone and the tentorium 

osseum in dividing the cavity into cerebral and cerebellar compartments. Behind 

6 



82 THE SKELETON OF THE HORSE 

the crest is a depression for the hemisphere of the cerebellum. Behind this are the 
internal acoustic meatus and the openings of the aquseductus vestibuli and aquse- 
ductus cochleae. 

The roof and lateral walls are marked by digital impressions and vascular 
grooves. 

The ventral wall or floor (Basis cranii interna) (Fig. 53) may be regarded as 
forming three fosste. The anterior fossa (Fossa cranii oralis) supports the frontal 
and olfactory parts of the cerebrum. It is formed chiefly by the presphenoid, and 
lies at a higher level than the middle fossa. In front the fossa is divided medially 
b}^ the crista galli, lateral to which are the deep ethmoidal fossae for the olfactory 
buUjs. The ethmoidal foramen perforates the cranial wall at the outer side of these 
fossse. Further back the central part of the surface is slightly elevated, and is 
flanked by shallow depressions which support the olfactory peduncles. Posteriorly 
is a bony shelf which covers the entrance to the optic foramina; the edge of this 
shelf and the posterior borders of the orbital wings of the sphenoid may be taken as 
the line of demarcation between the anterior and middle fossae. The middle fossa 
(Fossa cranii media) is the widest part of the cavity. It extends backward to the 
sphcno-occipital and petrosal crests, thus corresponding to the postsphenoid. In its 
middle is the hji^ophyseal fossa in which the hypophysis cerebri lies. On either side 
are two grooves: the medial one transmits the cavernous sinus and the ophthalmic, 
third, and sixth nerves to the foramen orbitale; the lateral one leads to the foramen 
rotundum, and lodges the maxillary nerve. Lateral to the grooves is a depression 
for the pirifonn lobe of the cerebrum. The posterior fossa (Fossa cranii posterior) 
corresponds to the basilar part of the occipital bone. It contains the medulla 
oblongata, pons, and cerebellum. In front is a metlian dejiression (Fossa ixjntis) 
for the pons. The surface behind this (Fossa medullae oblongatse) is concave trans- 
versely and slopes gently downward to the foramen magnum; it supports the 
medulla oblongata. On either side are the foramen lacerum and the hypoglossal 
foramen. 

The anterior or nasal wall (Fig. 3.3) is formed by the cribriform plate of the 
ethmoid, which separates the cranium from the nasal cavity. It is perforated by 
nmnerous foramina for the passage of the olfactory nerve-bundles. 



THE NASAL CAVITY 

The nasal cavity (Cavum nasi) is a longitudinal passage which extends through 
the upper part of the face. It is divided into right and left halves by a median 
septum nasi. The lateral walls are formed by the maxilla, premaxilla, the per- 
pentlicular part .of the palatine, and the turbinate and ethmoid bones in part. This 
wall is crossed obliquely by the lacrimal canal and groove for the naso-lacrimal 
duct, and its posterior part is perforated by the sphenopalatine foramen. The 
dorsal wall or roof is formed by the frontal and nasal bones, which form a median 
prominence at their junction. It is concave from side to side, and nearly straight 
longitutlinally, except in the posterior part, where it curves downward. The ven- 
tral wall or floor is formed by the palatine processes of the premaxillae and max- 
illae, and the horizontal parts of the palate bones. It is wider but considerably 
shorter than the roof. It is concave transversely, and nearly horizontal from 
before backward, except in the posterior third, where there is a slight declivity. 
The anterior part presents a median groove for the cartilage of the septum, and a 
furrow for the vomero-nasal organ (of Jacobson) on either side. Posteriorly there 
is a median elevation, the nasal crest, to which the vomer is attached. Lateral to 
the palatine process of the premaxilla is the palatine fissure. 

The septum nasi osseum is formed bj' the jjerpendicular plate of the ethmoid 



THE NASAL CAVITY 



83 



behind, and the vomer below. In the fresh state it is completed by ihe cartilage 
of the septum nasi (Cartilago septi nasi). 




Fig. 55. — Cross-sectiox of Nasal Region of Skull 
OF Horse; the Section- Passes Through the 
Anterior End of the Facial Crest, and Be- 
tween THE Third and Fourth Cheek Teeth. 
a. Dorsal, 6, ventral, turbinate bone; c, d, cavities 
of a and b; e, common meatus; /, g, h, dorsal, middle, 
ventral meatus; i, k, passages to cavities of turbinate 
bones; /, naso-lacrimal duct; m, infraorbital canal; n, 
anterior end of maxillary sinus; o, septal cartilage. 
(After Ellenberger, in Leisering's Atlas.) 



, Region 



Skull 
' About H.\i.f- 
THE Anterior 



Fig. 56. — Cross-section oi 

OF Horse; the Section is Cu 

WAY BETWEEN THE OrBIT AND 

End OF THE Faci.vl Crest, and Passes be- 
tween THE Fifth and Sixth Cheek Teeth. 
a, Dorsal, b, ventral, turbinate bone; c, d, cavities 
of a and b; e, common meatus; /, dorsal, g. middle, h, 
ventral meatus; i, placed over ridge in maxillary sinus; 
k, communication between outer and inner (turbinate) 
part of maxillary sinus; /, naso-maxillary opening; m, 
naso-Iacriraal canal; n, infraorbital canal. (After 
Ellenberger, in Leisering's Atlas.) 



The turbinate bones divide each half of the nasal cavity into three meatus 
nasi. 

The dorsal meatus (]\Ieatus nasi dorsalis) is a narrow passage between the 
roof and the dorsal turbinate bone. It ends at the cribriform plate of the ethmoid. 




Fig, 57. — Skull of Young Horse; I^ateral View, with Sinuses Opened Up. 
A', A, Anterior and posterior compartments of maxillary sinus; B, B', frontal and turbinate parts of frontal sinus, 
C, orbit; 1, septum between compartments of maxillary sinus; 2, 2, infraorbital canal; 3, turbinate part of maxillary 
sinus; 4, 5. fi, last three cheek teeth (covered by thin plate of bone) ; 7. anterior limit of maxillar>- sinus in older subject; 
8, infraorbital foramen; 9. anterior end of facial crest; 10, course of naso-lacrimal duct; 11, fossa for lacrimal sac; 12, 
dorsal turbinate bone; 13, fronto-maxillary opening. 



The middle meatus (Meatus nasi medius) is the space between the two turbinate 
bones. In its posterior part is the very narrow opening into the maxillary sinus. 
The ventral meatus (Meatus nasi ventralis) is the channel along the floor which is 



84 



THE SKELETON OF THE HORSE 



overhung by the ventral turbinate bone; it is much the largest and is the direct 
path between the nostrils and posterior nares. 

The osseous nasal aperture (Apertura nasi 
ossea) is bounded by the nasal bones and the 
premaxillse. 

The posterior extremity or fundus is separ- 
ated from the cranial cavity by the cribriform 
plate of the ethmoid, and is largely occupied by 
the lateral masses of that bone. 



THE PARANASAL SINUSES 

Connectetl directly or indirectly with the 
nasal cavity, of which they are diverticula, are 
four pairs of air-sinuses (Sinus paranasales), 
viz., maxillary, frontal, sphenopalatine, and 
ethmoidal. 

The maxillary sinus (Sinus maxillaris) is the 
largest. Its lateral wall is formed l)y the maxilla, 
the lacrimal, and the malar. It is Ijounded medi- 
ally- fiy the maxilla, the ventral turbinate, and the 
lateral mass of the ethmoid bone. It extends 
backward to a transverse plane in front of the 
root of the supraorbital process, and its anterior 
limit is indicated approximately by a line drawn 
from the anterior end of the facial crest to the 
infraorljital foramen. Its dorsal boundary cor- 
responds to a line drawn backward from the in- 
fraorbital foramen parallel to the facial crest. 
The ventral wall or floor is formed by the alve- 
olar part of the maxilla; it is very irregular and 
is crossed by bony plates running in various 
directions. The last three cheek teeth project 
up into the cavity to an extent which varies 
with age; they are covered by a thin plate of 
bone. The cavity is divided into anterior and 
posterior parts by an oblique septum (Septum 
sinus maxillaris). The lateral margin of the sep- 
tum is commonly about two inches (ca. 5 cm.) 
from the anterior end of the facial crest; from 
here it is directed inward, backward, and up- 
ward. The upper part of the septum (formed 
by the posterior end of the ventral turbinate 
bone) is very delicate and usually cribriform. 




Fig. 58. — Skcll or Yocng Hohse; Dorsal 
View, with Sinuses Opened Up. 
1, 2, Ends of frontal sinus: 3, fronto- 
maxillary opening; 4, dorsa! turbinate bone; 
5, lateral mass of ethmoid bone; 6, 6', two 
compartments of maxillary sinus; 7, septum 
between 6 and 6'; 8, orbit; 9. anterior end 
of facial crest; A, frontal bone; B, nasal 
bone; C, lacrimal bone; D, majdlla. Note 
difference in position and form of septum in 
maxillary sinus as compared with preceding 



The position and shape of the septum are very- 
variable. It is often further forward — in some cases 
even as far forward as the anterior end of the facial crest. Exceptionally it is much nearer the 
orbit than is stated above. In the recent state, i. e., when covered by the mucous membrane on 
both surfaces, it is nearly always complete, but in very exceptional cases there is an opening of 
variable size in the upper part. 

The anterior compartment, often called the inferior maxillary sinus, is partially 
divided by the infraorbital canal into a lateral maxillary part and a medial smaller 
turbinate part. The latter communicates with the middle meatus by a very narrow 
slit situated at its highest part. The posterior compartment, often called the 



THE PARANASAL SINUSES 



85 



superior maxillary sinus, is also crossed by the infraorbital canal, over which it 
opens freely into the sphenopalatine sinus. It communicates dorsally with the 
frontal sinus through the large oval fronto-maxillary opening, situated at the level 
of the osseous lacrimal canal and the corresjjonding part of the medial wall of the 
orbit; the orifice is commonly about one and a half to two inches (ca. 4 to 5 cm.) 
long and an inch or more (2 to 3 cm.) wide. Just in front of this, and covered by a 
thin plate, is the narrow naso-maxillary fissure (Aditus naso-maxillaris), by which 
the sinus opens into the posterior part of tlie middle meatus. 

The foregoing statements refer to the arrangement in the average adult animal. In the 
foal the cavity (with the exception of its turbinate part) is largely occupied by the developing 
teeth. In horses five to six years of age the maxillary part of the sinus is filled up to a large degree 
by the embedded parts of the teeth. As the teeth are extruded to compensate the wear, more 
and more of the ea\'ity becomes free, until in old age only the short roots project up in the floor, 
covered by a layer of bone. Other facts in this connection will be given in the description of the 
teeth. In exceptional cases the posterior part of the ventral turbinate is smaller than usual and 
leaves a considerable interval, through which the maxillary sinus communicates with the nasal 
cavity. The fronto-ma.xillary opening is very variable in size. 



Squamous 
Squamous Parietal temporal 
part of occip- bone bone Frontal 

ital li'ini' I ]__ bon 



Lacrimal Max- 
bone ilia 



I bone 




Basilar part of 
occipital bone 



w 

Miindible Incisor teeth 

{first and second) 

Fig. 59. — Skoll of Fo.tL .\BonT Two Months Old. 
This figure illustrates differential features of skull of young foal as compared with that of adult animal shown in 
Fig. 2S. 1, Occipital condyle; 2, paramastoid process; 3, mastoid process; 4, external acoustic meatus; 5, zygomatic 
process of temporal bone: 6. supraorbital process of frontal bone; 7, zygomatic process of malar bone: S, facial crest; 
9, infraorbital foramen; 10, mental foramen; 11, angle of mandible; 12, condyle of mandible; 13, coronoid process 
of mandible. 



The frontal or fronto-turbinate sinus (Sinus frontalis) consists of frontal and 
turbinate parts. The frontal part is bounded chiefly by the two plates of the 
frontal bone, but its floor is formed in part by the lateral mass of the ethmoid. It 
extends forward to a plane through the anterior margins of the orbits, backward to 
one through the temporal condyles, and outward into the root of the supraorbital 
process. It is separated from the sinus of the opposite side by a complete septum 
(Septum sinuum frontalium). It is partially subdivided by a number of bony 
plates. The turbinate part is situated in the posterior part of the dorsal turbinate 
bone, roofed in by the nasal and lacrimal bones. It extends forward to a transverse 
plane about half-way between the anterior margin of the orl)it and the end of the 
facial crest. It is in free communication behind with the frontal part over the 
lateral mass of the ethmoid. It is separated from the nasal cavity by the thin 



86 THE SKELETON OF THE HORSE 

turbinate plate. The frontal and maxillary sinuses communicate through the 
large opening described above. 

The sphenopalatine sinus (Sinus sphenopalatinus) consists of two parts which 
communicate under the lateral mass of the ethmoid. .The sphenoidal (posterior) 
part is excavated in the body of the presphenoid. The palatine (anterior) part is 
between the two plates of the perpendicular part of the palatine bone, under the 
lateral mass of the ethmoid; it communicates freely with the maxillary sinus. The 
septum between the right and left sinuses is not usually median in the sphenoidal 
part. 

In about one-third of the cases (according to Paulli) the sphenoidal and palatine parts are 
separated by a transverse septum, and the sphenoidal part then communicates only with the ven- 
tral ethmoidal meatuses. 

The term ethmoidal sinus is often applied to the cavity of the largest cthmo- 
turbinate. It communicates with the maxillary sinus through an opening in the 
lateral lamina. 



The Bones of the Thoracic Limb 
the scapula 

The scapula is a fiat bone which is situated on the anterior part of the lateral 
wall of the thorax; its long axis extends obliquely from the fourth thoracic spine 
to the sternal end of the first rib. It is curved slightly and slopes outward in 
adaptation to the form of the thoracic wall. It is triangular in outline, and has 
two surfaces, three borders, and three angles. 

The lateral surface (Facies lateralis) is divided into two fossae by the spine of 
the scapula (Spina scapulae), which extends from the vertebral border to the neck 
of the bone, where it subsides. The free edge of the spine is thick, rough, and in 
great part subcutaneous. A little above its middle there is a variable prominence, 
the tuber spinas, to which the trapezius muscle is attached. The supraspinous 
fossa (Fossa supraspinata) is situated in front of the spine, and the infraspinous 
fossa (Fossa infraspinata) behind it. The former is much the smaller of the two; 
it is smooth and is occupied by the supraspinatus muscle. The infraspinous fossa 
lodges the infraspinatus muscle; it is wide and smooth in its upper part, narrower 
below, where it is marked by several rough lines for muscular attachment; near 
the neck is the nutrient foramen, and a little lower is a vascular groove. 

The costal surface (Facies costalis) is hollowed in its length by the subscapular 
fossa (Fossa subscapularis) ; this occupies nearly the whole of the lower part of the 
surface, but is pointed above and separates two rough triangular areas (Facies 
serrata), to which the serratus ventralis is attached. In the lower third there is a 
vascular groove with several branches. 

The anterior border (Margo cranialis) is convex and rough above, concave and 
smooth below. 

The posterior border (Margo caudalis) is slightly concave. It is thick and 
rough in its upper third, thin in its middle, and thickens again below. 

The vertebral border (Margo vertebralis) carries the scapular cartilage (Car- 
thago scapulae). In the young subject this edge of the bone is thick, and is pitted 
by impressions into which the cartilage fits. The cartilage is the unossified part 
of the foetal scapula. Its lower edge fits the depressions and elevations of the bone. 
It thins out toward the free edge, which is convex and lies alongside of the vertebral 
spines. In front it continues the line of the bone, but behind it forms a rounded 
projection. The lower part of the cartilage undergoes more or less ossification, so 
that the vertebral border of the bone in old subjects is thin, irregular, and porous. 

The anterior or cervical angle (Angulus cranialis) is at the junction of the 



THE SCAPULA 



87 



,/' '- 






15 

Fig. 60. — Left Scapul.\ of Horse; Later-\l Surf.\ce, 
1, Spine; 2, tuber spinse; 3, cartilage; 4, anterior 
angh;; 5, posterior angle; 6, supraspinous fossa; 7, in- 
fra.spinous fossa; S, anterior border; 9, posterior bor- 
der; 10, muscular lines; 11, nutrient foramen; 12, 
vascular groove; 13, neck; 14, tuber scapulae; 15, glen- 
oid cavity. 



Fig. 01. — Right Scapul-A of Horse; Costal Surface. 
1, Anterior angle; 2, posterior angle; 3, anterior border; 
4, posterior border; o. neck; 6, vascular groove; 7, glenoid 
cavity; 8, coracoid process; 9, tuber scapuln:. 



anterior and vertebral borders and lies opposite to the seconii thoracic spine. It is 
relatively tliin and is about a right angle. 

The posterior or dorsal angle (Angulus caudalis) is thick and rough; it is 
opposite to the vertebral end of the seventh rib, and 
its position can be determined readily in the living 
animal. 

The glenoid or articular angle (Angulus glenoid- 
alis) is joined to the body of the bone by the neck 
of the scapula (Collum scapulte). It is enlarged, 
especially in the sagittal direction. It bears the 
glenoid cavity (Cavitas glenoidalis) for articulation 
with the head of the humerus. The cavity is oval 
in outline, and its margin is cut into in front bj- the 
glenoid notch (Incisura glenoidalis), and is rounded 
off laterally; just above its postero-lateral part is a 
tubercle to which a tendon of the teres minor is at- 
tached. The tuber scapulae' is the large rough 
prominence in front, to which the tendon of origin 

Fig. 62.— Distal Ext 
'■ Formerly termed the bicipital tuberosity. Scapula of Horse 




88 THE SKELETON OF THE HORSE 

of the biceps brachii is attached; projecting from its medial side is the small coracoid 
process (Processus coracoideus), from which the coraco-brachialis muscle arises. 

Development. — The scapula has four centers of ossification, viz., one each for 
the body of the bone, the tuber scapulse and coracoid process, the anterior part of 
the glenoid cavity, and the tuber spinse. The last ossifies after birth and fuses with 
the spine about the third year. The tuber scapuliE and coracoid process fuse with 
the body of the bone about the end of the first year. 

In old subjects the spongy substance disappears at the middle part of the fossae, so that the 
bone consists here of a thin layer of compact substance. Considerable ossification of the cartilage 
is usual, the borders become much rougher, the muscular Unes are more pronounced, and a medul- 
lary cavity may appear in the neck. Much variation occurs in dimensions and slope. The aver- 
age ratio between the length and breadth (scapular index) is about 1 : 0..5, but in many cases the 
base is relatively wider. The inclination on a horizontal plane varies from 50 to 65 degrees. Ex- 
ceptionally the coracoid process reaches a length of an inch or more (2I2 to 3 cm.), and the chief 
nutrient foramen may be on the posterior border or in the subscapular fossa. 



THE HUMERUS 

The humerus is a long bone which extends from the shoulder above, where it 

articulates with the scapula, to the elbow below and behind, where it articulates 
with the radius and ulna. It is directed obliquely downward and backward, form- 
ing an angle of about 55 degrees with a horizontal plane. It consists of a shaft 
and two extremities. 

The shaft (Corpus humeri) is irregularly cylindrical and has a twisted appear- 
ance. It may be regarded as having four surfaces. The lateral surface (Facies 
lateralis) is smooth and is spirally curved, forming the musculo-spiral groove 
(Sulcus musculi brachialis), which contains the brachialis muscle; the groove is 
continuous with the posterior surface above and winds around toward the front 
below. The medial surface (Facies medialis) is nearly straight in its length, 
rounded from side to sitlc, and blends with the anterior and posterior surfaces. 
Just above its middle is the teres tuberosity (Tuberositas teres), to which the 
tendon of the latissimus dorsi and teres major muscles is attached. The nutrient 
foramen is in the distal third of this surface. The anterior surface (Facies crani- 
alis) is triangular, wide and smooth above, narrow and roughened below. It is 
separated from the lateral surface by a distinct border, the crest of the humerus 
(Crista humeri), which bears above its middle the deltoid tuberosity (Tuberositas 
deltoidea). From the latter a rough line curves upward and backward to the 
lateral surface of the neck, and gives origin to the lateral head of the triceps muscle. 
Below the tuberosity the border inclines forward, becomes less salient, and ends at 
the coronoid fossa. The posterior sxuiace (Facies caudalis) is rounded from side 
to side and smooth. 

The proximal extremity (E.xtremitas proximalis) consists of the head, neck, 
two tuberosities, and the intertuberal groove. The head (Caput humeri) presents 
an almost circular convex articular surface, which is about twice as extensive as the 
glenoid cavity of the scapula, with which it articulates. In front of the head is a 
fossa, in which are several foramina. The neck (Collum humeri) is well defined 
behind, but is practically ab.sent elsewhere.^ The lateral tuberosity (Tuberositas 
lateralis)- is placed antero-laterally, and consists of two jjarts: the anterior part 
forms the lateral boundary of the intertuberal or bicipital groove and gives attach- 
ment to the lateral branch of the supraspinatus muscle; the posterior part gives 
attachment to the short insertion of the infraspinatus, while its outer surface is 
coated with cartilage, over which the chief tendon of the same muscle passes to be 

' The proper "anatomical neck" (CoUum anatomicum) is, however, indicated by the shallow 
depression which separates the head from the tuberosities, and gives attachment to the joint capsule. 

^ The term "tubercle" as used in human anatomy does not apply well to the domestic ani- 
mals. 



THE HUMERUS 



89 



inserted into a triangular rough area below the anterior part. The medial tuber- 
osity (Tuberositas medialis) is less salient, and consists of anterior antl posterior 
parts; the anterior part forms the medial boundary of the intertuberal groove, 
and furnishes insertion to the medial branch of the supraspinatus above, and the 
posterior deep pectoral muscle below; the posterior part gives attachment to the 
subscapularis muscle. The intertuberal or bicipital groove (Sulcus intertuberalis)^ 
is situated in front; it is boundetl by the anterior jjarts of the tuberosities, and is 
subdivided by an intermediate ridge. - The groove is covered in the fresh state by 



Intertuberal 
{or bicipital) Lateral 
groove tuberosity 



Deltoid . 
tuberosity 



Lateral 
condyloid ..^ 

crest 

Coronoid v. 
fossa 


Jm^^^a 


i 






MUSCUIO- 

spiral 

groom 

Lateral 

condyloid 

cresi 


Medial i 
condyle | 




mi 






Lntiiid 
epicoHili/li 


1 

Lateral _ 
condyle 


Lateral 
cpicondyle 


Olecra- 
non fossa 


I 
,dyle 





Fig. 63. — Left Humerus^of^Horse; Lateral View. 
1, Rough area to which tendon of infraspinatus is 
attached; 2, crest; 3, depression for attachment of 
lateral ligament. 






— Nutrient 


ii'^ni 


foramen 


b^t \ 


Coronoid 




fossa 
^Medial 
epicondyle 


Medial 
condyle 





Lateral 
condyle 

Fig. 64. — Right Humerus of Horse; Front View. 

1, Rough area for attachment of extensor carpi 

radialis and extensor digitalis communis; 2, synovial 

fossa. 



cartilage, and lodges the tendon of origin of the biceps brachii muscle. Just below 
the intermediate ridge is a small fossa in which several foramina open. 

The distal extremity has an oblique surface for articulation with the radius 
and ulna, which consists of two condyles of very unequal size, separated by a ridge. 
The medial condyle (Condylus medialis) is much the larger, and is crossed by a 
sagittal groove, on the anterior part of which there is usually a synovial fossa. Pos- 
teriorly the groove extends upward considerably above the rest of the articular 
surface and reaches the olecranon fossa, and this part articulates with the semilunar 

'The name "intertuberal" i.s designative of the position of the groove, while the term 
"bicipital" has reference to its occupation by the tendon of the biceps brachii. The term "sulcus 
intertubercularis" is also in common use. 



90 



THE SKELETON OF THE HORSE 



notch of the ulna. The lateral condyle (Conclylus lateralis) is much smaller and 
is placed somewhat lower and further back, giving the extremity an oblique ap- 
pearance ; it is marked by a wide shallow groove. The coronoid fossa (Fossa coro- 
noidea) is situated in front, above the groove on the medial condyle; it furnishes 
origin to part of the extensor carpi, and lateral to it is a rough depression from 
which the common digital extensor arises. Behind and alcove the condyles are two 
thick ridges, the epicondyles. The medial epicondyle (Epicondylus medialis) 
is the more salient; it furnishes origin to flexor muscles of the carpus and digit, 
and bears a tubercle for the attachment of the medial ligament of the elbow joint. 
The lateral epicondyle (Epicondylus lateralis) bears laterally the condyloid crest 
(Crista cond\-loidea), which forms here the outer boundary of the musculo-spiral 
groove, and gives origin to the extensor carpi radialis. Below this is a rough excava- 
tion in which the lateral ligament is attached. The distal border of the epicondyle 
gives attachment to the ulnaris lateralis. Between the epicondyles is the deep 
olecranon fossa (Fossa olecrani), into which the processus anconseus projects. 




Fig. 65.— Pi 



1, Intertuberal (or bicipital) groove: 2, 3, anterior 
parts of lateral and medial tuberosities: 4, fossa: 5, 6, 
posterior parts of lateral and medial tuberosities: 7, 
head. 




Fig. 66. — Dist.\l Extremity of Left Humerus of 
Horse; E.xd View. 
1, Medial condyle: 2, lateral condyle: 3, part of 
medial epicondyle to which medial ligament is attached; 

4, depression in which lateral Ugament is attached: 

5, 6. areas of attachment of fiexor and extensor musclea 
of carpus and digit: 7, olecranon fossa. 



Development. — The humerus ossifies from six centers, viz., three primary 
centers for the shaft and extremities, and three secondary centers for the lateral 
tuberosit.v, the deltoid tuberosity, and the medial condyle respectively. The 
proximal end fuses with the shaft at about three and one-half years, the distal at 
about one and a half j'ears of age. 



THE RADIUS 

The radius is much the larger of the two bones of the forearm in the horse. 
It extends in a vertical direction from the elbow, where it articulates with the hum- 
erus, to the carpus. It is gently curved, the convexity being dorsal. It consists 
of a shaft and two extremities. 

The shaft (Corpus radii) is curved in its length, somewhat flattened from before 
backward, and widened at its ends. It presents for description two surfaces and 
two borders. The dorsal surface (Facies dorsalis) is smooth, slightly convex in 
its length, and rountled from side to side. The volar surface (Facies volaris) 



THE RADIUS 



91 



is correspondingly concave in its length and is flattened in the transverse direction. 
At its proximal part there is a smooth shallow groove, which concurs with the ulna 
in the formation of the interosseous space of the forearm (Spatium interosseum 
antibrachii) ; the nutrient foramen is in the lower part of this groove. Below this 
there is in the young subject a narrow, rough, triangular area to which the ulna is 



Olecranon 

4 



Processus anconoeus 




Processus 

ancon(Fus 
Semilunar notch 



Olecranon 




1, Tuberosity for attachment of lateral ligament of 
elbow joint, and common and lateral extensor muscles; 
2, tuberosity for attactiment of lateral ligament of 
carpal joint; 3, groove for common extensor tendon; 
4, groove for lateral extensor tendon. 



Carpal articular 
surface 



Fig. 68.— Left R. 



1, Tuberosity for attachment of short part of 
medial ligament of elbow; 2, prominence for long part 
of same; 3, groove for end of brachialis muscle: 4, 
tuberosity for attachment of medial ligament of carpal 
joint: 5. oblique groove for tendon of extensor carpi 
obliquus. 



attached by an interosseous ligament; in the adult the two bones are fused here. 
A variable rough elevation distal to the middle and close to the medial border gives 
attachment to the radial check ligament. The medial border (Margo medialis) 
is slightly concave in its length and is largely subcutaneous; at its proximal end 
there is a smooth area on which the tendon of insertion of the brachialis muscle lies, 
and a small rough area just below gives attachment to that muscle and the long 



92 THE SKELETON OF THE HORSE 

medial ligament of the elbow-joint. The lateral border (Margo lateralis) is more 
strongly curved, but presents no special features. 

The proximal extremity or head ((Extremitas proximalis s. capituluni radii) 
is flattonotl from Ix'forc backwarti and wide transversely. It presents the humeral 
articular surface (Fades articularis humeralis) which corresponds to that of the 
distal end of the humerus; it is crossed by a sagittal ridge, which has a synovial 
fossa on its posterior part, and ends in front at a prominent lip, the coronoid proc- 
ess (Processus coronoideus). Just below the posterior border, and separated by 
a depression, there are two concave facets (Facies articularis ulnaris) for articula- 
tion with the ulna, and between these and the interosseous space is a quadrilateral 
rough area at which the two bones are united by an interosseous ligament. At 
the medial side of the dorsal surface is the radial or bicipital tuberosity (Tulierositas 
radii), into which the biceps tendon is inserted. The medial tuberosity (Tuber- 
ositas proximalis medialis) is continuous with the preceding eminence, and fur- 
mshes attachment to the short part of the medial ligament. The lateral tuberosity 
(Tuberositas proximalis lateralis) is more salient; it gives attachment to the lateral 
ligament and to tlie common and lateral extensor muscles of the digit. 

The distal extremity is also compressed from before backward. It presents 
the carpal articular surface (Facies articularis carpea), which consists of three parts. 
The medial facet is the largest, is quadrilateral, concavo-convex from before back- 
ward, and articulates with the radial carpal bone; the intermediate one is some- 
what similar in form but smaller, and articulates with the intermediate carpal ])one; 
the lateral facet is smaller, is convex, and articulates below with the ulnar carpal 
and behintl with the accessory carpal. The dorsal surface presents three grooves, 
separated by ridges. The middle one is vertical and gives passage to the tendon 
of the extensor carpi radialis; the lateral one is similar and contains the tendon of 
the common digital extensor; the medial one is small and oblique and lodges the 
tentlon of the extensor carpi obliquus. The volar aspect is crossed by a rough 
ridge, Ijelow which are three depressions. On either side is a tuberosity (Tuber- 
culum ligamenti) to which the collateral ligament is attached. The lateral one is 
marked Ijv a small vertical groove for the passage of the lateral extensor tendon. 

Development. — The radius ossifies from four centers, viz., one each for the 
shaft, the two extremities, and the lateral part of the distal end ; the last is morpho- 
logically the distal end of the ulna which has fused ^vith the radius, and the line of 
fusion is often indicated by a distinct groove on the carpal articular surface. The 
proximal extremity unites with the shaft at about one and a half years, the distal 
end at about three and a half years usually. 



THE ULNA 

The ulna of the horse is a reduced long bone situated behind the radius, with 
which it is partially fused in the adult. 

The shaft (Corpus ulnse) is three-sided and tapers to a point distally. The 
dorsal surface (Facies dorsalis) is applied to the volar surface of the radius, antl be- 
low the interosseous space the two bones are fused in the adult. The surface which 
enters into the formation of the space is smooth and usually presents a small nu- 
trient foramen, directed upward. Above the space it is rough and is attached to 
the radius by an interosseous ligament which is usually permanent. The medial 
surface (Facies medialis) is smooth and slightly concave. The lateral surface 
(Facies lateralis) is flattened. The medial and lateral borders (Margo medialis, 
lateralis) are thin and sharp, except at the interosseous space. The volar border 
(Margo volaris) is slightly concave in its length and is rounded. The distal cntl is 
pointed and is usually a little below the middle of the radius. It is commonly 



THE CARPUS 



93 



continued by a fibrous cord to the distal tuberosity of the radius, but this band may 
be replaced in part or entirely by bone. 

The proximal extremity (Extreniitas proximalis) is the major part of the bone. 
It projects upward and somewhat backward behind the distal end of the humerus, 
and forms a lever arm for the extensor muscles of the elbow. The medial surface 
is concave and smooth. The lateral surface is convex and is roughenetl al)ove. 
The dorsal border bears on its midtllc a pointed projection, the processus anconseus 
or "beak," which overhangs the semilvmar notch 
(Incisura semilunaris).' The latter is triangular 
in outline, concave from above downward, convex 
transversely, and articulates with the humerus; in 
its lower part there is an extensive synovial fossa. 
Just below the notch are two convex facets which 
articulate with those on the volar aspect of the 
proximal end of the radius. The volar border is 
nearly straight, and is thick and rounded. The 
free end or summit is a rough tuberosity, the ole- 
cranon, which gives attachment to the triceps 
brachii and other muscles. 

The primitive distal extremity has, as pre- 
viously stated, fused with the radius. 

Development. — The ulna ossifies from three 
centers, of which one is for the main part of the 
bone, one for the olecranon, and one for the distal 
end. The cartilaginous embryonic ulna extends 
the entire length of the forearm. The distal part 
of the shaft is usually reducetl to a small fibrous 
band or may disappear entirely; in some cases a 
variable remnant of it ossifies. The distal ex- 





FiG. 69.— Di( 



En 



Ra 



i AND Ulna 



Ho 



End Fig. VO.- 



-Sagittal Sectio 
' Radius and Uln'j 



1, 2, 3, 4, Facets which articulate with radial, intermediate, ulnar, 
and accessory carpal bones respectively; 5, groove for tendon of exten- 
sor carpi radialis; 6, groove for tendon of common digital extensor; 7, 
tuberosity for attachment of medial ligament of carpal joint. 



Cm, Medullary cavity of uln 



tremity fuses before birth with the radius. The olecranon unites with the rest 
of the bone at about three and a half years. A medullary cavity appears to occur 
constantly in the adult — contrary to the statements of some authors. 



THE CARPUS 

The carpus of the horse consists of seven or eight carpal bones (Ossa carpi) 
arranged in two rows, proximal or antibrachial and distal or metacarpal. The 
' Formerly called the sigmoid cavity. 



94 



THE SKELETON OF THE HORSE 



(alibreviated) names and relative positions of the bones of the left carpus are in- 
dicated below: 



Radial 



Proximal Row: 
Intermediate Ulnar 



Distal Row: 
First Second Third 



Accessory 
Fourth 



The Radial Carpal Bone 

The radial carpal bone (Os carpi radiale)' is the largest bone of the proximal row; 
it is somewhat compressed transversely, and is clearly six-sided. The proximal 
surface is convex in front, concave behind, and articulates with the medial facet 
on the distal end of the radius. The distal surface is also convex in front and con- 
cave behind; it articulates with the second and third carpal bones. The lateral 
surface bears upper and lower facets on its anterior part for articulation with the 
intermediate; between and behind these it is excavated and rough. The dorsal 
surface is rough and slightly convex. The medial surface and the volar surface 
are rough and tuberculate. 

The Intermediate Carpal Bone 

The Lntermediate carpal Iwne (Os carpi intermedium)- is somewhat wedge- 
shaped, wider in front than behind. The proximal surface is saddle-shaped, and 
articulates with the middle facet on the distal end of the radius. The distal sur- 
face is smaller, convex in front, concave behind, and articulates with the third and 
fourth carpal bones. The medial surface has upper and lower facets for articula- 
tion with tlie radial carpal, and between these it is excavated and rough. 
The lateral surface is similar to the preceding and articulates with the ulnar car- 
pal. The dorsal surface is rough and slightly convex. The volar surface bears a 
tuberosity on its lower part. 

The Ulnar Carpal Bone 

The ulnar carpal bone (Os carjii ulnare)''' is the smallest and most irregular 
bone of the proximal row. The proximal surface is concave and fits the lower part 
of the lateral facet on the distal end of the radius. The distal surface is oblicjue 
and undulating for articulation with the fourth carpal bone. The medial surface 
has up]3er and lower facets for articulation with the intermediate. The dorsal and 
lateral surfaces are continuous, convex, and rough. The volar surface is obliciue, 
and bears a concave facet for articulation with the accessor}^ carpal bone; below 
this is a tubercle. 

The Accessory Carpal Bone 

The accessory carpal bone (Os carpi accessorium)^ is situated behind the ulnar 
carpal bone antl the lateral part of the distal end of the radius. It is discoid and pre- 
sents for description two surfaces and a circumference. The medial surface is con- 
cave and forms the lateral wall of the carpal groove. The lateral surface is con- 
vex and rough; a smooth groove for a tendon crosses its anterior part oblicjuely 
downward and slightly forward. The dorsal border bears two facets; the proximal 
one is concave and articulates with the back of the lateral facet on the distal end of 
the radius; the distal one is convex and articulates vAth the ulnar carpal bone. 
The remainder of the circumference is rounded and rough. 

' .\lso known as the scaphoid. " Also known as the semilunar or lunar. 

' Also known as the cuneiform. 

* Also known as the pisiform and erroneously as the trapezium. 



THE FIRST CARPAL BONE THE SECOND CARPAL BONE 



95 



The accessory does not directly bear weight, and may be regarded as a sesamoid bone 
interposed in the course of the tendons of the middle and lateral flexors of the carpus, which it 
enables to act at a mechanical advantage. The posterior border furnishes attachment to the 
transverse carpal ligament, which completes the carpal canal for the flexors of the digit. 

The First Carpal Bone 

The first carpal bone (Os carpale primum)' is a small inconstant bone, com- 
monly about the size and shajse of a pea, which is situated in the distal part of the 
medial ligament of the carpus, behind the second carpal bone. 

This bone appears to be absent on both sides in about half of the cases; in a good many 
subjects it is present on one side only. In size it varies from a minute nodule to a discoid or cylin- 
drical mass 12-15 mm. in length. In exceptional cases it articulates with both the second carpal 
and the second metacarpal bone; in other cases with the former only, but in the majority of speci- 
mens no articular facet is present. 




Fig. 71. — Left Carpus of Horse, with Parts of Adjacent Bones; Lateral View. 
C(", Intermediate carpal; Cu, ulnar carpal; Ca, accessory carpal; CS, third carpal; C4, fourth carpal; McIII, 
McIV, metacarpal bones; 1, groove for common extensor tendon; 2, groove for lateral extensor tendon; 3, groove 
for long tendon of ulnaris lateralis; 4, metacarpal tuberosity; 5, original distal end of ulna, which is fused with the 
radius and regarded as part of the latter. 



The Second Carpal Bone 

The second carpal l)one (Os carpale secuiiflum)- is the smallest constant bone 

of the distal row, and is irregularly hemispherical in sha]ie. The proximal surface 

is a convex facet, which is continued upon the volar surface and articulates with the 

radial carpal. The lateral surface faces obliquely outward and forward, and bears 

' Also known as the trapezium, and often erroneously called the pisiform. 
' Also known as the trapezoid. 



96 THE SKELETON OF THE HORSE 

three facets for articulation with the third carpal bone. The dorsal and 
medial surfaces are continuous and bear a tuberosity to which the collateral liga- 
ment is attached. The distal surface is articular and consists of a large flattened 
facet for the second or inner metacarpal bone, and a small one for the third or large 
metacarpal bone. Some specimens have a small facet on the lower part of the volar 
surface which articulates with the first carpal bone. 



S 



The Third Carpal Bone 

The third carpal bone (Os carpale tertium)' is much the largest bone of the 

distal row, forming more than 
two-thirds of the width of the 
latter. It is flattened from 
above downward, and is twice as 
wide in front as behind. The 
proximal surface consists of two 
facets separated l)y an antero-pos- 
terior ridge; the medial facet is 
concave and articulates with the 
radial carpal; the lateral facet — 
for the intermediate carpal — is 
concave in front and convex be- 
hind, where it encroaches on the 
volar surface. The distal surface 
is slightly undulating, and articu- 
lates almost entirely with the third 
or large metacarpal bone, but it 
usually bears a small oblique facet 
at its medial side for the second 
metacarpal, and there is commonly 
a non-articular depression later- 
ally. The medial surface faces 
liackward and inward, and bears 
three facets for articulation with 
the second carpal, between which 
it is excavated and rough. The 
lateral surface has two facets for 
articulation with the fourth car- 
pal, and is depressed and rough 
in its middle. The dorsal sur- 
face is convex and is crossed 
by a rough transverse ridge. The 
volar surface is relatively small, 
and is rounded; its upper part 




Fig. 72. — Left Caepcs of Horse, -niTH Parts of Adjacent 
Bones; Medial View. 
Cr, Radial carpal; Ca, accessory carpal; CI, first carpal; 
C2, second carpal; McII, McIIT, metacarpal bones; 1, tuber- 
osity of radius for attachment of medial ligament of carpus; 
2, groove for tendon of extensor carpi obliquus; 3, third "car- 
pal; 4, metacarpal tuberosity. 



is encroached upon by the proximal articular surface, below which it is rough. 



The Fourth Carpal Bone 
The fourth carpal bone (Os carpale ciuartum)- is somewhat wedge-shaped, and 
is readily distinguished from the second by its greater size and its volar tubercle. 
The proximal surface articulates with the intermediate and ulnar; it is convex and 
curves outward, backward, and downward, encroaching on the lateral and volar sur- 
faces. The distal surface bears two medial facets for the third or large metacarpal 

' Also known as the os magnum or capitatum. 
' Also known as the unciform or hamatum. 



THE FOURTH CARPAL BONE 



97 



a^id a lateral one for the fourth or lateral metacaq3al hone. The medial surface 
has two or three facets for articulation with the third carpal, between which it is 
excavated and rough. The dorsal surface is convex and rough. The lateral sur- 




McII 



Fig. 



-Left Carpus op Horse 



Parts of Adjacent Bones; Volar View. 
The accessory and first carpal bones have been moved out of their natural position and their articular connectiona 
indicated by arrows. Cr, Radial carpal; 3, intermediate carpal; Cu, ulnar carpal; Ca, accessory carpal; CI, first 
carpal; C2, second carpal; 4, third carpal; C4, fourth carpal; 1, groove for lateral extensor tendon; 2, tuberosity 
of radius for medial ligament of carpal joint; 5, volar tubercle of fourth carpal; 6, rough area on large metacarpal 
bone for attachment of suspensory ligament. 



I ntermediate 




Fig. 74. — Proximal Row of Left CARPtrs of Horse; 

Proximal View. 

1-4, Articular facets corresponding with those on Fig. 69; 

5, groove for tendon of ulnaria lateralis. 




Second 



1, Articulatii 
facets for radial 
facet for ulnar. 



First 



L Row OF Left Carpus of Horse: 

Proximal ^'IEW. 
ion of first carpal with second; 2, 2', 
3', facets for intermediate; 4, 



98 



THE SKELETON OF THE HORSE 



face is small, being encroached upon by the proximal articular surface, 
surface bears a tubercle on its distal iDart.^ 



The volar 



The Carpus as a Whole 
The bones of the carpus, exclusive of the accessory, form an irregular quadran- 
gular mass, the width of which is about twice the height or the dorso-volar diameter. 
The dorsal surface is convex from side to side, depressed along the line of junction 
of the two rows, and prominent below. The volar surface is in general slightly 
convex, but very irregular. It forms with the accessory 
carpal the carpal groove (Sulcus carpi), which in the recent 
state is rendered smooth by the volar ligament; it is con- 
verted into the carpal canal (Canalis carpi) for the flexor 
tendons by the transverse carpal ligament, which stretches 
across from the accessory bone to the medial side. The 
proximal surface is widest medially and is elevated in front, 
concave behind ; it is entirely articular and adapted to the 
carpal articular surface of the radius. The distal surface 
is also articular and is irregularly faceted in adaptation to 
the surfaces of the metacarpal bones; each of the distal 
bones usually articulates with two metacarpal bones, but 
sometimes the third rests on the third metacarpal only. 
The medial and lateral surfaces are both irregular and 
rough, the former being the wider. With the exception of 
the accessory, ulnar, and second, each bone articulates 
with two liones of the other row. 

Development. — Each ossifies from a single center. 





McIV 



Mclll 



McII 



Fig. 76. — Left Metacahpal 
Bones of Horse; Vol-\r 
View. 

1, Nutrient foramen of 
large (third) metacarpal bone; 
2, 3, 4. proximal extremities: 5, 
surface for attachment of sus- 
pensory ligament; 6, sagittal 
ridge of distal end of large meta- 
carpal bone; 7, 7', distal ends of 
small (second and fourth) meta- 
carpal bones. 



Fig. 77. — Proxim.al Ex 



Es OF Left Metacarpal Bones of Horse; End 
View. 
Facets for second carpal bone; 3, 3', facets for third carpal bone; 4, 4', facets 
for fourth carpal bone; 5, metacarpal tuberosity. 



THE METACARPUS 



Three metacarpal bones (Ossa metacarpalia) are 
present in the horse. Of these, only one, the third or 
large metacarpal bone, is fully developed and carries a 
digit; the other two, the second and fourth, are much 
reduced, and are commonly called the small metacarpal or "splint" bones. 

The Third or Large Metacarpal Bone 
This (Os metacarpale tertium) is a very strong long bone, which is situated ver- 
tically between the carpus and the first phalanx. It consists of a shaft and two ex- 
tremities. 

1 This bone is probably equivalent to the fourth and fifth carpals of forms in which five 
carpal elements are present in the distal row. 



THE SMALL METACARPAL BONES 99 

The shaft (Corpus) is semicylindrical, and presents two surfaces and two" 
borders. The dorsal sixrface is smooth, convex from side to side, and nearly 
straight in its length. The volar surface is somewhat convex from side to side and, 
with the small bones, forms a wide groove which lodges the suspensory ligament. 
On either side of its proximal two-thirds it is roughened for the attachment of the 
small metacarpal bones. The nutrient foramen occurs at the junction of the 
proximal and middle thirds. The distal part is wider and flattened. The JDorders 
are rounded. 

The proximal extremity (Extremitas proximalis s. basis) bears an undulating 
articular surface adapted to the distal row of carpal bones. The greater part sup- 
ports the third carpal bone; the oblique lateral part, separated from the preceding 
by a ridge, articulates with the fourth, and a small facet for the second is usually 
found at the medio-volar angle. On either side is a notch separating two small 
facets which articulate with the proximal ends of the small metacarpal bones. 
Toward the medial side of the dorsal surface is the metacarpal tuberosity, into 
which the extensor carpi radialis is inserted. The volar surface is roughened for 
the attachment of the suspensory ligament. 

The distal extremity (Extremitas di.stalis s. capitulum) presents an articular 
surface for the first phalanx and the proximal sesamoid bones, which is composed of 
two condyles, separated by a sagittal ridge; the medial condyle is slightly the larger. 
On either side is a small fossa, surmounted by a tubercle, for the attachment of the 
collateral ligaments of the fetlock joint. 

The large metacarpal is one of the strongest bones in the skeleton. The compact substance 
is specially thick in front and medially. The medullary cavity extends further toward the ends 
than in most of the long bones of the horse and there is httle spongy substance. 

The Small Metacarpal Bones 

These, numerically the second and fourth metacarpal bones (Ossa metacarpalia 
secundum et quartum) , are situated on either side of the volar surface of the large 
metacarpal bone, and form the sides of the metacarpal groove. Each consists of a 
shaft and two extremities. 

The shaft (Corpus) is three-sided and tapers to the distal end. It is variably 
curved, convex toward the middle line of the limb. The attached surface is flat- 
tened and is rough, except in its lower part; it is attached to the large metacarpal 
bone by an interosseous ligament, except near the distal end. The dorsal or ab- 
axial surface is smooth and rounded from side to side above, grooved below. The 
volar or axial surface is smooth and concave from edge to edge, except below, 
where it forms a rounded edge. 

The proximal extremity (Extremitas proximalis s. basis) is relatively large. In 
the case of the metlial bone it usually bears two facets above which support the sec- 
ond and third carpal bones, while the lateral bone has here a single facet for articu- 
lation with the fourth carpal bone. Each has also two facets for articulation with 
the large metacarpal, and is elsewhere roughened for the attachment of ligaments 
and muscles. The medial bone may present a small facet behind for the first carpal 
bone. 

The distal extremity (Extremitas distalis s. capitulum) is usually a small nod- 
ule, which projects to a variable extent in difi^erent subjects, and is easily felt in the 
living animal. It is situated two-thirds to three-fourths of the way down the region. 

The small metacarpal bones vary much in length, thickness, and curvature. In the ma- 
jority of cases the medial bone is the longer; in other subjects the lateral one is the longer or there 
is no material difference. Sometimes the curvature is very pronounced, so that the distal end 
causes a decided projection. The distal end is very variable in size and may be a mere point; in 
other cases, especially in large draft horses, it may present a prolongation which is regarded as the 
vestige of the digital skeleton. 

Development. — The large metacarpal bone ossifies from three centers. The 



100 



THE SKELETON OF THE HORSE 



proximal extremity unites with the shaft before birth, the distal extremity toward 
the middle of the second year. The small metacarpal bones ossify from two cen- 
ters, one of which is for the proximal extremity. Their distal ends are cartilaginous 
at birth. Fusion of the middle part of the shaft with the large metacarpal bone is 
common. 



THE PHALANGES 
The First Phalanx 
The first phalanx (Phalanx prima)' is a long bone, and is situated between the 
large metacarpal bone and the second phalanx. It is ilirected obliquely downwanl 
and forward, forming an angle of 50 to 55 degrees with the horizontal plane in well- 
formed limljs. It consists of a shaft and two extremities. 



Distal end of small meta- 
carpal hone 



Proximal sesnmoid hoiie 




Distill {lid of large melncarpnl lione 
Proxiiiiiil end of first phiilnnx 



''Jxtensor process 

urface 



Distal eiid of first phalanx 
Proximal end of second phalanx 



Distal sesatnoid bone 



Dorsal groove 

I iistnl border of third phalanx 
Fig. 7S. — Skeleton of Digit and Distal Part of Metacarpus of Horse; Lateral View. 
1-7, Eminences and depression for attachment of ligaments. Cartilage of third phalanx is removed. 




The shaft (Corpus) is wider and much thicker aliove than l)elow, and j^resents 
two surfaces and two Ijorders. The dorsal surface is convex from side to side and 
smooth. The volar surface is flattened, and l)oars a triangular rough area, bounded 
by ridges which begin at the proximal tuberosities and converge distally ; this area 
furnishes attachment to the distal sesamoidean ligaments. The borders, medial 
and lateral, are rounded and have a rough area or a tubercle on their midiUe parts. 

The proximal extremity (Extremitas proximalis s. basis) is relativelj^ large. 
It bears an articular surface adapted to the distal end of the large metacarpal bone, 
' This bone is also called the large pastern bone or os suffraginis. 



THE FIRST PHALANX 



101 



consisting of two glenoid cavities separated by a sagittal groove ; the medial cavity 
is a little larger than the lateral one. On each side is a buttress-like tuberosity for 
ligamentous attachment. The dorsal surface has a slight elevation for the attach- 
ment of the extensor tendons. 

The distal extremity (Extremitas distalis) is smaller, especially in its dorso- 
volar diameter. It presents a trochlea for articulation with the second phalanx, 
consisting of a shallow sagittal groove separating two condyles; the medial con- 



I ntennediatc groove ' 
Proximal arlicular surface ' 
Tuherositij 
Eminence for extensor tendons 



Dorsid surface 

Eminence for collalend ligament - 

Distal ariicnhir surface " 

Proximal articular surface - 

Dorsal surface ■- 

Eminence for collateral ligament - 

Distal arlicular surface - 



Articular surfi 
Angle __, 

Dejyression for collateral 
ligaments. 

Dorsal groove - 
Coronary border - 
Articular surface 

Extensor process - 

Dorsal surface 



Distal border 

Fig. 79.— Phalanqes and Distal Sesa 




First phalanx 






Second phalanx 



Third sesamoid 




Third phalanx 



llORSB; DOHSAL AsPECT. 



dyle is a little the larger, and the two are separated posteriorly by a notch. On 
either side, just above the margin of the articular surface, is a depression sur- 
mounted by a tubercle, to both of which the collateral ligament is attached. Be- 
hind the tubercle is a distinct mark to which the superficial flexor tendon is 
attached. 

Development. — The first phalanx ossifies from three centers. The distal end 
unites with th(^ shaft before birth, the proximal end at about one year of age. 

The first phalanx contains a small medullary cavity in the middle of the shaft. It may be 



102 



THE SKELETON OF THE HORSE 



.^Proximal 



Tuberosity 



remarked that the bone is twisted slightly; when placed volar surface down on the table, it touches 
the latter by three points only, the proximal tuberosities and the medial condyle. 

The Second Phalanx 
The second phalanx (PhalaiLx secunda)' is situated between the first and 
third phalanges, its direction corresponding to that of the first phalanx. It is 
flattened from before backward, and its width is greater than its height. It may 
be described as possessing four surfaces. , 

The proximal surface presents two glenoid cavities separated by a low ridge, 

and articulates with the first phalanx. 
The middle of the dorsal border is ele- 
vated and roughened in front for the 
attachment of the common extensor 
tendon. The volar border is thick and 
overhanging ; in the fresh state its mid- 
dle part is covered with cartilage, over 
which the deep flexor tendon passes. 
On either side there is an eminence, to 
which the collateral ligament and the 
superficial flexor tendon are attached. 
The distal surface is trochlear, 
and articulates with the third phalanx 
and distal sesamoid bone. It resem- 
bles somewhat the trochlea of the first 
phalanx, but is more extensive and en- 
croaches more on the dorsal and volar 
surfaces. 

The dorsal surface is convex from 
side to side and smooth in its middle; 
on each side of its distal part is a rough 
depression, surmounted by a tuber- 
osity, to both of which ligaments are 
attached. 

The volar surface is smooth and 
flattened. The borders which separate 
the dorsal and volar surfaces are con- 
cave from above downward, rounded 
from before backward. 

Development. — The second pha- 
lanx ossifies like the first, but the proxi- 
mal end unites with the shaft two or 
three months earlier. 

The Third F*halanx 
The third phalanx (Phalanx ter- 
tia)- is entireh' inclosed by the hoof, 
to which it conforms in a general way. It presents for examination three sur- 
faces, three borders, and two angles. 

The articular surface (Facies articularis) faces upward and backward, and is 
chiefly ada]ited to the distal surface of the second phalanx, but a narrow, flattened 
area along the volar border articulates with the distal sesamoid. The proximal or 
coronary border bears a central eminence, the extensor process (Processus exten- 

' This bone is also called the small pastern bone or os coronae. 
^ This bone is also called the os pedis or coffin bone. 




THE THIRD PHALANX 



103 



sorius), to which the common extensor tendon is attached. On either side is a de- 
pression for the attachment of the collateral ligament. 

The dorsal or wall surface (Facies dorsalis) slopes downward and forward. 
The angle of inclination on tlie groimd plane is about 45 to 50 degrees in front. 



Cartilugi 



Articular surface 

Extensor process 
Depression for collateral liyai. 
Dorsal surface 




Fig. 81. — Third Phalanx of Horse; Lateral View. 
a, b, .\nterior and posterior extremities of cartilage. 



Laterally the height diminishes, and the slope becomes steeper, especially' on the 
medial side. From side to side the curvature is almost semicircular. The surface 
is rough and porous, resembling pumice stone somewhat. It is perforated by nu- 
merous foramina of various sizes; a series of larger ones is situated on or near the 
distal border. On either side the dorsal groove (Sulcus dorsalis)^ passes forward 
from the angle and ends at one of the 
larger foramina. In the fresh state this 
surface is covered by the corium of the 
wall of the hoof. The distal border is 
thin, sharp, and irregularly notched; 
there is commonly a wider notch in 
front. 

The volar surface (Facies volaris) 
is arched, and divided into two unequal 
parts by a curved rough line, the semi- 
lunar crest (Crista semilunaris). The 
larger area in front of the crest is cres- 
cent-shaped, concave, and compara- 
tively smooth; it corresponds to the 
sole of the hoof, and may be termed 
the sole surface. The part behind the 
crest is much smaller, and is semilunar; 
it is related to the deejj flexor tendon, 
and is hence called the flexor surface 
(Facies flexoria). It presents a central 
prominent rough area, on either side of 
which is the volar foramen (Foramen 

volare), to which the volar groove (Sulcus volaris) conducts from the angle.' 
The foramina lead into the semilimar canal (Canalis semilunaris) within the 
bone, from which small canals leatl to some of the foramina of the dorsal sur- 

' Formerly termed the pyramidal process. - Formerly termed the preplantar groove. 

' Formerly termed the plantar groove and foramen. 




Fig. 82. — Section of Third Phaianx of Horse. 

Section is cut approximately parallel with volar ! 
face and opens up the semilunar canal (C.s.). Volar 
amina indicated by arrows. 



104 



THE SKELETON OF THE HORSE 



face. The deep flexor tendon is inserted into the semilunar crest and the central 
rough area behind it. 

The volar grooves and foramina transmit the terminations of the digital arteries into the 
semilunar canal, where they meet and form a terminal arch, from which branches pass through 
canals in the lione and emerge through the foramina on the dorsal surface. 

The angles or wings (Anguli) are prismatic masses which project backward on 
either side; the medial one is usually the shorter. Each is divided into upper and 
lower parts by a notch, or is perforated by a foramen which leads to the dorsal 
groove.^ The proximal border carries the cartilage. 

The cartilages of the third phalanx (Cartilagines phalangis tertise)- are rhom- 
boid curved plates which surmount the angles on either side. They are relatively 
large and extend above the margin of the hoof sufficiently to be distinctly palpable. 
The abaxial surface is convex, the axial, concave. The proximal border is sinuous 

and thin; the distal is thicker and is in 
part attached to the wing. The anterior 
end is attached by ligament to the side 
of the second phalanx. The posterior 
end curves toward its fellow at the heel, 
and is perforated by numerous for- 
amina for the passage of veins. 

It will be noted that the size and form 
of the angles vary much in different specimens. 
In the new-born foal the angle is a small, 
pointed projoction. Later the process of ossi- 
fication invades the lovver part of the car- 
tilage to a varying extent. In some cases the 
greater part of the cartilage is ossified — a con- 
dition commonly termed " sidebone. " In the 
yoinig subject the cartilage is hyaline, but later 
it changes to the fibrous type. 

Development. — The ossification of 
the third phalanx is peculiar. While 
the proximal articular part is still car- 
tilaginous, a perichondrial cap of bone 
is formed in relation to the hoof. Later 
the process extends into the upper part. 
Structure. — The interior of this 
bone is channeled by numerous canals 
for vessels, most of which radiate from 
the semilunar canal to the dorsal sur- 
face; these are not canals for nutrient 
vessels- of the bone, but transmit 
arteries to the corium of the hoof. Thick la.ycrs of compact substance are found 
at the articular and flexor surfaces and the extensor process, i. e., at the points of 
greatest pressure and traction. 

The Sesamoid Bones 

The two proximal sesamoids (Ossa sesamoidea phalangis primae) are situated 

behind the distal end of the large metacarpal bone, and are closely attached to the 

first phalanx by strong ligaments. Each has the form of a three-sided pyramid. 

The articular surface (Fades articularis) conforms to the corresponding part of the 

' The upper and lower divisions of the angle are sometimes termed the basilar and retrossal 
processes respectively. 

- These are usually called the lateral cartilages, but this designation could not be retained. 
They have the same relation to the third phalanx that the cartilage of the scapula has to the latter 
bone, and are here named in similar fashion. 




Fig. S3. — Phalanges of 
New-bohn Foal; Dor- 
sal View. 

Cartilages of third phalanx 



Fig. S4. — Phalak 

DistAL Sesa 

>^Ew-BORN Foal: \ 

LAR View. 
Cartilages of third phala 
removed. 



OS COXJE — THE IHUM 105 

distal end of the large metacarpal bone. The flexor surface (Facies flexoria) is 
flattened and oblique; in the fresh state it is covered b_y a layer of cartilage which 
also fills the interval between the opposed borders of the tw(j Isones, and forms a 
smooth groove for the deep flexor tendon. The abaxial surface is concave, and 
gives attachment to part of the suspensory ligament; it is separated from the 
flexor surface by a rough everted border. The base is distal, and furnishes attach- 
ment to the distal sesamoidean ligaments. The apex is proximal and is rounded. 

The distal sesamoid or navicular bone (Os sesamoideum phalangis tertije) is 
shuttle-shapetl, and is situated behind the junction of the second and third pha- 
langes. Its long axis is transverse, and it possesses two surfaces, two borders, and 
two extremities. The articular surface ' (Facies articularis) faces upward and 
forward; it consists of a central eminence, flanked by concave areas, and articulates 
with the distal end of the second phalanx. The flexor or tendon svirface (Facies 
flexoria) is directed downward and backward. It resembles the articular surface 
in form, but is more extensive and not so smooth. In the fresh state it is coated 
with cartilage and the deep flexor tendon plays over it. The proximal border 
(Margo proximalis) is wide and grooved in its middle, narrower and njunded on 
either side. The distal border (Margo distalis) bears in front a narrow facet for 
articulation with the third phalanx. Behind this is a groove, which contains a 
numl)er of relatively large foramina, and is bounded behind by a prominent edge. 
The extremities are l)lunt-pointed. 

Development. — Each ossifies from a single center. 



The Bones of the Pelvic Limb 

The pelvic girdle (Cingulum extremitatis pelvinse) consists of the ossa cox- 
arum, which unite ventrally at the symphysis pelvis, and articulate with the sacrum 
dorsally. •. 

OS COX^ 

The OS coxae or hip bone' is the largest of the flat bones. It consists primarily 
of three parts, the ilium, ischium, and pubis, which meet to form the acetabulum, 
a large cotyloid cavity for articulation with the head of the femur. These parts 
are fused at about one year of age, but it is convenient to describe them separately.^ 

The iLmM 

The ilium (Os ilium) is the largest of the three parts. It is irregularly triangu- 
lar and presents two surfaces, three bordefs, and three angles. 

The wide part of the bone -is the wing (Ala ossis ilium). Its gluteal surface 
(Facies glutsea) faces dorso-laterally and backward. It is wide and concave in 
front, narrower and convex behind. The wide part is crossed b}^ the curved 
gluteal line (Linea glutsea), which extends from the middle of the medial border 
toward the tuber coxae. This surface gives attachment to the middle and deep 
gluteal nuiscles." 

The pelvic surface (Facies pelvina) faces in the opposite direction; it is convex, 
and consists of two distinct parts. The medial triangular part (Pars articularis) 
is roughened for ligamentous attachment, and bears an irregular facet, the auricu- 
lar surface (Facies auricularis), for articulation with the sacrum. The lateral cjuad- 
rilatcral part (Pars iliaca) is in general smooth. It is crossed by the ilio-pectineal 
line (Linea iliopectinea), which begins below the auricular surface and is continued 

1 Formerly called the os innominatum. 

- The proper terms, strictly speaking, for these bones are os ilium, os ischii, and os pubis, but 
the names given above are sanctioned by common usage. 



106 



"M^ 



THE SKELETON OF THE HORSE 



on the shaft of the bone to join the anterior border of tlie pubis. The hne is inter- 
rupted by furrows for the iliaco-femoral vessels, and below these it bears the psoas 
tubercle (Tuberculum psoadicum), which gives attachment to the psoas minor mus- 
cle. The iliacus muscle is attached to the surface lateral to the ilio-pectineal line. 

The anterior border or crest (Crista iliaca) is concave, thick, -and rough. 

The medial border (Margo medialis) is deeply concave. Its middle part forms 
the greater sciatic notch (Incisura ischiadica major) and it is continuous behind 
with the ischiatic spine. 

The lateral border (Margo lateralis) is concave and in great part rough. Its 
anterior part is crossed by grooves for the ilio-lumbar vessels, which are continued 



Sacral spines 



Tuber sacralc Cresl of ilium 



, Apex of sacrum 




Symphyscal branch 
of pubis 



Vciilral ischiatic 
spine 

E]lG. 85. — Right Os Cox.e and Sacrum of Horse; Right Lateral View. 
1, Gluteal line; 2, impression of ilio-Iumbar artery; 3, impression of iliaco-femoral artery; 4, depression.^ for at- 
tachments of tendons of origin ofj rectus femoris; 5, crest to which lateral tendon of rectus femoris and capsularis are 
attached; 6, 6', articular surface of acetabulum (facies lunata); 7, acetabular fossa; 8, obturator foramen; 9, line for 
attachment of gemellus muscle; 10, lateral border of sacrum; 11, dorsal sacral foramina. 



on the jjelvic surface. The nutrient foramen is usually situated on or near" the 
posterior part of this border. 

The medial angle is termed the tuber sacrale; it curves upward and a little 
backward opposite to the first sacral spine, and forms here the highest point of the 
skeleton. It is somewhat thickened and rough. 

The lateral angle, tuber coxae, forms the basis of the point of the hip. It is a 
large quadrangular mass, narrow in its middle, and enlarged at either end, where 
it bears a pair of tuberosities. It is roughened for muscular attachment. 

The acetabular angle (Angulus acetabularis) meets the other two bones at the 
acetabulmn, of which it forms about two-fifths. Its prominent dorsal border forms 



THE ISCHIUM 



107 



part of the ischiatic spine (Spina ischiadica), which is roughened laterally, smooth 
medially. Two depressions above and in front of the acetabulum give attachment 
to the tendons of origin of the rectus femoris muscle. This angle is connected with 
the wing or wide part of the bone by a constricted part, termed the shaft (Corpus 
ossis ilium). The latter is of three-sided, prismatic form. Its lateral surface is 
convex and rough, and gives attachment to the deep gluteus muscle. Its pelvic 
surface is smooth and is grooved for the obturator vessels and nerve. Its ventral 
surface is crossed l)y vascular grooves, below which there is a rough area, which is 
bounded medially by the psoas tubercle. 



Crifti nf ilium 




Ischifiiic spine 



Ischial arch 
Fig. 86. — Ossa Cox.\rum of Hokse; Dorsal View. 
A, Wing; A% shaft of ilium; S, acetabular, B\ symphyseal branch of pubis; C, body, C, acetabular branch (or 
shaft), C"\ symphyseal branch, of ischium: 1, gluteal line; 2, grooves for obturator nerve and vessels; 3, symphysis 
pelvis; 4, greater sciatic notch; 5, ilio-pectineal eminence; 6* pubic tubercle. Dotted lines indicate primitive separa- 
tion of three bones. 



The Ischium 

The ischium (Os ischii) forms the posterior part of the ventral wall or floor of 
the bony pelvis. It slopes a little downward and inward, but is practically hori- 
zontal in the longitudinal direction. The body of the ischium (Corpus ossis 
ischii) is irregularly quadrilateral, and may be described as having two surfaces, 
four borders, and four angles. 

The pelvic surface (Facies pelvina) is smooth and slightly concave from side 
to side. 

The ventral surface (Facies ventralis) is nearly flat, and is in great part rough- 
ened for the attachment i>f the adductor muscles. 

The anterior border forms the posterior margin of the obturator foramen. 



108 



THE SKELETON OF THE HORSE 



The posterior border is thick and rough. It slopes medially and forward 
to meet the border of the other side, forming with it the ischial arch (Arcus 
ischiadicus). 

The medial border meets the opposite bone at the symphysis ischii. 

The lateral border is thick and rounded, but concave in its length; it forms 
the lesser sciatic notch (Incisura ischiadica minor), the lower boundary of the lesser 
sciatic foramen. 

The antero-medial angle or S5rmphyseal branch (Ramus symphyseos) 



Crest of ilium 




Depression for 

medial tendon 

of rectus 

femoris 



Obturator foro 



Fig. 87. — Os.sa Co: 
A, Wing, A', shaft of ilium; B, acetabular br 
branch (shaft), C". symphyseal branch, of ischium; 
arcuate line; 4, articular part, 5, iliac part, of pelvic 
acetabular fossa; 9, articular surface of acetabulun 
lines indicate primitive division of oa coxae. 



:arum of Mare; Ventral View. 

inch, S', symphyseal branch, of pubis; C, body, C, acetabular 
1, auricular surface; 2, ilio-pectineal line; 2', psoas tubercle; 3, 
surface of ilium; 6, ilio-pectineal eminence; 7, pubic tubercle; 8, 
(facies lunata) ; 10, symphysis pelvis; 11, pubic groove. Dotted 



meets the pubis, with which it forms the medial Ijoundary of the oliturator 
foramen. 

The antero-lateral angle or acetabular branch (Ramus acetabularis) joins the 
other two bones at the acetabuhim, of which it forms more than half. Dorsally 
it bears part of the ischiatic spine (Spina ischiadica), and medially it is grooved for 
the obturator vessels. The term shaft is often applied to the constricted part of 
the acetabular branch. 

The postero-medial angle joins its fellow at the symphysis. 

The postero-lateral angle is a thick, three-sided mass, the tuber ischii (Tul)er 
ischiadicuin); its lower Ixjrder is the ventral ischiatic spine, to which the biceps 
femoris and semitendinosus muscles are attached. 



the pubis — the obturator foramen 109 

The Pubis 

The pubis (Os pubis) is the smallest of the three parts of the os coxae. It 
forms the anterior part of the pelvic floor, and may be described as having two 
surfaces, three Isorders, and three angles. 

The pelvic surface (Facies pelvina) is convex in the j'oung suljject and the 
stallion, concave and smooth in the mare and usually in the gelding also.' 

The ventral surface (Facies ventralis) is convex, and in great part rough for 
muscular attachment. Near the anterior border it is crossed by the pubic groove 
(Sulcus jjubis), the medial part of which is occupied by a large vein, the lateral part 
by the accessory ligament; the groove leads to the acetabular notch. 

The anterior border is thin in its medial part (except in the young subject and 
the stallion), forming the pecten ossis pubis. Laterally it bears the rough ilio- 
pectineal eminence (Eminentia iliopectinea), beyond which it is continuous with 
the ilio-pectincal line. Near the symphysis is a variable prominence, the tuber- 
culum pubicum. 

The medial border joins the opposite bone at the symphj;sis pubis. 

The posterior border forms the anterior margin of the obturator foramen, and 
is marked laterally 1>\' the obtiu'ator groove. 

The medial angle meets its fellow at the anterior end of the s.ymphysis. This 
part is very thick in the young subject and the stallion, but in the mare, and usually 
in the gelding also, it becomes tliin with atlvancing age. 

The acetabular angle joins the ilium and ischium at the acetabulum. 

The posterior angle joins the ischium, with which it forms the inner boundary 
of the obturator foramen. 

The pubis may conveniently be regarded as consisting of a body (Corpus ossis 
puliis) and two branches; the latter are termed the acetabular branch (Ramus 
acetabularis) and the 'symphyseal branch (Ramus symphyseos). 

The Acetabulum 
The acetabulum is a cotyloid cavity which lodges the head of the femur. It 
faces vcntro-laterally, and consists of an articular and a non-articular part. The 
articular part (Facies lunata) is crescontic, and is cut into internally by a rough 
non-articular depression, the acetabular fossa (Fossa acetalmli). The medial 
part of the rim is correspondingly cut into by the acetabular notch (IncisiU'a 
acetabuli), which is converted into a foramen by the transverse ligament in the 
fresh state, and transmits the accessory and round ligaments to the head of the 
femur. 

The Obturator Foramen 

The obturator foramen (Foramen olituratum) is situated between the pubis 
and ischiiun. It is oval in outline, the longer axis being directed forward and 
outward. Its margin is grooved antero-laterally for the obturator nerve and ves- 
sels. 

* Development. — Each division of the os coxee ossifies from one chief center. 
The center for the ilium first appears near the acetabulum, followed quickly by one 
for the ischium, and a little later by the pubic center. Secondary centers appear 
for the crest and tuljer coxae of the ilium, the tuljer and posterior border of the 
ischium, and the acetabular part of the pubis. The symphyseal branches of the 
pubis and ischium are united with each other at birth or soon after, but the three 

' The pdvie surface of the pubis is quite variable. In the mare and in geldings which have 
been castrated early the two puljic bones form a central depression of varialile depth and curvature. 
This d(']iression is bounded posteriorly by two oblique convergent lines or ridges, to which the 
obturator internus muscle is attached. Not rarely small eminences may be present along the 
symphysis. 



110 



THE SKELETON OF THE HORSE 



bones are not fused until the second year. The epiphyseal parts fuse with the 
main mass at four and a half to five years of age. 

The acetabular part of the pubis ossifies from a separate center. It is most distinct in the 
embryo at three months, and is often called the os acetabtdi. Martin says that the ilium has a 
center for the acetabular part, one for the shaft and wing, and a third for the crest. He also 
states that there is a special center for the acetabular part of the ischium, and a transitory nucleus 
in the symphyseal part of the pubis. 

THE PELVIS 
The bony pelvis is composed of the o.ssa coxarum, the sacrum, and the first 
three coccygeal vertebrae. The dorsal wall or roof is formed by the sacrum and 
first three coccygeal verteljrae, and the ventral wall or floor l)y the pubic and ischial 



Crest of ilium 



Scleral 
sidnes 




Ilio-peclineal eminence 



Pubic tubercle 



Ischium 



r Front .vxd Somewhat from Below. 



Fig. 88. — Pelvic Bones of M.\re, Viewed 
1, Body of first sacral segment; 2, surface on wing of sacrum for articulation with like surface on transverse process 
of last lumbar vertebra: 3, wing of sacrum; 4, sacro-iliac articulation; 5. sacral canal; 6, promontory: 7, apex of sac- 
rum; S, ilio-pectineal line; 9, ischiatic spine; 10, grooves for ilio-lumbar vessels; 11, grooves for iliaco-femoral vessels. 



bones. The lateral walls are formed by the ilia and the acetabular part of the 
ischia. The defect in the skeleton here is supplied in the fresh state by the sacro- 
sciatic ligaments and semimcmbrano.sus muscles. 

Tlie anterior aperture or inlet of tlie pelvis (Apertura pelvis cranialis) is bounded 
by the terminal line (Linea terminalis) or brim, which is composed of the base of 
the sacrum dorsally, tlie ilio-pectineal lines laterally, and the pecten pubis ventrally. 
It is almost circular in the mare, semi-elliptical in the stallion, and faces obliquely 
downward and forward. It has two principal diameters. Of these, the con- 
jugate or sacro-pubic diameter (Conjugata anatomica) is measured from the sacral 
promontory to the anterior end of the symphysis. The transverse diameter 



THE PELAIS 



111 



(Diameter transversa) is measured at the greatest width, i. e., just above the psoas 
tubercle. 

The posterior aperture or outlet of the pelvis (Apertura pelvis caudalis) is 
much smaller and is very incomplete in the skeleton. It is bounded dorsally by the 




Fig. 90. — Pelvic Bones of Mare; Front View. 
C, Conjugate, D.t., transverse, diameter of pelvic inlet. 



third coccygeal vertebra and ventrally by the ischial arch; in the fresh .state it is 
completed laterally by the sacro-sciatic ligament and the semimembrano.sus muscle. 

The axis of the pelvis is an imaginarj' line drawn through the centers of the 
inlet, cavity, antl outlet. 

Sexual Differences. — Marked differences exist in the size and form of the pel- 
vis in the two sexes. The average conjugate diameter is about 93-'2 inches (ca. 23 to 



112 THE SKELETON OF THE HORSE 

24 cm.) in the mare, 73-2 inches (ca. 18.75 cm.) in the stallion. The transverse 
diameter of the inlet is about the same as the conjugate in the mare, l^ut is about 
8 inches (ca. 20 cm.) in the stallion. The obliquity of the inlet or inclination of the 
pelvis (Inclinatio pelvis) is greater in the female ; the difference is indicated by the 
fact that a vertical plane from the pecten cuts the fourth sacral segment in the fe- 
male, the second in the male. The outlet is also larger in the mare, the ischial arch 
being about one-third wider than in the stallion. The cavity is much more roomy 
in the female; the transverse diameter between the middles of the superior ischiatic 
spines is about 8 inches (20 cm.) in the mare, 6 inches (15 cm.) in the stallion. The 
pubic part of the floor in the female is concave and lies considerably lower than the 
ischiatic part, which is wide and almost flat. In the stallion the pubis is very thick 
medially, and this part of the floor is convex, while the ischial part is relatively nar- 
row, and is concave from side to side. The obturator foramina are correspondingly 
larger in the female. The ilium is shorter, especially with regard to its shaft, and 
the greater sciatic notch is deeper and narrower in the male. The pelvis of the geld- 
ing, when castration has been performed early, resembles that of the mare; other- 
wise the male characters appear to be retained to a large degree. 

THE FEMUR 

The femur or thigh bone (Os femoris) is the largest and most massive of the 
long bones. It extends obliquely downward and forward, articulating with the 
acetabulum above and the tibia and patella below. It presents for examination a 
shaft and two extremities. 

The shaft (Corpus femoris) is in general cylindrical, but flattened behind, and 
larger above than below. The anterior, medial, and lateral surfaces are continuous 
and strongly convex from siile to side; there is often a central vertical rough line 
on the proximal part, but otherwise these surfaces are smooth. They are covered 
by the quadriceps femoris muscle. The posterior stirface is wide, flat, and smooth 
in its proximal fourth. Distal to this part there is a rough elevation laterally for 
the attachment of the femoral tendon of the biceps femoris, and a rough line medi- 
ally to which the quadratus femoris is attached. The middle third is narrower, 
and is rough for the attachment of the adductor muscle. Just distal to this area 
an obliciue groove crosses the surface, indicating the position of the femoral vessels. 
The medial border bears on its proximal part the trochanter minor, a thick rough 
ridge, to which the ilio-psoas muscle is attached. From this a rough line curves 
up to the front of the neck and indicates the posterior limit of the attachment of 
the vastus medialis muscle. A narrow rough area about the middle of the border 
gives attachment to the pectineus muscle, and the nutrient foramen is usually 
found just in front of this mark. The medial supracondyloid crest (Crista supra- 
condyloidea medialis) is situated below the groove for the femoral vessels, and gives 
origin to the medial head of the gastrocnemius. The lateral border is prominent 
in its u]iix'i' part, and bears at the junction of its proximal and middle thirds the 
trochanter tertius;^ this process is curved forward, and has a thick edge to which 
the tendon of the superficial gluteus muscle is attached. At the distal part is the 
supracondyloid fossa (Fossa supracondyloidea),^ in which the superficial digital 
flexor arises; it is bounded laterally by a thick, rough margin, the lateral supra- 
condyloid crest (Crista supracondyloidea lateralis), to which the lateral head of the 
gastrocnemius muscle is attached. 

The proximal extremity (Extremitas proximalis) is large and consists of the 
head, neck, and trochanter major. The head (Caput femoris) is placed at the 
medial sifle and is directed inward, upward, and somewhat forward. It is ap- 
proximately hemispherical and articulates with the acetabulum. It is cut into 

' Also termed the external trochanter. - Also termed the fossii plantaris. 



THE FKMUR 



113 



medially by a deep notch, the fovea capitis, in which the accessory and round liga- 
ments are attached. The articular surface is surrounded by a distinct margin. 
The neck (Collum femoris) is most distinct in front and medially. The trochanter 
major is situated laterally; it presents three features. The anterior part or con- 
vexity is situated opposite to the head and rises little above the level of the latter; 
it gives attachment to the deep gluteus muscle, and in the fresh state its lateral 
surface is coated with cartilage, over which a tendon of the middle gluteus passes, 
to l)e inserted into the crest, which is placed below and behind the convexity. 
The posterior part or siunmit is separated from the anterior part l)y a notch ; it is 
situatetl behind the plane of the head antl rises to a much greater height. It 



Tro- 
chanter 
tertius 




Head 
Fovea 







Head 


Neck 




Foi'ea 


Tro- 
chanter 
minor 


cli 


Neck 
Tro- 
ll nteric 



Lateral 

epi- 

condyle 



_Tro- 
I chanter 
major 



' Crest 



Trochlea 
91. — Right Femur of Horse; Front View. 





Tro- 
chanter 




_ 


Tro- 
r hauler 
iertius 




minor 




m 


" Promi- 
nence for 
tendon of 
biceps 




Nutrient ' 






femoris 












foramen 


ir^ « 








Groorefor 
femoral 










P^^A 






eesseh 






Supra- 




M,„i:,,l — 




— 


- condyloid 




iMeaiai 






fossa 




xiipra- 










conilytoiil 










crest 


* <t *'« 






Medial 




/ il * 


k 




cpi- 




/ f ■ ■■ J 


v 




condyle 




M : •'^^'■■■7f..,TJ^ 


^ 




Medial 
condyle 


Medial - 
ejncondyle 




1 


1 

_ Lateral 




Medial - 


ft ~'ij^!^hh 


• 


condyle 




condyle 




w 








I ntercondyloid fossa 




T View. 


Fig. 92.— Rig: 


HT Femdr of Horse 


; Posterior View 



furnishes insertion to part of tlie middle gluteus muscle. Its posterior l^order is 
continued downward as the trochanteric ridge (Crista trochanterica), which forms 
the lateral wall of the trochanteric fossa (Fossa trochanterica). A number of 
foramina are found in the concave area medial to the convexity. 

The distal extremity (Extremitas distalis) is large in both directions and com- 
prises the trochlea in front and two condyles behind. The trochlea consists of two 
ridges separated by a groove, and forms an extensive surface (Facies patellaris) for 
articulation with the patella. It is very unsymmetrical ; the medial ridge is much 
wider, more prominent, and extends up higher than the lateral one, and the two 
converge below. The condyles, medial and lateral (Condylus medialis, lateralis), 



114 



THE SKELETON OF THE HOKSE 



are separated by the deep intercondyloid fossa (Fossa intercondyloidea), and 
articulate with the condyles of the tibia and the menisci of the stifle joint. A ridge 
connects each condyle with the lower part of the corresponding ridge of the trochlea. 
The intercondyloid fossa lodges the spine of the tibia and the cruciate ligaments of 
the stifle joint, which are attached here. 

The condyles are obliquely placed with their long axes directed downward, forward, and 
inward. The articular surface of the lateral condyle is more strongly convex from side to side 
than that of the medial one, and the ridge which connects it with the trochlea is much narrower. 

The medial epicondyle (Epicondylus medialis) is a rounded prominence on 
the medial surface of the distal extremity, to which the collateral ligament and the 
adductor muscle are attached. The corre.sponding lateral epicondyle (Eijicondylus 





Fig. 93. — Proximal Extremity of Right 

Horse; _End,View. 
1, Head; 2, fovea capitis: 3, neck; 4, .5, a 
posterior parts of trochanter majo 




Intercondyloid jo. 



Fig. 94. — Distal Extremity of Right Femur of 
Horse; End View. 
1, 1', Medial and lateral ridges of trochlea; 2, 2', 
medial and lateral condyles; 3, 3', medial and lateral 
epicondyles; 4, extensor fossa; 5, depression for origin 
of popliteus. 



lateralis) is less distinct; it presents a mark where the lateral ligament is attached, 
below and behind which there is a depression (Fossa musculi poplitei) in which the 
popliteus muscle arises. Between the lateral condyle and trochlea is the extensor 
fossa (Fossa extensoria), in which the common tendon of origin of the extensor 
digitalis longus and peroneus tertius is attached. 

Development. — The shaft and the distal end each ossify from one center, but 
the proximal end has two centers, one of which is for the head and the other for the 
trochanter major. The Sdge of the trochanter tertius also has a separate center. 
The proximal end fuses with the shaft at three to three and a half years, the distal 
at about three and a half years. 



THE TIBIA 

The tibia is a long bone which extends obliquely downward and backward 
from the stifle to the hock. It articulates above with the femur, below with the 
tarsus, and laterally with the fibula. It possesses a shaft and two extremities. 

The shaft (Corpus tibiae), large and three-sided above, becomes smaller and 
flattened in the sagittal direction below, but witlens at the distal end. It presents 
for notice three surfaces and three Ijorders. The medial surface (Fades medialis) 
is broad above, where it presents rough prominences for the attachment of the 



THE TIBIA 



115 



medial ligament and the sartorius and gracilis muscles; below this it is narrower, 
convex from edge to edge and subcutaneous. The lateral surface (Facies lateralis) 
is smooth and somewhat si^iral. It is wide and concave in its ])roximal fourth, 



Fig. 95.— R 





Lat- 



1, Tuberosity; 2, sulcus rauscularis; 3, crest; 4, 
spine; 5, lateral condyle; 6, head of fibula; 7, impres- 
sion of anterior tibial vessels; 8, shaft of fibula; 9, lat- 
eral border of tibia; 10, lateral malleolus; 11, groove 
for lateral extensor tendon. 



Fig. 90. — Right Tibia and Fibula of Horse; Poste- 
rior View. 
1, Medial condyle; 2, lateral condyle; 3. spine; 4, 
fossa for anterior cruciate ligament; 5, popliteal notch; 
6, tubercle for posterior cruciate Hgament; 7, head of 
fibula; S, vascular impression; 9, interosseous space; 
10. shaft of fibula; 11, muscular hnes; 12. tubercle; 13, 
nutrient foramen; 14, medial malleolus; 15, groove for 
tendon of flexor digitalis longus; 16, lateral malleolus. 



]x4ow which it becomes narrower and convex, and wincts gradually to the front of 
the bone; near the distal end it widens a little, becomes flat, and faces forward. 
The posterior surface (Facies caudalis) is flattened, and is divided into two parts 
by the rough popliteal line (Linea poplitea), which runs obliquely from the proxi- 



116 



THE SKELETON OF THE HORSE 



mal part of the lateral border to the middle of the medial border. The triangular 
area above the line is occupied by the popliteus muscle, while the area below is 
marked by rough lines (LineiE musculares) to which the deep flexor muscle of the 

digit is attached; the lines fade out distally, 
I where the surface is smooth and flat. The 

nutrient foramen is situated on or near the 
popliteal line. The anterior border is very 
prominent in its proximal third, forming the 
crest of the tibia (Crista tibiie) ; distally it is 
reduced to a rough line, which ends at a small 
elevation near the distal end of the bone. The 
medial surface of the crest presents a rough 
prominence for the attachment of the ten- 
don of the semitendinosus. The medial border 
(Margo medialis) is rounded in its proximal 
half, to which the popliteus muscle is attached, 
and a tubercle is found on this part. The dis- 
tal part is a rough line on well-marked bones. 
The lateral border (Crista interossea) is con- 
cave in its proximal part and concurs with the 
fibula in the formation of the interosseous space 
of the leg (Spatium interossemn cruris) ; a 
smooth impression indicates the course of the 
anterior tibial vessels through the space to the 
front of the leg. About the middle of the bone 
the border divides and incloses a narrow trian- 
gular surface. 

The proximal extremity (Extremitas proxi- 
malis) is large and three-sided. It bears two 
articular eminences, the medial and lateral con- 
dyles (Condylus medialis, lateralis). Each pre- 
sents a somewhat saddle-shaped surface for ar- 
ticulation with the corresponding condyle of the 
femui- and meniscus. The spine or intercondy- 
loid eminence (Eminentia intcrcondyloidea) is 
the central prominence, upon the sides of which 
the articular surfaces are continued ; it consists 
of a high medial part and a lower lateral part ' 
(Tuberculum intercondyloideum mediale, lat- 
erale). On, before, and behind the spine are 
the intercondyloid fossae, in which the anterior 
cruciate ligament and the menisci are attached. 
The condyles are separated behind by the deep 
popliteal notch (Incisura poplitea), on the 
medial side of which there is a tubercle for 
the attachment of the posterior cruciate liga- 
ment. The lateral condyle has an overhang- 
ing outer margin (Margo infraglenoidalis), be- 
low which there is a facet (Facies articularis 
fibularis) for articulation -ndth the fibula. The 
large anterior eminence is the tuberosity of the 
tibia (Tuberositas tibiae). It is marked in front by a groove (Sulcus ligament!) , 
the lower part of which gives attachment to the middle patellar ligament, ancl 
the groove is flanlced by rough areas for the attachment of the medial and lateral 




Fig. 97.— R 

Anterior View. 
1, Spine; 2, tuberosity; 3, groove for 
middle patellar ligament; 4, medial condyle; 
5, sulcus muscularis; 6, lateral condyle; 7, 
head of fibula ; 8, interosseous space; 9, lateral 
surface of tibia; 10, shaft of fibula: 11, imprint 
for attachment of gracihs: 12, crest; 13, promi- 
nence for attachment of semitendinosus; 14, 
media] surface of tibia; 15, medial malleolus; 
16, lateral malleolus. 



THE FIBULA 



117 



patellar ligaments. A semicircular smooth notch, the sulcus muscularis, separates 
the tuberosity from the lateral condyle, antl gives passage to the common tendon 
of origin of the extensor digitalis longus and the peroneus tertius. 

The distal extremity (Extremitas distalis) is much smaller than the proximal 
one; it is r|uadrangular in form and larger medially than laterally. It presents an 
articular surface (Cochlea tibiis), which is adapted to the trochlea of the tibial 
tarsal bone, and consists of two grooves separated by a ridge. The ritlge and 
grooves are directed obliquely forward and laterally, and are bounded on either 
side by the malleoli, to which the collateral ligaments of the hock joint an* at- 
tached. A shallow synovial fossa is usually present on the middle of the articular 
ridge. The lateral groove is wider antl shallower than the medial one; it is fre- 
quently marked by a line or groove which indicates the former demarcation between 
the tibia and fibula. The medial malleolus (Malleolus medialis) is the more prom- 
inent of the two, and forms the anterior l)oundary of a groove for the tendon of the 
flexor digitalis longus. The lateral malleolus (Malleolus lateralis) is broader, and 
is marked by a vertical groove for the passage of the lateral extensor tendon. 

Development. — The tibia has the usual three chief centers of ossification and 
supplementary ones for the tuberosity and the lateral malleolus. The latter is 
really the distal end of the fibula; it is a separate piece at birth, and the line of 
union is commonly quite evident in the adult in the articular groove. The proxi- 
mal end unites with the shaft at about three and a half years, and the distal end at 
about two years of age. 




Fig. 9S.— Proximal Extrenmty of Right Tibia of 
Horse; End View. 
1, Medial condyle; 2, lateral condyle; 3, groove 
■"on 2 for popliteus tendon; 4, popliteal notch; 5. tuber- 
osity; 0, groove for middle patellar ligament; 7, tuber- 
cles of spine; 8, 'sulcus muscularis; l.c.a., I.e. p., depres- 
sions for attachment of anterior and posterior cruciate 
ligaments; /, m. m, depressions for attachnient of 
menisci. 




Fig. 



Tib 



-Distal iExtremity of 
Fibula) of Horse; End View. 
1. 1', Articular grooves; 2, intermediate ridge and 
synovial fossa; 3, line of fusion of primitive distal end 
of fibula with tibia; 4, medial malleolus; 5, 5', lateral 
malleolus; 6, posterior border. 



THE FBULA 

The fibula of the horse is a much reduced long bone, situated along the lateral 
border of the tibia. 

The shaft (Corpus fibulce) is a slender rod which forms the lateral boundary of 
the interosseous space of the leg; it usually terminates below in a pointed end aljout 
one-half to two-thirtls of the way down the lateral border of the tibia. 

The proximal extremity or head (Caiiituluni fibute) is relatively large, and is 
fiattenetl transversely. Its medial surface presents a narrow area (Facies articu- 
laris capituli) along the upper border for articulation with the lateral condyle of 
tibia. The lateral surface is rough and gives attachment to the lateral ligament 
of the stifle joint. It has rounded anterior and posterior borders. 



118 THE SKELETON OF THE HORSE 

The distal extremity is fused with the tibia, constituting the lateral malleolus. 

Development. — This resembles that of the ulna. The embryonic cartilaginous 
filiula extends the entire length of the leg, but does not articulate with the femur. 
The distal part of the shaft is usually reduced to a fibrOus band. Three centers of 
ossification appear, one each for the shaft and the extremities. The distal end 
unites early with the tibia, forming the lateral malleolus. 

It is interesting to note that in some cases the entire shaft of the fibula develops, a reversion 
to the condition in the Miocene ancestors of the horse. 

THE PATELLA 

The patella is a large sesamoid bone which articulates with the trochlea of the 
femur. It presents for description two surfaces, two borders, a base, and an apex. 

The anterior, free surface (Facies libera) is quadrilateral, convex, and rough 
for muscular and ligamentous attachment. 

The articular surface (Facies articularis) is also quadrilateral, but much less 
extensive. It presents a vertical rounded ridge, which corresponds to the groove 



Base 





Later- 
al 
angle 



Apex Accessory cartilage Apex 

Fig. 100. — Right Patella of Horse; Antehior View. Fig. 101. — Right Patella of Horse; Posterior View. 

1, .Attachment area of middle patellar ligament: 1, Medial part, 2, lateral part, of articular surface. 
2, attachment area of lateral patellar ligament and 
biceps femoris. 

on the trochlea of the femur, and separates two concave areas. Of the latter, the 
medial one is much the larger, and is not very well adapted to the corresponding 
ridge of the trochlea; in the fresh state, however, it is completed and rendered more 
congruent Ijy the curved accessory fibro-cartilage. 

The borders, medial and lateral, converge to the apex below, and each forms an 
angle at the base. The medial border is concave. The lateral border is rounded 
and its angle is less prominent. The medial angle and the adjacent part of the 
posterior margin of the base give attachment to the fibro-cartilage of the patella 
(Fibrocartilago patellae). 

The base (Basis patellae) faces upward and backward, and is convex trans- 
versely, concave from before ]:)ackwanl. 

The apex (Apex patellar) forms a blunt point directed distally. 

Development. — The patella develops as a sesamoid bone from a single center 
in a cartilaginous deposit in the tendon of the Cjuadriceps femoris muscle. 

THE TARSUS 
The tarsus or hock of the horse usually comprises six short bones (Ossa tarsi), 
but exceptionally seven are present. 









119 



120 



THE SKELETON OF THE HORSE 



The Tibial Tarsal Bone 

The tibial tarsal bone (Os tarsi tibiale)' is the medial bone of the proximal row. 
It is extremely irregular in form, but may be considered as offering six surfaces for 
description. 

The proximal and dorsal surfaces are continuous, and form a trochlea (Troch- 
lea tali) for articulation with the distal end of the tiljia. The trochlea consists 

of two oblique ridges wdth a deep groove 
between them; these curve spirally for- 
ward, downward, and outward, forming 
an angle of 12 to 15 degrees with a sagittal 
plane. There is usually a shallow synovial 
fossa in the groove. The distal surface is 
convex from before backward, and most 
of it articulates with the central tarsal; 
laterally it has an oblique facet for the 
fourth tarsal, and a non-articular groove 
cuts into the surface to its middle. The 
plantar surface (Facies plantaris) is ob- 
lique and extremely irregular; it presents 
four facets for articulation with the fibular 
tarsal bone; the facets are separated by 




Pro 



Me 



Ho 




Bone of Horse; Plan- 



1-4, Facets for articulation witli fibular tarsal; 5, fossa; 
6, distal tuberosity; 7, proximal tuberosity. 



Ti, Tibial tarsal (trochlea); TV, fibular tarsal 
(body); Tc, central tarsal; T3, third tarsal; Ti, 
fourth tarsal; 1, depression for attachment of lateral 
ligament; 2, processus cochlearis; 3, prominence for 

attachment of lateral ligament; 4, groove for great i , i i xl l i 

metatarsal artery; 5, tuber calcis; Mt. III. IV. met.- ^^OUgh eXCaVatcd arCaS, and the krgCSt 

tarsal bones. Arrow points to vascular canal. fossa (Sulcus tali) forms with a Corres- 

ponding one on the fibular tarsal a cavity 
termed the sinus tarsi. The mediaJ surface Ijears on its distal part a large tuber- 
osity and on its proximal part a small one for the attachment of the medial liga- 
ment of the hock joint. The lateral surface is smaller than the medial, and is 
marked by a wide rough fossa in which the lateral ligament is attached. 



The Fibular Tarsal Bone 
The fibular tarsal bone (Os tarsi fibulare)- is the largest bone of the hock. It 
is elongated, flattened from side to side, and forms a lever for the muscles which 



' Also termed the astragalus or talus. 



- Also termed the calcaneum or os calcis. 



THE CENTRAL TARSAL BONE 



121 



extend the hock joint. It consists of a body and a medial process, the sustentacu- 
lum tali. 

The body (Corpus) is enlarged at its proximal end to form the tuber calcis or 
"point of the hock"; the posterior part of this eminence gives attachment to the 
tendon of the gastrocnemius, while in front and on each side it furnishes insertion 
to tendons of the superficial digital flexor, biceps, and semitendinosus muscles. 
The distal extremity bears a concave facet for articulation with the fourth tarsal 
bone. The medial surface of the body has on its lower part a strong process, the 
sustentaculum tali, which projects inward. The process has a large, oval, slightly 
concave facet in front for articulation with the tibial tarsal, and sometimes a small 
articular surface below for the central bone. Its plantar surface forms wth the 
smooth medial surface of the body a groove for the deep flexor tendon (Sulcus tarsi). 
Its medial surface has a prominence on the distal part for the attachment of the 
medial ligament. The lateral surface of the Ijody is flattened, except below, where 
there is a rough prominence for the attachment of the lateral 
ligament. The dorsalborder is concave in its length, smooth 
and rounded in its upper part. About its middle is a blunt- 
pointed projection (Processus cochlearis) which bears facets 
on its medial and lower surfaces for articulation with the 
tibial tarsal lione, and is roughened laterally for ligamen- 
tous attachment. Below this are two facets for the tibial 
tarsal, and an extensive rough fossa which concurs in 
the formation of the sinus tarsi. The plantar border is 
straight and broad, and widens a little at each enil ; it is 
rough, and gives attachment to the long plantar ligament. 





Fig, 107. — Right Fibular 
Tarsal Bone of Horse; 
Dorsal View. 

1-4, Facets for articulation with 
tibial tarsal bone; 5, fossa. 



Fig. 108. — Right Central Tarsal Bone of Horse; Proximal Surface. 
1, Articular surface for tibial tarsal; 2, facet for fibular tarsal; 3, non-articular 
deprt 



The Central Tarsal Bone 

The central tarsal bone (Os tarsi cent rale)' is irregularly cjuadrilateral, and is 
situated between the tibial tarsal and the third tarsal. It is flattened from above 
downward, and may be described as having two surfaces and four borders. The 
proximal surface is concave from before backward, and almost all of it articulates 
with the tibial tarsal; a non-articular depression cuts into its lateral part, and 
sometimes there is a facet for the fibular tarsal bone on the posterior angle. The 
distal surface is convex, and is crossed by a non-articular groove, which separates 
facets for articulation with the third and the first and second (fused) tarsals. The 
dorsal border and the medial border are continuous, convex, and rough. The 
plantar border bears two j^rominences, separated by a notch. The lateral border 
is olilique, and liears anterior and po.sterior facets for articulation with the fourth 
tarsal, between which it is excavated and rough. 

' Also termed the scaphoid or navicular bone. 



122 



THE SKELETON OF THE HORSE 



First and Second Tarsal Bones 

The first and second tarsal bones (Os tarsale primum et secundum)' are usually 
fused in the horse, forming a Ijone of very irregular shape, situated in the medio- 
plantar part of the distal row, below the central and behind the third tarsal. It is 
the smallest of the tarsal bones, and may be described as having four surfaces and 
two extremities. The medial surface faces backward and inward, and is convex. 
Its anterior part is ridged, and gives attachment to the medial ligament, and its 
posterior part bears an imprint where the medial tendon of the tibialis anterior is 
inserted. The lateral surface is marked by a deep notch which indicates the divi- 
sion between the first and second tarsal elements; it bears on its anterior part a 
facet for the third tarsal. The proximal surface is concave and has two facets for 
articulation with the central tarsal; it is separated from the medial surface by a 
prominent Ijorder. The distal surface is broail in front, where it articulates with 




Fig. 109. — Right First and Sec- 
ond (Fused) Tarsal Bones 
OF Horse; Lateral Surface. 
Tl, T-2, First and second tarsal 
bones; 1, 1', articular surface for 
central tarsal; 2, facet for third tar- 
sal; 3, facet for medial small meta- 
tarsal bone. Separation between 
two bones (when present) is indi- 
cated so far as visible by dotted 
line between 1 and 1'. 




Fig. 110. — Right Third Tarsal 
Bone of Horse; Proximal 

Surface. 

1, 2, Facets for central tarsal; 
3, 4, facets for fourth tarsal; 5, non- 
articular depression ; 6, dorsal ridge. 




Bo 



— Right Fourth Tarsal 
5 of Horse; Medial Sur- 



1, 1', Facets for central tarsal; 
2,2', facets for third tarsal ; 3, facet 
for tibial tarsal; 4, 4', facets for 
fibular tarsal; 5, facet for large 
metatarsal bone; 6, groove which 
concurs with central and third tar- 
sals in formation of vascular canal 
of tarsus. 



the large and medial small metatarsal bones. The dorsal extremity bears a ridge 
or tubercle. The plantar extremity is a blunt point. 

In some cases the first and second tarsal liones remain separate — a remarkable reversion to 
the condition in the early ancestors of the horse. In such specimens the first tarsal is a discoid 
bone, articulating above with the central, below with the small metacarpal bone. The second 
tarsal is qu;ulrangular, equivalent to the thick anterior part of the bone as described above, and 
overlapped in part by the first tarsal. 



The THmo Tarsal Bone 

Tlie third tarsal bone (Os tarsale tertium)- resembles the central, but is smaller 
and triangular in outline. It is situated between the central above and the large 
metatarsal bone l)elow. It possesses two surfaces and three borders. 

The proximal surface is concave, and is crossed by a non-articular depression 
which divides it into two unequal facets; it articulates with the central tarsal. 
The distal surface is slightly convex, and rests on the large metatarsal bone; it 
has an extensive central rough excavation. The dorsal border is convex and bears 
a rounded ridge on its medial part. The medial border is deeply notched and has 
a small facet for the second tarsal on its anterior part. The lateral border is also 
divided by a notch into two parts, and bears two diagonally opposite facets for 



1 Also termed the cuneiform parvum. 



- Also termed the cuneiform magnum s. tertium. 



THE METATARSUS 



123 



articulation with the fourth tarsal. In some cases there is a facet for the medial 

small metatarsal bone. 

The Fourth Tarsal Bone 
The fourth tarsal bone (Os tarsale quartum)' is the lateral bone of the distal 

row, and is equal in height to the central and third together. It is culioid in shape 

and presents six surfaces. 

The proximal surface is convex from side to side, and articulates chiefly 

with the fibular tarsal, but to a small extent with the tibial tarsal also. 
The distal surface rests on the large and lateral 
small metatarsal bones. The medial surface bears 
four facets for articulation with the central and 
third tarsal bones. It is crossed from before back- 
wartl by a smooth groove, which by apposition with 
the adjacent bones forms the canal of the tarsus (Can- 
alis tarsi) for the passage of the perforating tarsal 
vessels. The dorsal, lateral, and plantar surfaces are 
continuous and rough. A tuberosity Ijehind gives 
attachment to the plantar ligament. 

Development. — The fibular tarsal bone has two 
centers of ossification, one for the main mass and the 
other for the tuber calcis; the latter fuses with the rest 
of the bone at about three years of age. The first and 
second tarsals have separate centers, but fusion usu- 
ally occurs before birth. Each of the other bones 
ossifies from a single center. 




THE METATARSUS 

The metatarsal bones (Ossa metatarsalia), three 
in number, have the same general arrangement as 




MIL n Mt. Ill 



Mf. i V 



Fig. 112. — RioHT Metatarsal Bones 
OF Horse; Plantar View. 
1, Rough area for attachment of 
suspensory hgament: 2. nutrient fora- 
men. Compare with Fig. 76. 



Fig. 113. — Proximal Extremities of Right Me 
Horse; End View. 
1, Facet for first tarsal; 2, 2', facets for second tarsal; .3, 3', facets for 
third tarsal; 4, 4', 4", facets for fourth tarsal: 5, noi 
Compare with Fig. 77. 



AL Bones of 



• depi 



the metacarpal bones, but present some important differences. Their direction is 
slightly obhque, downward, and a little forward. 

The third or large metatarsal bone (Os metatarsale tertium) is about one- 
sixth longer than the corresponding metacarpal; in an animal of medimn size the 

'■ Also termed the cuboid. 



124 



THE SKELETON OF THE HORSE 




difference is about two inches. The shaft is more cyhndrical, and is almost cir- 
cular on cross-section, except in its distal part. At the proximal part of its lateral 
surface there is a groove, which is directed obliquely downward and backward, and 
is continued by the furrow formed by the apposition of the fourth or lateral meta- 
tarsal bone; it indicates the course of the great metatarsal artery. A shallow im- 
pression in a similar place on the medial side marks the position of the corresponding 

vein. The nutrient foramen is rela- 
tively higher than on the metacar- 
pal bone. The proximal extremity 
is much wider from before back- 
ward than that of the metacarpal 
bone. Its articular surface is 
slightly concave, and is marked 
by a large central non-articular de- 
pression, continued outward by a 
deep notch. The greater part of 
the surface articulates with the 
third tarsal, but there is a lateral 
facet for the fourth, and usually a 
small facet postero-medially for the 
second tarsal bone. Posteriorly there are two pairs of facets for articulation with 
the small metatarsal bones. The front is crossed by a rough ridge for insertion, 
which becomes larger and turns downward on the lateral side behind the vascular 
groove. The distal extremity closely resembles that of the corresponding meta- 
carpal bone. 

In some cases the distal part of the shaft is bent backward somewhat. The distal articular 
surface extends a little higher behind than in the case of the metacarpal bone. The large meta- 
tarsal bone is even more strongly constructed than the metacarpal. The shell of compact sub- 
stance is very tliick in the middle of the shaft, especially in front and medially. 






Fig. 114. 


Fig. 115. 


Figs. 


114, 115.— Cross-sections of 
Metatarsal Bo 


Left Metacarpai 



Sections are cut a little above middle of bones. 





Fig. 116.— Third Pm 



■ Limb of Horse. Fig. 117.— Third Pii 



The small metatarsal bones (Ossa metatarsalia secundum et quartum) are a 
little longer than the corr(>spontling metacarpals. The lateral (fourth) metatarsal 
bone is relatively massive, especially in its upper part. The head is large antl out- 
standing, and bears one or two facets above for the fourth tarsal, and two in front 
and medially for articulation with the large metatarsal ; elsewhere it is roughened 
for attachment. The medial (second) metatarsal lione is much more slender than 
the lateral one, especially in its proximal part. The head bears two facets above for 
the first and second tarsals, and sometimes one for the third tarsal. 



SKELETON OF THE OX 



125 



THE PHALANGES AND SESAMOID BONES 

The axis of the phalanges of the hind limb forms with the ground plane an 
angle which is about five degrees greater than that of the fore limb, and the chief 
differences in the form and size of the bones are as follows: 

The first phalanx is a little shorter, wider above, and narrower below. 

The second phalanx is narrower and slightly longer. 

The third phalanx is narrower, the angle of inclination of the dorsal surface is a 
little (ca. 5 degrees) greater, the plantar surface is more concave, and the angles 
are less prominent and closer together. The term plantar is to be substituted for 
volar in the designation of corresponding features. 

The proximal sesamoids arc a little smaller, except in thickness. The distal 
sesamoid is narrower antl shorter. 



SKELETON OF THE OX 



VERTEBRAL COLUMN 

The usual vertebral formula is C7Ti3L6S5Cyi8-2o- 

The cervical vertebrae are much shorter than those of the horse and are smaller 
in their other dimensions. The articular processes are smaller than in the horse, 
and a plate of bone comiects each two of the same side. The transverse processes 
of the third, fourth, and fifth are double; the upjDer part projects backwartl, and 
is short and stout; the lower part is directed 
do\\aiwarcl and forward, and is longer and 
more plate-like. The lower part of the sixth 
transverse process is a large, thick, quadri- 
lateral and almost sagittal plate, directetl 
ventrally. The seventh transverse process is 
single, short, and thick, and presents no fora- 
men transversarium ; it is in series with tlie 
upper part of the preceding processes. The 
spinous processes are well developed, and in- 
crease in height from before jjackward. They 
are directed upward and forward, with the ex- 
ception of the last, which is nearly vertical 
and is about four or five inches (ca. 10 to 12 
cm.) in height. The summit of that of the 
third vertebra is usually bifid. The ventral 
spines are prominent and thick in their pos- 
terior part; they are absent on the last two. 

The atlas has a large rough tuberosity 
on its dorsal arch. The ventral arch is very 
thick. The wings are less curved than in the 

horse, and the foramen transversarium is absent. The anterior articular cavities for 
the occipital condyles are partially divided into dorsal and ventral parts by a non- 
articular area, and are separated by a narrow interval below. The posterior artic- 
ular surfaces are flattened behind and are continued into tlie vertebral canal, form- 
ing an extensive area for the dens of the axis. 

The axis is short. The spine projects a little in front, and increases in height 
and thickness behind ; its posterior border descends abruptly. The dens is wide, 
and its dorsal surface is deeply concave from side to side. The intervertebral 




Fig. 118. — Third Cervical Vertebra 
Lateral View. 
1, Spinoua process; 2 
terior articular processes; 
4, 4', transverse process; 
sarium; 6, ventral spine. 



anterior and pos- 
3', ends of body; 
foramen transver- 



126 



SKELETON OF THE OX 




VERTEBRAL COLUMN 



127 



foramen is circular and not so close to the anterior border of the arch as in 
the horse. The posterior notches are not so deep. The transverse processes are 
stouter, but the foramen transversarium is small and sometimes absent. 

The thoracic vertebrae, thirteen in number, are larger than those of the horse. 





Fig. 120.— Sixth Cervical Vertebra of Ox; Pos- 
terior View. 
1, Posterior cavity of body; 2, vertebral foramen; 
3, arch; 4, 4', posterior articular processes; 5, 5, an- 
terior articular processes; 6, 6', lateral branches of trans- 
verse processes; 7, 7', ventral branches of transverse 
processes; S, foramen transversarium; 9, spinous proc- 



FiG. 121. — Seventh Ce 



1, Posterior cavity of body; 2, 2', facets for head 
of first rib; 3, vertebral foramen; 4, 4', arch; 5, 5', ar- 
ticular processes; 6, 6', transverse processes; 7, spinous 
process. 





Fig. 122.— Atlas of Ox; Dorsal View. 
1, Dorsal tubercle; 2, intervertebral foramen; 3, 
foramen; 4, wing; 5, 5, posterior articular surfaces; 6, 
tral arch (surface for dens of axis). 



Fig. 123. — Axis of Ox; Lateral View. 

1, Body; 2, ventral spine; 3, anterior articular 
process; 4, posterior articular process; 5, dens; 6, 
arch; 7, intervertebral foramen; 8, transverse proc- 
ess; 9, foramen transversarium and canalis trans- 
(dotted line) ; 10, spinous process. 



128 



SKELETON OF THE OX 



The body is longer and is distinctly constricted in the middle. It bears a thin- 
edged ventral crest. The arch — in addition to the usual notches, which are 
shallow — is perforated in the posterior part by a foramen. The transverse proc- 



1. Cavity of post. 




processes: 5. spinous process; C, transverse process. 



Median crest 



ess is thick and strong, and l)ears a rounded mammillary process (except at the 
posterior end of the series) ; the last two, although prominent, do not always articu- 
late with the ribs. The spinous process is long. The first is much higher than in 

the horse, the next two are usu- 
ally the most prominent, and be- 
hind this there is a very gradual 
diminution in height. The back- 
ward slope, slight at first, in- 
creases to the tenth; the last is 
vertical and lumbar in charac- 
ter. The summit is usually 
pointed on the first, and the 
thickening on those further back 
is less than in the horse. The 
width diminishes from the fifth 
to the eleventh usually. Both 
borders of the spines are in gen- 
eral thin and sharp, but the last 
three or four sometimes have 
thick posterior margins. 

The lumbar vertebrae, six in 

number, are mucli longer than in 

the horse. The body is much 

constricted in the middle, ex- 

i \ panded at either end, and bears 

j J 1 a rudimentarj' ventral crest. 

J\' I The fourth and fifth arc usually 

the longest. The intervertebral 

foramina are often tlouble in 

the anterior part of the sei'ies, 

and are very large further back. 

The articular processes are 

large, and their facets are more 

strongly curved than in the 

horse. The transverse proc- 

They arc separated by considerable intervals, and form 

Their borders are thin and 




^^ 



Fig. 125. — Sacrum of Ox; Dorsal View. 
1-4, Dorsal sacral foramina; 5, sacral canal; 6, 6, articul 
7, auricular surface; 8, apes. 

esses all curve forward 

no articulations with each other or with the sacrum. 



VERTEBRAL COLUMN 



129 




/ 



irregular, and often bear projections of variable size and form. The first is the 
shortest and the length increases to the fifth, the last being consitlerably shorter. 
The spinous processes arc relatively low and wide, the last lieing the smallest; 
their summits are moderately thickcneil. 

The sacrum is longer than that of the horse. It consists originally of five 
segments, but fusion is more complete and involves the spinous processes, which 
are united to form a median sacral crest (Crista sacralis media), with a convex 
thick and rough margin. A lateral sacral crest is formed by the fusion of the ar- 
ticular processes. The pelvic surface is concave in both directions, and is marked 
by a central groove (Sulcus vasculosus), which indicates the course of the middle 
sacral artery. The ventral sacral foramina are large. The wings curve downward 
and forward; they are quad- 
rangular, short, compressed 
from before backward, and 
high dorso-ventrally. They 
have an extensive anterior 
surface, which is concave 
from side to side and non- 
articular. The posterior sur- 
face is rough, and at its lower 
part there is a triangular area 
for articulation with the 
ilium. The body of the first 
segment is very wide, and the 
entrance to the sacral canal 
correspondingly wide and 
low. The anterior articular 
processes are large and 
widely separated; they are 
concave and seraicylindrical 
in curvature medially . The 
lateral borders are thin, 
sharp, and irregular. The 
bone does not become nar- 
rower posteriorly, so that the 
apex is usually a little wider 
than the part just behind the 
wings; the posterior end of 
the median crest forms a 
pointed projection over the 
opening of the sacral canal. 

The coccygeal vertebrae 
are longer and better devel- 
oped than in the horse. The first five or six have complete arches and spinous 
processes. The transverse processes are relatively large in the anterior part of 
the series, in which there are also anterior articular processes (which do not articu- 
late), and a pair of ventral spines which form a groove (Sulcus vasculosus) for the 
middle coccygeal artery. 

Vertebral Curves. — The cervical curve is very slight and is concave dorsally. 
The thoracic and lumbar regions form a gentle curve, concave ventrally. The 
promontory is more pronounced than in the horse, especially in subjects in which 
the sacrum is inclined upward behind. Another prominence occurs at the junction 
of the sacrum and first coccygeal vertebrae. 

Length. — The following table gives the lengths (inclusive of the inter- 
9 



Fig. 120. — Sacrum of Ox; Ventral View. 
Segments; 1—4, ventral sacral foramina; 5, anterior end of body 



7-1 

of first sacral vertebra; 
last sacral vertebra. 



, vascular groove; 7, posterior end of body of 



130 



SKELETON OF THE OX 



vertebral fibro-cartilages) of the vertebral regions of a shorthorn cow of 
medium size: 

Cervical 50 cm. 

Thoracic ' 80 cm. 

Lumbar 40 cm. 

Sacral 25 cm. 

Coccygeal "5 cm. 

270 cm. 

Variations. — Sometimes fom'teen thoracic vertebrie and fom'teen pairs of ribs are present; 

reduction to twelve with the normal number 
Tij 1. rp , J of lumbar vertebra; is very rare. According to 

iVc'c/c i ubercle Franck there are sometimes seven lumbar verte- 

brae with tlie normal number in the thoracic 

region. The number of coccygeal vertebrae may 

Head '-^iBl^&^^^H^i. vary from sixteen to twenty-one. 



THE RIBS 



Anterior border- 




Thirteen pairs of ribs are present 
normally, of which eight are sternal and 
five asternal. They are in general longer, 
wider, flatter, less curved, and less regular 
in form than in the horse. The eighth, 
ninth, and tenth are the longest and 
widest. The width of most of the ribs 
increases considerably in the middle, and 

Tubvrcle 



Head 



Neck 



Anterior border 



Sternal end 
Fig. 127. — Right Eighth Rib of Ox; Medial View. 



-Sternal end 
■ Cartilage 
Fig. 12S. — First Rib of Ox; Medial View. 




the breadth of the intercostal spaces is correspondingly diminished; this is not the 
case in the posterior part of the series, where the intercostal spaces are very wide. 



THE STERNUM THE THORAX — THE SKULL 131 

The neck is long, and forms (except in the posterior part of the series) a smaller 
angle with the shaft than in the horse. The articular surface of the tubercle is 
concave transversely, except on the last two or three, where the facet is small and 
flat or absent. The ventral ends of the second to the tenth or eleventh inclusive 
form diarthrodial joints with the costal cartilages. The first costal cartilages are 
very short; they articulate by their medial surfaces with the sternum, but not with 
each other. 

The presence of a fourteenth rib is not very rare. It is usually floating and may correspond 
to an additional thoracic vertebra or to the first lumbar. Reduction of the tliirteenth is more 
common. The eighth cartilage often does not reach the sternum, but articulates nath the seventh. 



THE STERNUM 
The sternum consists of seven stcrnebriB, most of which are developed from 
two lateral centers. It is wider, flatter, and relatively longer than in the horse, 
and the ventral crest or "keel" is absent. The manubrium is somewhat wedge- 
shaped and laterally compressed. Its base forms a diarthrodial joint with the 
body of the bone, and laterally it bears extensive facets for articulation with the 
first pair of costal cartilages. The body widens from before backward, but behind 
the last pair of costal facets it becomes much narrower. The ventral surface is 
prominent on the second and third segments, concave further back. The lateral 
borders are notched for the passage of vessels. The cariniform cartilage is absent. 
The xiphoid cartilage is like that of the horse but is smaller. 



THE THORAX 

The bony thorax is shorter than in the horse. The inlet is higher. The roof 
is short, and the floor is wider and relatively longer. The transverse diameter is 
wider in the posterior part. The summits of the spinous processes are almost in a 
straight line from the second thoracic vertebra to the middle of the liunbar region. 



The Skull 
Bones of the Cranium 
The occipital bone forms the lower part only of the posterior surface of the 
skull, and is separated from the highest part (the frontal eminence) by the parietal 
and interparietal bones. The supraoccipital, interparietals, and parietals fuse 
before birth or soon after, and the mass so formed is separated from the lateral 
parts of the occipital bone by a transverse suture in the skull of the calf. Above 
this suture is a central tuberosity, the external occipital protuberance, to which 
the ligamentum nuchse is attached, and the surface on either side is depressed and 
rough for muscular attachment. There is commonly a median occipital crest 
which extends ventrally from the protuberance. Below the suture the bone is 
much wider than that of the horse. The foramen magnum is wide, so that the 
condyles are further apart, except below. The paramastoid processes are short and 
wide and are bent inward. Usually at least two foramina are found in the condy- 
loid fossa; the ventral one is the hypoglossal, the other (often double) conducts a 
vein from the condyloid canal.^ The latter passes upward from a foramen on the 
medial side of the condyle and opens into the temporal canal. The mastoid for- 

^The number of foramina here is variable. In exceptional cases the foramen which opens 
into the condyloid canal is very small or absent; much oftener there are two, and sometimes three. 
In some cases there are two hypoglossal foramina. Thus as many as five foramina may be present 
here. 



132 



SKELETON OF THE OX 



amen is situated on each side, at the junction of the occipital and temporal bones; 
it communicates with the temporal and condyloid canals at their junction. The 
cerebral surface of the supraoccipital presents a central depression, and above this 
is a variable but never very pronounced eminence, the internal occipital protuber- 
ance. A groove on either side leads to the temporal canal. The basilar part is short 
and wide ; its cerebral surface is deeply concave, and the'internal spheno-occipital crest 
is prominent. Two large tubercles ventrally mark the junction with the sphenoid. 




Ar^glc of mandible 



Mental foramen 



Fig. 129.— Skull of Ox; Later.^l View. 
The jaws are separated for the sake of clearness. A, Parietal bone; B, squamous temporal bone; C, occipital bone; 
D, perpendicular part of palatine bone: E, maxilla; F, malar bone; G, lacrimal bone; H, premardlla; 1, occipital 
condyle; 2, paramastoid process; 3, meatus acusticus externus; 4, bulla ossea; 5, zygomatic process of temporal bone; 
6, 6', zygomatic and temporal processes of malar bone; 7, supraorbital process; 8, orbital part of lacrimal bone; 9, 
lacrimal bulla; 10, fossa sacci lacrimalis; 11, facial tuberosity; 12. infraorbital foramen; 13, condyle of mandible; 14, 
coronoid process of mandible. 



The foramen lacerum is short and very narrow. In the adult animal the bone is 
excavated to contain an air-cavity which is regarded as a part of the frontal sinus. 

The sphenoid bone is short. The cerebral surface of the body presents a deep 
sella turcica, in front of which it rises abruptly. The high anterior part bears a 
central ridge, the ethmoidal spine, which joins the crista galli of the ethmoid. 
Two foramina occur on either side. Of these, the large anterior one is equivalent 
to the foramen rotundum, orbitale, and trochleare of the horse; it may be termed 



BONES OF THE CKANIUM 



133 




Fig. 130. — Cross-section of Cranium of Ox. 

The section cuts the posterior part of the temporal condyle and is viewed from behind, a, Body of sphenoid; 6, 

bulla ossea; c, temporal condyle; 1, dorsum sellse; 2, foramen ovale; 3, hypophyseal or pituitary fossa; 4, foramen 

orbito-rotundum; 5, optic foramina: 0. crista galli; 7, cribriform plate of ethmoid; S, orbital wing of sphenoid; 9, 

temporal wing of sphenoid; 10, internal plate of frontal bone; 11, frontal sinus; 12, temporal process of malar bone. 




Fig. 131. — Cross-section of Cranium of Ux. 
The section cuts the posterior part of the temporal condyle and is viewed from in front, a. Basilar part of occipital 
bone; 6, bulla ossea; c, paramastoid process; d, meatus acusticus externus; e, temporal fossa; 1, tympanic cavity; 2, 
internal opening of condyloid canal; 3, internal opening of temporal canal; 4, depression for vermis cerebelli; 5, internal 
occipital protuberance; 6, internal plate of parietal bone; 7, internal plate of frontal bone; 8, frontal sinus; 9, petrous 
temporal bone; 10, poatglenoid process; 11, hyoid process. 



134 



SKELETON OF THE OX 



the foramen orbito-rotundum. The posterior one is the foramen ovale, which 
transmits the manchlaular nerve. The orlaital wing is thick and is overlapped by 
the frontal in such manner as to appear externally to divide into two branches ; 
the anterior part joins the ethmoid at the sphenopalatine foramen, and contains a 
small sinus which communicates with an ethmoidal meatus The temporal wing is 
small, but forms a prominent thick pterygoid crest. The pterygoid process is 
wide, and there is no alar canal. The sphenoidal sinus is absent in the calf and 
small in the adult ; it communicates by one or two small openings with an ethmoidal 
meatus, and so with the nasal cavity. 




Fig. 132. — Crani.\l and Orbital Regions of Skull of Ox. 
The horn core, supraorbital process, and greater part of zygomatic arch have been sawn off: A, Frontal bone; 
A', A", temporal and orbital parts of same; B, parietal bone; C, squamous temporal bone; D, D', orbital and facial 
parts of lacrimal bone; E, malar bone; F, maxilla; G, perpendicular part of palatine bone; 1, occipital condyle; 2, 
paramastoid process; 3, temporal crest; 4, temporal condyle; 5, postglenoid process; 6, external opening of temporal 
canal; 7, meatus acusticus externus; S, bulla ossea; 9, stylo-masloid foramen; 10, muscular process of temporal bone; 
11, tip of basilar tubercle; 12, foramen ovale; 13, foramen orbito-rotundum; 14, optic foramen; 15, ethmoidal foramen; 
16, orbital opening of supraorbital canal; 17, pterygoid crest; 18, ridge of orbital wing of sphenoid; 19. pterygoid proc- 
ess of sphenoid; 20, hamulus of pterygoid bone; 21, lacrimal bulla; 22, fossa sacci lacrimalis; 23. root of supraorbital 
process; 24, processus cornus (section) ; 25, frontal eminence. 



The ethmoid bone has an extensive perpendicular plate. The lateral mass 
consists of five endoturbinates and eighteen ectoturbinates (Paulli). The largest 
ethmoturbinate is so extensive as to be termed a third or middle turbinate bone; it 
projects forward between the dorsal and ventral turbinates. The lamina lateralis 
appears to a small extent externally in the pterygo-palatine fossa, forming part 
of the dorsal margin of the sphenopalatine foramen. 

The interparietals are primitively paired, but unite before birth. As already 
mentioned, fusion occurs before or shortly after birth with the parietals and supra- 
occipital. The bono has no intracranial projection. 

The parietal bones do not enter into the formation of the roof of the cranium. 



BONES OF THE CRANIUM 



135 



They constitute the upper part of the posterior wall, bend sharply forward along 
the lateral wall, and enter into the formation of the temporal fossa. The line of 
inflection is marked by the prominent parietal crest, which is continuous with the 
temporal crest below and the frontal crest anteriorly. The parietals are excavated 
to form part of the frontal sinuses in the adult animal. 





Parietal 




miiwHce 


boite 


Processus 




^_^ 


cornus 



Zygomatic arch 



Temporal 
fossa 

Supraorbital foramen 
Supraorbital groove 




Nasal bone 



Palatine fissure 



Nasal process of premaxilla 



Palatine process of premaxiUa 



Body of premaxilla 



Fig. 133. — Skull of Jersey Cow; Dorsal View. 



The condition in the young subject is as follows: The two parietals are united with each other 
and also with the interparietal and supraoccipital. The resulting mass is somewhat horseshoe- 
shaped. Its occipital part (Planum occipitale) forms the gi-eater part of the posterior wall of 
the cranium and bears about its center the tuberosity for the attachment of the ligamentum 
nuchas. From either side of this a line curves outward and divides the surface into an upper 
smooth area and a lower area which is rough for muscular attachment. The upper border joins 
the frontal bone and concurs in the formation of the frontal eminence. The temporal parts 
(Plana temporaUa) are much smaller and are concave externally; they join the frontal above and 
the squamous temporal below. A median occipital crest extends ventrally from the external 
occipital protuberance. 



The frontal bones are very extensive, forming about one-half of the entire 



136 



SKELETON OF THE OX 



length of the skull, and all of the roof of tlic cranium. The posterior borders 
form with the parietals a large central frontal eminence (Torus frontalis), the 
highest point of the skull. At the junction of the posterior and the lateral border 
is the processus comus or "horn core, " for the support of the horn. These proc- 




Fia. 134. — Skull of Ox. without M.\ndible; Ventral View. 
1. Foramen magnum; 2, occipital condyle; 3, paramastoid process; 4, condyloid foramen; 5. foramen la 
6, basilar part of occipital bone; 7, 7', basilar tubercles; 8. bulla ossea; 9, foramen ovale (concealed by muscular proc- 
ess) ; 10. meatus acusticus externus; 11, zygomatic process of temporal bone, 12, condyle of same; 13, external opening 
of temporal canal ; 14, processus cornus; 15. muscular process of temporal bone; 16, pterygoid crest; 17, orbital open- 
ing of supraorbital canal; 18, choana or posterior nares; 19, hamulus of pterygoid bone; 20, crest formed by pterygoid 
processes of sphenoid and palatine bones; 21, horizontal part of palatine bone; 22, anterior palatine foramen; 23, 
lacrimal bulla; 24, maxillary tuberosity; 25, palatine process of maxilla; 26, zygomatic process of malar bone; 27, 
facial tuberosity: 28, body of premaxilla; 29, palatine process of same; 30, palatine fissure; 31, incisive fissure; 32, 
premolars; 33, molars. 



esses are of elongated conical form, and vary greatly in size, length, curvature, 
and direction. The external surface is rougli and porous, marked by numerous 
grooves and foramina; in the fresh state it is covered by the corium of the horn. 
The base has a constriction, the neck. The interior is excavated to form a number 
of irregular spaces, partially divided by bony septa, and communicating with the 



BONES OF THE FACE 137 

frontal sinus. In the polled breeds these processes are absent, the skull is narrower 
here, and the frontal eminence more pronounced (Fig. 139) . The sujiraorbital proc- 
ess is situated about half-way between the anterior and posterior margins; it is 
short and joins the frontal process of the malar bone. The supraorbital foramen 
(often double) is situated about an inch medially from the root of the process; it 
is the external orifice of the supraorbital canal (Canalis supraorbitalis), which passes 
downward and forward to the orbit. The foramen is in the course of the supra- 
orbital groove (Sulcus supraorbitalis), which marks the course of the frontal vein. 
The anterior ends of the naso-frontal parts form a notch which receives the nasal 
bones, and sutural (or Wormian) bones are often found at this junction (naso- 
frontal suture). The orbital part is extensive; it is perforated behind by the or- 
bital opening of the supraorl)ital canal, and below l)y the ethmoidal foramen. It 
does not articulate with the palatine bone, from which it is separated by the or- 
bital vnng of the sphenoid. The temporal part is also more extensive than in the 
horse. The frontal sinus is very extensive, being continued into the parietals and 
occipital, and the horn processes when present. 

The squamous antl petrous parts of the temporal bone fuse early — in fact 
union is nearly complete at birth. The squamous part is relatively small. Its 
lateral surface is divided into two parts by the prominent temporal crest, which is 
continuous with the parietal crest above and turns forward below, ending at a 
tubercle above the external acoustic meatus. The part behind the crest faces 
backward, and is partly free, partly united with the occipital. The area in front 
of the crest is concave and enters into the formation of the temporal fossa; it is 
perforated by foramina which communicate with the temporal canal. The zygo- 
matic process is much shorter and weaker than in the horse, and articulates with the 
malar only. The condyle is convex in both directions. The postglenoitl process 
is less prominent, and behind it is the chief external opening of the temporal canal. 
The cerebral surface is almost completely overlapped by tlie parietal and sphenoid. 
The petrous part is small, but the tympanic part is extensive. The external 
acoustic meatus is smaller than in the horse and is directed laterally. From it a 
plate projects downward and helps to inclose the deep depression in which the hyoid 
process is placed. Behind this plate is the stylo-mastoid foramen. The muscular 
process is large and often bifid at its free end. The bulla ossea is large and later- 
ally compressed. It is separated from the occipital bone by a narrow opening 
which is equivalent to part of the foramen lacerum of the horse. The temporal 
canal is formed entirely in the temporal bone. The facial canal, on the other 
hand, is bounded partly by the occipital bone. 

Bones of the Face 
The maxilla is shorter but broader and relatively higher than in the horse. 
Its lateral surface bears the rough facial tuberosity (Tuber faciale), placed above the 
third and fourth cheek teeth; a rough line which extends backward from it to the 
upper part of the malar bone may be regarded as the facial crest. The infraorbital 
foramen — often double — is situated above the first cheek tooth. The tuber maxil- 
lare is small, laterally compressed, and usually bears a small pointed process (Pro- 
cessus pterygoideus) . The zygomatic process is very small. The interalveolar 
border is concave, and there is no alveolus for a canine tooth. The palatine 
process is wider, but somewhat shorter than in the horse. It incloses a large 
air-space, which is continuous behind with a like cavity in the horizontal part of 
the palate bone, forming the palatine sinus (Sinus palatinus). This communi- 
cates laterally (over the infraorbital canal) with the maxillary sinus; in the 
macerated skull it communicates with the nasal cavity by a large oval opening, 
whiph is closed by mucous membrane in the fresh state. A median septum sepa- 



138 



SKELETON OF THE OX 



rates the two palatine sinuses. The alveoli for the cheek teeth increase in size 
from before backward. The maxillary sinus proper is small and is undivided. 
The maxillary foramen is a narrow fissure, deeply placed at the medial side of the 
lacrimal bulla. The maxilla takes no part in the formation of the palatine canal. 
Sutural (or Wormian) bones are often present at its junction with the lacrimal and 
malar bones. 

The body of the premaxilla is thin and flattened, and has no alveoli, since 
the canine and upper incisor teeth are absent. A deep notch takes the place of 
the foramen incisivum. The nasal process is short, convex laterally, and does not 
reach to the nasal bone ; the space between the two processes is greater than in the 
horse. The palatine process is narrow and is grooved on its nasal surface for the 
septal cartilage and the vomer. The palatine fissure is very wide. 

The palatine bone is very extensive. The horizontal part forms one-fourth or 




Fig. 135. — Sagittal Section of Skull of Ox, without Mandible. 
A, A\ Sriuamous and basilar parts of occipital bone; B, B' , postsphenoid, presphenoid; C, lateral mass of ethmoid 
bone: £), internal plate of frontal bone; £^, parietal bone; /^, petrous temporal bone; G, pterygoid bone; //.perpendicu- 
lar part of palatine bone; /, outline of vomer (dotted line) ; J, palatine process of maxilla; K, nasal process of premaxilla; 
L, dorsal turbinate bone; M, ventral turbinate bone; A^, middle turbinate bone (great ethmo-turbinate) ; 1, occipital 
condyle; 2, paramastoid process: 3, bulla ossea; 4, basilar tubercle; 5, muscular process: 6, hypoglossal foramen: 7, 
openings of condyloid canal; S, direction of condyloid canal (dotted line); 9, internal opening of temporal canal; 10, 
meatus acusticus internus ; 11, foramen lacerum; 12, sella turcica: 13, optic foramen; 14, sphenoidal sinus; 15, orbital 
wing of sphenoid bone; 16, frontal sinus; 16', anterior limit of frontal sinus (dotted line) ; 17, dorsal nasal meatus; 18, 
middle nasal meatus; 18', dorsal branch of middle meatus; 19, ethmoidal meatuses: 20, maxilla: 21, sphenopalatine 
foramen; 22, opening into maxillary sinus: 23, opening into palatine sinus, and arrow indicating communication of 
latter with maxillary sinus; 24, palatine sinus; 25, cross indicates anterior end of palatine sinus: 26, palatine fissure. 



more of the hard palate. The anterior palatine foramen opens near the junction 
with the maxilla, aljout half an inch from the median palatine suture and crest. 
Accessory palatine foramina (Foramina palatina accessoria) are also present. The 
palatine groove is usually not very distinct. The palatine canal is formed entirely 
in this part, and there is no articulation with the vomer. A rounded ridge occurs 
on the nasal side of the median suture. The interior is hollow, forming part of the 
palatine sinus. The perpendicular part is an extensive, quadrilateral, thin plate, 
which forms the posterior part of the lateral wall of the nasal cavity and in part 
bounds the choanse or posterior nares. Its nasal surface is nearly flat, and is smooth 
and free, except behind, where it is overlapped by the pterygoid bone. The lateral 
surface is attached to a small extent to the pterygoid process behind, and is free else- 
where. The sphenopalatine foramen is a long, elliptical opening, formed by a deep 
notch in the upper edge of the palate bone and completed by the ethmoid and sphe- 



BONES OF THE FACE 139 

iioid. The edge behind this foramen articulates with the orbital wing of the sphe- 
noid, not the frontal, as in the horse. 

The pterygoid bone is wider than in the horse, and forms the greater part of the 
lateral boimdary of the posterior nares. Its lateral surface is almost entirely united 
to the palatine bone and the pterygoid process, but a small part is free in the pterj^go- 
palatine fossa. The hamulus is distinctly hook-like, thin, and sharp. 

The nasal bone is little more than half the length of that of the horse. It is 
straight in its length, but strongly curved from side to side. It does not fuse later- 
ally with the adjacent bones, even in old age. The posterior extremity is pointed 
and fits into the notch between the frontal bones. The anterior end is broader, 
and is divided into two parts by a deep notch. In old animals there is a small 
extension of the frontal sinus into this bone. 

The lacrimal bone is very large. The extensive facial part is concave in its 
length, and bears no lacrimal tubercle. The orbital margin is marked l^y several 
notches. The orbital part bears ventrally the remarkable lacrimal bulla ; this is a 
large and very thin-walled protuberance, which bulges backward into the lower 
part of the orbit, and contains an extension of the maxillary sinus. The fossa for 
the lacrimal sac is small, and is just behind the orbital margin. 

The malar bone is relatively long. The facial surface is extensive ; it bears a 
curved crest (Crista facialis) just below the orbital margin which is continued on 
the maxilla, and below this it is concave dorso-ventrally. The zygomatic process 
divides into two branches; of these, the frontal branch (Processus frontalis) turns 
upward and backward and joins the supraorbital process of the frontal bone; 
the temporal branch (Processus temporalis) continues backward, and is over- 
lapped by the zygomatic process of the temporal l)one, completing the zygomatic 
arch. 

The dorsal turbinate bone is less cribriform and fragile than in the horse, and 
is widest in its middle, small at either end. It is attached to the turbinate crest 
of the nasal bone, and curves downward, outward, and then upward to be applied 
outwardly to the frontal and lacrimal bones. It thus incloses a cavity which com- 
municates with the middle meatus nasi. (In the macerated skull it opens into the 
frontal sinus, but this communication is closed by mucous membrane in the fresh 
state.) 

The ventral turbinate bone is shorter but much broader than in the horse. It 
is attached to the maxilla by a basal lamella about an inch (ca. 2 to 3 cm.) wide, 
which slopes ventro-medially. At the inner edge of this it splits into two plates 
which are rolled in opposite directions, and inclose two separate cavities, sub- 
divided by several septa. The dorsal one opens into the middle meatus, the 
ventral one into the ventral meatus nasi. 

The vomer forms a wider and deeper groove than in the horse. Its anterior 
end rests in a groove formed by the ends of the palatine processes of the premaxillse. 
The anterior third of its thin ventral edge fits into the nasal crest of the maxilla; 
behind this it is free and is separated by a considerable interval from the nasal floor. 

The two halves of the mandible do not fuse completely even in advanced age, so 
that a symphysis mandibultB is present. The sjanphyseal surfaces are extremel^y 
rough and are marked by reciprocal projections and cavities. The body is shorter, 
wider, and flatter than in the horse, and has eight round and relatively shallow 
alveoli for the lower incisors. The interalveolar border is long, curved, thin, and 
sharp. There are no alveoli for the canine teeth, which are absent. The anterior 
part of the ramus is narrow. The mental foramen is further forward than in the 
horse, and is in the posterior end of a fossa. The rami diverge more, so that the 
mandibular space is wider than in the horse. They are also more strongly curved, 
and the angle is more pronounced. The molar part is not so high, especially in its 
anterior part. Its ventral border is convex in its length. Its alveolar border bears 



140 



SKELETON OF THE OX 



six alveoli for the lower cheek teeth; the first is quite small, and they increase in 
size from before backward. The vertical part is much smaller than in the horse 
and its posterior border is relatively thin below, concave and wider above. The 
mandibular foramen is about in the middle of its medial surface, and a groove for 



Coronoid process 




Comhjle 



Incisor teeth 




r),*. 



Symphyscal surface 

Fig. 136.— Right H.\lf of Mandible of Ox; Mei 
1, Mandibular foramen; 2, groove for Ungual i 



^ 
^ 



A ngle 



the lingual nerve curves downward and forward from it. The condyle projects 
medially further than in the horse, and is concave from side to side. The coronoid 
process is extensive and curves backward. 

The hyoid bone has a short tuberous Ungual process. The middle cornua 

are almost as large as the small cornua. 
The great cornua are narrow, except 
at the ends. The upper end divides 
into two branches, which correspond 
to the two angles of that of the horse. 
The thyroid cornua do not fuse with 
the body except in old age. 




SKULL OF THE OX AS A WHOLE 

The skull of the ox is more clearly 
pyramidal than that of the horse, and 
is shorter and relatively wider. The 
cranium is quadrangular and larger 
externally than in the horse; its large 
size is due mainly to the great extent 
of the frontal sinuses and does not 
affect the cranial cavity, which is 
smaller than in the horse. 

The frontal surface (Fig. 133) is 

formed V)}' the frontals, nasals, and 

premaxillae. The frontal part is 

quadrilateral and very extensive, the greatest width being at the orbits. It 

presents a central depression on its anterior part, and on either side are the 

supraorbital grooves and foramina. Behind is the median frontal eminence, 



Fig. 137. — Htoid Bone of Ox. 
a, Body: b, lingual process; c, thyroid cornu and cartil 
age, c': d, small cornu; e, middle cornu; /, great cornu; g 
muscular angle. (EUenberger-Baum, Anat. d. Hauatiere.) 



SKULL OF THE OX AS A WHOLE 141 

and at the lateral angles the "horn cores" project in horned cattle. The 
nasal part is very short. The osseous nasal aperture is wide. The premaxillae 
do not bend downward as in the horse; they are relatively thin and weak, 
and are separated by an interval which has a wide anterior part in place of 
the foramen incisivum. 

The lateral surface (Fig. 129) is more triangular than in the horse. The temporal 
fossa is confined to tliis surface. It is deep and narrow, and its boundaries are more 
complete. It is limited dorsally by a crest which extends from the postero-lateral 
angle of the frontal bone to the supraorbital process, and is analogous to the pari- 
etal crest of the horse. It is bounded behind by the temporal crest. It is clearly 
marked off from the orbit by a rounded ridge and the pterygoid crest. The zygo- 
matic arch is short, weak, and flattened, and is formed by the temporal and malar 
onlj'. Its condyle is convex and is wide from before backward. The glenoid cavity 
and postglenoid process are small. The orbit is encroached upon below by the 
lacrimal bulla, and presents the orifice of the supraorbital canal behind. The or- 
bital margin is completed behind by the frontal process of the malar; its lower part 
is prominent and rough, not smooth and rounded as in the horse. The pterygo- 
palatine fossa is much larger, deeper, and more clearly defined. It has a long nar- 
row recess between the vertical plate of the palate bone medially and the maxilla 
and lacrimal bulla laterally; thus the sphenopalatine and maxillary foramina are 
deeply placed. The prcorbital region is short but relatively high. A tuberosity 
and curved line correspond to the facial crest of the horse. The infraorbital fora- 
men is situated above the first cheek tooth and is often double. 

The basal surface (Fig. 132) is short and wide, especially in its cranial part. The 
occipital condyles are limited in front by transverse ridges. The basilar tubercles at 
the junction of the occipital and sphenoid are large. The condyloid fossiE contain two 
foramina, the hypoglossal below and in front, and the condyloid above and behind ; 
other inconstant ones occur. The paramastoid processes are short and convergent. 
The foramen lacerum is slit-like. The bulla ossea is a large, laterally compressed 
prominence. The muscular processes are usually long and narrow triangular plates, 
with one or two sharp points. The external acoustic process is directed almost 
straight outward. A curved plate extends ventrally from it and joins the bulla 
ossea medially, completing the deep cavity which receives the articular angle of 
the hyoid bone. The chief external opening of the temporal canal is in front of 
this plate, and an accessory one lies behind it. The infratemporal fossa is small, 
and presents the foramen ovale. The posterior nares are very narrow, and the 
vomer does not reach to the level of their ventral margin. The hard palate is wide, 
and forms about three-fifths of the entire length of the skull. A small central part 
only of its posterior border enters into the formation of the posterior nares; the 
lateral parts are notched and just above them are the posterior palatine foramina. 
The anterior palatine foramina are an inch or more from the posterior margin, 
and about the same distance apart. The palatine grooves are distinct for a short 
distance only. Just beyond the cheek teeth the palate narrows and becomes con- 
cave; beyond this it widens and flattens. 

The nuchal surface is extensive and somewhat pentagonal in outline in the 
adult. About its center is the external occipital protuberance for the attachment 
of the ligamentum nuchse. From this a median occipital crest extends toward the 
foramen magnum, and laterally two lines (Linese nuchse superiores) curve outward, 
marking the upper limit of the area which is roughened for muscular attachment. 
The surface above the lines is relatively smooth, and is covered only by the skin 
and the thin auricular muscles in the living animal. It is separated from the 
frontal surface by a thick border, which forms centrally the frontal eminence, and 
bears at its extremities the processus cornus — except in the polled breeds. The con- 
dyles are further apart, and the articular surfaces are more clearly divided into 



142 



SKELETON OF THE OX 



upper and lower parts than in the horse. The mastoid foramen is at the junction 
of the occipital and temporal bones; it is frequently very small. 




\^^- 



Fig. 138. — Cranium of Jersey Cow, Nuchal View. The Fig. 139. — Cranium op Polled Angus Cow, Nuchal 
Greater Part of the Processus Cornus has been View. 

Sawn Off. 
1, Foramen magnum; 2, occipital condyle; 3, paramastoid proceas; 4, bulla ossea; 5, meatus acustieus externus; 
6. mastoid foramen; 7, external occipital protuberance; 8, median occipital crest; 9, linea nuchae superior; 10, frontal 
eminence. 



Dorsal meatus 

Middle meatus 



Dorsal part of ventral turbinate 
Bdsal lamella 



Ventral part of veritral 
turbinate 



Fig. 140. — Cross-section 



1, Cartilage of sept 
sinus; 6, infraorbital canal and 
closes gap in bony floor of nasal ca\*ity. 




3, ventral meatus; 4, anterior extremity of maxillary sinus; 5, palatine 
7, palatine process of maxilla. Dotted lines indicate mucous membrane which 



The cranial cavity is shorter and its long axis is more obHque than in the horse, 
but it is relatively high and wide. The anterior fossa lie's at a much higher level 



SKULL OF THE OX AS A WHOLE 143 

than the rest of the floor. The ethmoidal fossffi are smaller, and the hypophyseal 
fossa or sella turcica is much deeper than in the horse. A deep groove leads from 
the petrous temporal forward over the foramen ovale to the foramen rotundum. 
Behind the sella there is often a distinct prominence (Dorsum sellse) . The internal 
parietal crest is prominent anteriorly, but subsides further back. A faintly marked 
elevation represents the internal occipital protuberance. The petrous temporal 
bone projects into the cavity laterally. The ridges and digital impressions are very 
pronounced. The temporal canal is formed entirely in the temporal bone, and 
opens internally at the apex of the petrous, where it is joined by the condyloid 
canal. The foramen lacerum is divided into two parts (For. lacerum orale et ab- 
orale). 

The nasal cavity is incompletely divided by the septum, which does not reach 

Dorsal meatus Nasal bone 

Dorsal turhimdc •— -^^z^jj^ flSftk'^ Lacrimal bone 

Middle '«en(iiJi-^^ JI^HMI^^BC- '~<''^^A'«so-?ao-j»iai canal 

Maxilla 




Fig. 141. — Cross-section of Nasal Region of Skull of Ox. Section is Cut between Fourth and Fifth Cheek 

Tooth. 
1, Cartilage of septum nasi; 2, vomer; 3, ventral meatus; 4, 4', maxillary sinuses; 5, 5', palatine sinuses; 6, infra- 
orbital canal and nerve; 7, horizontal part of palatine bone; 8, communication between maxillary and palatine sinuses. 
Dotted lines indicate mucous membrane which closes gap in bony floor of nasal cavity. 



the floor posteriorly. The floor is relatively long, and is more concave from side to 
side than in the horse. In the dry skull it has a large oval ojjening (Hiatus maxillaris) 
into the palatine sinus, which is closed during life by mucous membrane. The 
middle meatus is divided behind into upper and lower branches by the great eth- 
moturbinate. The choanee or posterior nares are narrow and oblique. 

The frontal sinus is very large. It involves almost all of the frontal bone and 
a large part of the posterior wall of the cranium. It also extends for a variable dis- 
tance into the horn processes when these are present. A complete median septum 
separates the right and left sinuses. The anterior limit is indicated by a transverse 
plane through the middle of the orbits. It extends laterally to the crest, which 
limits the temporal fossa above, and into the root of the supraorbital process. At 
the highest part of the cranial cavity and at the external occipital protuberance 



144 



SKELETON OF THE OX 



the two plates of the bone come together. The cavity is very irregular and is sub- 
divided into numerous spaces by ridges and partial septa. This multilocular 
character is most marked in the anterior part, and here several small spaces appear 
to be cut off from the main cavity. The supraorbital canal passes through the 
sinus. Several small openings lead from the sinus to the ethmoidal meatuses, 
and thus indirectly to the upper division of the middle meatus nasi. The communi- 
cations with the cavity of the dorsal turbinate and with the lacrimal part of the 




Fig. 142. — Skull of Ox; Dorsal View. 
The outer plate of bone has been removed to show the sinuses, a, Frontal sinus; a', cranial plate of frontal bone; 
a", anterior part of frontal sinus, which is separated from remainder by a septum (6) ; c, c' , communications between 
frontal sinus and hasat cavity; d, supraorbital foramen; e, supraorbital canal; /, cavity of dorsal turbinate bone, 
and ff, its opening into the nasal cavity; A, lacrimal sinus; r, its communication with the maxillary sinus: /:, maxillary 
sinus; ^, orbit; ^, frontal bone; 7', processus cornus; :2, nasal bone; 5, premaxilla (nasal process) ; .}, maxilla; 5, lacri- 
mal bone; 5, malar bone; 7, dotted line indicating course of nasolacrimal duct. (After EUenberger, in Leisering'a 
Atlas.) 



maxillary sinus which are seen in the macerated skull are closed in the fresh state 
by mucous membrane. 

The maxillary sinus is excavated chiefly in the maxilla, lacrimal, and malar, 
and is not divided by a septum as in the horse. It extends forward as far as the 
facial tuberosity, or a little further in old animals. Its dorsal limit is indicated 
appro.ximately by a line drawn from the infraorliital foramen to the upper margin 
of the orbit. It is continued into the lacrimal bulla to a point nearly opposite to 



BONES OF THE THORACIC LIMB 



145 



the bifurcation of the zygomatic process of the malar. It also extends upward and 
backward through a large opening into a cavity formed by the lacrimal, frontal, 
ethmoid, and turbinal bones, at the medial side of the orbit.' The floor of the cavity 
is irregular and the roots of the last three or four cheek teeth project up into it, 
covered by a plate of bone. The sinus communicates with the palatine sinus freely 
over the infraorbital canal through an oval opening aljout two to three inches (ca. 
5 to 7.5 cm.) long. Above this it communicates by a shorter and much narrower 
opening with the middle meatus nasi. 

The palatine sinus is excavated in the hard palate, and is separated from that 
of the opposite side by a median septum. It extends from the posterior border of 
the palate to a plane an inch or more (2.5 to 3 cm.) in front of the first cheek tooth. 
As mentioned above, there is a large communication with the maxillary sinus over 
the infraorbital canal, so that the cavity is sometimes regarded as a part of that sinus. 
The large defect in the bony roof of the sinus is closed by two layers of mucous 




■Ox; La 



. View withopt Ma 



Fig. 143.— S 

The maxillary, lacrimal, and turbinate sinuses have been opened, and part of the orbital margin removed, a, Cavity 
of dorsal turbinate bone: b. lacrimal sinus; c, maxillary sinus; d, communication between maxillary and palatine 
sinuses: e, opening between maxillary and lacrimal sinuses: /, thin osseous bulla: s, lacrimal bulla; h, orbit; i-6, cheek 
teeth; 7, nasal bone; 8, premaxilia (nasal process); 9, maxilla; 5', infraorbital foramen; 10, frontal bone; 11, lacri- 
mal bone; 13, malar bone; 13, fissure between nasal bone and maxilla; i^, temporal bone (squamous) ; /5, external 
acoustic meatus; )(?, paramastoid process: ? 7, occipital condyle; 7^, palate bone (perpendicular part); 7 P, pterygoid 
bone (hamulus); ,80, tympanic part of temporal; 20', musouJar process of petrous temporal. (After Ellcnberger, in 
Leisering's Atlas.) 



membrane in the fresh state. The palatine canal passes obliciuely through the 
posterior part of the sinus. 

The sphenoidal sinus is almost entirely in the sphenoid bone and does not 
communicate with tlie palatine sinus. It has one or two openings into the ventral 
ethmoidal meatuses. There is no cavity in the perpendicular part of the palate 
bone. 

There are several small air-cavities between the lateral mass of the ethmoid 
and the anterior part of the frontal sinus, which communicate separately with 
ethmoidal meatuses. 



BONES OF THE THORACIC LIMB 

The scapula is more regularly triangular than in the horse, relatively wider at 

the vertebral end and narrower at the distal end. The scapular index is about 

1 : 0.6. The spine is more prominent and is placed further forward, so that the 

supraspinous fossa is narrow and does not extend to the lower part of the bone. 

' This is termed the lacrimal sinus by some authors. It is similar in location and in the posi- 
tion of its orifice to the turbinate part of the frontal .sinus of the horse with the important differ- 
ence that it does not communicate with the frontal sinus in the ox. 
10 



146 



SKELETON OF THE OX 



The spine is sinuous, bent backward in its middle, forward below. Its free border 
is somewhat thickened in its middle, but bears no distinct tuber. Instead of sub- 
siding below as in the horse, the spine becomes a little more prominent, and is pro- 
longed by a pointed projection, the acromion, from which part of the deltoid muscle 
arises. The subscapular fossa is shallow. The areas for the attachment of the 
serratus muscle are not very distinct. The nutrient foramen is usually in the 
lower third of the posterior border. The glenoid cavity is almost circular and 
without any distinct notch. The tuberosity is small and close to the glenoid cavity. 



1, Anterior angle: 2, post 
bordei 




A OF Ox; L 
^, i^woiti.v-i U..BI'. . •->. .supraspinous fossa; 4, infraspinous fossa 
•r; 7, spine; S, acromion; 0, tuber scapulae; 10, glenoid 



anterior border; 6, posterior 
ity; 11, nutrient foramen. 



The coracoid process is short and rounded. The cartilage resembles that of 
the horse. The tuberosity unites with tlie rest of the bone at seven to ten months. 
The humerus has a shallow musculo-spiral groove. The deltoid tuberosity 
is less prominent than in the horse, and the curved line running from it to the neck 
bears a well-marked tubercle on its upper part. The nutrient foramen is usually 
in the distal third of the posterior surface. The lateral tuberosity is very large, 
and rises an inch or more (ca. 3 cm.) above the level of the head. Its anterior part 
curves medially over the intertuberal or bicipital groove, and below it laterally 
there is a prominent circular rough area for the insertion of , the tendon of the infra- 
spinatus. The anterior part of the medial tuberosity has a small projection which 



BONES OF THE THORACIC LIMB 



147 



curves over the groove. The groove is undivided. The distal articular surface 
is decidedly oblique, and the grooves and ridge are very well marked. The coro- 
noid and olecranon fossae are deep and wdde. The condyloid crest is represented by 
a rough raised area. The proximal end unites with the shaft at three and one-half 
to four years, and the distal at about one and one-half years. 

The radius is short and relatively broad. It is somewhat oblique, the distal 
end being nearer the median plane than the ]3roximal. The curvature is more 
pronounced below than above. The shaft is prismatic in its middle part and has 




Fig. 145. — Left Huiv 

Lateral View. 
1, Head; 2, neck; 3. 3', lateral 
tuberosity; 4, rough prominence for 
attachment of infraspinatus tendon; 
5, deltoid tuberosity; 6, coronoid 
fossa; 7, lateral condyle; S, lateral 
epicondyle ; 9, medial epicondyle ; 
10, olecranon fossa. 




Fio. 146.— Left Humerus 
Anterior View. 
1, Lateral tuberosity; 2, medial 
tuberosity; 3, intertuberal groove; 
4, rough prominence for attach- 
ment of infraspinatus tendon; 5, 
deltoid tuberosity; 6, teres tubercle; 
7, muscuio-spiral groove; 8, coro- 
noid fossa; 9, medial condyle; 10, 
lateral condyle. 




. 147. — Left Radius an 
fOx; Pqstero-medial View. 
1, Olecranon; 2, processus an- 
!, semilunar notch; 4, 
proximal extremity of radius; 5, 5', 
proximal and distal interosseous 
spaces; 6, shaft of radius; 7, shaft 
of ulna; 8, vascular groove; 9, sty- 
loid process of ulna. 



dorsal, volar, and lateral faces. There is a marked increase in width and tliickness 
distally. The proximal articular surface presents a synovial fossa which extends 
medially from the deep groove between the two glenoid cavities. The radial 
tuberosity is represented by a slightly elevated rough area. The facets for the ulna 
are larger than in the horse. The two bones commonly fuse above the proximal 
interosseous space and always fuse below it, except near the distal end, where there 
is a small distal interosseous space. A groove connects the two spaces laterally. 
The distal extremity is large, and is thickest medially. Its articular surface is 
oblique in two directions, i. e., from within upward and backward. The grooves 



148 



SKELETON OF THE OX 



for the extensor tendons are shallow. The proximal end unites with the shaft at 
one to one and one-half years, and the distal at three and one-half to four years. 

The approximation of the lower ends of the forearms andthe carpi gives the "knock-kneed" 
appearance in cattle. The obliquity of the joint surfaces produces lateral deviation of the lower 
part of the limb in flexion. The facets for the radial and intermediate carpaLs are narrower than 
in the horse and run obliquely dorso-laterally. The surface for the ulnar carpal is extensive and 
saddle-shaped; its lateral part is furnished by the ulna. 

The ulna is more fully developed than in the horse. The shaft is complete, 
three-sided, and strongly curved. It is fused with the radius in the adult, except 
at the two interosseous spaces mentioned above. Its proximal part contains a 
medullary cavity which extends somewhat into the proximal end. The olecranon is 




— u 



C.u. 



C.4 



Fig. 148.— Left Carpus and Adjacent Bonks of Ox; 
Front View. 
R, RacUus; V, ulna; C. r., radial carpal; C. u., 
ulnar carpal; C. ^ -{- 3, fused second and third carpals; 
C. 4. fourth carpal; 1, 2, 3, grooves for extensor tendons; 
4, metacarpal tuberosity; 5, vascular groove. Inter- 
mediate carpal bone (between radial and ulnar) not 
marked. 




Fig. 149. — Left Carpus and .\djacent Bones of 

Ox; L.ATERAL \'IEW. 

R, Distal end of radius; U, styloid process of 
ulna; /, distal interosseous space; C. i., intermediate 
carpal; C. u., ulnar carpal; C a., accessory carpal; 
C. 2 ■'r S, fused second and third carpals; C 4. fourth 
carpal; Mc. 5+4. fused third and fourth (large) 
metacarpal; Mc. 5, fifth (small) metacarpal; T, meta- 
carpal tuberosity. 



large and bears a rounded tuberosity. The distal end is fused with the radius; it 
projects below the level of the latter, forming the styloid process of the ulna (Pro- 
cessus styloideus ulna'), which furnishes part of the facet for the ulnar carpal. 
The summit of the olecranon and the distal end imite with the shaft at three and 
one-half to four years. 

The carpus consists of six bones, four in the proximal row and two in the distal. 
The proximal row is oblique in conformity with the carpal articular surface of the 
radius. The radial and intermediate resemble in general those of the horse, but 
are less regular in shape, and their long axes are directed obliquely backward and 
medially. The radial is narrower than in the horse and curves upward behind. The 
intermediate is constricted in its middle, and wider behind than in front. The 
ulnar is large and very irregular. Its proximal surface is extensive and sinuous and 
articulates with both radius and ulna; it has a large oval facet behind for articula- 
tion with the accessory carpal. The accessory is short, thick, and rounded; it 



BONES OF THE THORACIC LIMB 



149 



articulates with the ulnar carpal only. The first carpal is absent. The second and 
third carpals are fused to form a large quadrilateral bone. The fourth carpal is a 
smaller cjuadrilateral bone. 

The metacarpus consists of a large metacarpal and a lateral small metacarpal 
bone. The large metacarpal bone (Mc. 3 + 4) results from the fusion of the third 
and fourth bones of the foetus, and bears evidences of its double origin even in the 
adult state. The shaft is shorter than in the horse, and is relatively wider and 
flatter. The dorsal surface is rounded, and is marked by a vertical vascular 
groove connecting two canals which traverse the ends of the shaft from before 
backward. The volar surface is flat and presents a similar but much fainter groove. 
The borders are rough in the proximal third. The proximal end bears two slightly 
concave facets for articulation ^\^th the bones of the lower row of the carpus; the 
medial area is the larger, and thej' are separated by a 
ridge in front and a notch behind. The lateral angle 
has a facet behind for the small metacarpal bone. The 
medial part of the extremity has anterior and posterior 
tuberosities. The distal end is divided into two parts 
by a sagittal notch. Each division bears an articular 
surface similar to that in the horse, but much smaller. 
The medullary cavity is divided into two parts by a ver- 
tical septum which is usually incomplete in the adult. 
The small metacarpal bone (Mc. 5) is a rounded rod 
about an inch and a half (ca. 3.5 to 4 cm.) in length, 
Avhich lies against the- proximal part of the lateral bor- 
der of the large bone. Its proximal end articulates with 
the latter, but not with the carpus. The distal end is 
pointed. 

Four cartilaginous metacarpals are present in the early foetal 
state, v-iz., the second, third, fourtli, and fifth. The second com- 
monly either disappears or unites witli the third; sometimes it 
develops as a small rod of bone. Tlie third and fomlh gradually 
unite, but can be cut ajiart at bii'th. Each has three centers of 
ossification; the proximal epiphysis fuses with the shaft before 
birth, the distal at two to two and one-half years. 




\' 



MjUp 



Fig. 150. — Left Metacarpal 

Bones of Ox; Front View. 

The Small Bone has been 

Moved Laterally. 

1, Metacarpal tuberosity; 2, 
vascular groove; 3, 3', foramina; 
4, 4', condyles; 5, articular facet 
of fifth (small) metacarpal bone. 



Four digits are present in the ox. Of these, two — 
the third and fourth — are fully developed and have 
three phalanges and three sesamoids each. The second 
and fifth are vestiges and are placed behind the fetlock; 
each contains one or two small bones which do not ar- 
ticulate with the rest of the skeleton. 

The first phalanx is shorter and narrower than in 
the horse and is three-sided. The interdigital surface is 
flattened and its volar part bears a prominence for the 

attachment of the interdigital ligaments. The proximal extremity is relatively 
large, and is somewhat compressed from side to side. The articular surface is con- 
cave from before backward and is divided bj^ a sagittal groove into two areas, of 
which the abaxial one is the larger and higher. Behind these are two facets for 
articulation with the sesamoid bones. The volar surface bears two tuberosities 
separated by a deep tlepression. The distal extremity is smaller than the proximal, 
especially in the dorso-volar direction. Its articular surface is divided by a sagittal 
groove into two convex facets, of which the abaxial one is dccidedh' the larger. 
There are depressions on either side for ligamentous attachment. The bone con- 
sists at birth of two pieces — the di.stal end and the fused shaft and proximal ex- 
tremity. Union occurs at one and one-half to two years. 

The second phalanx is about two-thirds of the length of the first and is dis- 



150 



SKELETON OF THE OX 



tinctly three-sided. The proximal articular surface is divided by a sagittal ridge 
into two glenoid cavities, of which the abaxial one is much the larger. There is a 
central dorsal prominence and two tubercles are present on the volar face. The 
distal extremity is smaller than the proximal. Its articular surface encroaches eon- 
siderabl}^ on the dorsal and volar surfaces, and is divided into two parts by a 
sagittal groove. There is a deep depression for ligamentous attachment on the inter- 
digital side. The bone contains a small medullary canal. The distal end unites 
with the rest of the bone about the middle of the second year. 

The third phalanges resemlile in a general way one-half of the bone of the horse. 
Each has four surfaces. The dorsal surface is marked in its distal part by a shal- 
low groove, along which there are several foramina of considerable size; the 
posterior one of the series is the largest, and conducts to a canal in the interior of 
the bone. Distal to the groove the surface is prominent, rough, and porous. 



; 




Fig. 1."j1.--]5<i.\l> .11- L>i>rAL Taut of Fore Limb ( 
Ox; Lateral View. 
1, Distal end of metacarpal _bone: 2, first phalan 
3, proximal sesamoid bone; 4, second phalanx; 5, e 
tensor process of third phalanx: 0, dorsal surface; 
angle; S, distal sesamoid bone. 




Fig. 1.52.— Bones of Distal P.vrt of Fore Limb op 
Ox; Volar View. 
1, Metacarpal bone; 2, proximal sesamoid bones; 
3. first phalanx; 4, second phalanx; 5, distal sesamoid 
bone; 6, third phalanx. 



Near and on the extensor process are several relatively large foramina. The slope 
of the surface is very steep posteriorly, but in front it forms an angle of 25 to 30 de- 
grees with the ground plane. The articular surface is narrow from side to side, and 
slopes downward and backward. It is also oblique transversely, the interdigital 
side being the lower. It is adapted to the distal surface of the second phalanx, with 
the exception of a facet behind for the distal sesamoid. The extensor process is 
very rough. The volar surface is narrow and slightly concave, and presents two 
or three foramina of considerable size. It is separated from the dorsal surface 
by a border which is sharp in front, rounded Ischind. There is no semilunar crest, 
since the deep flexor tendon is attached to the thick posterior border of the volar 
surface. The interdigital surface is smooth and grooved below, rough and porous 
above. At the proximal angle it is perforated by a large foramen, which is equiva- 
lent to the volar foramen of the horse and leads to a cavity in the middle of the bone. 
The surface is separated by a rounded border from the dorsal surface, and by a sharp 



BONES OF THE PELVIC LIMB 151 

edge from the volar surface. The angle is very short and blunt, and there is no 
cartilage. 

Four proximal sesamoids are present, two for each digit. They are much 
smaller than in the hor.se. The l)ones of each pair articulate with the correspond- 
ing part of the distal end of the large metacarpal bone I3.V their dorsal surfaces, 
with each other and with the first phalanx by .small facets. 

The two distal sesamoids are short and their ends are but little narrower than 
the middle. 

BONES OF THE PELVIC LIMB 

The ilia are almost parallel to each other and are also less oblique with regard 

to the horizontal plane than in the horse. They are relatively small. The gluteal 

line is prominent and is nearly parallel to the lateral border; it joins the ischiatic 

spine. A rounded ridge separates the two parts of the pelvic surface. The surface 



Tuber sacrale 



Lesser sciatic Ischiatic 

Tuber ischii notch spine 

\ ytSk \ I 





Tube 

COXIC 



Shrift of ilium 



Acetabulum. 
Ridge Obturator Pubis 
foramen 

Fig. 153.— Right Os Cox.e of Ox; Lateral View. 
1, Gluteal line; 2, fossa acetabuli- 

for articulation with the sacrum is triangular. The tuber sacrale is truncated, does 
not extend as high as the vertebral spines, and is separated from the opposite angle 
bjr a wider interval than in the hor.se. The tuber coxae is relatively large and prom- 
inent; it is not so obliciue as in the horse, and is wide in the middle, smaller at either 
end. The shaft is short and compressed from side to side. 

The ischitmi is large. Its long axis is directed obliciuely upward and back- 
ward, forming an angle of about 4.5 to 50 degrees with the horizontal plane. The 
transverse axis is oblique downward and inward at a similar angle, so that this 
part of the pelvic floor is deeply concave from side to side. The middle of the 
ventral surface bears a rough ridge or imprint for muscular attachment. The 
ischiatic spine is high and thin, and bears a series of almost vertical rough Unes 
laterally. The tuber ischii is large and three-sided, bearing dorsal, ventral, and 
lateral tuberosities. The ischial arch is narrow and deep. The symphysis bears a 
ventral ridge, which fades out near the ischial arch. 

The acetabular branch of the pubis is narrow, and is directed laterally and a 



152 



SKELETON OF THE OX 



little forward. The anterior border is marked by a transverse groove which ends 
below the rough ilio-pectineal eminence. The symphyseal branch is wide and 
:hin. 

The acetabulum is smaller than in the horse. The rim is rounded and is 
usually marked by two notches. One of these is postero-medial and is narrow 
and deep; it leads to the deep acetabular fossa and is often almost converted 
into a foramen by a bar of bone. The other notch is antero-medial, small, and 
sometimes replaced by a foramen or absent. 

The obtxu-ator foramen is large and elliptical. Its medial border is thin and 
sharp. 

Fusion of the three bones occurs at seven to ten months. 

The pelvic inlet is elliptical ami is more oblique than in the horse. In a cow 



Median 
Wing of crest uf Tuber 
sacrum sacrum sacrale 




Fig. 134. — Pe 



FROM Below. 



of medium size the conjugate diameter is about nine and a half inches (ca. 23 to 24 
cm.), and the transverse diameter al>out seven inches (ca. 18 cm.). The anterior 
end of the symphysis lies in a transverse plane through the junction of the third and 
fourth sacral segments. The dorsal wall or roof is concave in both directions. The 
ventral wall or floor is deeply concave, particularly in the transverse direction. 
The cavity is narrower and its axis is inclined .strongly upward in the posterior part. 
The distance between the acetabuluna and the tul3er coxae is only a little (ca. 3 to 
4 cm.) more than the distance between the former and the tuber ischii. 

The femur has a relatively small shaft, which is cylindrical in its middle, pris- 
matic distally. The trochanter minor has the form of a rough tuberosity, and is 
situated higher up than in the horse and encroaches on the posterior surface. The 
trochanteric ridge (Crista intertrochanterica posterior) connects it with the tro- 



BONES OF THE PELVIC LIMB 



153 



chanter major. The third trochanter is absent. The supracondyloid fossa is 
shallow. The proximal extremity is very wide. The head is smaller than in the 
horse, and the articular surface extends considerably on the upper surface of the 
neck. The fovea capitis is a small depression on the middle of the head for the 
attachment of the round ligament. The neck is well defined except above. The 
trochanter major is very massive and is undivided; its lateral surface is very rough. 




Fig. 155. — Right Femur of O 
RiOR View. 
1, Head; 2, neck; 3, trochanter ma- 
jor; 4, trochanteric fossa; 5, trochanter 
minor; 6, nutrient foramen; 7, vascular 
groove; S, lateral supracondyloid crest; 
9, supracondyloid fossa; 10, 10', medial 
and lateral condyles; 11, 11', medial and 
lateral epicondyles; 12, intercondyloid 



Lateral View. 
Numbers around bone: 1, 
Head; 2, neck; 3, trochanter 
major; 4, lateral border; 5, lateral 
supracondyloid crest; 6, supra- 
condyloid fossa; 7, lateral condyle; 
S, trochlea. Numbers on bone: 1, 
Eminence for attachment of gluteus 
profundus; 2, lateral epicondyle; 
3, depression for origin of popUteua 
muscle; 4, extensor fossa. 



Fig. 157. — Left Tibia and Prox- 
imal Part of Fibula of Ox; 
Posterior View. 
Numbers around bones: 1, 1', 
Medial and lateral condyles of 
tibia ; 2, nutrient foramen ; 3, 
lateral border; 4, distal extrem- 
ity; 5, medial malleolus; 6, shaft 
of fibula. Numbers on bone: 1,1', 
Tubercles of spine; 2, intercondy- 
loid fossa; 3, muscular lines. 
Arrow indicates groove for flexor 
digitalis longus. 



The trochanteric fossa is deep, but does not extend so far distally as in the horse. 
The distal end presents no very striking differential features, but the ridges of the 
trochlea are le.ss oblique than in the horse, and converge very sHghtly below. The 
proximal extremity unites with the shaft at about three and one-half years, the 
distal at three and one-half to four years. 

The tibia resembles that of the horse rather closely, but is somewhat shorter; 



154 



SKELETON OF THE OX 



The shaft is distinctly curved, so that the medial side is convex. The posterior 
surface is not divided into two areas, and the linese musculares are fewer and extend 
up higher than in the horse. The articular grooves and ridge of the distal end are 
almost sagittal in direction, and present an extensive but shallow synovial fossa. 
The lateral groove is separated by a sharp ridge from an outer area which is for 
articulation with the lateral malleolus. The anterior part of the medial malle- 
olus is prolonged downward and has a pointed end. The groove behind it is broad 
and well defined. Laterally there is a deep narrow groove which separates two 
prominences. The proximal extremity fuses with the shaft at three and one-half 
to four years, the distal at two to two and one-half years. 

Tuber calcis 



M. m.' 




M.l. 



T. 2+S 



Fig. 158. — Right Tarsus 
Mei 
M. VI., Medial malleolus; 
tarsal bone (sustentaculum) 
second and third tarsal bone 
foiuth metatarsal bones 



.1//. 3+Jf 




^ND Adjacent Boxes of Ox; Fig. 159. — Right Tarsus and Adjacent Bones of 
AL View. Ox; Dorso-lateral View. 

M. I., lateral malleolus (distal end of fibula) ; T. tibia; T. (., tibial tarsal bone; T. /., fibular 
T. f.+4. fused central and fourth tarsal bones; T, 1, first tarsal bone; T. ^+5, fused 
!s; Ml. 2, small or second metatarsal bone; Mt. 3+ A. large metatarsal or fused third and 
groove for tendon of flexor digitalis longus; 2, groove for deep flexor tendon. 



The fibula usually consists of the two extremities only. The head is fused with 
the lateral condyle of the tibia and is continued by a small, blunt-pointed prolonga- 
tion below. The distal end remains separate and forms the lateral malleolus (some- 
times called the os malleolare) . It is quadrilateral in outline and compressed from 
side to side. The proximal surface articulates with the distal end of the tiliia, and 
bears a small spine which fits into the groove on that bone. The distal surface 
rests on the fibular tarsal, and the medial articulates with the lateral ridge of the 
tibial tarsal bone. The lateral surface is rough and irregular. 

The early cartilaginous fibula is complete, but later the shaft is reduced to the 
small prolongation noted in speaking of the head and a fibrous cord which connects 
it with the distal end (lateral malleolus). In some cases, however, the upper part 
undergoes partial ossification, forming a slender rod which is usually united with 
the lateral border of the tibia and is joined to the head jjy fibrous tissue. 



BONES OF THE PELVIC LIMB 



155 



The patella is long, narrow, and very thick. The free surface is strongly con- 
vex and very rough and irregular. The articular surface is convex from side to 
side and nearly straight in the vertical direction. The large prominence on the 
medial side for the attachment of the fibro-cartilage allows prompt determination 
of the side to which the bone belongs. The apex is more pointed than in the horse. 

The tarsus consists of five pieces; the central and fourth and the second and 
third tarsal bones are fused. 

The tibial tarsal Ijone is relatively long and narrow, and is somewhat flattened 
from before backward. It bears a trochlea at either end. The groove and ridges 
of the proximal trochlea are not spiral, but almost sagittal ; the lateral ridge is the 
wider, and articulates with both tibia and fibula. The distal trochlea consists 
of two condyles divided by a groove, and articulates with the 
combined central and fourth tarsals. The plantar surface bears 
a large oval facet for articulation with the fibular tarsal; this 
occupies most of the surface, and is convex and grooved from 
above downward. The lateral surface presents two facets for 
articulation with the fibular tarsal, and is excavated and rough 
elsewhere. The medial surface bears a tuberosity at its upper 
part, and is flattened below. 

The fibular tarsal bone is longer and more slender than in 
the horse. The distal part of the body is compressed laterally, 
and bears a projection in front which articulates with the lateral 
malleolus. The tuber calcis is marked posteriorly by a wide 
shallow groove, which is coated with cartilage in the fresh state. 

The central and fourth tarsals are fused to form a large 
bone (Os centrotarsale quartum, scapho-cuboid), which extends 
across the entire width of the tarsus and articulates with all of 
the other bones. The greater part of the proximal surface is 
molded on the distal trochlea of the tibial tarsal, and its medial 
part rises high above the rest posteriorly. Laterally there is a 
narrow, undulating surface for articulation with the distal end 
of the filjular tarsal bone. The plantar surface bears two tuber- 
osities, of which the lateral one is rounded, the medial more 
prominent antl narrower. 

The first tarsal bone is quatlrilateral and small. It articu- 
lates with the central above, the metatarsus below, and the 
second tarsal in front. 

The second and third tarsals are fused to form a rhomboid 
piece. The proximal surface is concavo-convex, and articulates 
with the central component. The distal surface is undulating 
and rests on the metatarsus. The lateral surface bears a small 
facet in front for the fourth tarsal component, and the plantar ''^''''^' 
surface a very small one for the first tarsal bone. 

The large metatarsal bone is about one-seventh (ca. 3 cm.) longer than the 
corresponding metacarpal. Its shaft is compressed transversely and is distinctly 
four-sided. The groove on the dorsal surface is deep and wide. The plantar 
surface is marked by variable grooves. The proximal foramen on this surface does 
not perforate the shaft, but passes obliquely through the extremity, opening on the 
posterior part of its proximal surface. The medio-plantar angle of the proximal 
end bears a facet for articulation with the small metatarsal bone. 

The small metatarsal bone is a quadrilateral disc a little less than an inch in 
width and height. Its anterior face bears a facet for articulation with the large 
metatarsal bone. 




Fig. IGO. — I- a R G E 
Metatarsal Bone 
OF Ox; Dorsal 
View. 
1. Vascular groove; 

2, foramen; 3, 3', con- 



156 SKELETON OF THE SHEEP 

The large metatarsal bone is usually regarded as consisting of the fused third and fourth 
metatarsal bones, and the small bone as the second metatarsal. The medullary cavity is subdivided 
like that of the large metacarpal bone. Some anatomists, however, consider that the ridges at 
the upper end of each border represent the second and fifth metatarsals (Rosenberg and Retterer). 
On this basis the small bone would be the fii'st metatarsal. 

The phalanges and sesamoids resemble those of the thoracic limb so closely 
as to render separate description uimecessary. 



SKELETON OF THE SHEEP 

VERTEBRAL COLUMN 

The vertebral formula may be given as CVTisLe-TSiCyie-is, but it should he 
noted that, except in the cervical region, variation in number is common. 

It is not very rare to find twelve thoracic and seven lumbar, or an ambiguous intermediate 
vertebra. More commonly there are seven lumbar vertebra; without reduction in the thoracic 
region. In some cases there are fom-teen thoracic and five or six lumbar vertebra, and Lesbre 
records a case in which twelve thoracic and seven lumbar were present. In some cases the fourth 
sacral vertebra remains separate, and in others the first coccygeal unites with the sacrum, although 
the fusion here is rarely complete. Nathusius states that the nimiber of coccygeal vertebrae 
varies from tlxree to twenty-four or more. 

The cervical vertebrae are relatively longer than those of the ox. The atlas 
differs chiefly in that the prominence on the dorsal arch is much less developed. 
The anterior articular cavities are often separated by a central ridge. The wings 
are produced to form blunt points behind. The spinous process of the axis is not 
enlarged posteriorly; those of the succeeding vertebra? are less developed than in 
the ox; they increase in length from the third to the last. The ventral spines are 
rudimentarj'. The arches are separated dorsally by interarcuate spaces. 

The thoracic vertebrae are usually thirteen in number, but fourteen may be 
present, or, more rarely, only twelve. Their bodies are relatively wider and less 
constricted than those of the ox, and their extremities are not so sti'ongly curved, 
especially toward the end of the series. The intervertebral foramina are larger, in 
correlation with the absence of the foramina which usually occur in the arches of 
these vertelirte in the ox. 

The lumbar vertebrae number six or seven, the former ])cing a little more fre- 
quent than the latter. It is not common to find the number reduced to five. In 
some cases there is an ambiguous vertebra at the junction of the thoracic and liun- 
bar regions. The bodies are more flattened dorso-ventrally than those of the ox; 
their anterior ends are somewhat concave transversely, and the posterior ends are 
almost flat. The anterior articular processes are strongly curved and overlap the 
posterior ones. The transverse processes curve forward and have expanded ends. 

The sacrum consists ordinarily of four segments, but the last vertebra may re- 
main separate or undergo only partial fusion. There is no vascular groove on the 
pelvic surface. The spines are not fused, with the exception of the first and second, 
which may be partially united. The transverse processes of the last segment are 
distinct and outstanding. 

The coccygeal vertebrae vary in number from three (in short-tailed sheep) to 
twenty-four or more. The bodies have no hemal processes on the ventral surface. 
The transverse processes are long and thin and project backward. 



THE RIBS 
The ribs usually number thirteen pairs, but the occurrence of fourteen pairs is 
not at all uncommon. The thirteenth rib is floating and has a cartilage about an 



THE STERNUM — THE SKULL 157 

inch long. The fourteenth ril:i, when present, is also floating. As compared with 
tho.se of the ox, they are narrower and are more strongly curved in the anterior part 
of the series. The lateral surface is in general smooth and rounded. The second 
to the eleventh form diarthroses with their cartilages. 

The thirteenth rib may be more or less rudimentary on one side or both, and may be fused 
with the corresponding vertebra; the latter may, therefore, be ambiguous in character. 

THE STERNXJM 
The sternum resembles in general that of the ox. The munber of segments 
may be reduced to six, and the primitive division of the next to the last sternebra 
into two lateral halves maj^ persist for a long time. The first segment is cylindrical, 
with enlarged ends; the second and third are wide and flat; the last is long and nar- 
row. 

THE SKULL 

The more important differences in the skull of the sheep as compared with 
that of the ox are in regartl to the cranium. Viewed from above, the cranium is 
irregularly hexagonal in outline; it is widest in the frontal region, between the 
posterior parts of the orl^its, and narrows greatly both anteriorly and posteriorly. 
In profile the roof of the cranimn is strongly convex; the highest part of the curve 
coincides with the greatest width, and the posterior part slopes at an angle of about 
45 degrees with the basal plane. 

The occipital bone forms all of the nuchal surface of the cranium, except a 
small lateral area occupied by the mastoid part of the temporal bone. A narrow 
part (about 1.5 cm. in width) enters into the formation of the roof of the cranium 
also; it joins the parietal bones at a transverse suture. The parietal and nuchal 
surfaces are separated by a rough transverse ridge, the central part of which is 
united below with the external occipital protuberance, to which the ligamentum 
nuchse is attached. The mastoid foramen is situated between the lateral border 
and the petro-mastoid part of the temporal bone. The paramastoid process is 
grooved laterally, has a concave anterior border, and tapers to a blunt jioint. The 
basilar part is wde; the tuliercles at its junction with the sphenoid are placed 
laterally, and are Ijroad and short. 

The sphenoid bone resembles that of the ox. The posterior wall of the deep 
hypophyseal or pituitary fossa is formed by a plate (Dorsum sellse) which is di- 
rected forward and upward, and bears a projection (Processus clinoideus posterior) 
at each side of its upper part. The sphenoidal sinus is commonly absent or rudi- 
mentary. 

The ethmoid bone resemlsles that of the ox. 

The parietal bone fuses soon after birth with its fellow and with the inter- 
parietal. From this union there result a central quadrilateral curved plate which 
forms part of the roof of the cranium, and, separated from it by a curved line, a 
narrower lateral part, which extends forward on either side as part of the medial 
wall of the temporal fossa. The frontal sinus does not extend into the parietal bone. 
There is no internal occipital protuberance. 

The frontal bone is relatively less extensive than in the ox. The naso-frontal 
part is strongly curved, but varies considerably in contour in different breeds. In 
horned breeds the processus cornus projects from the lateral part of the external 
surface a little (ca. 1.5 cm.) behind a transverse plane through the posterior margin 
of the orbit. The process varies in size and shape, and does not contain an extension 
of the frontal sinus. In other cases there is a rounded tuberosity or a slight rough- 
ened elevation. The supraorbital foramen is further forward than in the ox, being 
just behind a transverse plane through the middle of the orbit; it is a little nearer 



158 



SKELETON OF THE SHEEP 



to the orbital margin than to the median line. The groove which leads forward 
from it is often rather faint. The orbital part is deeply concave. The infraorbital 
canal opens on the medial wall of the orbit as in the ox.- The frontal sinus extends 
backward to a transverse plane through the posterior part of the temporal con- 
dyle, and forward to one through the anterior margin of the orbit. 

The temporal bone consists of distinct squamous, tympanic, and petro-mastoid 
parts. The squamous part in general resembles that of the ox, but has, like that of 
the horse, a notch through which the external acoustic process protrudes. The root 
of the zygomatic process is perforated by a foramen which opens ventrallj' behind 
the postglenoid process, in front of the chief external opening of the temporal canal. 
The latter extends upward and backward between the petro-mastoitl and squamous 
parts and the parietal bone, and opens into the cranial cavity in front of the apex 
of the petrous. The tympanic part includes the external acoustic process, the bulla 




Fig. 161. — Skull of Sheep; Latehal View. 
j4 , Occipital bone : B, parietal bone; C, squamous temporal bone; Z), frontal bone; £, nasal bone; i'', lacrimal bone; 
G, malar bone; H, maxilla; I, premaxilla; ./, mandible; K, perpendicular part of palatine bone; L, hyoid bone; 1, 
occipital condyle; 2, paramastoid process; 3, mastoid process; 4, meatus acusticus externus; .5, bulla ossea; 6. zygo- 
matic process of temporal bone; 7, condyle of mandible; 8, coronoid process; 9, supraorbital process; 10, processus 
cornus; 11, 11', openings of supraorbital canal; 12, ethmoidal foramen: 13, optic foramen; 14, fossa sacci lacrimalis; 
15, bulla lacrimalis;" 16, external lacrimal fossa; 17, facial tuberosity; IS, infraorbital foramen; 19, mental foramen. 



ossea, and the muscular process; the first resembles that feature in the horse, the 
others those of the ox, but the cavity of the bulla is undivided. The cerebral sur- 
face of the petrous part presents the floccular fossa on its upper part, and a round 
eminence Ijehind the internal acoustic meatus. 

The bones of the face present, aside from the difference in size, few important 
special features. 

In regard to the maxilla it may be noted that the junction with the lacrimal and 
malar is less oblique than in the ox, since the facial parts of these bones are quadri- 
lateral and not produced to a point anteriorly. The facial tuberosity and the infra- 
orbital foramen are a little further back, and lie about over the second and fourth 
cheek tooth respectively. The palatine sinus extends from-a point opposite to the 
first cheek tooth backward to the transverse palatine suture. The defect (in the 
dry skull) in its nasal wall is quite small — in marked contrast to that of the ox — 



THE SKULL 



159 



since the basal lamella of the ventral turbinate bone curves ventro-medially, joins 
the palatine bone, and is separated only by a narrow hiatus from the nasal plate of 
the palatine process of the maxilla. The anterior palatine foramen is at the trans- 
verse palatine suture. The anterior end of the palatine process tapers to a point. 
The maxillary sinus resembles that of the ox, but is relatively small. 

The premaxilla has a narrow and pointed body. The palatine process is ex- 
tremely narrow in front and is grooved laterally. The palatine fissure is long and 
narrows to a very acute angle l)ehind. 

The palatine bone resembles that of the ox, but there is no air-cavity in its 
horizontal part. The spheno- 

OccipUul hone Parietal bone 



Temporal crcsl 
< nroHoid process 



Frontal bon 



Orbit 

Sii jiraorbital 



Malar bone 
Lacrimal bone 



palatine foramen is large and 
oval. 

The pterygoid bone is 
very broad above and narrow 
below, where it ends in a sharp- 
pointed hamulus. 

The nasal bone tapers to 
a point at its anterior end, 
which is not notched. 

The facial part of the 
lacrimal bone has an elongated 
quadrilateral outline; in front 
of the orbit it forms, with the 
adjacent part of the malar, the 
external lacrimal fossa (Fossa 
lacrunalis externa) which 
lodges a cutaneous cul-de-sac 
known as the infraorbital or 
lacrimal pouch. The bone here 
may be more or less cribriform. 
The lacrimal bulla is relatively 
small, is usually cribriform, 
and has a pointed posterior 
end; the maxillary sinus ex- 
tends into it. The orbital 
margin forms a distinct promi- 
nence, and behind the latter is 
the fossa for the lacrimal sac. 

The facial part of the 
malar bone is extensive and 

quadrilateral. Its upper part concurs in the formation of the external lacrimal 
fossa; this area is limited below by a curved crest which continues backward on 
the zygomatic process. The latter divides into two branches, as in the ox. 

The turbinates and the vomer resemble those of the ox. 

The mandible differs from that of the ox chiefly in that the ventral border of 
the ramus, from the body to the angle, is only slightly curved. 

On account chiefly of the limited extent of the frontal sinuses, the cranial 
cavity corresponds to the ex-ternal form of the cranium more closely than is the case 
in the ox. It is ovoid, and is much longer relatively, but has a much shorter dorso- 
ventral diameter than that of the ox. The parietal bone forms a distinct ridge on 
the lateral wall between the cerebral and cerebellar compartments, but, on the other 
hand, the petrous temporal projects very little into the cavity. 

The nasal cavity resemjjles that of the ox, but is relatively narrow (especially 
anteriorly), and there is no large hiatus in the nasal plate of the maxilla. 




'osity 



Nasal process of pre- 
maxilla 



Palatine process of pre- 
maxilla 
Palatine fissure 

Body of premaxilla 



Incisor teeth 



Fig. 162. — Skull ( 



160 SKELETON OP THE SHEEP 



BONES OF THE THORAaC LIMB 

The scapula differs cliiefly from that of the ox in tlie following points : The ver- 
tebral liorder is longer and the neck narrower. The spine is less sinuous. The 
glenoid extremity is relatively long, since the tuber scapulae is connected with the 
rim of the glenoid cavity. The subscapular fossa is more extensive. 

The hiunerus is relatively longer and more slender than that of the ox. The 
anterior part of the lateral tuberosity is blunt and less incurved, while the posterior 
part is small. The deltoid tuberosity is nearer to the proximal end and is less 
prominent. 

The bones of the forearm are relatively longer than those of the ox. The 
radius is a little more curved than that of the ox, and its dorsal surface is more 
regularly rounded. The shaft of the ulna is more slender, especially in its distal 
half; its fusion with the radius occurs later and is usually much less extensive than 
in the ox. 

The carpal bones resemble those of the ox except in size. The accessory is 
long and less tuberous. 

The large metacarpal bone (Mc. 3 + 4) is long and slender. The lateral small 
metacarpal bone (Mc. 5) is often absent or is represented by a ridge on the large 
metacarpal. 

The phalanges of the chief digits are relatively long and narrow. The third 
phalanx in particular is much flattened on its abaxial side, so as to form a prominent 
dorsal border. Of the proximal sesamoids, the abaxial ones are compressed from 
side to side, and the axial ones from before backward. The flexor surface of the 
distal sesamoids forms a shallow groove, not divided by a ridge. The accessory 
digits usually have no phalanges. 

BONES OF THE PELVIC LIMB 

The OS coxae differs greatly from that of the ox. The long axis of the ilium 
is almost in a line with that of the ischium. The gluteal line appears as a ridge 
which is nearly parallel with the lateral border. The tuber coxa; is only slightly 
thickened, and the tuber sacrale is pointed. The crest is concave medially, convex 
laterally. The shaft is relatively long and is flattened laterally. The superior 
ischiatic spine is low and everted. The pubis resembles that of the ox, but its an- 
terior border (pecten) is thin and sharp. The ischivun slopes clo^vnward and back- 
ward, and forms a much larger angle with its fellow than in the ox. The lesser 
sciatic notch is very shallow. The tuber ischii is flattened and everted; it bears a 
long, blunt-pointed lateral process, and a very short and blunt dorsal prominence. 
There is a very low ventral ridge on the symphysis. The latter is not usuallj^ com- 
pletely ossified, even in old animals. The acetabulum is further back than in the 
ox, and is relativelj^ larger and deeper; it has a deep notch posteriorly. The 
pelvic inlet is very ol)liciue, so that a vertical plane from the anterior end of the 
symphysis cuts the first coccygeal vertebra. The brim is elliptical; the conjugate 
diameter is about five inches (ca. 12 cm.), and the transverse about three and a 
half to four inches (ca. 9.5 cm.). The floor of the pelvic cavity is wide and shallow 
as compared with the ox, and the pelvic axis inclines downward posteriorly. 

The shaft of the femur is slightly curved, the convexity being anterior. A dis- 
tinct line separates the lateral and posterior surfaces. The supracondyloid fossa 
is very shallow. The head has a shallow fovea and the neck is distinct. The tro- 
chanter major is little higher than the head. The ridges of the trochlea are similar 
and parallel, but slightly oblique. 

The tibia is long and slender, but otherwise resembles that of the ox. The 
fibula has no shaft, and its proximal end is represented by a small prominence be- 



SKELETON OF THE PIG — VERTEBRAL COLUMN 



161 



low the lateral margin of the lateral condyle of the tibia; the distal end forms the 
lateral malleolus, as in the ox. 

The patella is relatively longer and narrower than that of the ox. 

The tarsal bones resemble those of the ox except in size. 

The metatarsal and digital bones present special characters similar to those of 
the correspoirding part of the thoracic limb. 



SKELETON OF THE PIG 

VERTEBRAL COLUMN 

The vertebral formula is C7Ti4_i5L6-7S4Cy2o-23. 

Tlie cervical vertebrae are short and wide. The bodies are elliptical in cross- 
section, the long diameter being transverse. The anterior articular surfaces are 
slightly convex from side to side and concave dorso-ventrally ; the posterior ones 




Fig. 163. — Skeleton of Pig; Lateral View. 
a. Cranium; i>, maxilla; c. mandible; 1H.-7H., cervical vertebra; IR.w., first thoracic vertebra; IS R.w , thir- 
teenth thoiacic vertebra (next to last); IL., first lumbar vertebra; 6L., sixth lumbar vertebra (next to last usually); 
A',, sacrum; S., coccygeal vertebrse; IR., first rib; l^R,, last rib; R,kn.t costal cartilages; St., sternum; d, supraspin- 
ousfossa; rf', infraspinous fossa; 7, spine of scapula; 5, neck of scapula; e, humerus; 5, head of humerus; 4. tuberosities 
of humerus; 5, deltoid tuberosity: ff, lateral epicondyle of humerus; /.radius; ff, ulna; 7, olecranon; /i, carpus: 18-25, 
carpal bones; i—i"", metacarpus; A:-A:"", proximal phalanges; W", middle phalanges; m—m"", distal phalanges; n, o, 
sesamoids: p, ilium; 5, tuber coxeb; 5, tuber sacrale ; 1 , superior ischiatic spine; g, ischium: 7.^, tuber ischii; r, pubis; 
1^, acetabu'.uni; s, femur; 13, trochanter major; I4. trochanter minor; 15, lateral epicondyle; /. patella: u. tibia; 
i(>, crest of tibia; J 7, lateral condyle of tibia; u, fibula; w, tarsus; Sff-3i, tarsal bones; .25', tuber calcis. (After Ellen- 
berger, in Leisering's Atlas). 



are slightly concave. A ventral spine is not present. The arches are wide trans- 
versely, but the lamina? are narrow, so that a considerable interval (>Spatium inter- 
arcuale) separates adjacent arches dorsally. The pedicles are perforated by a 
foramen in addition to the usual intervertel^ral foramina. The transverse processes 
divide into two branches, both of which increase in size from the third to the sixth. 
The dorsal branch projects outward and backward; it is short and is thickened at 
its free end. The other branch is a quadrilateral plate directed ventrally; each 
overlaps the succeeding one to a small extent, and the series forms the lateral 
boundary- of a deep and wide ventral groove. The spines increase in height from the 
11 



162 



SKELETON OF THE PIG 



third to the last; the anterior ones are inchned backward, the posterior ones for- 
ward. The last cervical is recognized by the great length of its spine (ca. 10 cm. 
in the adult), the absence of the ventral plate of the transverse process, and the flat- 
ness of the ])ody, which bears a pair of small facets on its posterior margin for the 




FiQ. 164. — Fourth 

Vertebra of Pig ; Lat- 
i View. 

1, 1', Anterior and pos- 
terior ends of body; 2, arch; 
3, foramen of arch; 4, anterior 
articular process; 5, spinous 
process; 6, ventral branch of 
transverse process. 



Fifi. Ki.').— Sixth Cervipal Vertebra 
OF Pig; Anterior View. 
1, Body; 2, transverse process; 
3. foramen transversarium; 4, addi- 
tional foramen of arch; 5, articular proc- 
ess; 6, arch; 7, spinous process. 



1, 1', Anterior and posterior 
ends of body; 2, facet for head of 
first rib; 3, arch; 4, transverse 
process; 5, 5', articular processes; 
6, spinous process; 1 (number on 
bone), foramina of arch. 





Fig. 1{J7.— Atlas of Pig; Dorsal View. 
1, Dorsal tuberosity; 2, alar foramen; 3, wing; 
4, intervertebral foramen; 5, dorsal arch; 6, ventral 
tubercle; 7, surface for dens. 



Fig. 168.— Atlas of Pig; Anterior View. 
1, Dorsal tuberosity; 2, wing; 3, alar foramen; 4, 
rior articular cavity; 5, ventral tubercle. 



heads of the first ribs. It has foramina transversaria, and usually two foramina in 
each side of the arch. 

The dorsal tuberosity of the atlas is large. The ventral tubercle is long, com- 
pressed laterally, and projects back under the axis. The wing is flattened and 
bears a posterior tuberosity. The foramen transversarium passes through the 



VERTEBRAL COLUMN 



163 





Fig. 169. — Axis of Pig; Lateral View. 
1, Dens; 2, 2', anterior and posterior articular 
processes; 3, posterior end of body; 4, transverse proc- 
ess; 5, foramen transversarium ; 6, arch; 7, spinous 
process. Arrow indicates intervertebral foramen. 



Fig. 170.— Axis op Pig; A 
1, Dens; 2, 2', anterior and posterior articular 
processes; 3, foramen transversarium; 4, arch; 5, spi- 
nous process. 




\ 



posterior border of the wing to the fossa under the latter, and is not visible dorsally ; 
it is sometimes very small or absent. The 
sides of the vertebral foramen bear two lat- 
eral projections which partially divide it 
into a ventral narrow part, which receives 
the dens, and a dorsal larger part for the 
spinal cord. In the fresh state the division 
is completed by the transverse ligament, 
which is attached to the projections. 

The axis has a large spinous process, 
which is directed upward and backward. 
The dens is a thick cylindrical rod. The 
transverse process is very small and the 
foramen transversarium is often incom- 
plete. 

The thoracic vertebrae are commonly 
fourteen or fifteen in number. Their 
bodies are relatively long, constricted in 
the middle, and without ventral spines. 
Their extremities are elliptical, depressed 
in the middle, and prominent at the peri- 
phery. The arch is perforated by a fora- 
men on each side and in most of the series 
there is also a foramen in the posterior 
part of the root of the transverse process 
which communicates with the former or 
with the posterior intervertebral foramen. 
Sometimes there is a foramen in the an- 
terior part of the process also. There are 
mammillary processes except on the first 
two; in the posterior five or six vertebrae 
they project from the anterior articular 
processes. The facet for the tubercle of the 
rib is absent or fused with that for the 
head in the last five or six. The last trans- 




Vertebr-b 



Fig. 171.— Second and Third Ti 

OF Pig; Lateral View. 
Numbers around bones: 1, 1', Anterior and poster- 
ior ends of bodies; 2. cavities for heads of ribs; 3, 3', artic- 
ular process; 4, facet for head of rib; 5, spinous process. 
Numbers on bones: 1, 1', Foramina of arches; 2, 2% 
transverse processes; 3, 3', facets for tubercles of riba. 



164 SKELETON OF THE PIG 

verse process is lumbar in character, plate-like, and about an inch (2 cm.) long. 
Small accessory processes occur in the posterior part of the region. The first 
spinous process is broad, very high, and inclined a little forward. The others di- 
minish very gradually in length to the tenth, beyond which they are about equal. 
The second to the ninth are inclined backward, the tenth is vertical (anticlinal), and 
the rest incline forward. The width decreases decided!}' from the fourth to the 
tenth, beyonil which there is a gradual increase. The summits are slightly enlarged 
and lie almost in a straight line. 

The lumbar vertebrae are six or seven in number. The bodies are longer than 
in the thoracic region and bear a ventral crest. They become wider and flatter 
in the posterior part of the series. The ar6hes are deeply notched, and are separated 
by an increasing space dorsally. The mammillary processes project outward and 
backward. The transverse processes are lient downward and incline a little for- 
ward. Their length increases to the fifth and is much diminished in the last. They 
form no articulation with each other or with the sacrum. The posterior edge of the 
root of the process is marked by a notch in the anterior part of the series, a fora- 




FiG. 172. — Fourth Lumbar Vertebra of Pig; Anterior View, 
1, Body; 2, transverse process: 3, anterior articular process; 4, mammillarj- process; 5, posterior articular process; 

6, spinous process. 

men in the posterior part. The spines are broad and incline forward, with the ex- 
ception of the last, which is narrow and vertical. 

Lesbre states that six and seven lumbar vertebrae occur with almost equal frequency. The 
number may be reduced to five, and the number of i^resacral vertebrae varies from twenty-six to 
twenty-nme. • 

The sacrum consists usually of four vertebrae, which fuse later and less com- 
pletely than in the other domesticated animals. It is less curved than in the ox. 
The spines are little developed and commonly in part absent. The middle of the 
dorsal surface is flattened and smooth, and presents openings into the sacral canal 
between adjacent arches (Spatia interarcualia) . On either side are the dorsal 
sacral foramina, and tubercles which indicate the fused articular processes. The 
wings resemble those of the ox. The anterior articular processes are very large. 
The pelvic surface resembles that of the ox, but is not so strongly curved, and the 
transverse lines are very distinct. 

The coccygeal vertebrae are specially characterized hy the presence of func- 
tional articular ]n-ocesses on the first four or five, beyond which these processes 
become non-articular and smaller. The arches of the first five or six are complete. 
The transverse processes are broad and plate-like in the anterior part of the series 



THE RIBS 165 

and diminish very gradually. Not rarely the first coccygeal vertebra unites with 
the sacrum. 

Vertebral Curves. — The cervical region is practically straight. The thoracic 
and lumbar regions form a gentle curve, concave ventrally, the highest point of 
which is at the junction of the two regions. The sacral promontory is not so pro- 
nounced as in the ox, and the sacral curve is flatter. 



B A 



C B A 




173.— S.v 



. Verteb 



>;d First Cocctge. 
^Pig; Dorsal View. 
I-IV, Arches of sacral vertebrse; 1,2, 3, dorsal sacral 
foramina; 4, similar foramen between sacrum and first 
coccygeal vertebra; .-1, body of first sacral vertebra; B, 
articular process; C, wing: £*. auricular surface; E, articu- 
lar processes: ^i first coccygeal vertebra. 



■Sacrum and Fir 
Pig; Vexi 



' Coccygeal Vertebra of 



I-IVj Sacral vertebrse (bodies) ; 1, 2, 3, ventral sacral 
foramina; 4, similar foramen between sacrum and first 
coccygeal vertebra; A, body of first sacral vertebra: B, 
articular process; C, wing; D, auricular surface; E, first 
coccygeal vertebra. 



Length. — The regional lengths of the vertebral column of a large Berkshire sow were as fol- 
lows: Cervical, 24 cm. ; thoracic, 53.5 cm.; lumbar, 31 cm.; sacral, 17 cm.; coccygeal, 35 cm. 

Variations. — The occurrence of fifteen tlioracic vertebrEe is quite common, and the existence 
of sixteen or even seventeen has been recorded. Reduction to thii-teen is very rare. Six and 
seven lumbar vertebrse seem to occur with about equal frequency, and reduction to five is on rec- 
ord. The number of coccygeal vertebrae varies from twenty to twenty-six according to the records 
of several observers. LeslDre states that he has found twenty-three most frequently. 



THE RIBS 
The ribs numlier fourteen or fifteen pairs, of which seven are sternal and seven 
or eight asternal usually. They are in general strongly curved in the improved 
breeds, so that there is a fairly distinct angle, except toward the end of the series. 



166 



SKELETON OF THE PIG 



The backward slope of the posterior ribs is slight. Thfe first rib is prismatic, has a 
large sternal end, and a very short cartilage. The width is greatest in the third 
to the sixth, and the length in the sixth and seventh usually. The tubercle fuses 
with the head on the last five or six. The second 
to the fifth form diarthrodial joints with their car- 
tilages, which are wide and plate-like. 

The fifteenth rib, when present, may be fully developed 
and its cartilage enter into the formation of the costal arch; 
but in most cases it is floating, and in some cases it is only 
about an inch (ca. 2-3 cm.) in length. 



THE STERNUM 

The sternum consists of six segments and re- 
sembles that of the ox in general form. The first 
;A segment (Manubrium) is long, flattened laterally, 





Fig. 175.— Eighth Rib of Pig; Lat- 
eral View. 
1, Head; 2, neck; 3, tubercle; 4, ante- 
rior border; 5, sternal extremity. 



Fig. 176.— First Rib of Pig; Lateral View. 

1, Head; 2, neclc; 3, tubercle; 4, anterior border; 5, vascular impression; 

6, sternal extremity. 



and bears a blunt-pointed cartilage on its anterior end; its posterior end forms a 
diarthrodial joint with the body. The latter is flattened, wide in its middle, narrow 
at either end. The widest segments are formed of two lateral parts, which are 
not completely fused in the adult. The last segment has a long, narrow part which 
bears the xiphoid cartilage. 

The thorax is long and is more barrel-shaped than in the horse or ox, since the 
ribs are more strongly curved and differ less in relative length. 



BONES OF THE SKULL 
Crantom 

The occipital bone has an extensive squamous part, which forms a very broad 
and prominent nuchal crest. The latter is concave, and is thick and rough above, 
where it forms the highest part of the skull; laterally it becomes thinner, turns 



BONES OF THE SKULL — CRANIUM 



167 



downward, and is continuous with the temporal crest. Two divergent ridges pass 
upward from the foramen magnum, and the surface between them is concave and 
smooth. The greater part of the cerebral surface of the squamous part is united 
with the parietal bones, but a ventral concave area faces into the cranial cavity. 
The foramen magnum is almost triangular, and is narrow above, where it is flanked 
by two small tuberosities. The paramastoid processes are extremely long and pro- 
ject almost straight ventrally. The hypoglossal foramen is at the medial side of 
the root of the process. The basilar part is short and wide; its ventral surface 




Fig. 177. — Skull of Pig; Lateral View. 
.4, Occipital bone; B, squamous temporal bone; C, parietal bone; D, frontal bone; E, lacrimal bone; F, malar 
bone; G, maxilla: //. premaxilla; /, nasal bone; J, os rostri; K, mandible; 1, occipital condyle; 2, paramastoid proc- 
ess; 3, condyle of mandible; 4, meatus acusticus externua; 5, temporal fossa; 6, parietal crest; 7, supraorbital process; 
8, orbital part of frontal bone; 9, fossa for origin of ventral oblique muscle of eyeball; 10, orbital opening of supraorbital 
canal; 11, lacrimal foramina; 12, supraorbital foramen and groove; 13, infraorbital foramen; 14, zygomatic process of 
temporal bone; 15, temporal, and 15', zygomatic, process of malar bone; 16, incisor teeth; 17, canine teeth; 18, 18', 
premolars; 19, 19', molars; 20, mental foramina; 21, mental prominence; 22, angle of mandible. 



bears a thin median ridge and two lateral imprints or tubercles which converge at 
the junction with the sphenoid bone. 

The interparietal bone fuses before Ijirth with the occipital. The internal 
occipital protuberance is absent. 

Tlie parietal bone is overlapped by the occipital bone behind and concurs in the 
formation of the nuchal crest. Its external surface is divided by the parietal crest 
into two parts. The medial part (Planum parietale) faces upward and forward, 
and is flattened and smooth. Its medial border is short and straight and unites 
early with the opposite bone. Its anterior border is concave and joins the frontal 



168 



SKELETON OF THE PIG 



bone. The lateral part (Planum temporale) faces outward and is more extensive; 
it is concave, forms a large part of the temporal fossa, and is overlapped ventrally 
by the squamous temporal. The parietal crest extends in a curve from the nuchal 
crest forward and outward to the supraorbital process. The cerebral surface is con- 
cave and is marked by digital impressions. The ventral border projects into the 
cranial cavity and forms a crest which separates the cerebral and cerebellar compart- 



Squamous part 
of occipital bone 



Occipital condyle 
Paramastoid process {tip) 



Fig. 17S. — Skull 
1, Hypoglossal foramen; 2, fora 
sphenoid; (i, pterygoid bone, and 6', hainul 
bone; 9, pterygoid process of palatine bone 




Basilar part of 
occipital bone 

Mastoid process 
X Temporal condyle 



Maxillary recess 

Zygomatic process 
of malar bone 



Maxilla 



Premolar teeth 



.NDIBLE AKD HTOID. 

3, foramen lacerum posterius; 4, bulla ossea; 5, body of 
8, horizontal, and 8', perpendicular, part of palatine 
10, pterygoid process of sphenoid bone; II, supraorbital process: 12, or- 



bital opening of supraorbital canal ; 13, choanae ( 
palatine fissure. 



■ posterior nares; 14, 14', anterior palatine foramen and groove: 15, 



ments laterally. The interior is excavated and forms part of- the frontal sinus in 
the adult. There is no temporal canal. 

The frontal bone is long. The frontal surface slopes downward and forward, 
the inclination varying in different subjects. The anterior part is concave and is 
marked liy the supraorbital foramen and the groove leading forward from the 
foramen to the nasal bone. The supraorbital canal opens into the orbit at the 



CRANIUM 169 

upper part of the medial wall of the latter. The supraorbital process is short and 
blunt-pointed, and is not connected with the zygomatic arch. The gap in the or- 
bital margin is closed by the orbital ligament in the fresh state. The orbital part 
is extensive and forms the greater part of the medial wall of the orbit. Its upper 
part is perforated by the orbital orifice of the supraorbital canal, in front of which 
is the distinct fovea trochlearis. The ethmoidal foramen is situated in the ventral 
part near the junction with the orl)ital wing of the sphenoid. The temporal part 
is very narrow and is separated from the orbital plate by a ridge which joins the 

Parietal bone 
Temporal fossa 

Squamous temporal 
bone 

External acoustic 
meatus 



Zyqomatie priirrss 
of temporal hone 
Siipraorhitiit pro- 
cess 
Frontal bone 

Supraorbital fora- 
men 
Zygomatic process 
of malar bone 
Lacrimal bone 



Lacrimal foramen 
Preorbital fossa 



Infraorbital foramen 

Nasal process of premaxilla 

Nasal bone 

Canine tooth 

Palatine fissure 
Body of premaxiUa 




Fig. 179.— Skull of Pig; Dorsal View. 



pterygoid crest below. The interior of the laone is e.xcavateil by the frontal sinus in 
practically its entire extent in the adult. In the young subject the cavity is con- 
fined to the anterior part and the rest of the bone is thick. 

The temporal bone has a general resemblance to that of the ox. The zygo- 
matic process is short and stout and is ))ent at a right angle. The dorsal border of 
the process is thin; traced from before backward it curves sharply upward and 
forms a high prominence in front of the external acoustic meatus; beyond this 
it drops rather abruptly and is then continued upward to the nuchal crest. The 
anterior part of the ventral border joins the zj'gomatic process of the malar, which 



170 SKELETON OF THE PIG 

is deeply notched. The condyle is concave in the transverse direction. The post- 
glenoid process is absent, but the articular surface is bounded behind and medially 
by a crest. There is no temporal canal. The external acoustic meatus is very 
long and is directed dorso-laterally. The bulla ossea is large, compressed laterally, 
and bears a pointed muscular process in front. A narrow space intervenes between 
the bulla and the basilar part of the occipital bone, so that the foramen lacerum 
resembles that of the horse. The small hj'oid process is situated in a deep de- 
pression in front of the root of the paramastoid process, and the stylo-mastoid 
foramen is lateral to it. The petrous part presents no important differential fea- 
tures. The squamous part (including the root of the zygomatic process) contains 
an air-cavity, which is continuous with the sphenoidal sinus. 

The sphenoid bone is short and resembles that of the ox in general. The body 
is narrow. The hypophyseal or pituitary fossa is very deep, and is limited behind 
by a prominent dorsum sellje; the dorsum bears lateral projections, the posterior 
clinoid processes (Processus clinoidei aborales). The foramen ovale is absent, 
being included in the foramen lacerum antcrius. The other foramina are like those 
of the ox. The pterygoid process is broad and twisted. Its base is not perforated 
and its free edge is thin and sharp. It concurs ^vith the pterygoid and palate bones 
in the formation of the pterygoid fossa (Fossa pterygoidea), which opens backward 
and is not present in the horse or ox. The sphenoidal sinus is very large and oc- 
cupies the body, the temporal ^vangs, and a great part of the pterygoid processes 
in the adult; it is continued into the temporal bone as mentioned above. 

The ethmoid bone has a relatively long perpendicular plate, which is marked 
by ridges corresponding to the ethmoidal meatuses. The criljriform plate is ex- 
tensive and very oblique, so that it and the crista galli are almost in line with the 
basi-cranial axis. A linear series of relatively large foramina is found on either 
side of the crista. The lateral mass consists of five endoturbinates and eighteen 
ectoturbinates (Paulli). The lamina lateralis concurs in the formation of the 
pterygo-palatine fossa. The lamina transversalis separates the fundus of the 
nasal cavity from the naso-pharyngcal meatus. 

Face 

The maxilla is extensive. Its facial surface forms a longitudinal groove, 
which is continued upon the preraaxilla in front and the facial parts of the lacrimal 
and malar behind. The infraorbital foramen — sometimes double — is large and 
is situated above the third or fourth cheek tooth. The alveolus for the canine 
tooth produces a ridge (Juga canina) at the anterior end which is very pronounced 
in the boar. The facial crest extends forward from the root of the zygomatic proc- 
ess and fades out behind the infraorbital foramen; in some specimens it is prom- 
inent and thin-eilged, in others it is rounded and projects little. The zygomatic 
process is short but stout and buttress-like; it is overlapped laterally by the malar. 
The maxillary tuberosity forms in the young subject a long bulla, which occupies 
most of the pterygo-palatine fossa and contains the developing permanent molars; 
after the eruption of the teeth the tuberosity flattens and joins the vertical part of 
the palate bone. The palatine process is very long and is marked in its anterior 
part by transverse grooves (Sulci palatini transversi) corresponding with those of 
the mucous membrane of the palate. The anterior palatine foramen is near the 
junction with the palate bone; from it the palatine groove can be traced distinctly 
along the entire length of the process. The alveolar border presents a large alveolus 
for the canine tooth at its anterior end ; behind this are seven alveoli for the cheek 
teeth, which increase in size from first to last. The maxillary foramen and infraor- 
bital canal are very large. The maxillary sinus is small. 

The body of the premaxilla is narrow and prismatic. It presents three alveoli 
for the incisor teeth, which are separated by short intervals and diminish in size 



FACE 171 

from before backward. As in the ox, a narrow space separates the right and left 
bones and takes the place of the foramen incisivum. The palatine process is long 
and narrow. The nasal process is very extensive and is somewhat rhomboid in 
outline. Its dorsal border forms a very long suture with the nasal bone, and the 
ventral articulates to about the same extent with the maxilla. The palatine fissure 
is relatively wide. 

The horizontal part of the palatine bone forms a foiu'th to a fifth of the length of 
the palate; its palatine surface is triangular, the ai^ex l^eing anterior; its nasal 
surface is deeply grooved antl smooth. A pterygoid process (Processus pyramidalis 
of man) projects backward and downward, and its thick rounded end is received 
between the pterygoid jirocess of the sphenoiil antl the pterygoid bone. The 
perpendicular part is largely overlapped laterally by the maxilla and concurs in 




Fig. ISO. — Sagittal Section of Skull of Pig, without Mandible, 
A, A\ Basilar and squamous parts of occipital bone; S, body, 5', temporal wing, B", orbital wing, of sphenoid 
bone; C, parietal bone; /), D', internal and external plates of frontal bone; E^ E', cribriform and perpendicular plates 
of ethmoid bone; F, pterygoid bone; G, G', perpendicular and horizontal parts of palatine bone; H, palatine process of 
maxilla; 7, vomer; J, nasal bone; K, body of preniaxilla; L, dorsal turbinate bone; M, ventral turbinate bone; 
/, //, ///, fossae cranii; 1, hypoglossal foramen; 2, foramen lacerum posterius; 3, meatus acusticus internus; 4, fora- 
men lacerum anterius; 5, hypophyseal or pituitary fossa; 6, foramen orbito-rotundum; 7, lateral crest between cerebral 
and cerebellar parts of cranial cavity; S, optic foramen; 9, ethmoidal foramen; 10, frontal sinus; 11, meatus naso- 
pharyngeus; 12, 13, 14, dorsal, naiddle, and ventral nasal meatuses; 15, incisor teeth; 16, canine tooth; 17, premolar 
teeth; IS, molar teeth; 19, paramastoid process; 20, bulla ossea. 



forming part of the palatine canal. The two plates separate dorsally and inclose 
an air-cavity which opens into an ethmoidal meatus. The inner plate curves 
inward and unites with the vomer and ethmoid to form a horizontal plate, the 
lamina transversalis, which divides the posterior part of the nasal cavitj^ into a 
dorsal olfactory part and a ventral respiratory part. 

The pterygoid bone is nearly vertical in direction, and is narrow in its middle, 
wide at each (>nd. The lateral surface is free below and forms the medial wall of 
the pterygoid fossa. The ventral end is notched and forms a distinct hamulus. 

The nasal bone is very long and its width is almost uniform, except at the 
anterior end, which is pointed and reaches almost as far forward as the preniaxilla. 
The facial surface is flattened from side to side. In profile it is nearly straight in 
some suljjects, variably concave in others. The lateral border is free to a small 
extent in front only; otherwise it is firmly connected with the premaxilla and 



172 



SKELETON OF THE PIG 



maxilla. In the adult the frontal sinus extends into the posterior part of 
the bone. 

The lacrimal bone is verj' sharply bent. Its facial surface presents a deep 
depression, surmounted by a ridge or tubercle. On or close to the orbital margin 
are two lacrimal foramina which leail to the lacrimal canals. The orbital surface 
presents a fossa in which the inferior oblique muscle of the eyeball arises, and its 
lower part bears a crest, which is crossed obliquely by a vascular furrow. The 
dorsal border articulates with the frontal only. The bone concurs in the formation 
of the maxillary sinus. 

The malar bone is strongly compressed from side to side. Its facial surface 

is srnall and presents a fossa which is con- 
tinuous ^vith the depressions of the maxilla 
and lacrimal. The orbital surface is still 
smaller and is smooth and deeply grooved. 
The zygomatic process is very extensive, 
especially in the vertical direction. Its 
lateral surface is convex and free, and 
bears a rough eminence in its middle. Its 
medial surface is concave; it is over- 
lapped in front by the maxilla, and in the 
rcmaintler of its extent is free and smooth. 
The dorsal border is thick antl rounded in 
front, where it forms the lower part of the 
orbital margin; behind this it forms an 
extensive notch which receives the zygo- 
matic process of the temporal. (It might 
be regarded as dividing into frontal and 
temporal branches.) The ventral border 
is convex and becomes thinner behind. 

The turbinate bones resemble those 
of the ox. The dorsal turbinate is, how- 
ever, relatively longer, less fragile, and 
more firmly attached to the nasal bone. 
There is no middle turbinate. 

The vomer is very long. The anter- 
ior extremity reaches to the body of the 
premaxilla or very close to it. The ven- 
tral border is received into a groove 
formed by the nasal crest of the maxilliB 
and palatine bones and in front by the 
palatine processes of the premaxillse. The 
posterior border is concave, thin, and 
sharp. 

The OS rostri (or prenasal bone) is 
situated in the snt)ut between the nostrils. 
It has the form of a short, three-sided prism. The dorsal surface is convex and is 
notched at each end. The lateral surfaces are concave, smooth, and converge 
below, forming a grooved ventral border. The posterior surface is triangular, 
notched centrally, and rough laterally. The anterior surface is deeply pitted and 
is surrounded by an irregular sharp border. 

The mandible is very strong, and differs very much from that of the horse or 
ox. The body narrows decidedly in front; the lingual surface is deeply concave; 
the mental surface is strongly convex, slopes downward and backward, and forms 
a distinct prominence (Tuber mentale) at the point of divergence of the rami. 




Fig. ISl. — Mandible of PiopDoRSAL View. 
A, Body: B, B', horizontal and vertical parts of 
ramus: C, condyle: -D, coronoid process; 1, 2, 3, in- 
cisor teeth; 4, canine tooth; o, 6, 7, premolar teeth 
(first absent) ; 8, 9, 10, molar teeth. 



THE SKULL AS A WHOLE 173 

Above this prominence is a pair of foramina. The alveolar border presents six 
alveoli for the incisor teeth, and a little further back two large cavities for the 
canine teeth. There are two pairs of mental foramina of consideral^le size and a 
variable number of smaller ones. The rami diverge more than in the horse or ox, 
and the upper part is somewhat incurved. The horizontal part is very thick and 
strong. Its lateral surface is stronglj' convex from above downward. The medial 
surface is prominent over the roots of the molar teeth and overhangs the concave 
lower part. The alveolar border is thin in front and widens behind; it does not 
follow the axis of the ramus, but runs nearly straight and produces the marked over- 
hang noted above. There are seven alveoli for the lower cheek teeth, which in- 
crease in size from before backward. The first is small, not always present in the 
adult, and is separated by short spaces from the second and the canine alveolus. 
The vertical part is relatively ■wide above. The condyle is convex in both direc- 
tions, wide in front, narrow and declivitous behind. The ver.y small and thin- 
edged coronoid process is not quite so high as the condyle, from which it is separated 
by a very wide notch. The mandibular foramen is large. The two halves of the 
bone unite soon after birth in the improved breeds. 

The body of the hyoid bone is broatl from before l^ackward, short trans versel.y, 
and bears on its ventral aspect a very short pointetl lingual process. The thjToid 
cornua are wide and curved, concave and grooved dorsallj*; their ends are attached 
to the thyroid cartilage of the larynx b.v rather long bars of cartilage. The small 
cornua are short, witle, and flattened dorso-ventrally; they are attached to short 
bars which project from the junction of the bodj' and thyroid cornua. The middle 
cornu is a little longer than the small cornu, but is relativelj' slender; it is largelj' 
cartilaginous in the young subject and does not ossify at either end. The great 
cornu is a very slender rod, slightly enlarged at either end; the dorsal ext remit j' is 
attached to the hyoid process of the temporal bj' a rather long and wide bar of 
cartilage. 

THE SKULL AS A WHOLE 

The length antl the profile vary greatly in tlifferent subjects. Primitively 
the skull is long — especially in its facial part — and the frontal profile is almost 
straight. The condition is very pronounced in wild or semi-feral pigs, and exists 
also — though in less degree — in the improved breeds during extreme youth. Most 
of the latter are decidedly brachycephalic when fully developed; the face is 
"dished" in a pronounced fashion. The frontal region slopes sharply upward, 
and the nasal region is shortened, and in some specimens even distinctly concave 
in profile. The supraorbital foramina are about midway between the orbital mar- 
gin and the frontal suture. The supraorbital grooves extend forward from the 
foramina to the nasal region and turn ventro-laterally toward the infraorbital 
foramina over the ridges which separate the nasal and lateral regions. 

The lateral surface is triangular when the mandible is included. The tem- 
poral fossa is entirely lateral and its long axis is almost vertical. It is bounded 
above by the nuchal crest, liehind b.v the temporal crest, in front by the parietal 
crest, and is marked off from the orbital cavity by the supraorbital process and a 
curved crest which extends from it to the root of the pter.ygoid process. The 
zygomatic arch is strong, high, and flattened from side to side. Its root is notched 
dorsally and bears a projection ventrally. It curves sharply upward behind and 
forms a pointed recurved projection above and in front of the external acoustic 
meatus. The orbit is small. Its margin is deficient behind in the dry skull, thick 
and rounded in front and below. The cavity is limited below by a ridge on the 
frontal and lacrimal bones, and is separated by a crest from the temporal fossa. 
The medial wall is perforated above by -the orbital opening of the supraorbital 
canal, and below by the optic and ethmoidal foramina; on its antero-inferior part 



174 



SKELETON OF THE PIG 



is the fossa in which the inferior obhque muscle of the eye takes origin. Two lac- 
rimal foramina are found on or close to the anterior margin. The pterygo-palatine 
fossa is well defined ; its upper part forms a deep groove which leads from the fora- 
men orbito-rotundum to the very large maxillary foramen. The preorbital region 
is deeply grooved in its length and is clearly marked off by a ridge from the nasal 
and frontal regions. The facial crest is short, usually thin-edged, and lies above the 
fifth and sixth cheek teeth. A little (ca. 2 cm.) in front of it is the infraorbital fora- 



Nuchal crest 




Fig. 1S2, — SsnLL of Pig; Posterior Vii 
1, 2, 3, Squamoua, lateral, and basilar parts of occipital bone; 4, foramen magnum; 5, occipital condyle; 6, para- 
mastoid process; 7, squamous temporal bone; 8, meatus acusticus externus; 9, temporal condyle; 10, zygomatic 
process of malar bone; 11, bulla ossea; 12, 12', perpendicular and horizontal parts of palatine bone; 13, 13', choanae or 
posterior nares; 14, vomer; 15, pterygoid process of sphenoid bone; 16, pterygoid process of palatine bone; 17, con- 
dyle of mandible; 18, mandibular foramen; 19, body of mandible. 



men. There is a ridged prominence over the canine alveolus. In some skulls the 
anterior part of the upper jaw is inclined upward. 

The most striking features of the basal surface are as follows: The basioc- 
cipital is wide and flattened; it bears a median crest and two lateral tubercles. 
The paramastoid process is extremely long, less flattened than in the horse and ox, 
and nearly vertical. At the medial side of its root is the hypoglossal foramen, 
and in front of it are the stylo-mastoid foramen and a deep cavity in which the 
hyoid process is concealed. The bulla ossea is long, compressed laterally, and bears 
a sharp, short, muscular process. The posterior nares are small and are wider be- 
low than above. On either side of them is the tuberosity of the palate bone, and 



THE SKULL AS A WHOLE 175 

above this is the pterygoid fossa. The palate constitutes about two-thirds of the 
entire length of the skull, and is relatively narrow. It is widest between the canines 
and premolars and narrow at each end. It is marked by a crest medially and by 
the palatine foramen and groove laterally. The anterior part bears transverse 
ridges. It is moderately arched from side to side. In some specimens it is nearly 
straight or slightly concave in its length; in others it curves upward to a variable 
degree in front. The posterior end always slopes upward more or less. 

The nuchal surface is remarkable for its height and the breadth of the nuchal 
crest. The central part above the foramen magnum is smooth and concave from 
side to sitle, and is bounded laterally by ridges, which converge ventrally and end 
on two tubercles at the upper margin of the foramen magnum. The surface is 
separated from the temporal fossse by the temporal crests, which curve downward 
and outward and blend with the external acoustic meatus. The mastoid process 
has the form of a plate which overlaps the root of the paramastoid process and bears 
a crest on its anterior part. 

The cranial cavity is small, in spite of the great size of the cranium; the 
discrepancy is due to the enormous development of the frontal sinuses in the atlult. 
It is relatiyely longer, but much lower than that of the ox. Its width is greatly 
diminished between the orliits. The olfactory fossas are extensive and verj^ ob- 
lique. The floor resembles that of the ox, but the foramen ovale is absent, the 
dorsum sellse is more developed, and the foramen lacerum is like that of the horse. 
Two oblique lateral crests clearly mark the limit between the cereliral and cerel)ellar 
compartments. The internal occipital protuberance and the temporal canal are 
aljsent. 

The nasal cavity is very long. Its posterior part is divided by the lamina 
transversalis into olfactory and respirator}' parts. The olfactory part or funrlus is 
dorsal, and contains the ethmoturbinates and ethmoidal meatuses. The ventral 
part is continuous with the ventral meatus and leads to the pharyngeal orifice; 
hence it is called the naso-pharyngeal meatus. The bony roof is almost complete 
in front on account of the great length of the nasal bones. 

The frontal sinus is a vast excavation in the adult animal. It involves all of 
the roof and almost all of the sides of the cranium, and extends forward into the 
roof of the nasal cavity a variable distance — sometimes as far as a transverse plane 
through the infraorbital foramina. The septum between the right and left sinuses 
is usually deflected in an irregular manner in its middle part, but is practically 
median at either end. Each sinus is subdivided by numerous septa, some of which 
are complete. Thus the sinus is divided into compartments, each of which com- 
municates with an ethmoidal meatus. 

In the young pig the sinus is small and is confined to the anterior part of the frontal bone. 
Later it extends backward, outward, and to a kss extent forward. In the old subject it penetrates 
laterally into the supraorbital process and the root of the zygomatic process of the temporal bone, 
and behind almost down to the foramen magnum and the occipital condyles. It then consists 
of six to eight compartments usually. 

The maxillary sinus is relatively small. Its anterior end is a little less than 
an inch (ca. 2 cm.) behind the infraorbital foramen, and it extends upward into 
the lacrimal and backward into the malar bone. The infraorbital canal passes 
along its floor, and the roots of the molar teeth do not project up into it. It does 
not communicate wth the frontal and sphenoidal sinuses, but with the posterior 
part of the middle meatus nasi by means of a considerable orifice. 

The sphenoidal sinus is very large. It involves the body, pter3'goid processes, 
and temporal wings of the sphenoid bone, and extends into the squamous temporal. 
It communicates with the ventral ethmoidal meatus. 

There is a small sinus in the perpendicular part of the palatine bone which 
communicates with an ethmoidal meatus. 



176 



SKELETON' OF THE PIG 



BONES OF THE THORACIC LIMB 
The scapula is very wide, the index Ijeing about 1 : 0.7. The spine is tri- 
angular and is very wide in its middle, which curves backward over the infra- 
spinous fossa and bears a large tuberosity. Its lower part bears a small projection 
(rudimentary acromion). The anterior border is strongly convex in profile, sinuous 
when viewed from the front, and thick and rough in its middle. The posterior 
border is wide, slightly concave, and bears a rough outer lip. The vertebral border 
is convex, and the cartilage is not so extensive as in the horse and ox. The anteri- 
or angle is thin and bent medially a little. The posterior angle is thick anil is aliout 



/ 






Fig. 1^3. — Left Scapula of Pig; Lateral View. 
Anterior angle: 6, posterior angle; c, anterior border; d, posterior border; e, neck; /, glenoid 
scapula?; 1, spine; 2, tuber spinse; 3, acromion; 4, supraspinous fossa; o, infraspinou:; fossa; 6, 



a right angle. The neck is well defined. The rim of the glenoid cavity is rounded 
and not notched. The tuber scajjulee is just above the antero-medial part of 
the glenoid cavity and bears no distinct coracoid process; it unites with the rest of 
the bone at about one year. 

The humerus has an appearance in profile somewhat like'an italic / minus the 
cross-bar; this is due to the marked backward and forward inclination of the prox- 
imal and distal ends respectively. The shaft is decidedly compressed from side to 
side. The medial surface is extensive and flattened; it is separated from the 
anterior surface by a distinct border, and bears no teres tubercle. The nmsculo- 
spiral groove is shallow. The deltoid tuberosity is small, and there is a larger 
rounded eminence midway between it and the lateral tuberositv. The nutrient 



BONES OF THE THORACIC LIMB 177 

foramen is on the posterior surface Ijelovv its middle. The head is more strongly 
curved and the neck better marked than in the horse or ox. The lateral tuber- 
osity is very large and extends upon the front of the extremity. It is divided into 
two high prominences by a wide deep groove. There is a third eminence below 
and laterally for the attachment of the supraspinatus muscle. The intertuberal or 
bicipital groove is at the front of the nieilial side; it is undivided and is almost con- 
verted into a canal. The lateral groove on the distal articular surface is so shallow 
as to give the appearance of two condyles of similar size. The olecranon fossa is 
very deep, and the plate of bone which separates it from the coronoid fossa is thin 
and sometimes ]>erforated. The proximal end unites with the shaft at three and a 
half years, the distal at one year. 




!7 

Fin. IS4.— Left Scapula of Pig; Medial View. 

a, Anterior angle; b, posterior angle; r, anterior border; d, posterior border; r, neclc; /, vascular groove; ff, glenoid 

cavitj-; h, tuber scapula'; 1, subscapular fossa; 2, serratus area; 3, cartilage. 

The radius is short and narrow, but thick. The shaft increases in size distally. 
The greater part of the volar surface is in apposition with the ulna; this part is 
marked by a vascular furrow which runs distally from the proximal interosseous 
space, and has the nutrient foramen at its proximal end. The radial tuberosity is 
represented by a rough area. The distal end is relatively large. Its carpal sur- 
face consists of concavo-convex facets for the radial and intermediate carpal bones. 
There is a wide shallow groove on the middle of the front. The proximal end fuses 
with the shaft at one year, the distal at three and a half years. 

The ulna is massive. It is much longer and considerably heavier than the 
radius. The shaft is curved. The dorsal surface is convex and most of it is rough 
and attached to the radius by the interosseous ligament. There is a smooth area 
on the upper third, which concurs with the ratlius in forming the proximal inter- 



178 



SKELETON OF THE PIG 




Coronoid fossa 

Medial 
condyle 

Lateral ._,., 
condyle vl^'^^kJ 

Lateral 
epicondyle 
Fig. 185. — Left Humerus of Pig; La 



Intertuberal groove 
Lateral 
tuberosity 
Head 




Medial 
condyle 



Medial Lateral 
epicondyle condyle 
Fig, 186. — Left Hu.merus of Pig; Medial View. 




Shaft of ulna 



< 'iirpfil surface 
of radius 
Fig. 1S7. — Left Radius and Ulna of Pig; Lateral 
View. 




Distal end 
of radius 
Fig. ISS. — Left Radius and Ulna of Pig; Medial 
View. 



BONES OF THE THORACIC LIMB 



179 



osseous space, and is marked in its upper part by the nutrient foramen. From this 
space a vascular furrow descends to the distal part of the shaft, where there is often 
a distal interosseous space for the passage of vessels. The medial surface is exten- 
sive, concave, and smooth. The lateral surface is slightly convex, and its proximal 
part is marked by an oblique rough line or ridge. The proximal extremity is 
large and is bent medially somewhat; its length is more than one-third of that of 
the entire bone. The distal extremity is relatively small; it articulates with the 
ulnar and accessory carpal bones, and is notched in front to accommodate the ridge 




u 


U 


C.u. 


C. a. - 




C. u. - 


C.4 


C.4- 



Mc.5 



Fig. 1S9. — Skeleton of Distal Part of Left Thor- 
acic Limb of Pig; Dorsal View. 
R, Distal end of radius; U, distal end (styloid proc- 
ess) of ulna; C. v., radial carpal; C. i., intermediate 
carpal; C. u., ulnar carpal; C 2, C. 5, C. 4i second, 
third, and fourth carpal bones; Mc. 2-5, metacarpal 
bones; Pk.l, Ph. 2, Ph. 3, first, second, and third pha- 



FlG. 




190. — Skeleton of Distal Part of Left 
Thoracic Limb of Pig; Volar View. 
R, Distal end of radius ; U, distal end (styloid proc- 
ess) of ulna; C. r., C. t., C. u., C. a., radial, intermedi- 
ate, ulnar, and accessory carpal bones; C 1-4, first to 
fourth carpal bones; Mc. 2-5, metacarpal bones; Ph. 1, 
Ph. 2, Ph. 3, first, second, and third phalanges; S, prox- 
imal, and S', distal sesamoid bones. 



on the radius. The bone contains a consideral^le medullary canal, and is con- 
solidated at three to three and a half years. 

The carpus comprises eight bones, four in each row. The bones of the prox- 
imal row resemble those of the ox, with the exception of the accessory, which is more 
like that of the horse, but has no lateral groove. The first carpal is small, elon- 
gated from before backward, rounded, and articulates in front with the second carpal. 
The latter is high and narrow, and articulates with the second and third metacarpal 
bones distally. The third carpal articulates with the radial and intermediate 
above, the third metacarpal bone below. The fourth is the largest bone of the row; 
it articulates with the intermediate and ulnar above, the fourth and fifth meta- 
carpals below, and bears a tuberosity on its volar aspect. 



180 



SKELETON OF THE PIG 



Four metacarpal bones are present. The first is absent, the third and fourth 
are large antl carry the chief digits, while the second and fifth are much smaller and 
bear the accessor}^ digits. Their proximal ends articulate with each other and with 
the carpus as indicated above. The distal ends fuse with the shafts at about two 
years of age. 

The third and fourth metacarpals are flattened from before backward, three-sided, and 
placed close together. The distal end of each bears a trochlea for articulation with the first 
phalanx and tlie sesamoids. The third is the wider of the two, and articulates with all of the distal 
row of tlie carpus except the first. The fourth articulates witli the fourth carpal chieflj', but has a 
small facet for the third. The second and fifth metacarpals are placed further back than the cliief 
bones. The fifth is consideral)l>- the tliickcr of the two. The proximal ends are small and articu- 
late with the corresponding carjial and mctacari^al bones. The distal end is relatively large; its 
articular surface is condyloid in front, trochlear behind. 

Each chief digit comprises three phalanges and three sesamoids. The bones 
of the chief digits resemble those of the ox in form, but there is no foramen on the 
interdigital side of the extensor process and the proximal sesamoids are narrow and 
ridged behind. The phalanges of the accessory digits (which do not reach the 
grounil ordinarily) are similar in form but much smaller. Fusion of the proximal 
ends with the shafts takes place at about two years for the first phalanges, at about 
one year for the second phalanges. 



Crest of ilium Gluteal line 



Lesser sciatic Tuber 
notch ischii 




Tuber eoxii 



Ilium (.s/,f/./7i 

Acetabulum Ischium 

Fig. 191.— Left Os Cox.e of Pig; Lateral View. 



Tuber sacrale 



Crest of ilium 



Lesser 
Tuber sciatic 
ischii notch 




Auricular 
surface 



Obturator \ lUo-peetineal 

fvrameu \ eminence 

Pubis {acetab- 
ular branch) 
Fig. 102.— Left Os Cox.e of Pig; J 



BONES OF THE PELVIC LIMB 
The OS coxae is long and narrow. The ilium and ischium are almost in line 
with each other and nearly sagittal in direction. The wing of the ilium bends out- 
ward much less than in the horse or ox. The gluteal surface is divided into two fossae 



BONES OF THE PELVIC LIMB 



181 



by a ridge, which is continuous with the superior ischiatic spine behind. The 
pelvic surface presents an extensive rough area behind, which is in apposition with 
the wing of the sacrum. The smooth iliac area is narrow, and is bounded above 
by a ridge. The crest is convex, and is thick, rough, and prominent in its middle, 
which forms the highest point of the bone. The tuber sacrale is lower than the 
crest, is directed backward, and articulates internally with the sacrum. The tuber 
coxse is lower still and is very little thickened. The ischia in the female are some- 
what divergent and flattened behind. The tubora are everted and bear three prom- 
inences. There is a crest or tuberosity on the ventral surface. The superior 
ischiatic spine is like that of the cow, but is slightly incurved and the muscular 



Trnclmnter 

niiijor Iliad 




Lateral A ; - 
epico ndyle fl^j j 



• r'rondylc 



Trochan- 
teric Trochanter 
Head fossa /major 



chlca Medial 
condyle 

Fig. 193. — Right Femur of Pig; Anterior Vii 




Lalercd ^ ' 

condyle 



Medial condyU condyloid Lateral condyle 
fossa 

Fig. 194. — Right Femur of Pig; Posterior View. 



ridges on its lateral face are more pronounced. The symphyseal part of the pubis 
is thick antl the two bones are almost in a horizontal plane. The ilio-pectineal 
eminence is prominent and the psoas tubercle is well marked. 

The acetabulum is placed a little further back than in the ox. The rim is 
thick and is cut into posteriorly by a narrow fissure, which leads into the deep fossa 
acetabuli. The three pieces of the os coxse are fused by the end of the first year, 
but the crest and the tuber ischii are partially separate till the sixth or seventh year. 
The symphysis does not usually undergo complete ankylosis. Interischial bones 
are present. 

The inlet of the pelvis is elliptical and very oblique. In a sow of full size the 
conjugate diameter measures five to six inches (12.5-15 cm.), and the transverse 



182 



SKELETON OF THE PIG 



about three and a half to four inches (ca. 8.75 to 10 cm.). In the female the floor 
is relatively wide and flattened, especially at the outlet, where the tubera are 
everted; it also has a decided ventral inclination behind. The pelvic axis is there- 
fore correspondingly oblique. The ischial arch is wide. In the boar the pubis is 
much thicker and the ischia are not everted posteriorly. The inlet is smaller; the 
conjugate diameter is about four and a half to five inches (ca. 11-12.5 cm.), and the 
transverse three to three and a half inches (ca. 7.5-8.75 cm.). The floor is concave 
from side to side and slopes decidedly less than in the sow. The superior ischiatic 
spines are more incurved, and the ischial arch is much narrower and deeper. 

The femur has a relatively wide and massive shaft, on which four surfaces 
might be recognized. The principal nutrient foramen is situated in the proximal 



Spine of tibia Tuberosity 

Lateral condyle >Ji/i«.^ Medial 

'eoxdyle 



Crest of tiliia 



Medial condyle 




Spine of tibia 

Lateral condyle 



Head of 
fibula 



Lateral 
malleolus 



Fig. 195. — Right Tibia and Fibula of Pig; Ante- 
rior View. 
Arrow indicates muscular notch of proximal end of 
tibia. 




Lateral 
malleolus 



Distal cud of tiliia 



tiGHT Tibia and Fibula of Pk 

TERioR View. 
; medial malleolus for tendon of fie 

italis longus. 



third of the anterior surface. The posterior surface is wide, and is limited laterally 
by a ridge which extends from the trochanter major to the large lateral supra- 
condyloid crest. There is no supracondyloid fossa. The head is strongly curved, 
and is marked toward the medial side by a rather large fovea for the attachment of 
the round ligament. The neck is distinct. The trochanter major, although massive, 
does not extend above the level of the head. The trochanteric ridge and fossa re- 
semble those of the ox. The third trochanter is absent. The ridges of the trochlea 
are similar and almost sagittal. The extremities unite with the shaft at about 
three and a half years. 

The shaft of the tibia is slightly curved, convex medially. The tuberosity 
is grooved in front, and a narrow sulcus separates it from the lateral condyle. 
The facet for the fibula is on the posterior border of the latter, and is bounded 



BONES OF THE PELVIC LIMB 



183 



medially by an eminence. The proximal part of the crest is very prominent and 
curves outward. The distal end resembles in general that of the ox, but is rela- 
tively narrower transversely and thicker from before backward. The proximal 
end unites with the shaft at about three and a half years, the distal at about two 
years. 

The fibula extends the entire length of the region, and is separated from the 
tibia by a wide interosseous space. The shaft is flattened from side to side; the 
proximal part is wide and deeply grooved laterally; the distal part is narrower 



Tuber call 



MLS 



ML 2 




Tuber calcis 



ML 2 




Fig. 197. — Skeleton of Right P: 



Pig; Dorsal 



T. (., Tibial tarsal; T. /., fibular tarsal; T. c, cen- 
tral tarsal; T. 3, third tarsal; T. 4, fourth tarsal; Mt. 
S-B, metatarsal bones; Ph. I, Ph. £, Ph. S, first, second, 
and third phalanges. 



Fig. 19S. — Skeleton of Right Pes of Pig; Plantar 
View. 
T.t., Tibial tarsal; T. /., fibular tarsal; T.c, cen- 
tral tarsal; T.l, T.4, first and fourth tarsal bones; 
Ml. 2-0, metatarsal bones; Ph. 1, Ph. S. Ph. 3, first, sec- 
ond, and third phalanges; .S', proximal sesamoid bones; 
distal sesamoids shown but not marked; a, tarsal 
sesamoid bone. 



and thicker. The proximal end is flattened, grooved laterally, and articulates 
medially with the lateral condyle of the tibia. The distal end forms the lateral 
malleolus. It is grooved laterally, and articulates with the tibia and tibial tarsal 
medially, with the fibular tarsal bone distally. The proximal end unites with the 
shaft at about three and a half years, the distal at about two and a half years. 

The patella is very much compressed transversely and presents three surfaces. 

The tarsus comprises seven bones. The tibial and the fibular tarsals resemble 
in general those of the ox. The axis of the tibial is, however, slightly oblique (ven- 
tro-medial), and its distal end bears a double trochlea for articulation with the cen- 



184 SKELETON OF THE DOG . 

tral and fourth tarsals. The tuber calcis is deeply grooved posteriorly. The 
central tarsal is narrow transversely and thick. Its proximal surface is deeply 
concave, and the plantar bears a large tubercle. The first tarsal is high and 
narrow; it articulates with the central and second tarsals and the second metatarsal 
bone. The second tarsal is small and somewhat prismatic; it articulates with 
the central above, the third in front, the first behind, and the second and third 
metatarsals below. The third tarsal is much larger, and is compressed from above 
downward, wide in front, narrow behind. It articulates with the central tarsal 
above, the third metatarsal below, the second tarsal medially, and the fourth tarsal 
laterally. The fourth tarsal is large. Its lateral face is crossed by an oblique 
groove for the tendon of the pcroneus longus. The medial surface articulates 
with the central and third tarsals. The proximal surface supports the tibial and 
fibular tarsal bones, and the distal surface rests on the fourth and fifth metatarsals. 
It ossifies from two centers. The summit of the tuber calcis fuses with the rest 
of the bone at two to two and a half years. 

The four metatarsal bones resemble the corresponding bones of the fore limb, 
but are somewhat longer. The proximal ends of the third and fourth each have a 
considerable plantar projection; the process on the third has a facet for articulation 
with a discoid sesamoid bone. The second and fifth are placed more toward the 
plantar aspect of the large bones than is the case in the fore limb. 

The first and second phalanges are a little longer and narrower than those of 
the fore limb. 



SKELETON OF THE DOG 
VERTEBRAL COLUMN 

The vertebral formula is C7Ti3L7S3Cy20-23. 

The cervical vertebrae are relatively longer than in the ox and the pig. The 
bodies of the typical vertebrse diminish in length from first to last and are com- 
pressed dorso-ventrally. The anterior extremity is moderately convex and the 
posterior slightly concave ; both are oblique. The median ridge antl lateral grooves 
on the dorsal surface of the body are very well marked. The second, third, and 
fourth have distinct ventral spines. The spinous process of the third has the 
form of a long low crest; in the remainder it is higher, blunt-pointed, and inclined 
forward. The transverse processes of the third, fourth, and fifth project ventrally 
and backward, and divide into two branches; of these, the anterior one is thin, 
and the posterior is thick and tuberculate at its free end. The process of the 
sixth has two parts; one of these is an extensive quadrilateral plate which is di- 
rected ventro-laterally and is ridged on its medial surface; the other part is short and 
blunt, and is directed outward and a little backward and upward. The seventh is 
readily distinguished by its shortness, the length of its spine, and the single trans- 
verse process. The posterior articular processes bear tubercles which are large on 
the third, fourth, and fifth. 

The ventral arch of the atlas is narrow from before backward, and bears a 
small tubercle posteriorly. The dorsal surface of the' dorsal arch is strongly convex 
and rough centrally. The wings are wide, flattened, and almost horizontal. The 
dorsal surface is rough. There is an alar notch (Incisura alaris) on the anterior 
border instead of the alar foramen. The foramen transversarium is present. 

The body of the axis is flattened dorso-ventrall}', especially in front. The 
dens is rounded and relatively long, reaching almost to the occipital bone; it is 
inclined upward a little. The articular surfaces which flank it are condyloid in 
form and very oblique. The ventral surface is wide, and is divided by a median 



VERTEBRAL COLUMN 



185 




Fig. 199. — Skeleton of Dog; Lateral View. 
a. Cranium; b, face; c, mandible; 1II-7H, cervical vertebrEe; ISB, last thoracic vertebra; lLe~7L, lumbar verte- 
brae; K, sacrum; S, coccygeal vertebrte; IR-ISR, ribs; R.kn., costal cartilages; St., sternum; d, scapula; d', supra- 
spinous fossa; d", infraspinous fossa; i, spine of scapula; ^.acromion; 5, tuberosity of scapula; 3', articular end of 
scapula; e, humerus; 4. head of humerus; o, lateral tuberosity of humerus; 3', deltoid ridge; 6, 6', epicondyles of 
humerus; 7, lateral condyloid crest; 7', coronoid fossa; /.radius; ;;, ulna; S, olecranon; 5, "beak" of ulna; A, carpus; 
I, metacarpus; k, proximal phalanges; I, middle phalanges; m, distal phalanges; «, sesamoid; p, ihum; 10, wing of 
ilium; 11, shaft of ilium; 12, crest of ilium; 13, tuber coxae; 14, tuber sacrale; 15, superior ischiatic spine; q, pubis; 
r, ischium; ifi, tuber ischii; 27, acetabulum; s, femur; /5, head of femur; i5, trochanter major; ^0, trochanter minor; 
21, trochanter tertius; 22, 23, condyles; 24, 25, epicondyles; 26, trochlea; t, patella; u, tibia; 27, tuberosity of tibia; 
^5, ;?5, condyles of tibia; 50, medial malleolus; v, fibula; 32, lateral malleolus; 35, head of fibula; ir, tarsus; i, meta- ■ 
tarsus; y, phalanges; 33, occipital bone; 34, paramastoid process; 35, parietal bone; 36, frontal bone; 37, lacrimal 
bone; 35, malar bone; 35, squamous temporal; 40, maxilla; ^f^'. infraorbital foramen; 4?. premaxilla; ^;3, nasal bone; 
43, external acoustic meatus; 44t canine tooth; ^J, masseteric fossa; 4^, angular process of mandible. (After Ellen- 
berger, in Leisering's Atlas.) 





Fig. 200. — Third Cervical Vertebra of Dog; Left 
Lateral View. 
1, 3, Anterior and posterior ends of body; 3, 3, 
articular processes; 4. spinous process; 5, 6, transverse 
process; 7, foramen transversarium. 



Fig. 201.— Fouhth Cervical Vertebra of Dog; 
Left Lateral View. 
1, 1', Anterior and posterior ends of body; 2, 2', 
articular processes; 3, transverse process; 4, spinous 
process. 



186 



SKELETON OF THE DOG 



crest into two fossse. The transverse processes are single, pointed, directed back- 
ward and outward, and perforated by relatively large foramina transversaria. The 

spinous process is thin and of moderate 
height, but very long; it is prolonged for- 
ward so as to overhang the dorsal arch of 
"6 the atlas, and is terminated behind by a 

tuberosity which is connected by two 
crests with the posterior articular proc- 
esses. The anterior notches are large 
and are never converted into foramina. 




Fig. 202. — Seventh Cervical ^'ERTEB^A of Dog; 
Posterior View. 
1, Body; 2, costal facet; 3, transverse process; 
4, notch; 5, 5', articular processes; 6, spinous process. 



Fig. 203. — Atlas of Dog; Dorsal View. 
1, Dorsal arch; 2, 2, posterior articular cavities; 3, 
ventral tubercle: 4, 4' intervertebral foramina; 5, 5', wings; 
6, 6', alar notches; 7, T, foramina transve 



The bodies of the thirteen thoracic vertebrae are wide and compressed dorso- 
ventrally, especially at each end of the region. Their con- 
vex anterior surfaces are depressed in the middle. The 
posterior facets for the heads of the ribs are absent on the 
last three or four. The transverse processes resemble those 
of the horse. They bear mammillary processes except at 
the anterior end of the region. The facets for the tubercles 
of the ribs are large and concave in the anterior part of the 
series, and become smaller and slightly convex further back. 




Fig. 204, — Axis of Dog; Left Lateral View. 
; 2, anterior articular process; 3, posterior end of body; 4, arch; 5, pos- 
process; 7, intervertebral foramen; 8, posterior articular 



1, Den 

terior note! 

process; 9, spinous process. 




■4- 2' 



Fig. 205. — Fourth Thoracic 
Vertebra op Dog; Left 
View. 

1, Body; 2, 2', costal facets 
of body; 3, posterior notch; 
4, 4', articular processes; 5, 
transverse process; 6, facet for 
tubercle of rib; 7, mammillary 
process; 8, spinous process. 



VERTEBRAL COLUMN 



187 



The last three have accessory processes also. The first three or four spinous proc- 
esses are about equal in length. Behind this they become gradually shorter to the 
tenth, and then remain equal. The backward slope is most marked in the ninth 
and tenth. The eleventh is practically vertical (anticlinal vertebra), and the last 
two incline slightly forward. 

The bodies of the seven lumbar vertebrae are decidedly flattened dorso-ventrally, 
and increase in width from first to last. The length increases to the sixth. The 
transverse processes are plate-like and are directed forward and dowiiward. Their 
length increases to the fifth and sixth. They form no joints with each other or 
with the sacrmn. Their extremities are enlarged, with the exception of the last. 
The accessory processes project backward over the posterior notches of the first 
five. The anterior articular processes are large, compressed laterally, and bear 
mammillary processes. The spinous processes are broad below, narrower above, 
and with the exception of the last, incline a little forward. Their height diminishes 
behind the fourth. 

The sacrum results from the earlv fusion of three vcrtebra>. It is short, 




Fm. 206. — Fifth Lumbar Vertebra of Dog; Dorsal View. 
1, Anterior end of body; 2, spinous process; 3, 3', artic- 
ular processes; 4, transverse process; 5, accessory process; 
6, groove for spinal nerve. 




Fig, 207. — Sacrum of Dog; Ventral View. 
/, //, ///, Bodies of vertebrae; 1. 2, ventral sac- 
ral foramina; 3, 4, lineae transversse; 5, anterior end 
of body of first sacral vertebra; 6, 6', anterior artic- 
ular processes: 7, 7', wings; 8, posterior end of body 
of last sacral vertebra; 9, 9', posterior articular proc- 
esses; 10, sacral canal: 11, spinous [process; 12, 
12', transverse processes ; 13, auricular surface. 



wide, and quadrangular. The spines are fused to form a median crest, which is 
notched, however, between the summits of the spines. On either side are two 
tubercles, vestiges of the fused articular processes. The pelvic surface is deeply 
concave and presents two pairs of foramina. The wings are prismatic and very 
high. Their lateral surfaces are extensive, face almost directly outward, and bear 
an auricular surface on the lower part. The anterior surface of the body of the 
first vertebra is extensive, depressed in its middle, and bears a prominent lip below. 
The anterior articular processes are large and have extensive, slightly concave 
facets which face dorso-medially. The posterior articular processes are small. 
The transverse processes of the last vertebra project backward and may articulate 
or fuse with those of the first coccj-geal. The sacral canal is strongly compressed 
dorso-ventrally. 

The coccygeal vertebrae are fully developed in the anterior part of the region. 
The arch is complete in the first six usually. The first three or four have well de- 
veloped articular processes at each end. Behind this the posterior processes 
quicldy disappear, and the anterior ones become non-articular and gradually re- 



188 SKELETON OF THE DOG . 

duced in size. The transverse processes of the first five or six are relatively large; 
behind this they quickly disappear. Hemal arches (or chevron bones) in the form 
of a V or Y occur ventrally at the intercentral junctions of the third, fourth, and 
fifth usually. They transmit the middle coccygeal artery, which passes between 
pairs of ventral tubercles further back. 

Curves. — A gentle curve, convex ventrally, is formed by the cervical and the 
anterior part of the thoracic region. The posterior thoracic and the lumbar 
vertebrae form a second curve, concave ventrally. The sacral promontory is well 
marked. The sacrum and the anterior part of the coccygeal region constitute 
a third and more pronounced curve, concave ventrally. In long-tailed dogs the 
sacro-coccygeal region is somewhat S-shaped. 

Variations. — Numerical variations are not common except in the coccygeal region. The 
number of thoracic vertebra- may be twelve or fourteen, with or without compen.satory change in 
the lumbar region. Girard recorded a case with eight lumbar and the usual number of thoracic 
vertebrte. Six lumbar with fom'teen thoracic vertebrae have been met with. The first coccygeal 
sometimes unites \vith the sacrum. 

THE RIBS 
Thirteen pairs of ribs are present, of which nine are sternal and four asternal. 
They are strongly curved, narrow, and thick. Those in the middle of the series 
are the longest. The first eight or nine increase in width in their lower part. I'he 
last rib is usually floating. The costal cartilages are long and curve ventrally and 
forward; the length and curvature of the first pair are striking special features. 



THE STERNUM 

This is long, laterality compressed, and consists of eight sternebrse, which fuse 
only in exceptional cases and in extreme old age. The first segment is the longest-; 
its anterior end is blunt-pointed and bears a short conical cartilage. It widens 
at the point of articulation of the first pair of cartilages. The last segment is 
also long, thinner than its predecessors, wide in front, and narrow behind, where it 
bears a narrow xiphoid cartilage. 

The thorax is distinctly barrel-like and is not tlecidedly compressed anteriorly 
like that of the horse and ox. The inlet is oval and is relatively wide on account 
of the marked curvature of the first pair of ribs and cartilages. 



BONES OF THE SKULL i 

CRANmM 

The occipital bone is similar in position to that of the horse. The nuchal crest 
is prominent, angular, and directed backward. Just below the crest are two rough 
imprints or tul;)ereles for muscular attachment. The surface below these is convex 
from side to side and concave dorso-ventrally. On each side, at the junction 
with the squamous temporal, is the mastoitl foramen which opens into the cranial 
cavity. The condyles are somewhat flattened and are widely separated above; 
at the medial side of each is a short condyloid canal, which opens into the temporal 
canal. The paramastoid processes are very short. The basilar part is wide and 
joins the bulla ossea on either side; its ventral surface is flattened and the tubercles 
are at the junction with the bulla. The hypoglossal foramen is small and is close 
to the foramen lacerum posterius ; the latter is bounded in front by the bulla ossea, 
behind and medially by the occipital bone. 

' In the following descriptions of the separate bones an intermediate type — e. g., a fox teirier, 
— is selected, and the most striking differences in the brachycephaUc and dohchocephalic breeds 
will be considered in the section on the skull as a whole. 



BONES OF THE SKULL — CRANIUM 



189 



The interparietal bone fuses with the occipital Ijefore birth. It bears the high 
posterior part of tlie parietal crest, and is wedged in between the two parietal bones. 
It forms the central part of the tentorium osseum, which is thin and curved, con- 
cave ventrally. Its base concurs with the occipital and parietal bones in the for- 
mation of a transverse canal which is continuous with the temporal canals. 

The parietal bone is rhomboid in outline and is strongly curved. It is exten- 
sive and forms the greater part of the roof of the cranial cavity. At the junction 
of the right and left bones there is a prominent parietal crest which is continued 
upon the frontal bones. The ventral bonier articulates with the temporal wing 
of the sphenoid by its anterior part and with the squamous temporal in the remain- 
der of its extent. The external surface enters into the formation of the temporal 




f& 'i, 3 



y 



Fig. 208. — Skull or Dog; Lateral View. 
A, Occipital bone; J5, parietal bone; C, squamous temporal bone; Z>, frontal bone; E^ lacrimal bone; F, malar 
bone; 6', perpendicular part of palatine bone; H, maxilla; /, premaxilla; J, nasal bone; K, mandible; 1, parietal 
crest: 2, occipital condyle: 3. pararaastoid process; 4, stylo-mastoid foramen; 5, bulla ossea: G, meatus acusticua 
externus; 7, external opening of temporal canal; 8, postglenoid process; 9, zygomatic process of temporal bone; 10, 
zygomatic process of malar bone; 11, supraorbital process; 12, entrance to lacrimal canal; 13, infraorbital foramen; 
14, mental foramina; 15, condyle of mandible; IG, coronoid process; 17, mandibular notch; IS, angular process; 19, 
masseteric fossa; i. i', incisor teeth c, c', canine teeth. 



fossa. The cerebral surface is marked liy digital impressions, and jj.y grooves for 
the middle meningeal artery and its branches. 

The external surface of the frontal bone is crossed by a frontal crest, which 
extends in a curve from the parietal cre.st to the supraorbital process, and separates 
the frontal and temporal parts. The frontal parts of the two bones form a central 
depression and slope downward and forward. The supraorbital process is very 
short, so that the supraorbital margin is incomplete as in the pig. The supraor- 
bital foramen is absent. In front there is a narrow pointed nasal part which fits 
in between the nasal bone and the maxilla. The orbital and temporal parts are 
relatively extensive. Two ethmoidal foramina are commonlj' present. The 
frontal sinus is confined to the frontal bone. 

The parts of the temporal bone fuse early. The zygomatic process curves 
widely outward and forward. Its anterior part is beveled ventrallj^ and articulates 



190 



SKELETON OF THE DOG 



extensively with the corresponding process of tlie malar. The articular surface 
for the condyle of the mandible consists of a transverse groove which is continued 
upon the front of the large postglenoid process. Behind the latter is the lower 
opening of the temporal canal. There is no condyle. The mastoid part is small, 
but bears a distinct mastoid process. The external acoustic meatus is wide and 
very short, so that one can see into the tympanum in the dry skull. The bulla ossea 
is very large and is rounded and smooth; its medial side is united to the basilar 
part of the occipital bone. Above this jiuietion and roofed in by the union of the 
petrous part and the basioccipital is the petro-basilar canal (Canalis petrobasilaris) ; 
this transmits a vein from the floor of the craniiun to the foramen lacerum posterius. 
The latter opens into a narrow depression behind the Imlla ossea. It transmits the 



Interparietal bone 



Parietal crest 



Zygomatic process of 

temporal hone ~l 
Coronoid process — 

Frontal crest 
Supraorbital process 



Zygomatic process of 

malar bone 

Lacrimal bone 



I nfraorbital foramen. 

Nasal process of premaxilla 

Canine tooth 
Incisor teeth 




Parietal bone 
Squamous temporal bone 
Frontal hone 



Body of premaxilla 



Fig. 209. — Skull of Dog; Dorsal View. 



ninth, tenth, and eleventh cranial nerves. The carotid canal branches off from 
the petro-basilar, passes forward lateral to it through the medial part of the bulla 
ossea, and opens in front at the carotid foramen; it transmits the internal carotid 
artery. The Eustachian opening is immediately lateral to the carotid foramen. 
The muscular and hyoid processes are extremely rudimentary. The petrous part 
projects into the cranial cavity and forms a sharp prominent petrosal crest. The 
medial surface presents a deep floccular fossa above the internal acoustic meatus. 
The anterior surface is also free. The ant(>rior angle is perforated by a canal for 
the fifth cranial nerve (Canalis norvi trigemini). 

The body of the sphenoid bone is flattened dorso-ventrally. The hypophyseal 
fossa is shallow, but the tlorsum sellae is well developed and bears posterior clinoid 
processes. A pair of anterior clinoid processes (Processus clinoidei orales) pro- 



FACE 191 

ject back from the roots of the orbital wings. The latter are relatively small and 
are crossed laterally by a crest, which is continued forward upon the palatine bone. 
The temporal wings are extensive and articulate dorsally with the parietals. Per- 
forating the roots of the wings are the following foramina, named from before back- 
ward: The optic passes through the orbital wing. The foramen orbitale is a little 
lower and is at the junction of the wings. The foramen rotundum opens into the 
alar canal, which passes through the root of the short but wide pterygoid process. 
The foramen ovale is near the posterior border of the temporal wing. There is no 
sphenoidal sinus. 

The ethmoid bone is highly developed. The cribriform plate is extensive, 
and the olfactory fossae are very deep. The crista galli is little developed, and often 
incomplete. The perpendicular jjlate is long. The lateral masses are greatly 
developed and project into the frontal sinus. There are four large endoturbinates 




Fig. 210. — Cranial and Ohbital Regions of Skull of Dog. The Zygomatic Arch Has Been Sawn Off. 
A, Occipital bone; B, interparietal bone; C, parietal bone; D, aquamoua temporal bone; E, E' , temporal and 
orbital parts of frontal bone; F, F' , orbital and temporal wings of sphenoid bone; G, perpendicular part of palatine bone; 
//, pterygoid bone; /, lacrimal bone; y, maxilla; 1, parietal crest; 2, nuchal crest: 3. occipital condyle; 4, paramastoid 
process; 5, stylo-mastoid foramen; 6, bulla ossea; 7, meatus acusticus externus; S, articular surface for condyle of 
mandible; 9, section of root of zygomatic process of temporal bone; 10, alar canal; 11, foramen orbitale; 12, optic 
foramen; 13, ethmoidal foramen; 14, posterior palatine foramen; 15, sphenopalatine foramen; 16, entrance to lacrimal 
canal; 17, supraorbital process; IS, zygomatic process of malar bone (section); 19, maxillary foramen; 20, last molar 
tooth. 

and six ectoturbinates. The lamina lateralis is extensive and forms the medial wall 
of the maxillary sinus. Its ventral border joins the palatine process of the maxilla 
and the horizontal part of the palate bone. A shelf-like plate extends inward from 
its lower jiart and concurs with the similarly incurved part of the palatine bone in 
forming the lamina transversalis, which divides the olfactory fundus of the nasal 
cavity from the naso-pharyngeal meatus. 



Face 
The maxilla is short, but very high posteriorly. The facial crest is absent. 
The infraorbital foramen is over the alveolus for the third premolar. The frontal 
process fits into a deep notch between the nasal and orl)ital parts of the frontal 
bone, and the middle part of the posterior border lies along the orbital margin. 
There are more or less pronounced ridges, juga alveolaria, over the canine and 
molar teeth. The zygomatic process is short and thin; it is completely overlapped 
laterally by the malar, and is perforated by a number of foramina (Foramina 



192 



SKELETON OF THE DOG 



alveolaria). A maxillary tuberosity is not present in the adult, but there is a 
pointed projection, the pterygoid process, behind the last alveolus. The nasal 
surface bears a short turbinate crest on its anterior part, behind which it is deeply 
concave and forms the lateral wall of the maxillary sinus. The palatine process is 
short, wide behind, and moderately arched from side to siile. The anterior palatine 



Foramen Foramen. Occipital 
hijpoglossi magnum condyle 



Foramen lacerum poslerius -.^ ^^ 
Stylo-mastoid foramen—,^^ 
Meatus acusticus e.rfer 




Molar teeth 



Premolar teeth'- 



Canine tooth 




tic praci ss of malar 



Palatine process of maxiWi 



Prcmaxilla 



Incisor teeth 



Vl: 



WiTHOtTT Ma 



Fig. 211. — Skull of Dog; Vent 
A, Basilar part of occipital bone; B, body ol sphenoid bono; C, vomer; D, D', perpendicular and horizontal parts 
of palatine bone; E, pterygoid bone; 1, Eustachian opening; 2, external carotid foramen; 3, foramen ovale; 4, 5, 
posterior and anterior openings of alar canal; 6, foramen orbitale; 7, postglenoid process; S, articular groove of temporal 
bone; 0, supraorbital process; 10, meatus naso-pharyngeus; 11, anterior palatine foramen; 12, palatine groove; 13, 
palatine fissure; 14, foramen incisivuni. 



foramen is situated at or close to the transverse palatine suture and about midway 
between the median suture and the alveolar border. The palatine groove is dis- 
tinct. The large alveolus for the canine tooth is completed bj^ the premaxilla. 
The small alveolus for the first premolar is separated from the preceding one by a 
small interval. The next two consist of anterior and posterior parts for the roots 
of the teeth. The fourth and fifth are much larger and are divided into three 



FACE 193 

parts. The last is small and consists of three divisions. The infraorbital canal is 
short. 

The body of the premaxilla is compressed dorso-ventrally, and contains three 
alveoli for the incisor teeth, which increase in size from first to third; it also com- 
pletes the medial wall of the large alveolus for the canine tooth. The foramen 
incisivum is very small except in large skulls. The interalveolar border is wide 
and very short. The nasal process is wide at its origin and tapers to a sharp point 
behind; the anterior part curves upward, backward, and a little inward, and forms 
the lateral margin of the osseous nasal aperture; the posterior part extends back- 
ward a long distance between the nasal bone antl the maxilla. The palatine process 
turns upward and outward, forming with its fellow a wide groove for the septal 
cartilage; the posterior end is pointed and fits into a notch between the palatine 




Fig. 212. — Sagittal Section or Skull of Dog, Without Mandible. 
A, A', Basilar and squamous parts of occipital bone; S, B', presphenoid and postsphenoid; C, C, perpendicular 
and cribriform plates of ethmoid bone; /), parietal bone ; £?, frontal bone; F, pterygoid bone; G, 6"', vertical and hori- 
zontal parts of palatine bone; //.vomer; /.premaxilla; 7, nasal bone; A', dorsal turbinate bone; L, ventral turbinate 
bone; /, //, ///, anterior, posterior and middle fossee of cranium; 1, occipital condyle; 2, opening of condyloid canal; 
3, canal for intertransverse sinus of dura mater; 4, internal occipital protuberance; 5, internal opening of temporal 
canal; 6, mastoid foramen; 7, fJoccular fossa; 8, meatus acusticus internus: 9, canal for trigeminal nerve; 10, internal 
carotid foramen ; 11, 12, openings into petro-basilar canal; 13, foramen hypoglossi ; 14, petrosal crest; 15, dorsum sellse; 
16, h>*pophyseal or pituitary fossa; 17, optic foramen; 18, ethmoid foramen; 19, meatus naso-pharyngeus; 20,21,22, 
dorsal, middle, and ventral meatus nasi; 23, incisor teeth; 24, canine tooth; 25, premolar teeth; 26, molar teeth; 27, 
septum between frontal : 



processes of the maxillae, and supports the end of the vomer. The palatine fissure 
is short but wide. 

The horizontal part of the palatine bone is extensive, forming about one-third 
of the hard palate. It presents a variable number of accessory palatine foramina. 
There is usually a pointed posterior nasal spine (Spina nasalis aboralis) at the end 
of the median suture. The palatine canal is sometimes formed entirely in this bone. 
The perpendicular part is even more extensive. Its lateral surface is chiefly free 
and forms most of the medial wall of the large pterygo-palatine fossa. The max- 
illary foramen is situated in a deep recess between this bone and the zygomatic 
process of the maxilla. Just above it there is commonly another foramen which 
opens into the nasal cavity. The posterior palatine and sphenopalatine foramina 
are situated further back and a little lower ; the former is ventral to the latter. A 
horizontal plate extends from the nasal surface, meets that of the opposite bone, and 
completes the lamina transversalis spoken of in the description of the ethmoid bone. 
There is no palatine sinus. 

The pterygoid bones are very wide and short. They form a considerable part 
13 



194 



SKELETON OF THE DOG 



of the lateral boundaries of the posterior nares. The lower and posterior borders 
are free and at their angle of junction there is a variable hamulus. 

The nasal bones are (in most breeds) long and wider in front than behind. 
The facial surface is variably concave in its length and is inclined toward the 
median suture so as to form a central groove. The medial borders turn downward 
and form an internal nasal crest which becomes very prominent behind. The pos- 
terior parts fit into a notch formed by the frontal bones. The anterior ends form 
an almost semicircular nasal notch. 

The lacrimal bone is ver}^ small. The facial part extends very little or not 
at all beyonil the orbital margin. The orbital surface is small and triangular, 
and presents the entrance to the lacrimal canal. 

The large zygomatic process constitutes the bulk of the malar bone. It is 
very long and is strongly curved. The dorsal border is convex, free in front, where 
it forms part of the orbital margin, beveled behind for articulation with the similar 
process of the temporal bone. Between these it bears an eminence, the processus 
frontalis, to which the orbital ligament is attached. The body of the bone may l)e 
considered to consist of a lacrimal process directed dorsally and fitting in between 



Incisor Carmie 
teeth tooth 



Symphyseal 
surface 




Angular 
jvocess 



Fig. 213.— R 



the lacrimal anil maxilla, and a maxillary process directed ventrally. The facial 
surface is convex. 

The dorsal turbinate bone is in its anterior part a simple plate, attached by 
one edge to the nasal bone; it curves ventro-medially, and its free border is thick- 
ened and everted. The posterior part is wider and resembles the ethmoturbinates, 
with whicli it is connected. 

The ventral turbinate bone is short and very complex. It is attached to the 
nasal surface of the maxilla by a basal lamina, which divides into two secondary 
lamellfe. The latter detach numerous tertiary lamellae, which are coiled and have 
thick free edges. 

The vomer is not in contact wth the posterior part of the floor of the nasal 
cavity, and does not divide the posterior nares. The posterior end is narrow and 
deeply notched. Near the posterior nares the two plates curve outward and join 
the palatine bones and assist in forming the lamina transversalis. 

The two halves of the mandible do not fuse completely even in old age, so that 
there is a permanent symph^'sis mandibulse. The body presents six alveoli for the 
incisor teeth and two for the canines. The incisor alveoli increase in size from first 
to third. The canine alveoli extend deeply downward and backward. The rami 
diverge less than in the pig. The ventral border of the horizontal part is convex 
in its length and is thick and rounded. The alveolar border is slightly concave in 



THE SKULL AS A WHOLE 195 

its length and is a little everted, especiall}' in its middle; it presents seven alveoli 
for the lower cheek teeth, which resemble those of the upper jaw except that the 
fourth and sixth are much smaller and the fifth is like the fourth of the upper series. 
The interalveolar space is very short or even absent. There are two or three men- 
tal foramina on either side. The vertical part is relatively small. Its lateral sur- 
face presents a deep masseteric fossa (Fossa masseterica) which encroaches on the 
coronoid process and is limited by ridges in front and below. The medial surface 
is convex and is marked by the usual mandibular foramen. At about the same 
level as the latter is the rough angular process (Processus angularis), which pro- 
jects backward from the posterior liorder, and is equivalent to the angle of the 
other animals. The contlyle is placed very low — not much higher than the apex 
of the canine tooth when the bone is resting on a flat surface. It is long trans- 
versely and the medial part of the articular surface is much the wder and extends 
over the posterior surface. Its long axis is a little oblique, the medial end being 
inclined somewhat downward and forward. The coronoid process is very exten- 
sive and is bent slightly outward and backward. 

The body of the hyoid bone is a slightly curved transverse rod ; it is compressed 
from before backward, and bears no lingual process. The thyroid cornua are per- 
manently attached to the body l)y cartilage ; they diverge widely, curve inward, and 
are compressed laterally. The small cornua are short, prismatic, and strong. The 
middle cornua are commonly a little longer than the great cornua; they are com- 
pressed laterally, and are slightly enlarged at the ends, which are joined by cartilage 
to the adjacent cornua. The great cornua are bent outward and are somewhat 
twisted. 

THE SKULL AS A WHOLE 
The different breeds of dogs display great variations in the form and size of 
the skull. Those which have a long narrow skull (e. </., greyhound, collie) are 
designated doUchocephalic. Other dogs {e. g., l)ulldog, small spaniels, pugs) have 
very broad, short skulls and are termed brachycephalic. Intermediate forms 
(e. g., fox terrier, dachshund) are mesaticephalic. , 

The length is usually measured from the nuchal crest to the anterior end of the prema.xil- 
lary suture, and the breadth between the summits of the zygomatic arches. The cephalic index 
is the relation of the breadth to the length, assuming the latter equal 100; the formula is: 

j — — r = cephalic index. The index of extreme dolichocephalic breeds is about .50, 

as in the greyhound, and that of brachycephalic specimens may be as high as 90, as in the pug and 
some toy terriers. Among the inesaticephahc types are the fox terrier, with an index of about 
70, and the white Pomeranian, \vith one about 72 to 75. The cranio-facial index is the relation of 
the distance between the nuchal crest and the fronto-nasal suture to that between the latter and 
the nasal notch. It varies from 10 : S in extreme brachycephalic breeds to 10 : 7 in extreme 
dolichocephaUc subjects. 

The frontal surface shows the wide outward curve of the zygomatic arches 
and the great extent of the temporal fossae. The latter are separated bj^ the parietal 
crest, which in the larger breeds is verj' strong and prominent, and is continued by 
the diverging frontal crests to the supraorbital processes. The frontal and nasal 
regions are centrally depressed, and are more or less concave in profile. The nasal 
region is narrow and is terminated in front by a nasal notch. In the extreme 
brachycephalic breeds the differences are very striking. The cranium is strongly 
convex in both directions and is considerably longer than the face. The parietal 
crest is more or less effaced posteriorly and is formed by the interparietal only. The 
parietofrontal crests are separated by an interval behind and diverge to the supra- 
orbital processes, so that the temporal fossae are widely separated. The frontal 
region is wide, strongly convex, and has a shallow central depression. The nasal 
region is very short, relatively wide, and centrally depressed. In profile there is a 



196 



SKELETON OF THE DOG 



marked depression at the fronto-nasal junction, producing what is termed by fan- 
ciers the "stop" of the face. 

On the lateral surface the great extent of the temporal fossa is seen. The 
orbit communicates freely with the fossa, the posterior part of the orbital margin 
being absent in the dry skull. The axis of the orbital cavity forms a much smaller 
angle with the median plane than in the horse and ox. A distinct crest marks the 
limit between the orbital cavity and the extensive pterygo-palatine fossa. The 
preorbital region is somewhat triangular, concave in its length, and convex dorso- 
ventrally ; the infraorbital foramen is on its lower part above the third cheek tooth. 
In extreme brachycephalic breeds the orbit is relatively very large and the preor- 
bital region extremely short but high. In the Ijulldog the lower jaw protrudes be- 

3'ond the upper — a condition known as prog- 
nathism. The opposite condition, brachygna- 
thism, is seen in the dachshund. 

Striking features on the basal surface of 
the cranium are the width and flatness of the 
basilar part of the occipital bone, the small size 
of the paramastoid pi'ocesses, the large size and 




-Skull of DoLicHorEPHALir Dog; 
Dorsal View. 



KiG. 215,— Sku 




Dog: Dorsal Vi 



rounded shape of the liulla ossea, and the grooved form of the articular surfaces 
for the mandible. The posterior nares are long and narrow and are not divided 
by the vomer. The hard palate is usually about half the length of the skull. It 
is commonly marked by a median crest or rough hue, and on each side are the 
anterior and accessory palatine foramina and the palatine grooves. The width 
is greatest between the fourth pair of cheek teeth, and here there is in most skulls 
a pronounced depression on either side. The length, witlth, and contour vary 
greatly in different breeds. 

The angle of divergence of the rami of the mandible varies from 25 to 30 de- 
grees; it is smallest in the greyhound, largest in extreme brachycephalic t3Toes, 
e. f/., bulldog, iiug. 

The nuchal surface is somewhat triangular, with the Ijase ventral. The sum- 
mit is fonned by the nuchal crest, which projects very strongly backward in the 
large breeds. Below it there are two very distinct rough imprints for muscular 
attachment. In some skulls there is a thin median occipital crest, in others a 
rountled elevation. Laterally are the temporal crests and the mastoid processes. 



BONES OF THE THORACIC LIMB 197 

The mastoid foramen is at the junction of the occipital and temporal bones, above 
the root of the paramastoid process; it opens directly into the cranial cavity. 
The foramen magnum varies greatly in form ; most often the transverse diameter is 
the greater, but in some skulls it is equaled or exceeded by the vertical diameter. 

The cranial cavity (Fig. 212) corresponds in form and size with the cranium, 
especially' in those breeds in which the various crests are more or less effaced and the 
frontal sinuses are small. The basi-cranial axis is almost parallel with the palate, 
and the floor is flattened. The anterior fossa is narrow and is only slightly higher 
than the middle one. The ethmoidal fossiE are very deep and the crista galli is 
little developed. The hypophyseal fossa is variable in depth, and the dorsum sellffi 
is relatively high and bears clinoid processes laterally. The cerebral and cerebellar 
compartments are well marked off laterally by the petrosal crests and dorsally liy 
the tentorium osseum. The base of the latter is traversed by a canal which con- 
nects the two temporal canals. The anterior angle of the petrous temporal is 
perforated by a canal for the fifth cranial nerve. 

The nasal cavity (Fig. 212) conforms to the shape of the face. Its anterior 
aperture is large and nearly circular in most dogs. The complex ventral turbinates 
occupy the anterior part of the cavity to a large extent, except near the aperture. 
Behind the ventral turbinate is the large opening of the maxillary sinus. Behind 
this the cavity is divided by the lamina transversalis into a large upper olfactory 
region or fundus nasi and a lower naso-pharyngeal meatus. The fundus is occupied 
largely by the ethmoturbinates. The posterior nares are undivided and are in 
general long and narrow, but vary with the shape of the skull. 

The frontal sinus is of considerable size in the large breeds, but is confined to 
the frontal bone. It is usually divided into a small anterior and a much larger 
posterior compartment, each of which opens into the dorsal ethmoidal meatus. 
The sinus is very small in extreme brachycephalic types. 

The maxillary sinus is small, and is in such free communication \\ith the nasal 
cavity as to make it rather a recess than a true sinus. It is bounded medially by 
the lamina lateralis of the ethmoid, and its lateral wall is crossed oblicjuely bj' the 
naso-lacrimal canal. The roots of the molar teeth do not project up into it. 



BONES OF THE THORACIC LIMB 

The clavicle is a small, thin, irregularly triangular bony or cartilaginous plate. 
It is embedded in the brachiocephalicus nmscle in front of the shoulder-joint and 
forms no articulation ^vith the rest of the skeleton. (It is nearly an inch long in 
a large cat and is a slender curved rod.) 

The scapula is relatively long and narrow. The spine increases gradually 
in height from above downward and divides the lateral surface into two nearly 
equal fossse. Its free edge is thick and rough above, and at the lower part is thin 
and bent backward. The acromion is short and blunt and is opposite the rim of 
the glenoid cavity. The subscapular fossa is very shallow and is marked by rough 
lines (Linese musculares). The rough area above it for the attachment of the ser- 
ratus ventralis is large and quadrilateral in front, narrow and marginal behind. 
The anterior border is thin, strongly convex, and sinuous. The posterior border 
is straight and thick. The vertebral border is convex and thick and bears a band 
of cartilage. The anterior angle is rounded. The posterior angle is thick and square. 
The neck is well defined and bears a rough eminence posteriorly, from which the 
long head of the triceps arises. The glenoid cavity is continued forward upon the 
lower face of the tuber scapula, which is blunt and bears no coracoid process. The 
cervical angle is opposite the first thoracic spine; the dorsal angle lies above the ver- 
tebral end of the fourth rib, and the glenoid angle at a point just in front of the 
sternal end of the first rib in the ordinary standing position. The tuber scapulae 



198 



SKELETON OF THE DOG 



unites with the rest of the bone at six to eight months. The shoulder has a great 
range of movement on the chest wall. 

The humerus is relatively very long, rather slender, and has a slight spiral 
twist. The shaft is somewhat compressed laterally, especially in its proximal two- 
thirds; this part is curved in varying degree, convex in front. The deltoid tuber- 
osity has the form of a low ridge, and it is continued by a crest which runs up- 
ward and backward and bears a tubercle on its proximal part. Another line runs 
from it do^vn the anterior aspect and forms .the medial boundary of the very shallow 
musculo-spiral groove. The nutrient foramen is about in the middle of the posterior 
surface. A slight elevation on the proximal third of the medial surface represents 
the teres tubercle. The head is long and strongly curved from before backward. 
The neck is better marked than in the horse. The undivided lateral tuberosity is 
placed well forward and extends little above the level of the head. The medial tu- 



Cartilage 



Cartilage 




Tuber 
scapulm ^ I Clennid cnvitij 

Acromion 
Fig. 210. — Left Scapula op Dog; La 



uoer % ^ 
pulm — \_J 

Glenoid canity 



Fig. 217.— Rii 



Scapula or Dog; Medial Vie 



berosity is small. The intertubcral or bicipital groove is undivided and is displaced 
to the medial side by the extension forward of the lateral tuberosity. The distal 
end bears an oblique trochlear articular surface for articulation with the radius and 
ulna, the lateral part of which is the more extensive and is f aintlj' grooved. The epi- 
condyles are prominent. The coronoid and olecranon fossae often communicate 
through a large supratrochlear foramen. The proximal end unites with the shaft 
at about one year, the distal at six to eight months. 

The two bones of the forearm are relatively long and articulate with each other 
at each end in such a manner as to allow of slight movement. A narrow inter- 
osseous space separates their shafts. The radius is flattened from before back- 
ward and increases in size distally. The shaft forms two curves, so that it is con- 
vex dorsally and medially. The dorsal surface is convex in both directions and is 
marked in its distal half by a groove for the oblique extensor of the carpus. The 
volar surface presents the nutrient foramen in its proximal third, and bears a rough 



BONES OF THE THORACIC LIMB 



199 



line (Crista interossea) laterally for the attachment of the interosseous ligament. 
The proximal end (Capitulum radii) is relatively small and is supported by a dis- 
tinct neck (CoUum radii). It bears a concave surface (Fovea capituli) for articu- 
lation with the humerus, and a convex marginal area (Circumferentia articularis) 
behind for the ulna. The radial tuberosity is small. There is a large lateral tuber- 
osity and below this a rough eminence. The distal extremity is much wider. 
It has an extensive concave carpal articular surface. Its medial border projects 
downward, forming the styloid process of the radius. Laterally there is a concave 
facet (Incisura ulnaris radii) for articulation with the ulna. Dorsally are three 
distinct grooves for the extensor tendons. The ulna is well developed, but dimin- 




Medial I^i^'-i^beral 
tuberosity groove 



Cor out I hi fi 




Lateral epicondylc 



A'eck 
Deltoid tuberosity 



Museulo-spiral 
groove 



Lateral condyloid 
crest 

Olecranon fossa 



Medial epicomlyle 




Medial condyle 



1 



Fig. 21S. — Left Httmerus of Dog; Lateral Vu 



Fro. 219. — Left Humerus of Dog; Medial View, 

1, .\ttachrQent of medial ligament of elbow joint; 2, 

attachment of flexor muscles to medial epicondyle. 



ishes in size distally. It crosses the volar surface of the ratlins medio-laterall}\ 
The shaft is large and three-sided in its proximal two-thirds, smaller and more 
rounded below. Its dorsal surface is in general rough. The nutrient foramen is 
near the proximal end. A vascular groove descends from it and indicates the course 
of the interosseous artery. The proximal end is relatively short. It is concave 
and smooth medially, convex and rough laterally. The olecranon is grooved and 
bears three prominences, of which the posterior one is large and rounded. The 
semilunar notch is wide below and completes the surface for articulation with the 
trochlea of the humerus. Below it is a concave surface (Incisura radialis), which 
articulates with the back of the head of the radius, and below this is a fossa, which 
receives a tuberosity of the radius. The distal end (Capitulum ulnae) is small and 



200 



SKELETON OF THE DOG 



Processus anconmus 



Semilunar notch 
Fovea capiluli 



Shaft of ulna 



is produced to a blunt point (Processus styloideus ulnae). It articulates with the 
ulnar carpal distally, and has a convex facet on its dorso-medial aspect for the radius. 
The proximal end of the radius unites with the shaft at six to eight months, the 
distal at about one and a half years of age. The olecranon and the distal end of the 
ulna fuse mth the rest of the bone at about fifteen months. 

The carpus comprises seven bones — three in the proximal row and four in the 
distal. The numerical reduction in the proximal row is apparently due to the 
fusion of the radial and intermediate, constituting a large bone (radio-intermediate) 

which articulates with almost all of the 
Olecranon distal Surface of the radius and with the 

bones of the distal row. It projects promi- 
nently on the volar surface of the carpus. 
The ulnar carpal is long; it articulates with 
the radius and ulna al:)ove and the acces- 
sory behind; below it rests on the fourth 
carpal and is prolonged downward to ar- 
ticulate with the fifth metacarpal also. 
The accessory is cylindrical, constricted 
in its middle and enlarged at each end; the 
anterior extremity articulates with the 
ulna and ulnar carpal bone. The first car- 
pal is the smallest bone of the lower row; 
it articulates with the second carpal latei-- 
ally and the first metacarpal distall}^ The 
second carpal is wedge-shaped, the base be- 
ing posterior; its proximal surface is con- 
vex, and its distal is concave and rests on 
the second metacarpal. The third carpal 
is somewhat like the second ; its distal sur- 
face is concave and articulates chiefly with 
the third metacarpal. The fourth carpal 
is the largest of the row; it articulates with 
the fourth and fifth metacarpals. Two 
small bones or cartilages may be found on 
the volar surface at the junction of the two 
rows, and a third small bone articulates 
with the medial side of the radio-inter- 
mediate.' 

Five metacarpal bones are present. 
The first is much the shortest; the third 
and fourth are the longest, and are about 
one-fifth longer than the second and fifth. 
The fifth is the widest at the proximal end 
and is slightly shorter than the second. 
They are close together above, but diverge 
somewhat distally; the first is separated 
from the second by a consideralile interosseous space. They are so arranged as to 
form a convex dorsal surface and a concave volar surface, which corresponds to 
the hollow of the palm of the hand in man. Each consists of a shaft and two ex- 
tremities. The shaft is compressed from before backward. In the third and fourth 
it is almost four-sided, in the second and fifth three-sided, in the first rounded. 
The proximal ends (Bases) articulate with each other and with the corresponding 

' The third bone was termed the phacoid in the cat by Strauss-Dvirckeim, and is regarded 
by some authors as the vestige of an additional digit, the prepollex. 




Styloid process 
of ulna 



Fio. 220. — Left Radius and Ulna of Doa; Medial 
View. 
a, Rough area for attachment of bleeps brachii 
and brachialis muscles; b, groove for tendon of exten- 
Bor carpi obliquus. 



BONES OF THE THORACIC LIMB 



201 



carpal bones. The carpal articular surface formed by them is concave from side 
to side, convex from before backward. The distal ends (Capitula) have articular 
surfaces of the nature of a head, but bear a sagittal ridge on the volar aspect, ex- 
cept the first, which is grooved. Ossification is complete at five or six months of 
age. 

The five digits have three phalanges each, except the first, which has two. 
The third and fourth digits are the 
longest ; the first is very short and does 
not come in contact with the ground 
in walking. The first phalanges of the 
chief digits have four-sided shafts, 
which are slightly curved dorsally. 
The proximal end of each has a con- 
cave surface for articulation with the 
metacarpal bone and is deeply notched 
behind. The distal end has a trochlea 
for articulation with the second pha- 
lanx, and depressions on each side for 
ligamentous attachment. The second 
phalanges are about two-thirds of the 
length of the first phalanges. The 
proximal articular surface consists of 
two cavities separated by a sagittal 
ridge. The distal extremity is wider 
and flatter than that of the first. The 
third phalanges correspond in general 
to the form of the claws. The base has 
an [articular surface adapted to ! the 
second phalanx and is encircled by a 
collar of bone (Crista unguicularis). 
The volar surface bears a wing or tuber- 
osity, and on each side of this is a fora- 
men. The ungual part is a curved rod 
with a blunt-pointed free end. It is 
rough and porous. Its base forms with 
the collar previously mentioned a deep 
groove, into which the proximal border 
of the claw is received. The two pha- 
langes of the first digit resemble in ar- 
rangement the first and third phalanges 
of the other digits. Ossification is 
complete at five or six months. 

Nine volar sesamoids are usually 
present. Two are found at each meta- 
carpo-phalangeal joint of the chief 
digits. They are high and narrow, 
articulate with the distal end of the 

metacarpal bone in front, and have a small facet on the base for the first phalanx. 
On this joint of the first digit there is usually a single flattened sesamoid, but ex- 
ceptionally two are present. The distal volar sesamoids remain cartilaginous. A 
nodular dorsal sesamoid occurs in the capsule of the metacarpo-phalangeal joints, 
and cartilaginous nodules are found in a similar position in connection with the 
joints between the first and second phalanges. 




Fig. 221. — Skeleton of Distal Part of Right Thoracic 
Limb of Dog; Dobsal View. 
The digits are spread. /, Distal end of interosseous 
space; R, distal end of radius; C. r.+ t., radio-intermediate 
carpal; C. u., ulnar carpal; C. a., accessory carpal (very 
small part visible) ; C. l.C. 3. C. S, C. 4. first to fourtii car- 
pal bones; Mc. I, metacarpal bone of first digit; P. 1 + i, 
fused first and second phalanges of same; P. 3, third phalanx 
of same; Mc. V, fifth metacarpal bone; P. I, P. ^, P. 3, 
phalanges of fifth digit;^^, dorsal sesamoid; C, C, volar 



202 



SKELETON OF THE DOG 



BONES OF THE PELVIC LIMB 
The ilium is nearly parallel with the median plane and its axis is only slightly 
oblique with regard to the horizontal plane. The gluteal surface is concave. The 
pelvic surface is almost flat. The auricular surface faces almost directly inward, 
and in front of it there is an extensive rough area. The ilio-pectineal line is very 
distinct and is uninterrupted. The crest is strongly convex, thick, and rough. 
The tuber sacrale is represented by a thickened part which bears two eminences, 
homologous with the posterior superior and posterior inferior iliac spines of man. 
The tuber coxje also has two prominences, which are equivalent to the two anterior 
spines present in man. The shaft is almost sagittal and is compressed laterally. 
It is smooth and rounded dorsally, and it bears a ventro-lateral crest (Linea glu- 
tse ventralis), which terminates at a tuberosity in front of the acetabulum. 

The ischium has a twisted appearance, owing to the fact that its acetabular 
part is nearly sagittal while the posterior part is almost horizontal. The two bones 




Fir.. 22J.— rii.iiiT On CoxM OF Dog: Lateral View. 
1, Gluteal surface of ilium; 2, crest of ilium; 3. tuber sacrale: 4, tuber coxse: 5, shaft of ilium; 6, nutrient fora- 
men; 7, greater sciatic notch; S, ventral gluteal line; 9, tubercle to which rectus femoris is attached; 10, ilio-pectineal 
eminence; 11, 11', acetabular and symphyseal branches of pubis; 12, articular surface of acetabulum; 12', fossa acetab- 
uli; 13, obturator foramen; 14, ischiatic spine; 15, lesser sciatic notch; 16, 16', acetabular and symphyseal branches 
of ischium: 17, tuber ischii. 



also diverge behind and the tubera are flattened and everted. The superior ischiatic 
spine is low and thick ; its posterior part is marked by transverse grooves and has a 
prominent outer lip. The greater sciatic notch is elongated and very shallow. There 
is no lesser sciatic notch. The ischial arch is relatively small and is semi-elliptical. 

The symphyseal part of the pubis is thick and fuses late with the opposite bone. 
There is no subpubic groove. 

The acetabulimi is about twice as far from the tuber coxae as from the tuber 
ischii. The fossa acetabuli is deep, and is bounded medially by a flat plate of bone; 
its floor is so thin as to be translucent. There is a small notch behind. 

The obturator foramen resembles in outline an equilateral triangle with the 
angles rounded off. 

Union of the three parts of the os coxae has usuall.y taken place at six months, 
but the epiphyses of the ilium and ischium do not fuse with the main part of these 
bones till about the end of the second year. 

The inlet of the pelvis is very oblique. It is almost circular in the female, 
but in the male it is elliptical and the conjugate diameter is the longer. The cavity 
is narrowest between the acetabula, and very wide behind. The floor is concave 
and relatively narrow in front, wide and flat behind. 



BONES OF THE PELVIC LIMB 



203 



The femur is relatively much longer than in the horse or ox. The shaft is regu- 
larly cylindrical, except near the extremities, where it is wider and compressed from 
before backward. It is strongly curved in its distal two-thirds, convex in front. 
The posterior surface is flattened transversely, narrow in the middle, and widens 
toward each end. It is bounded by two rough lines (Labium laterale, mediale) 
which diverge toward the extremities. The third trochanter and the supracondyloid 
fossa are absent. There are two supracondyloid crests, the medial one being small. 
The nutrient foramen is in the proximal third of the posterior surface. The head 
is a little more than a hemisphere and has a shallow fovea behind and lateral to its 
center. The neck is well defined. The trochanter major does not extend as high 



Crest of ilium 



Wing of ilium 



Tuber coxa; 




Shaft of ilium 

Ilio-pectineal 
eminence 



Acetabular branch of 
pubis 

Symphyseal branch of 
pubis 
Symphyseal branch of 
ischium 



Ischial arch 
Fig. 223.— Pelvic Bones of : 
1, Body of first sacral vertebra; 2, wing of sacrum; 3, sacral < 



Vascular impression 

■ Sacro-iliac articulation 

Nutrient foramen 
Ilio-pectineal line 

Tubercle 
Acetabulum 



Obturator foramen 

Acetabular branch of 
ischium 

Tuber ischii 



3; Ventral ^'IEw. 
al; 4, median crest of 



5, pelvic surface of 



as the head; a thick ridge runs from its anterior surface to the neck. The trochanter 
minor has the form of a blunt tuberosity. The trochanteric fossa is round and 
deep. The ridges of the trochlea are practically sagittal in direction and are al- 
most similar. The intercondyloid fossa is wide. Just above each condyle pos- 
teriorly there is a facet for articulation with the sesamoid bone which is developed 
in the origin of the gastrocnemius muscle. Union of shaft and extremities takes 
place at about one and a half years. 

The tibia is about the same length as the femur. The shaft forms a double 
curve; the proximal part is convex medially, the distal part laterally. The prox- 
imal third is prismatic, but is compressed laterally and is long from before backward. 
The remainder is almost regularly cylindrical. The crest is short but very prom- 



204 



SKELETON OF THE DOG 



inent. The nutrient foramen is usualh^ in the proximal third of the lateral border. 
The tuberosity is not grooved, but bears a distinct mark where the ligamentum 
patellae is attached. There is a small facet for the fibula on the postero-lateral part 
of the lateral condyle, and a small sesamoid bone in the tendon of origin of the 
popliteus is in contact with the posterior angle of the latter. The distal end is quad- 
rangular and relatively small. The articular grooves and ridge are almost sagittal. 
There is a facet laterally for articulation with the fibula. There is a vertical groove 
medially and a shallower one behind — both for tendons. The proximal end unites 
with the shaft at about eighteen months, the distal at fourteen or fifteen months. 



Head 








Trochanteric 








fossa 




I 


Head^ 

i 


wki 


- Trochanter 
major 




Neck^ 


vy 




Neck 


Trochanter - 


-SH 


^ 


Trochanter 


minor 


^^v 




minor 










Medial 
Lateral — ^^Jl^ SBF epicondyle 
epicondyle 

Trochlea 
Fig. 224. — Right Femur of Dog; .\nterior View. 



Medial _L_ S* 4— Lateral 

condyle »k '' condyle 

I,tt<ir<,„.l,,h,„l 

Fig. 225. — Right Femur of Dog; Posterior \i 
1, 2, Sesamoid bones. 



The fibula extends the entire length of the region. It is slender, somewhat 
twisted, and enlarged at either end. The proximal part of the shaft is separated 
from the tibia by a considerable interosseous space, but the distal part is flattened 
and closely applied to the tibia. The proximal extremity is flattened and articu- 
lates with the lateral condyle of the tibia. The distal end is somewhat thicker and 
forms the lateral malleolus. It articulates medially with the tibia and the tibial 
tarsal bone. Laterally it bears two tubercles. 

The patella is long and narrow. The free surface is convex in both direc- 
tions. The articular surface is convex from side to side and slightly concave from 
above downward. 



BONES OF THE PELVIC LIMB 



205 



The tarsus comprises seven bones. The tibial tarsal consists of a body, neck, 
and head, like the bone in man. The body presents a proximal trochlea for articula- 
tion with the tibia and fibula. The plantar surface has three facets for articulation 
with the fibular tarsal bone. The head is directed a little inward and articulates 
with the central. The fibular tarsal has a long anterior process or "beak," but 
the sustentaculum is short. The tuber calcis presents a sagittal groove. The 
central has a concave proximal surface adapted to the head of the tibial tarsal. 
Its distal surface articulates with the first, second, and third tarsals. It bears two 
plantar tubercles. The first tarsal is flattened and irregularly quadrangular; its 
proximal surface articulates with the central and the distal with the first metatarsal. 



Spine 



Tiihcrosili/ 
Sulcus muscu- 

laris yJ^ 'T*^ ^j^ Medial con- 
dyle 



Head of fibula 



Interosseous 
space 
Shaft of fibula ' 



Crest of tibia 




Head of fibula 



Shaft of tibia — 



■I — Interosseous space 



Fibula of Dog; Ante- 




Lateral malleolus 



The second tarsal is the smallest and is wedge-shaped; it articulates distally with 
the second metatarsal bone. The third tarsal is also wedge-shaped, the base being 
in front; it articulates with the third metatarsal distally. The fourth tarsal is 
remarkably high, and resembles a quadrangular prism; its proximal surface 
articulates with the fibular tarsal, its distal with the fourth and fifth metatarsal, 
and the medial with the central and third tarsal bones. A groove for the tendon of 
the peroneus longus crosses its lateral and plantar surface, and above it are one or 
two tubercles. The tuber calcis fuses with the body of the bone at fourteen or 
fifteen months. 

Five metatarsal bones are present. The first is commonly very small and has 
the form of a blunt cone, somewhat compressed laterally. It articulates with the 



206 



THE ARTICULATIONS OR JOINTS 



first tarsal and furnishes insertion to the tibialis anterior muscle. In some cases 
it fuses with the first tarsal; when the first digit is well developed, its metatarsal 
may resemble the others (except in size) or be reduced in its proximal part to a 
fibrous band. The other metatarsals are a little longer than the corresponding 
metacarpals. Their proximal ends are elongated from before backward and have 
plantar projections, which in the case of the third and fourth usually have facets 




Fig. 228. — Skeleton op Distal Part of Left Pelvic Limb of Dog; Dorsal View. 
L, Lateral malleolus (distal end of fibula); T. t., tibial tarsal bone; T. /., fibular tarsal bone; T. c, central tarsal 
bone; T. 3, T. 3, T. 4, second, third, and fourth tarsal bones: P. 1 + S, fused first and second phalanges, and P. S, third 
phalanx, of first digit; Mc. 5, fifth metacarpal bone; P. 1, P. 2, P. 3, phalanges of fifth digit; S, dorsal sesamoid. 



for articulation with two small rounded sesamoid bones. In other respects they 
resemble the metacarpals. 

The first digit is often absent. When present, its development varies and it 
contains one or two phalanges. In other cases — especially in very large dogs — 
a sixth digit is present; it does not articulate with the metatarsus, but is attached 
by fibrous tissue. The phalanges of the other digits resemble those of the tho- 
racic limb. 

Ossification of the metatarsal bones and phalanges is comjjlete at five or six 
months. 



ARTHROLOGY 

THE ARTICULATIONS OR JQINTS 

An articulation or joint is foruiecl by tiie union of two or more bones or carti- 
lages by other tissue. Bone is tlie fundamental part of most joints; in some cases 
a bone and a cartilage, or two cartilages, form a joint. The uniting medium is 
chiefly fibrous tissue or cartilage, or a mixture of these. Union of parts of the 
skeleton by muscles (Synsarcosis), as in the attachment of the thoracic limb in 
the horse, will not be considered in this section. 

Joints may be classified — (a) anatomically, according to their mode of develop- 
ment, the nature of the uniting medium, and the form of the joint surfaces; (6) 
physiologically, with regard to the amount and kind of movement or the absence 
of mobilit}^ in them ; (c) by a combination of the foregoing considerations. 

The classification of joints is still in a very unsatisfactory state, and unfortunately the same 
term is used in various senses by different authors. The two main subdivisions proposed by Hep- 
burn are: (1) Those in which the uniting medium is coextensive with tlie opposed joint surfaces, 
and in which a direct union of these surfaces is thereby effected. (2) Those in which the uniting 
medium has undergone interruption in its structural continuity, and in which a cavity of greater 
or less extent is thus formed in the interior of the joint. This distinction is of considerable im- 
portance cUnically. 

Three chief subdivisions of joints are usually recognized — viz., S3marthroses, 
diarthroses, and amphiarthroses. 



SYNARTHROSES 

In this group the segments are united b>' fibrous tissue or cartilage, or a mix- 
ture of the two in such a manner as practically to preclude movement ; hence they 
are often termed fixetl or immovable joints. There is no joint cavity. Most of 
these joints are temporary, the uniting medium being invaded by the process of 
ossification, with a resulting ankylosis or synostosis. The chief classes in this 
group of joints are as follows: 

(1) Suture. — This term (Sutura) is applied to those joints in the skull in which 
the adjacent bones are closely united by fibrous tissue — the sutural ligament. In 
many cases the edges of the bones have irregular interlocking margins, forming the 
sutura serrata, e. g., the frontal suture. In others the edges are beveled and 
overlap, forming the sutura squamosa, c. g., the parieto-temporal suture. If the 
edges are plane or slightly roughened, the term sutura harmonia is applied to the 
joint, e. g., the nasal suture. 

(2) Syndesmosis. — In these the uniting medium is white fibrous or elastic 
tissue or a mixture. As examples are the union of the shafts of the metacarpal bones 
and the attachments to each other of costal cartilages. 

(3) Synchondrosis. — In these the two bones are united by cartilage, e. g., 
the joint between the basilar part of the occipital bone and the sphenoid bone. 
Very few of these joints are permanent. 

(4) Symphysis. — This term is usually limited to a few median joints which 
connect symmetrical parts of the skeleton, e. g., sjTnphysis pelvis, symphysis 
mandibulse. The uniting medium is cartilage and fibrous tissue. In some cases 
a cleft-like rudimentary joint cavity occurs. 

207 



208 



THE ARTICULATIONS 



(5) Gomphosis. — This term is sometimes applied to the implantation of the 
teeth in the alveoli. 

The gompliosis is not, properly considered, a joint at all, since the teeth arc not parts of the 
skeleton. 

DIARTHROSES 

These joints are characterized by the presence of a joint cavity and by their 
mobility. They are often called movable or true joints. A simple joint (Articu- 
latio simplex) is one formed by two articular surfaces; a composite joint (Articulatio 
composita), one formed by several articular surfaces. The following structures 
enter into their formation: 

1. The articular surfaces (Facies articulares) are in most cases smooth, and 
vary much in form. They are formed of specially dense bone, which differs his- 
tologically from ordinary compact substance. In certain cases (vide Osteology) 
the surface is interruptetl by non-articular cavities known as synovial fossae. 

2. The articular cartilages (C'artilagines articulares), u.sually hyaline in type, 
form a covering over the articular surfaces of the bones. They vary in thick- 
ness in different joints; they are thickest on those 
which are subject to the most pressure and fric- 
tion. They usually tend to accentuate the curva- 
ture of the bone, i. e., on a concave surface the 
peripheral part is the thickest, while on a con- 
vex surface the central part is the thickest. The 
articular cartilages are non-vascular, very smooth, 
and have a bluish tinge in the fresh state. They 
diminish the effects of concussion and greatly reduce 
friction. 

3. The articular or joint capsule (Capsula articu- 
laris) is, in its sunplest form, a tube, the ends of which 
are attached around the articulating surfaces. It 
consists of two layers — an external one, composed of 
fibrous tissue, and an internal one, the synovial la3'er 
or membrane. The fibrous layer (Stratum fibrosum) , 
sometimes termed the capsular ligament, is attached 
either close to the margins of the articular surfaces or 
at a variable distance from them. Its thickness varies 
greatly in different situations: in certain places it is extremely thick, and sometimes 
cartilage or bone develops in it; in other places it is practically absent, the cap- 
sule then consisting only of the synovial membrane. Tendons which pass over a 
joint msLy partially take the place of the fibrous layer; in these cases the deep face 
of the tendon is covered by the synovial layer. Parts of the capsule may undergo 
thickening and so form ligaments, which are not separable, except artificially, from 
the rest of the capsule. The synovial layer (Stratum sj^noviale) lines the joint 
cavity except where this is bounded bj- the articular cartilages; it stops normally 
at the margin of the latter. It is a thin membrane, and is richly supplied by close 
networks of vessels and nerves. It frequently forms folds (Plicfe synoviales) and 
villi (Villi synoviales), which project into the cavity of the joint. The folds com- 
monly contain pads of fat, and there are in many places masses of fat outside of the 
capsule which fill up interstices and vary in form and position in various phases of 
movement. The synovial membrane secretes a fluid, the synovia, which lubricates 
the joint; it resembles white-of-egg, but has a j^ellowish tinge.' In many places the 

'■ It is doubtful whether the synovia is a true secretion or a transudate containing products of 
friction. The view given above is that which is more commonly accepted. It contains albumen, 
mucin, and salts, and is alkaline. In it there are commonly cells derived from the synovial mem- 
brane, portions of cells, ceUs which have undergone fatty degeneration, particles of articular 
cartilage, etc. 




Fig. 229.— Diagram of Section of 

DiARTHROSIS. 

/.Z., Fibrous layer, s.L, synovial 
layer of joint capsule. The articular 
cartilages are white, bones dotted, and 
the joint cavity black in the figure. 



DIARTHROSES 209 

membrane forms extra-articular pouches, which facilitate the play of muscles and 
tendons. 

The articular or joint cavity (Cavum articulare) is enclosed by the synovial 
membrane and the articular cartilages. Normally, it is, strictly speaking, only a 
potential cavity, which contains nothing but a small amount of synovia. 

The student must guard against a false conception of the joint cavity which may result from 
dissections and diagrams in which an actual ca\'ity of considerable extent appears to exist. A 
correct idea of the intimate apposition of the parts is best obtained from the study of frozen sec- 
tions. On the other hand, it is instructive to examine joints which have been injected so as to 
distend the capsule fully. It is then seen that the cavity is often of much greater potential extent 
than one might suppose, and that the capsule is often very irregular in form, i. e., forms a variety of 
sacculations. 

The foregoing are constant and necessary features in all diarthroses. Other 
structures which enter into the formation of these joints are ligaments, articular 
discs or menisci, and marginal cartilages. 

4. Ligaments. — These (Ligamenta) are strong bands or membranes, usually 
composed of white fibrous tissue, which bind the bones together. They are pli- 
able, but practically inelastic. In a few cases, however, e. g., the ligamentum 
nuchse, thej' are composed tif elastic tissue. They may be subdivided, according 
to position, into periarticular ami intraarticular. Periarticular ligaments are fre- 
quently blended with or form part of the fibrous capsule; in other cases they are 
rjuite distinct. Those which are situated on the sides of a joint are termed col- 
lateral ligaments (Ligamenta collateralia) . Strictly speaking, intra-articular liga- 
ments, though within the fibrous capsule, are not in the joint cavity; the synovial 
membrane is reflected over them. The term seems justifiable, however, on prac- 
tical groimds. Tliose which connect directly opposed surfaces of bones are termed 
interosseous ligaments. In many places muscles, tendons, and thickenings of the 
fascia! function as ligaments and increase the security of the joint. Atmospheric 
pressure and cohesion play a considerable part in keeping the joint surfaces in appo- 
sition. 

5. Articular discs or menisci (Disci s. menisci articulares) are plates of fibro- 
cartilage or dense fibrous tissue placed between the articular cartilages, and divide 
the joint cavity partially or completely into two compartments. They render cer- 
tain surfaces congruent allow greater range or variety of movement and diminish 
concussion. 

6. A marginal cartilage (Labrum glenoidale) is a ring of fibro-cartilage which 
encircles the rim of an articular cavity. It enlarges the cavity and tends to pre- 
vent fracture of the margin. 

Vessels and Nerves. — The arteries form anastomoses around the larger joints, 
and give off brandies to the extremities of the bones and to the joint capsule. The 
synovial membrane has a close-meshed network of capillaries; the latter form loops 
around the margins of the articular cartilages, but do not usually enter them. 
Th(> veins form plexuses. The synovial membrane is also well supplied with lymph- 
vessels. Nerve-fibers are especially numerous in and around the synovial mem- 
brane antl there are special nerve-endings, e. </., Pacinian bodies and the articular 
end-bulbs described by Krause. 

Movements. — The movements of a joint are determined chiefly by the form 
and extent of the joint surfaces and the arrangement of the ligaments. They are 
usually classified as follows: 

1. Gliding. — This refers to the sliding of one practically plane surface on 
another, as in the joints between the articular processes of the cervical vertebrae. 

2. Angular Movements. — In these cases there is movement around one or 
more axes. Motion which diminishes the angle included by the segments forming 
the joint is termed flexion, while that which tends to bring the segments into line 
with each other is called extension. With reference to the joints of the distal parts 

14 



210 THE ARTICULATIONS 

of the limbs, it seems advisable to employ the terms dorsal and volar or plantar 
flexion, since these joints can be "overextended." Similarly the terms dorsal and 
ventral flexion are applied to the corresponding movements of the spinal column. 
The meaning of the term lateral flexion as applied to the vertebral column is evi- 
dent. These movements are all rotations around axes which are approximately 
either transverse or vertical. Depression, elevation, and transverse movement of 
the lower jaw fall in this category. 

3. Circumduction. — This designates movements in which the distal end of 
the limb describes a circle or a segment of one. In man such movement is easily 
performed, but in quadrupeds it is possible to a limited degree only, and is to be 
regarded usuallj' as an indication of disease. 

4. Rotation.- — As a matter of convenience, this term is reserved to indicate 
rotation of one segment around the longitudinal axis of the other segment forming 
the joint. It is seen tj'pically in the atlanto-axial joint. 

5. Adduction and abduction designate respectively movement of a limb to- 
ward and away from the medial plane, or of a digit toward and away from the 
axis of the limb. 

Classification. — This is based on the form of the joint surfaces and the move- 
ments which occur. The following chief classes may be recognized : 

1. Arthrodia, or gliding joint. In these the surfaces are practically flat, ad- 
mitting of gliding movement. Examples: carpo-raetacarpal joints; joints be- 
tween the articular processes of the cervical and thoracic vertebrae. 

2. Ginglymus, or hinge-joint. In this class the joint surfaces consist usually 
of two condyles, or of a segment of a cylinder or cone, which are received by cor- 
responding cavities. In tj^iical cases the movements are flexion and extension, 
i. e., around a single transverse axis. Examples: atlanto-occipital and elbow 
joints. 

3. Trochoid, or pivot joint. In these the movement is limited to rotation of 
one segment around the longitudinal axis of the other. Example: atlanto-axial 
joint. 

4. Enarthrosis, or ball-and-socket joint. These are formed by a surface of 
approximately spherical curvature, received into a corresponding cavity. They 
are multiaxial, and allow of the greatest variety of movement, e. g., flexion, 
extension, rotation, abduction, adduction, circumduction. Examples: hip and 
shoulder joints. ^ 

AMPHIARTHROSES 

These joints, as the name indicates, share some characters with both of the 
preceding groups. In them the segments are directly united by a plate of fibro- 
cartilage, and usually by ligaments also. The amount and kind of movement are 
determined by the shape of the joint surfaces and the amount and pliability of the 
uniting medium.^ These joints are all medial in position, and are best illustrated 
by the joints between the bodies of the vertebrae. There is usuallj' no joint cavity, 
but in certain situations a rudimentary one exists. 

' This classification makes no claims to scientific accuracy, but is simply a statement of the 
terms in general use. A grouping based on mechanical principles is desirable, but appears to be 
almost impossible on account of the great variety and irregularity of form of the articular sui'faces. 

2 The movements in some of these joints are more extensive and varied than in some diar- 
tliroses. To illustrate this we may compare the movements of the cervical or coccygeal vertebra; 
with those possible in the carpo-metacarpal or the sacro-iliac joints. 



THE ARTICULATIONS OF THE HORSE — INTERCENTHAL ARTICULATIONS 



211 



THE ARTICULATIONS OF THE HORSE 
Joints and Ligaments of the Vertebre 

The movable vertebrie form two sets of articulations, viz., those formed by the 
bodies, and those formed by the articular processes of adjacent vertebrae ; the 
former are termed intercentral, and the latter intemeural. Associated with these 
are ligaments uniting the arches and processes; some of these are special, i. e., con- 
fined to a single joint, while others are common, i. e., extend along the entire ver- 
tebral column or a considerable part of it. The joints between the atlas and axis 
and between the former and the skull require separate consideration. 




Fig. 230. — Sagittal Section of Last Two Thoracic and 
Lumbar Vertebr.e, showing Ligaments and Spinal 
(Medulla), (.\fter Schmaltz, Atlas d. Anat. d. Pferdes.) 



First 
Cord 



intercentral articulations 

These are amphiarthroses, formed by the junction of the extremities of the 
bodies of adjacent vertebrae. The articular surfaces in the cervical region consist 
of a cavity on the posterior 
end of the body of the anter- 
ior vertebra, and a correspond- 
ing convexity or head of the 
succeeding vertebra. In the 
other regions the surfaces are 
much flattened. The uniting 
media are : 

1. The intervertebral 
fibro-cartilages (Fibrocartila- 
gines intervertebrales). Each 
of these is a disc which fits into 
the space between the bodies 
of two adjacent vertebrae, to 
which it is intimately attached. 
The discs are thinnest in the 
middle of the thoracic region, 
thicker in the cervical and lum- 
bar regions, and thickest in the 

coccygeal region. Each consists of a peripheral fibrous ring (Annulus fibrosus) 
and a soft central pulpy nucleus (Nucleus pulposus) . 

The fibrous ring consists of laminae of fibrous tissue and fibro-cartilage, wliich pass obliquely 
between the two vertebra; and alternate in direction, forming an X-shaped arrangement. The 
central part of the ring is largely cartilaginous, and gradually assumes the character of the pulpy 
center. The latter is very elastic and is compressed, so that it bulges considerably from the sur- 
face of sections; it consists of white and elastic fibers, connective-tissue cells, and peculiar clear, 
transparent cells of various sizes. It is a remnant of the notochord. There are joint cavities in 
the cervical intercentral joints, and in those between the last cervical and the first thoracic, and 
between the last lumbar and the sacrum. 

2. The ventral longitudinal ligament (Lig. longitudinale ventrale)^ lies on the 
ventral surface of the bodies of the vertebrae and the intervertebral fibro-car- 
tilages, to which it is firmly attached. It begins to be distinct a little behind the 
middle of the thoracic region, and is at first a narrow, thin band. Further back 
it becomes gradually thicker and \vider, and terminates on the pelvic surface of 
the sacrum by spreading out and blending with the periosteum. It is strongest in 
the lumbar region, where the tendons of the crura of the diaphragm fuse with it. 

3. The dorsal longitudinal ligament (Lig. longitudinale dorsale)- lies on the 
floor of the vertebral canal from the axis to the sacrum. It is narrow over the mid- 

1 Also termed the inferior common ligament. 
^ Also termed the superior common ligament. 



212 



THE ARTICULATIONS OF THE HORSE 



dies of the vertebral bodies, and widens over the intervertebral fibro-cartilages, to 
which it is very firmly attached. 

This ligament is in relation with the spinal veins on either side, and ih the middle of each 
vertebra a transverse anastomotic vein passes imder the ligament. 

INTERNEURAL ARTICULATIONS 
Each typical vertebra presents two pairs of articular processes, which form 
diarthroses with the two adjacent vertebrae. The articular surfaces are extensive, 
almost flat, and oval in the cervical region, small and flat in the thoracic region. 



Funicular part 



Expansion at loiUiers 




Last cervical 
vertebra 



First thoracic '' 
vertebra 



Fig. 231. — Ligamentum Nuch.e of Mori 
1, Scapula: 1' , cartilage of scapula; 4> lamellar part of ligamentuin nuchEe; 
Baum, Anat. fiir Kiinstler.) 



wing of atlas, (.^fter EUenberger- 



while in the lumbar region the anteripr ones are concave and the posterior convex. 
The joint capsule is strong and ample in the cervical region, in conformity with the 
large size antl greater mobility of these joints in the neck. In the thoracic and 
lumbar regions the capsule is small and close. These joints are arthrodia in the 
neck and back, trochoid in the lumbar region. 

Associated with these joints are the ligamenta flava, which connect the arches 
of adjacent verteljrse. They are membranous and consist largely of elastic tissue. 

The supraspinous ligament (Lig. supraspinale) extends medially from the 
occipital lione to the sacrum. Behind the withers it consists of a strong cord of 
white fibrous tissue, attached to the summits of the vertebral spines. In the neck 



SACHAL AND COCCYGEAL ARTICULATIONS 213 

and withers it is remarkably modified to form the hgamentum nuchse, whifli re- 
quires more extended notice. 

Tlie ligamentum nuchae is a powerful elastic apparatus, the principal function 
of which is to assist the extensor muscles of the head and neck. It extends from 
the occipital bone to the withers, where it is directly continuous with the lumbo- 
dorsal part of the supraspinous ligament. It consists of two parts — funicular and 
lamellar. The funicular part (Pars occipitalis) arises from the external occipital 
protuberance and is inserted into the summits of the vertebral spines at the withers. 
Two bursas are usually found under it in the adult. The atlantal bursa lies be- 
tween the ligament and the dorsal arch of the atlas. The supraspinous bursa is 
usually over the third and fourth thoracic spines, but maj' be over the second or 
extend to the fifth. ^ Another bursa may be present at the spine of the axis; this is 
l)etwecn the funicular part and the large digitation attached to the axis. In the 
neck the funicular part consists for the greater part of two bands closely applied and 
attached to each other. Near and at the withers it broadens greatly, forming an ex- 
pansion about five to six inches (ca. 12 to 15 cm.) in width, the lateral margins of which 
are thin and turn down over the trapezius and rhomboideus muscles. Behind the 
higher spines it l^ecomes narrower and thinner, and is continued bv the white fibrous 
lumbo-dorsal part.- A mass of fat and elastic tissue lies upon the ligament as far 
back as the withers. It varies greatly in amount in different subjects, and is most 
developed in stallions of draft breeds, in which it forms the basis of the so-called 
"crest." The lamellar part (Pars cervicalis) consists of two laminjE separated 
medially by a layer of loose connective tissue. Each lamina is formed of digitations 
which arise from the second and third thoracic spines and from the funicular part, 
are directed dowaiward and forward, and end on the spines of the cervical vertebra, 
except the first and last. The digitation which is attached to the spine of the axis 
is very thick and strong. Behind this they dmiinish in size and strength; the last 
one, which is attached to the sixth cervical vertebra, is quite thin and feeble, or may 
be absent. 

The interspinous ligaments (Ligg. interspinalia) extend between the spines 
of contiguous vertebraj. In the cervical region they are narrow elastic bands, and 
in the thoracic and lumbar regions they coiisist of white fibers directed obliquely 
downward and backward. 

The intertransverse ligaments (Ligg. intertransversaria) are membranes 
which connect adjacent transverse processes in the lumbar region. 

INTERTRANSVERSE ARTICULATIONS 
These joints (peculiar to t'([uidie) are diarthroses formed liy the transverse 
processes of the fifth and sixth lumbar vertebrae and between the latter and the alse 
of the sacrum. A similar joint between the fourth and fifth lumbar processes is 
frequently present. The articular surfaces have an elongated oval form, the 
anterior one being concave and the posterior one convex. The capsule is tight, 
and is reinforced ventrallv. 



SACRAL AND COCCYGEAL ARTICULATIONS 

In the foal the bodies of the five sacral vertebrae form joints which resemble 
somewhat those in the posterior part of the lumbar region. These joints are in- 

' In dissecting-room subjects these biirsse and the adjacent structures are coninionly the seat 
of pathological changes. They appear to be the starting-point of "poll evil" and "fistulous 
withers." Subcutaneous bursa; may be foimd over the ligament at the withers. 

- No natural line of demarcation exists between the ligamentum nuchae and the lumbo-dorsal 
part of the supraspinous ligament, since the change from the elastic to the white fibrous structure 
is gradual. 



214 



THE ARTICULATIONS OF THE HORSE 



vaded bj' the process of ossification early, so that the consolidation of the sacrum 
is usually complete, or nearly so, at three years. 

The coccygeal vertebrae are united by relatively thick intervertebral fibro-cartil- 
ages, which have the form of biconcave discs. Special ligaments are not present, but 
there is a continuous sheath of fibrous tissue. The movement in this region is exten- 
sive and varied. In old horses the first coccygeal vertebra is often fused with the 
sacrum. 

MOVEMENTS OF THE VERTEBRAL COLUMN 

The movements of the spine, exclusive of those at the atlanto-axial joint, are 
dorsal, ventral, and lateral flexion, and rotation. The range of movement at a 
single joint is small, but the sum of the movements is 
considerable. The movements are freest in the cervical 
and coccygeal regions. Rotation is extremely limited 
in the thoracic and lumbar regions. 



ATLANTO-AXIAL ARTICULATION 

This is a trochoid or pivot joint of a rather peculiar 
character. The articular .surf aces are : (1) On the lateral 
masses of the atlas, two somewhat saddle-shaped facets, 
which are separated by a wide notch above and a narrow 
one below; (2) on the axis, reciprocal saddle-shaped sur- 
faces which extend upon the dens and are confluent on 
its ventral aspect. It will be observed that the joint 
surfaces are not at all accurately adapted to each other, 
so that only limited areas are in contact at any time. 

The joint capsule is attached around the margins 
of the articular surfaces. It is loose and ample enough 
laterallj' to allow extensive movement. 

The dorsal atlanto-axial ligament (Lig. interar- 
cuale) is membranous and reinforces the capsule dor- 
sally. 

The interspinous ligament (Lig. interspinale) con- 
sists of two elastic l)an(ls which extend from the dorsal 
arch of the atlas to the spine of the axis. 

The ventral atlanto-axial ligament (Lig. dentis ex- 
ternum) arises from the ventral tubercle of the atlas and 
is attached by two branches on the ventral spine of the 
axis. 

The ligament of the dens or odontoid ligament (Lig. 
dentis internum) is short, very strong, and somewhat fan- 
shaped. It extends from the rough concave dorsal sur- 
face of the dens, widens in front, and is attached to the 
transverse rough area on the inner surface of the ventral 
arch of the atlas. 

Movements. — The atlas and the head rotate upon 
the axis ; the axis of rotation passes through the center 
of the bodj' of the axis. 




Fig. 232. — Atlaxto-occipitaland 
Atlanto-axial Joints op 
Horse; Dorsal View after 
Removal of Dorsal Arch of 
Atlas. 

a, Joint capsule of left part of 
atlanto-occipital joint; b, lateral 
ligament of same; c, c', ligament of 
the dens ; d, atlanto-axial joint cap- 
sule; e, joint capsule of articulation 
between axis and third cervical 
vertebra; /, interspinous ligament; 
i, occipital bone; 2, atlas; 3, axis; 
4, third cervical vertebra; 5, dorsal 
longitudinal ligament. (Ellenbor- 
ger-Baum, .\nat. d. Haustiere.) 



THE ATLANTO-OCCIPITAL ARTICULATION 

This joint may be classed as a ginglymus. The articular surfaces of this 
joint are: (1) On the atlas, two deep oval cavities; (2) the correspomling condyles 
of the occipital bone. 



ARTICULATIONS OF THE THORAX COSTO-VERTEBRAL ARTICULATIONS 



215 



The joint surfaces are oblique, coming very close to the median line ventrally, but separated 
by a considerable interval dorsally. A triangular rough area cuts into the medial part of each of 
the atlantal articular surfaces. 

There are two roomy joint capsules, which sometimes communicate ventralh-, 
especially in old subjects. 

The dorsal atlanto-occipital membrane (Membrana atlanto-occipitalis dorsalis) 
extends from the dorsal arch of the atlas to the dorsal margin of the foramen mag- 
num. It is blended with the capsules and contains many elastic fibers. 

The ventral atlanto-occipital membrane (Membrana atlanto-occipitalis ven- 
tralis) extends from tlie ventral arch of the atlas to the ventral margin of the fora- 
men magnum. It is narrower and thinner than the dorsal membrane, and also 
fuses with the joint capsules. 

The lateral atlantal ligaments (Ligg. lateralia atlantis) are two short bands 
which are partially bkmded with the capsules. Each is attached to the border of 
the wing of the atlas near the intervertebral foramen, and to the lateral surface of 
the paramastoid process of the occipital bone. 

Movements. — These are chiefly flexion and extension. A small amount of 
lateral obhque movement is also possible. 



Articulations of the Thorax 
costo-vertebral articulations 

Each typical rilj forms two joints with the verteljral column, one Ijy its head, 
and one tjy its tubercle. They are termed respectively costo-central and costo- 
transverse joints. 

I. The costo-central articulation (Articulatio capituli) is a trochoid or rotatory 
joint, formed Ijy the junction of the 
head of the rib with the bodies of 
two adjacent vertebrae and the 
intervertebral fibro-cartilage. The 
two facets on the head of the rib 
are separated by a non-articular 
groove, and correspond to the two 
concave facets (Foveae costales) on 
the vertebral bodies. The joint 
capsule is rather tight, and is cov- 
ered by the accessory ligaments, 
which are as follows : 1 . The radiate 
ligament (Lig. capituli costse radi- 
al uni) extends ventrally from the 
neck of the rib to spread out on 
the vertebral botlies and the in- 
tervertebral filiro-cartilage. 2. The 
conjugal ligament (Lig. conjugate) 
— absent from tlie first joint — is 
attached to the groove on the head 
of the rib, passes transversely into 
the vertebral canal, and divides 
under the dorsal longitudinal liga- 
ment into two branches: one of these is attached to the body of the anterior vertebra; 
the other is continued across to the head of the opposite rib, and is also attached to 
the intervertebral fibro-cartilage. The joint cavity is divided into two compart- 
ments by the conjugal ligament. 3. The ligament of the neck of the rib (Lig. colli 




-trans- 
verse ligament 
rment of neck 

^N^i?0'/("'c ligament 
Conjugal ligament 






— CoSTO-VERTEBRAL ARTICULATION; ANTERIOR ViEW. 

(After .Schmaltz, Atlas d. Anat. d. PferdeaJ 



216 THE ARTICULATIONS OF THE HORSE 

costae) is a strong band which crosses the joint clorsally. It is attached on the 
vertebra above the costal facet and on the neck of the rib. 

II. The costo-transverse articulation (Articulatio costo-transversaria). This 
is formed by the facet on the tul)ercle of the rib and on the transverse proc- 
ess of the vertebra. They are ghding joints. The capsule is reinforced by the 
dorsal costo-transverse ligament (Lig. costo-transversarium dorsale), a distinct 
strong band which arises on the transverse process and ends on the non-articular 
part of the tubercle. It is covered by the levator costse muscle, and begins to be 
quite distinct at the fifth joint. 

The cavity for the head of the first rib 18 formed by concave facets on the bodies of the last 
cervical and first thoracic vertebrae. The conjugal ligament is absent, but the ligament of the 
neck is short and strong. The radiate Hgament is very strong, and consists of two parts. In the 
case of the last two or three ribs the costo-central and costo-transverse joints are confluent, and the 
various structures are correspondingly modified. 

Movements. — The chief movement is rotation around an axis which connects 
the centers of the head and tubercle of the rib. The movement is very limited in 
the anterior part of the series of joints, but very considerable in the posterior part. 

In the case of the first rib the movement is evidently extremely limited. The facet for the 
tubercle of the rib is deeply concave, and the axis of rotation is almost transverse, so that the 
movement is cliiefly sagittal in direction. Further back the facets on the transverse processes 
become flat, and the axis of rotation gradually approaches a longitudinal direction. This, in 
connection with the mobiUty of the ventral ends of the asternal ribs and their elasticity, allows a 
great increase here in the range of movement which is largely transverse, the effect being to enlarge 
(chiefly) the transverse diameter of tlie thorax. 



COSTO-CHONDRAL ARTIOJLATIONS 
The costo-chondral junctions are synartlu-ose.s. The rib has a concave surface 
which receives the convex end of tlie cartilage. They are united l^y the continuity 
of tlie strong periosteum and perichondrium. 



CHONDRO-STERNAL ARTICULATIONS 

These joints (Articulationes sternocostales) are diarthroses formed by the 
junction of the cartilages of the sternal ribs with the sternum. The articular ends 
of the cartilages (except the first) are somewhat enlarged, and present surfaces of 
cylindrical curvature. The articular surfaces on the sternum for the first pair of 
cartilages are placed close together on the dorsal border of the cariniform cartilage; 
the other seven are placed laterally at the junctions of the segments. The capsules 
are strong and tight; the first pair of joints has a common capsule, and the cartil- 
ages articulate with each other medially. The ventral ends of the first pair of ribs 
are firmly attached to each other by dense fibrous tissue, which is prolonged for- 
ward along the upper margin of the cariniform cartilage and is continuous behind with 
the sternal ligament. Each of the other capsules is reinforced dorsally by the radiate 
costo-stemal ligament (Ligamentum sterno-costale radiatum), composed of radi- 
ating fibers which blend with the sternal ligament. Interarticular bands maj' be 
present. The movement is rotation around a nearlj' vertical axis, except in the 
case of the first pair of joints. 



INTERCHONDRAL LIGAMENTS 
The eighth and ninth costal cartilages are firmly united by fibrous tissue. The 
chondro-xiphoitl ligament attaches the ninth costal cartilage to the xiphoid carti- 
lage. The remaining cartilages are rather loosely attached to each other by elastic 

tissue. 



THE ARTICULATIONS OF THE SKULL SYNARTHROSES OF THE SKULL 217 

STERNAL ARTICULATIONS 
In the new-born foal the seven bonj' segments are united by persisting cartilage 
(Synchontlroses intersternales). The last two segments coalesce within a few weeks 
after birth. In okl subjects there is more or less ossification of the intersternebral 
cartilage, which may lead to fusion of adjacent segments, especially posteriorly. 
The internal sternal ligament (Lig. sterni proprium internum) lies on the thoracic 
surface of the sternum. It arises on the first segment, and divides opposite the 
second chondro-sternal joint into three bands. The median band passes back- 
ward and spreads out on the last segment and the xiphoid cartilage. The lateral 
branches — thicker and wider — lie along the lateral liorders above the chondro- 
sternal joints, and end at the cartilage of the eighth rib; they are covered by the 
transversus thoracis muscle. 



The Articulations of the Skull 
mandibular articulation 

This joint (Articulatio mandibiilaris) is a diarthrosis formed l)etween the ramus 
of the mandible and the scjuamous temporal bone on either side. 

The articular surfaces are dissimilar in form and size. That on the squamous 
temporal bone is concavo-convex, and the long axis is directed outward and some- 
what forward; it consists of a condyle in front and a glenoid cavity, which is con- 
tinued upon the postglenoid process behind. The mandible presents a trans- 
versely elongated condyle. 

The articular disc (Discus articularis) is placed between the joint surfaces, 
which it renders congruent. Its surfaces are molded upon the temporal and man- 
dibular surfaces respectively, and its circumference is attached to the joint capsule; 
thus it divides the joint cavity into upper and lower compartments, the former being 
the more roomy. . 

The joint capsule is strong and tight. It is reinforced by two ligaments. The 
lateral ligament (Lig. latcrale) extends obliquely across the anterior part of the 
lateral siu-face of the capsule, from which it is not distinctly separable. The pos- 
terior ligament (Lig. posterius) is an elastic band which is attached above to the 
postglenoid process, and below to a line on the posterior face of the neck of the 
mandible. 

Movements. — The chief movements take place around a transverse axis pass- 
ing through both joints. Associated with this hinge-like action is slight gliding 
movement, as in opening and shutting the mouth. When the mouth is shut, 
the condyle of the mandible lies under the glenoid cavity. When the mandible 
is depressed, the condyle moves forward under the articular eminence of the tem- 
poral bone, carrying the disc with it. In protrusion and retraction of the lower 
jaw the gliding movement just described occurs without the hinge-like rotation 
of the condyle. These movements are similar in both joints. In the transverse 
movements (as usually performed in mastication) the action consists of rotation 
of the condj-les around a vertical axis, while the disc glides forward on one side and 
backward on the other. 

SYNARTHROSES OF THE SKULL 

Most of the bones of the skull are united with the adjacent bones by sutures; 
a few are united by cartilage. The difference in the uniting medium depends on 
the fact that most of these bones are developed in membrane, but some are pre- 
formed in cartilage. Most of these joints are temporary, and are obliterated at 



218 THE ARTICULATIONS OF THE HORSE 

various periods during development and growth. Tiieir importance lies in tlie 
fact that so long as they persist, continuous growth is possible. They are usually 
designated according to the bones which enter into their formation, e. g., spheno- 
squamous, naso-frontal, etc. 

Detailed description of the sutures has not sufficient clinical value to justify much addition 
to the statements made in the osteology in this connection. The obUteration or closure of the 
sutures is, however, worthy of brief mention. The cranial sutures are usually all closed at seven 
years, but the apex only of the petrous temporal is fused with the occipital and squamous temporal. 
Most of the facial sutures are practically closed at ten years, although complete synostosis may in 
some be delayed for years or may not occur at all; the nasal suture, for example, usually persists 
even in advanced age, so far as its anterior part is concerned. 

The principal synchondroses are: (1) That between the ba,silar part of the 
occipital bone and the body of the sphenoid (Synchondrosis spheno-occipitalis) ; 
(2) that between the presphenoid and postsphenoid (Synchondrosis intersphenoid- 
alis) ; (3) those between the parts of the occipital bone (Synchondroses intraoc- 
cipitales) . The first is ossified at four or five years, the second at three years, and 
the occipital bone is consolitlated at two years. 

The sjrmphysis mandibulae ossifies at one to six months. 

THE HYOIDEAN ARTICULATIONS 

The temporo-hyoid articulation is an amphiarthrosis, in which the articular 
angle of the dorsal end of the great cornu of the hyoid bone is attached by a short 
bar of cartilage to the hyoid process of the petrous temporal bone. The cartilage 
(Arthrohyoid) is about half an inch (ca. 1-1.5 cm.) in length. The chief move- 
ment is hinge-like, the axis of motion passing transversely through both joints. 

The intercomual articulation is an amphiarthrosis formed by the junction of 
the ventral extremity of the great cornu \vith the dorsal end of the small cornu of 
the hyoid bone. They are united by a very short piece of cartilage, in which there 
is usually a small nodule of bone in the j^oung subject. This nodule, the epihyoid 
or middle cornu, is usually fused with the great cornu in the adult. The chief 
movement here is also hinge-like, the angle between the cornua being increased or 
diminished. 

The basi-comual articulation is a diarthrosis formed by the junction of each 
small cornu with the body of the hyoid bone. The small cornu has a concave facet 
which articulates ^\^th the convex facet on either end of the dorsal surface of the 
body. The capsule is ample enough to allow considerable movement, which is 
chiefly hinge-like. 

The movements of the hj^oid bone are concerned chiefly in the acts of mastica- 
tion and swallowing. In the latter the ventral parts of the hyoid bone are moved 
forward and upward, carrying the root of the tongue and the larynx with them, 
and then return to their former position. 



The Articulations of the Thoracic Limb 

In the absence of the clavicle the thoracic limb forms no articulation with the 
trunk, to which it is attached by muscles. The movement of the shoulder on the 
chest-wall is chiefly rotation around a transverse axis passing through the scapula 
behind the upper part of the spine. 

THE SHOULDER JOINT 

The shoulder or scapulo-lumieral joint (Articulatio scapulo-humeralis) is 
formed by the junction of the distal end of the scapula with the proximal end of 
the humerus. The articular surfaces are: (1) On the scapula, the glenoid cavity; 



THE ELBOW JOINT 



219 



(2) on the humerus, the head. Both surfaces are approximately spherical and 
similar in curvature, but the humeral surface is about twice as extensive as that of 
the scapula. 

The joint capsule is ample enough to allow the bones to be drawTi apart about 
an inch (ca. 2-3 cm.) ; but this requires a very considerable amount of force unless 
air is admitted into the joint cavity. The fibrous layer is not attached to the mar- 
gin of the joint surfaces, but at a distance of one to two centimeters from it. It is 
strengthened in front by two diverging elastic bands, which arise on the tuber 
scapulae and end on the tuberosities of the humerus. A pad of fat is interposed 
between the capsule and the tendon of the biceps. 

Ligaments are absent from this joint, but the muscles and tendons around it 
afford remarkable security, so that dislocation very seldom occurs. The large ex- 
tent of the head of the humerus is also of importance in this regard. 

The principal muscles which are attached around the joint and act as ligaments are: 
laterall}', the supraspinatus, infraspinatus, and teres minor; medially, the subscapularis; in 
front, the biceps and supraspinatus; behind, the triceps. Fibers of the brachiaUs are attached to 
the lower edge of the posterior part of the joint capsule, and would evidently tense the latter. In 
some cases the joint cavity communicates with the bicipital or intertuberal bursa. 

Movements. — While it is a typical enarthrosis in structure, and capable of the 
various movements of the ball-and-socket joint, the chief normal movements are 
flexion and extension. In the position of rest the angle formed between the scapula 
and humerus posteriorly is about 110° to 120°; in fle.xion it is reduced to about 80°, 
and in extension it is increased to about 145°. Adduction and abduction are very 
restricted, the former being limited chiefly by the infraspinatus, the latter by the 
subscapularis and the low insertion of the superficial pectoral muscles. Rotation 
is somewhat freer, but does not exceed 33° when 
all the muscles are removed (Franck). 



THE ELBOW JOINT 

This, the cubital articulation (Articulatio 
cubiti), is a ginglymus formed between the dis- 
tal extremity of the humerus and the proximal 
ends of the radius and ulna. 

The articular surfaces are: (1) A trochlear 
surface formed by the condyles of the humerus 
and the ridge between them ; (2) the correspond- 
ing glenoid cavities and groove on the proximal 
extremity of the radius, together with the semi- 
lunar notch of the ulna. 

The articular surface of the condyles does not ex- 
tend upon the back of the extremity, but the groove which 
receives the semilunar notch of the ulna extends up into 
the olecranon fossa. In the fore part of the groove there 
is a synovial fossa. The sm-face on the lateral condyle is 
much smaller than that of the medial one, and is sub- 
divided into two unequal parts by a shallow furrow. On 
the lower part of the semilunar notch and the adjacent 
part of the ridge on the radius are synovial fossa;. 




Fig. 23t. — Left Elbow Joint of HoRaE; 
Posterior View. The Capsule is Re- 
moved. (.\fter Schmaltz, Atlas d. Anat. 
d. Pfi-rdes.) 



In front it is strengthened by 



The joint capsule is extremely thin behind, 
where it forms a pouch in the olecranon fossa 
under the anconeus muscle and a pad of fat. 

oblique fibers (Lig. obliquum or anterior ligament), and on each side it fu.ses 
with the collateral ligaments. It also is adherent to the tendons of muscles 
which arise from the distal end of the humerus or end on the proximal end of the 
radius. The synovial membrane sends prolongations to the small radio-ulnar 



220 



THE ARTICULATIONS OF THE HORSE 




THE RADIO-ULNAR ARTICULATION — THE CARPAL JOIXTS 221 

joints and also pouches downward under the origins of the flexors of the digit and 
the lateral flexor of the carpus. There are two collateral ligaments. 

The medial ligament (Lig. coUaterale radiale) is attached above to an 
eminence on the medial epicondyle of the humerus, and divides into two parts: 
the long, superficial part ends on the medial border of the radius, just below the 
level of the interosseous space; the deep, short part is inserted into the medial tu- 
berosity of the radius. 

The lateral ligament (Lig. collaterale ulnare) is short and strong. It is at- 
tached above to a depression on the lateral epicond3de of the humerus, and below 
to the lateral tuberosity of the ratlins, just below the margin of the articular surface. 

Movements. — This joint is a typical ginglymus, the onh' movements being 
flexion and extension around an axis which passes through the proximal attachments 
of the collateral ligaments. In the staniling position the articular angle (in front) is 
about 140° to 150°. The range of movement is about 55° to 60°. Complete ex- 
tension is prevented chiefly by the tension of the collateral ligaments and the biceps 
muscle. (The axis of movement is slightly oblicjue, so that in flexion the forearm 
is carried somewhat outward.) 



THE RADIO-ULNAR ARTICULATION 

In the foal the shaft of the ulna is attached to tlie radius above and below the 
interosseous space by the interosseous ligament of the forearm (Lig. interosseum 
antibrachii) . Below the space the two bones become fused before adult age is 
reached. Above the space the ligament usually persists, but may undergo more 
or less ossification in extreme old age. The transverse or arciform ligament (Lig. 
transversum ulnare et radiale ulnte et radii) consists of fibers which pass above the 
interosseous space from each border of the shaft of the ulna to the posterior sur- 
face of the radius. The proximal radio-ulnar articulation (Articulatio radio-ulnaris 
proxuiialis), formed by two small convex facets on the ulna and the corresponding 
facets on the posterior surface of the proximal extremity of the radius, is inclosed 
in the capsule of the elbow-joint and does not require separate consideration. The 
distal extremity of the ulna fuses early with the radius, and is therefore regarded 
usually as a part of the latter. 

Movement. — This is inapprecialile, the forearm being fixed in the position of 
pronation. 

THE CARPAL JOINTS 

These joints taken together constitute the composite articulatio carpi, or what 
is popularly termed the "knee-joint" in animals.^ This consists of three chief 
joints, viz., (1) The radio-carpal or antibrachio-carpal joint (Articulatio radiocarpea) 
formed by the distal entl of the radius and the proximal row of the carpus; (2) the 
intercarpal joint (Articulatio iutercarpea), formed between the two rows of the car- 
pus; (3) the carpo-metacarpal joint (Articulatio carpometacarpea) , formed between 
the distal row of the carpus and the proximal ends of the metacarpal bones. The 
proximal and middle joints may be regarded as ginglymi, although they are not 
typical or pure examples of hinge-joints. The distal joint is arthrodial. In addi- 
tion there are arthrodial joints formed between adjacent bones of the same row 
(Articulationes interosseae). All these form a composite joint with numerous liga- 
ments. The articular surfaces have been described in the Osteology. 

The joint capsule may be regarded, so far as the fibrous part is concerned, as 
being common to all three joints. It is attached close to the margin of the articu- 

^ The term is a very unfortunate one, since it is a distinct misapplication of the name as it is 
used in regard to man. It is, liowever, very firmly establislied, and appears likely to persist in- 
definitely in the absence of a convenient popular equivalent. 



222 



THE ARTICULATIONS OF THE HORSE 



lar surface of the radius above and the metacarpus below; its deep face is also 
attached to a considerable extent to the carpal bones and to the small ligaments. 
Its anterior part, the dorsal carpal ligament, is loose, except during flexion, and 
assists in forming the fibrous canals for the extensor tendons. Its posterior part, 
the volar carpal ligament (Lig. carpi volare), is very thick and dense, and is closely 
attached to the carpal bones. It levels up the irregularities of the skeleton here, 
and forms the smooth anterior wall of the carpal canal. It is continued downward 
to form the subcarpal or inferior check ligament, which blends with the tendon of 
the deej) flexor of the digit about the middle of the metacarpus, and may well be 
regarded as the carj^al (tendinous) head of that muscle. 

The synovial membrane forms three sacs corresponding to the three joints. 

The radio-carpal sac is the 
most voluminous; it includes 
the joints formed by the acces- 
sory carpal bone, and also those 
between the proximal carpal 
bones as far as the interosseous 
ligaments. The intercarpal sac 
sends extensions upward and 
downward between the bones 
of the two rows as far as the 
interosseous ligaments; it com- 
nmnicates between the third 
and fourth carpal bones wth 
the carpo-metacarpal sac. The 
latter is very limited in extent, 
and is closely applied to the 
bones; it incloses the carpo- 
metacarpal joint, and lubri- 
cates also the lower parts of 
the joints between the distal 
carpal bones and the inter- 
metacarpal joints. 

The lateral ligament (Lig. 
carpi collaterale ulnare) is at- 
tached above to the lateral 
tuberosity of the distal end of 
the radius. Its long superficial 
part is attached below to the 
proximal end of the lateral 
small metacarpal chiefly, but 
some fibers end on the large 
metacarpal bone. A canal for the lateral extensor tendon separates a short deep 
band which ends on the ulnar carpal bone. Other deep fibers connect the latter 
with the foiu'th carpal bone, and the fourth carpal with the metacarpus. 

The medial ligament (Lig. carpi collaterale radiale) resembles the preceding 
in general, but is stronger and wider distally. It is attached above to the medial 
tuberosity of the distal end of the ratlins and ends below on the proximal ends of 
the large and medial small metacarpal bones. Deep fasciculi are detached to the 
radial and second carpal bones. The first carpal bone, when present, is usually 
embedded in the posterior part of the distal end of the ligament. The posterior 
part of the ligament is fused with the transverse ligament of the carptis (Lig. carpi 
transversum), and concurs in the formation of a canal for the tendon of the flexor 
carpi radialis. 




C. 



Mc. Ill 



Fig. 23S.- 



Carpal Joints op Horse; Dorsal View. Th 

Joint Capsule is Removed. 

R, Lateral distal tuberosity of radius; Jlf, medial ligament; L 

lateral ligament; C. r., radial carpal bone; C. u., ulnar carpal bent 

C. 5, third carpal bone; C, 4, fourth;carpal bone; Mc. Ill, Mc. 71 

metacarpal bones; 1, intermediate carpal bone; 2-6, dorsal ligaments 



INTERMETACARPAL JOINTS 



223 



A number of special short ligaments connect two or more adjacent bones; only the most 
distinct of these will be described here. 

The accessory carpal bone is connected witli adjacent bones by three ligaments (Fig. 2.34). 
The proximal one is a short band which extends from the accessory carpal in front of tlie groove on 
its lateral face and is inserted into the distal end of the radius behind the groove for the lateral 
extensor tendon. A middle band connects the accessory with the ulnar carpal. The distal liga- 
ment consists of two strong bands which pass from the distal margin of the accessory to the fourth 
carpal and the proximal end of the foiu-th 
metacarpal bone; these bands transmit the 
action of the muscles which are inserted into 
the accessory carpal bone. The other bones 
of the proximal row are connected by two 
dorsal ligaments, which are transverse in direc- 
tion, and two interosseous Ugaments. An 
oblique hgament passes from an eminence on 
the volar surface of the radial carpal bone to 
a small depression on the radius medial to the 
facet for the accessory carpal bone. 

Two ligaments connect the proximal and 
distal rows posteriorly. The medial one joins 
the radial to the second and third carpal, and 
the lateral one attaches the ulnar to the third 
and fomlh carpals. 

The bones of the distal row are con- 
nected by two strong transverse dorsal 
ligaments and two interosseous ligaments. 

There are four carpo-met acai'pal liga- 
ments. Two obhque dorsal ligaments (Ligg. 
carpometacai'pea dorsaha) connect the third 
carpal with the large metacarpal bone. Two 
interosseous ligaments pass downward from 
the interosseous ligaments of the distal row 
to end in depressions of the opposed surfaces 
of the proximal ends of the metacarpal bones. 
Volar ligaments (Ligg. carpometacarpea vo- 
laria) connect the second and third carpal 
bones with the metacarpus. Other short 
special Ugaments have been described, but 
some of them at least are artefacts. 

Movements. — Taking the joint as 
a wliole, the chief movements are flex- 
ion and extension. In the standing 
position the joint is extended. When 
the joint is flexed, slight transverse 
movement and rotation can be pro- 
duced by manipulation. The dorsal 
part of the capsule is, of course, tense 
during flexion, the volar part in exten- 
sion. 




The movement practically all occurs at 
the radio-carpal and intercarpal joints, the 
articular surfaces of which are widely separ- 
ated in front dui'ing flexion, but remain in 
contact beliind. The distal row remains in 
contact with the metacarpus. The inter- 
mediate and ulnar carpals move together as 

one piece, but the radial does not move so far as the intermediate, so that the dorsal and inter 
osseous ligaments connecting these bones become tense and obUque in direction. 



/?, Distal end of radius; M, medial ligament : L, 
lateral ligament; 1, 2, ligaments connecting radial carpal 
bone and radiua; 3, ligament connecting intermediate 
carpal with radius; 4, stump of ligament connecting inter- 
mediate and accessory carpal ; 5, ligament connecting radial 
and second carpal; 6, 6', ligaments connecting second 
carpal and metacarpal bones; 7, 7', ligaments connecting 
third carpal and metacarpal bone; 8, ligament connecting 
ulnar and third and fourth carpal bones; 9, deep short part 
of medial collateral ligament; 10, 11, 12, radial, inter- 
mediate, and ulnar carpal bones; 13, 14, 15, second, third, 
and fourth carpal bones; 16, 16', 17, metacarpal bones. 
(Of the preceding volar ligaments, 1, 3, and S are distinct 
from the capsule.) 



INTERMETACARPAL JOINTS 
The small joints formctl between the proximal ends of the metacarpal bones 
(Articulationes intermetacarpese) are enclosed by the carpal joint capsule, as des- 
cribed above. The opposed surfaces of the shafts of the bones are closely united by 
an interosseous metacarpal ligament (Lig. interosseum metacarpi), which often 
undergoes more or less extensive ossification. 



224 THE ARTICULATIONS OF THE HORSE 



THE FETLOCK JOINT 

This, the metacarpo-phalangeal articulation (Articulatio metacarpo-phalangea), 
is a ginglymus formed b>- the junction oi the chstal end of the large (third) meta- 
carpal bone, the proximal end of the first phalanx, antl the proximal sesamoid 
bones. 

Articular Surfaces. — The surface on the large metacarpal bone is approxi- 
mately cylindrical in curvature, but is divided into two slightly unequal parts by a 
sagittal ridge. This is received into a socket formed by the first phalanx below and 
the two sesamoids together with the intersesamoid ligament behind. The latter 
is a mass of fibro-cartilage in which the sesamoid bones are largely embedded. It 
extends above the level of the sesamoids, and is grooved to receive the ridge on the 
metacarpal bone; its volar surface forms a smooth groove for the deep flexor ten- 
don. 

The joint capsule is attached around the margin of the articular surfaces. It 
is thick and ample in front; here a bursa is interposed between it and the extensor 
tendons, but the tendons are also attached to the capsule. Posteriorly it forms a 
thin-walled pouch which extends upward between the metacarpal bone and the 
suspensory ligament about as high as the point of bifurcation of the latter.^ The 
capsule is reinforced by two collateral ligaments. 

The collateral ligaments, medial and lateral (Lig. collaterale ulnare, radiale), 
are partiallj- divided into two layers : the superficial layer arises from the eminence 
on the side of the distal end of the large metacarpal bone, and passes straight to 
the rough area below the margin of the articular surface of the first phalanx; the 
deep layer, shorter and much stronger, arises in the depression on the side of the 
distal end of the metacarpal bone, and passes obliquely downward and backward 
to be inserted into the abaxial surface of the sesamoid and the proximal end of the 
first phalanx. 

The capsule is further strengthened by a layer of oblique fibers which pass over the collateral 
ligament on either side and end on the e.xtensor tendon and tlie proximal extremity of the first 
phalanx. It may properly be regarded as fascia j;ather than ligament. 

Movements. — These are of the nature of flexion and extension, the axis of 
motion passing through the proximal attachments of the collateral ligaments. In 
the ordinary standing position the joint is in a state of partial dorsal flexion, the 
articular angle (in front) being about 140° to 150°. (In the hind limb it is about 
5° greater.) Diminution of this angle (sometimes termed "overextension") is nor- 
mally very limited on account of the resistance offered by the sesamoidean appa- 
ratus, but it varies considerably in amount in different subjects. Volar flexion is 
limited only by contact of the heels with the metacarpus. During volar flexion 
a small amount of transverse movement is possible. 



THE SESAMOroEAN LIGAMENTS 

Under this head will be described a number of important ligaments which are 
connected with the sesamoid bones and form a sort of stay apparatus or brace. 

The intersesamoidean ligament (Lig. intersesamoideum) not only fills the 
space between and unites the sesamoid bones, but also extends above them, enter- 
ing into the formation of the articular surface of the fetlock joint. Other facts 
in regard to it have been given above. 

The collateral sesamoidean ligaments, lateral and medial (Ligg. sesamoidea 

' This pouch is in part bound down by a layer of elastic tissue which arises by two branches 
from the distal part of the volar surface of the shaft of the large metacarpal bone and ends on the 
intersesamoid ligament. It was first described by Skoda who terms it the lig. metacarpo-inter- 
sesamoideum. 



THE SESAMOIDEAN LIGAMENTS 



225 



ulnare et radiale), arise on the abaxial surface of each sesamoid bone, pass forward, 
and divide into two branches, one of which ends in the depression on the distal end 
of the large metacarpal bone, the other on the eminence on the proximal end of the 
first phalanx. They are partly covered by the branches of the suspensory or 
superior sesamoidean ligament. 

The suspensory ligament or interosseous tendon (Tendo interosseus)' lies in 
great part in the metacarpal groove, where it has the form of a wide, thick 
band. It is attached above to the proximal part of the posterior surface of the large 



Extensor tendon 



Proximal end of capsule of fetlock 
joint 

Bursa 

Collateral ligament of fetlock joint 

Fascia 

Branch of suspensory ligament 



Lateral volar ligament of pastern 
joint 



Suspensory ligament of navicular 
bone 
Band from cartilage to extensor 
tendon 



Collateral ligament of coffin joint — 





Superficial flexor tendon 
Deep flexor tendon 
Suspensory ligament 
Lateral interosseous tendon 

Proximal end of digital sheath 
Ring of superficial flexor tendon 
Intersesamoidean ligament 
Posterior annular ligament {cut) 



Collateral sesamoidean ligament 
Superficial distal sesamoidean 

ligament 
Middle distal sesemioidean ligament 

\ Attachments of proximcd digiUd 
' annular ligament 



/-g Pouch of digital sheath 

^ - Distal digital annular ligament 

C 'artilage of third phalanx 



Fig. 240. — Ligaments and Tendons of Distal Part of Limb of Horse. 

Mc.lII, Large metacarpal bone; Ph. I, first phalanx; Ph. II, second phalanx; Ph. Ill, third phalanx; 1, deep flexor 

tendon; 2, band from first phalanx to digital cushion. (After Schmaltz, Atlas d. Anat. d. Pferdes.) 



metacarpal bone antl to the distal row of carpal l)ones. At the di.stal fourth of the 
metacarpus it divides into two diverging branches. Each branch passes to the 
abaxial face of the corresponding sesamoid, on which a considerable part is attached. 
The remainder passes obliquely downward and forward to the dorsal surface of the 
first phalanx, where it joins the extensor tendon; there is a bursa between this ex- 
tensor laranch and the proximal end of the first phalanx. This ligament possesses 

' This is also known as the superior sesamoidean ligament ; it is described here in deference 
to custom and on account of its ligamentous function. 
15 



226 



THE ARTICULATIONS OF THE HORSE 



considerable elasticity, and is the highly modified interosseous medius muscle. It 
consists mainly of tendinous tissue, but contains a variable amount of striped mus- 
cular tissue, especially in its deep part and in young subjects. Its principal func- 
tion is to support the fetlock, i. e., to prevent excessive dorsal flexion of the joint 
when the weight is put on the limb. The branches which join the common exten- 
sor tendon limit volar flexion of the interphalangeal joints in certain phases of move- 
ment. 

The distal sesamoidean ligaments are three in number. The superficial or 



3ifitrcntion of common digital artery 
Medial digital artery 



Oblique or middle distal sesamoid 



Straight or superficial distal 
sesamoid ligament 



Distal anmdar ligatnent of 
and reflected) 



Fig. 241. — Deep Dissection of Distal P. 




Large metacarpal hone 

Lateral small metacarpal hone 

Bifurcation of suspensory 
ligament 



Capsule of fetlock joint {proximal 

pouch) 
Sesamoid groove 

Volar annular ligament of fetlock 
(cut and reflected) 

— : Lateral sesamoid ligament 

Stump of proximal digital annular 

ligament 
Extensor branch of suspensory 

ligament 
Volar ligaments of paster7i joint 

Insertion of superficial flexor 

tendon 
Fibrous plate 
Deep flexor tendon 

Lateral ligament of pastern joint 
Distal end of digital sheath 
Suspensory ligament of navicular 

bone 
Dorsal brayich of digital artery 
Volar branch of digital artery 



Ligaments; 



OF Right Foke Limb of Hohse, Showing Joints . 
Posterior View. 
1, Cartilage of third phalanx; 2. flexor surface of navicular bone; 3, distal navicular ligament; 4, insertion of 
deep flexor tendon. Small arrows point to openings made in capsules of pastern and coffin joints. (After Schmaltz, 
Atlas d. Anat. d. Pferdes.) 

straight sesamoidean ligament (Lig. sesamoideum rectum) is a flat band and is 
somewhat wider above than Ijelow.^ It is attached aljove to the bases of the sesa- 
moid bones and the intersesamoid ligament, lielow to the complementary fil^ro- 
cartilage of the proximal end of the second phalanx. The middle sesamoidean 
ligament is triangular, with thick, rounded margins (Ligg. sesamoidea obliqua) and 
a thin central portion.- Its base is attached to the sesamoid bones and intersesa- 

' This is often called the Y-shaped ligament — a rather undesirable name, since it is not 
bifurcate. 

' It is also called the V-shaped ligament. 



THE SESAMOIDEAN LIGAMENTS 



227 



moid ligament, and its deep face to the triangular rough area on the volar surface 
of the first phalanx. The deep or cruciate sesamoidean ligaments (Ligg. sesamoidea 
cruciata) consist of two thin layers of fibers which arise on the base of the sesa- 
moid bones, cross each other, and end on the opposite eminence on the proximal 
end of the first phalanx. 

The two short sesamoidean ligaments (Ligg. sesamoidea brevia) are best seen 



Skin 

Tendon of common extensor 

Bursa 

Capsule of fetlock joint 
Cavity of fetlock joint 




Cavity of /jastern joint 

Cavity of coffin joint 

Corium of periople 
Periople 

Coronary corium 

Wall 

Lam in 



Middle sesamoidean ligament 
Digital synovial sheath 
Cavity of pastern joint 
Superficial sesamoidean ligament 
Deep flexor tendon 
Distal end of digital sheath 



11 

Digital cushion 



Sole Corium of sole 
Fig. 242. — Sagittal Section of Digit and Distal Part of Metacarpus of Horse. 
A, Metacarpal bone; B, first phalanx; C, second phalanx; D, third phalanx; E, distal sesamoid bone; 1, volar 
pouch of capsule of fetlock joint; 2, intersesamoidean ligament; 3. 4, proximal end of chgital synovial sheath: 5. ring 
formed by superficial flexor tendon; 6, fibrous tissue underlying ergot ; 7, ergot; 8, 9, 9', branches of digital vessels; 10, 
distal ligament of distal sesamoid bone; 11, suspensory ligament of distal sesamoid bone; 12, 12', proximal and distal 
ends of bursa podotrochlearis. By an oversight the superficial flexor tendon (behind 4) is not marked. 



by opening the joint in front and pushing the sesamoid bones liackward; they 
are covered by the synovial membrane. Each is a short band which extends from 
the anterior part of the base of the sesamoid bone outward or inward to the posterior 
margin of the articular surface of the first phalanx. 

The distal sesamoidean ligaments may be regarded as digital continuations 
of the suspensory ligament, the sesamoid bones being intercalated in this remark- 
able stay apparatus, by which the fetlock is sujiported and concussion diminished. 



228 THE ARTICULATIONS OF THE HORSE 



THE PASTERN JOINT 

This, the proximal interphalangeal articulation (Articulatio interphalangea 
proximalis s. phalaiigis secuncte), is a ginglymus formed by the junction of the 
distal end of the first phalanx and the proximal end of the second phalanx. 

The articular surfaces are: (1) On the first phalanx, two slightly unequal con- 
vex areas with an intermediate shallow groove; (2) on the second phalanx, a cor- 
responding surface, completed behind by a plate of fibro-cartilage. 

The joint capsule is close-fitting in front and on the sides, where it blends with 
the extensor tendon and the collateral ligaments respectively. Behind it pouches 
upward a little and is reinforced by the straight sesamoidean ligament and the 
branches of the superficial flexor tendon. 

There are two collateral and four volar ligaments. 

The collateral ligaments, medialand lateral (Lig. coUaterale radiale, ulnare), 
are very short and strong bands whicli are attached above on the eminence antl de- 
pression on each side of the distal end of the first phalanx, and below on the em- 
inence on each side of the proximal end of the second phalanx. The direction of 
the ligaments is about vertical antl, therefore, does not correspond to the digital 
axis. 

The volar ligaments (Ligg. volaria) consist of a central pair and lateral and 
medial bands which are attached below to the posterior margin of the proximal end 
of the second phalanx and its complementary fibro-cartilage. The lateral and 
medial ligaments are attached above to the middle of the borders of the first phalanx, 
the central pair lower down and on tlie margin of the triangular rough area. 

These ligaments are very commonly thickened as a result of clu'ouic inflammation, and then 
are not well defined. The central ones blend below with the branches of the superficial flexor 
tendon and with the straight sesamoidean ligament. 

Movements. — These are very limited, and consist of flexion and extension. 
The axis of motion passes transversely through the distal end of the first phalanx. 
In the standing position the joint is extended. A small amount of volar flexion is 
possible, and in this position slight lateral and medial flexion and rotation can be 
produced by manipulation. Dorsal flexion is prevented by the lateral, volar, and 
straight sesamoidean ligaments. 

THE COFFIN JOINT 

This joint, technically termed the distal interphalangeal articulation (Articu- 
latio interphalangea distalis s. phalangis tertise), is a ginglymus formed by the junc- 
tion of the second and third phalanges and the distal sesamoid bone. 

Articular Surfaces. — The surface on the distal end of the second phalanx is 
convex in the sagittal direction, concave transversely. The articular surface of the 
third phalanx slopes sharply upward and forward; its central part is prominent, 
and is flanked by two glenoid cavities. It is completed behind by the articular 
surface of the distal sesamoid or navicular bone. 

Joint Capsule. — This is attached around the margins of the articular surfaces. 
In front and on the sides it is tight, and is ]>lended with the extensor tendon and the 
collateral ligaments respectively. It forms a considerable pouch behind, which 
ex-tends upward to about the middle of the second phalanx, where it is separated by 
a fibrous membrane from the digital synovial sheath. On each side small pouches 
project (especially during volar flexion) against the cartilages of the third phalanx 
just behind the collateral ligaments.' 

Ligaments. — The collateral ligaments, medial and lateral (Lig. collaterale 

' Tills should be noted in regard to resection of the cartilage or other operations in this 
vicinity. 



THE ARTICULATIONS OF THE PELVIC LIMB 



229 



ulnare, radiale), are short, strong bands v/hich are attached above in the depressions 
on either side of the lower part of the second phalanx, under cover of the cartilage 
of the third phalanx. They widen below and end in the depressions on either 
side of the extensor process and on the anterior end of the cartilages. 

The collateral sesamoidean or suspensory navicular ligaments, medial and 
lateral (Lig. sesanioideuni collaterale ulnare, radiale),^ are strong, somewhat elastic 
bands, which form a sort of suspensory apparatus for the third sesamoid. They are 
attached superiorly in and above the depressions on each side of the distal end of 
the first phalanx and are here partly blended with the collateral ligaments of the 
pastern joint. They are directed obliquely downward and backward, and end 
chiefly on the ends and proximal border of the third sesamoid, but detach a branch 
to the axial surface of each cartilage and angle of the thirrl phalanx. 

The phalango-sesamoidean or distal navicular ligament (Lig. phalangeo-sesa- 
moideum) reinforces the capsule distally. It is a strong layer of fibers which 
extend from the distal border of the distal sesamoid to the flexor surface of the tliird 
phalanx. 

Movements. — The chief movements are flexion ana extension. In the stand- 
ing position the joint is extended. During volar flexion a verj^ small amount of 
lateral movement and rotation can be produced by manipulation. Dorsal flexion 
is very limited. 

Dorsal flexion appears to be checked mainly by the deep flexor tendon, since in cases of rup- 
ture of the latter the toe turns up. The mobihty of the posterior part of the socket for the second 
phalanx (formed by the distal sesamoid) diminishes concussion when the weight comes on the foot 



LIGAMENTS OF THE CARTILAGES OF THE THIRD PHALANX 

In addition to the bands mentioned above, which attach the cartilages to the 
extremities of the navicular bone, there are three ligaments on either side which 
attach the cartilages to the phalanges. 

An ill-defined elastic band passes from the middle part of the border of the first 
phalanx to the upper part of the cartilage, detaching a branch to the digital cushion. 

A short, strong band coimects the anterior extremity of the cartilage with the 
rough eminence on the second pha- 
lanx in front of the attachment of the 
collateral ligament of the coffin joint. 
. The lower border of the cartil- 
age is covered in part by fibers which 
attach it to the angle of the third 
phalanx. 



The Articulations of the 
Pelvic Limb 



Ventral sacro-iliac ligament 




Sacro-ilinc 
articulation 



243. — Left Sacro-iliac Articulation of Horse; An- 
terior View. (Adapted from Schmaltz, Atlas d. Anat. 
d. Pferdes.) 



THE SACRO-ILIAC ARTICULATION 

This joint (Articulatio sacro- 
iliaca) is a diarthrosis formed be- 
tween the auricular surfaces of the 
sacrum and ilimii. These surfaces 
are not smooth in the adult, but are 

marked by reciprocal eminences and depressions, and are covered by a thin layer of 
cartilage. The joint cavity is a mere cleft, and is often crossed by fibrous bands. 

' These are termed the postero-lateral Ugaments by M'Fadyean. Functionally they are 
suspensory ligaments of the navicular bone. 



230 



THE ARTICULATIONS OF THE HORSE 



The joint capsule is very close fitting, and is attached around the margins of 
the articular surfaces. It is reinforced by the ventral sacro-iliac ligament (Lig. 
sacro-iliacum vcntrale), which surrounds the joint; this is exceetlingly strong above, 
where it occupies the angle between the ilium and the wing of the sacrum; it con- 
sists chiefly of nearly vertical fibers. 

The movements are inappreciable in the adult — stability, not mobility, being 
the chief desideratum. 



LIGAMENTS OF THE PELVIC GIRDLE 

The following ligaments (Ligg. cinguli extremitatis pelvinse) may be regarded 
as accessory to the sacro-iliac joint, although not directly connected with it: 




Fig. 244.- 
1, Dorsal sacro-iliac ligament; 2, lateral 



-Pelvic Ligaments and Hip Joint. 
acro-iiiac ligament; 3, sacro-sciatic ligament; 



, greater sciatic foramen; 

5, lesser sciatic foramen; 6, line of attachment of intermuscular septum between biceps femoris and semitendinosus; 
7, capsule of hip joint; S, capsularis muscle; 9, lateral tendon of origin of rectus femoris; 10, tuber sacrale; 11, tuber 
coxffi; / 5, shaft of ilium; icf, superior ischiatic spine; i4. pubis; /.'J, tuber ischii; iff, trochanter major; i 7, semimem- 
branosus; IS, fifth lumbar spine; 10, iiO, first and second coccygeal vertebrae. 



The dorsal sacro-iliac ligament (Lig. sacro-iliacum dorsale breve) is a strong 
band wliich is attached to the tuber sacrale and the summits of the sacral spines. 

The lateral sacro-iliac ligament (Lig. sacro-iliacum dorsale longum) is a tri- 
angular, thick sheet which is attached in front to the tuber sacrale and adjacent 
part of the medial border of the ilium alcove the great sciatic notch, and below to 
the lateral border of the sacrum. It blends above with the dorsal sacro-iliac liga- 
ment, below with the sacro-sciatic ligament, and behind with the coccygeal fascia. 

The sacro-sciatic ligament (Lig. sacroischiadicum s. sacrospinosum et tuber- 
osum) is an extensive quadrilateral sheet which completes the lateral pelvic wall. 



SYMPHYSIS PELVIS THE HIP JOINT 231 

Its dorsal border is attaclietl to the border of the sacrum and the transverse processes 
of the first and second coccygeal vertebrse. Its ventral border is attached to the 
superior ischiatic spine and tul^er ischii. Between these it bridges over the lateral 
border of the ischium antl completes the lesser sciatic foramen (Foramen ischiadi- 
cuni minus). The anterior border is concave, and completes the greater sciatic 
foramen (Foramen ischiadicum majus). The posterior border is fused with the 
vertebral head of the semimembranosus muscle. 

The lefsser sciatic foramen is closed, e.xcept where the tendon of the obturator internus and 
a vein pass tlirough it, by a thin fibrous sheet given off from the sacro-sciatic ligament. 

The ilio-lumbar ligament (Lig. ilio-lumbale) is a triangular sheet which at- 
taches the emls of the lumbar transverse processes to the ventral surface of the 
ilium below the attachment of the longissimus muscle (Fig. 273). 



SYMPHYSIS PELVIS 
The symphysis pelvis is formed by the junction of the two ossa coxarum at 
the ventral nicilian- line. In the young subject the bones are united by a layer of 
cartilage (Lamina fibrocartilaginea) ; in the adult the latter is gradually' replaced 
by bone, the process beginning in the pubic portion and extending backward, 
but commonly the ischia are in part not fused. The union is strengthened by 
white fibrous tissue dorsally and ventrally. A transverse band also covers the 
anterior border of the pubis, and other fibers (Lig. arcuatmn ischiadicum) extend 
across at the ischial arch. No appreciable movement occurs even before synosto- 
sis takes place. 

OBTURATOR MEMBRANE 
This (Membrana obturatoria) is a thin layer of filjrous tissue which covers the 
obturator foramen, leaving, however, a passage (Canalis obturatorius) for the 
obturator vessels and nerve. 

THE HIP JOINT 

This joint (Articulatio coxae) is an enarthrosis formed by the proximal end of 
the femur and the acetabulum. 

Articular Surfaces. — The head of the femur presents an almost hemispherical 
articular surface, which is continued a short distance on the upper surface of the 
neck. It is more extensive than the socket which receives it. It is cut into medi- 
ally by a deep notch for the attachment of the round and accessory ligaments. 
The acetabulum is a typical cotyloid cavity. Its articular surface is somewhat 
crescentic, being deeply cut into medially by the acetabular notch and fo.ssa. 

The acetabulum is deepened by a ring of fibro-cartilage, the cotyloid ligament 
(Labrum glenoidale), which is attached to the bony margin; that part of the liga- 
ment which crosses the notch is calleil the transverse acetabular ligament (Lig. 
transversum acetabuli) (Fig. 291). 

The joint capsule is roomy. It is attached around the margin of the acetab- 
ulmn and the neck of the femur. It is thickest laterally. 

The attachment on the femur is about 1 cm. from the margin of the articular surface, except 
above, where 2 to 3 cm. of the neck is intracapsular. A thin, oblique band cunt si » mi ling in direc- 
tion with the capsularis muscle reinforces the antero-lateral part of the capsule; this appears to 
be the feeble homologue of the very strong ilio-femoral ligament of man. The capsule is very 
thin under the ilio-psoas, and is adherent to the muscle. Its fibrous part is perforated medially 
by the accessory and round ligaments and the articular vessels. 

The rovmd ligament (Lig. teres) is a short, strong band which is attached 
in the sulipubic groove close to the acetabular notch, passes outward, and ends 
in the notch on the head of the femur (Fig. 581). 



232 THE ARTICULATIONS OF THE HOUSE 

The accessory ligament (Lig. accessorium)' does not occur in the domestic 
animals other than the equidse. It is a strong band detached from the prepubic 
tendon of the aljtlominal muscles (Fig. 581). It is directed outward, backward, 
and upward, passes through the acetabular notch dorsal to the transverse ligament, 
and ends behind the round ligament in the notch on the head of the femur. The 
origin of the pectineus muscle is perforated by the ligament, which furnishes at- 
tachment to many fibers of the muscle. 

The synovial membrane is reflected over the intracapsular parts of these lig- 
aments and covers the fossa acetabuli. A pouch also extends from the acetabular 
notch for a varialjle distance along the subpubic groove above the accessory liga- 
ment. 

Movements. — This joint is capable of all the movements of a ball-and-socket 
joint, viz., flexion, extension, abduction, atlduction, rotation, and circumduction. 
The greatest range of movement is displayed in flexion and extension. When 
standing at rest, the joint is partially flexed, the articular angle (in front) being 
about 100° to 115°. The other movements occur to a very limited extent in normal 
action. Abduction appears to be checkeil by tension of the round and accessory 
ligaments. The accessory ligament is tensed most promptly by inward rotation of 
the thigh. 

THE STIFLE JOINT 

This joint (Articulatio genu), wiiich corresponds to the knee-joint of man, 
is the largest and most elaborate of all the articulations. Taken as a whole, it 
may be classed as a ginglymus, although it is not a typical example of the group. 
In reality it consists of two joints — the femoro-patellar and the femoro-tibial. 

The femoro-patellar articulation (Articulatio femoro-patellaris) is formed 
between the troclilea of the femur and the articular surface of tlie patella. 

Articular Surfaces. — The trochlea consists of two slightly oliilique ridges, 
wath a wide and deep groove between them. The medial ridge is much the larger 
of the two, especially at its proximal part, which is wide and rounded. The lateral 
ridge is much narrower, and is more regularly curved; its proximal part lies about 
an inch behind a frontal plane tangent to the medial one. The articular surface 
of the patella is much smaller than that of the trochlea. It is completed medially 
by a supplementary plate of filsro-cartilage (Fibrocartilago patellEe), which curves 
over the medial ridge of the trochlea. A narrow strip of cartilage is found along 
the lateral Ijorder also. The articular cartilage on the trochlea completely covers 
both surfaces of the medial ridge, but extends only a short distance on the lateral 
surface of the outer ridge. 

Joint Capsule. — This is thin and is very capacious. On the patella it is 
attached around the margin of the articular surface, but on the femur the line of 
attachment is at a varying distance from the articular surface. On the medial side 
it is an inch or more from the articular cartilage; on the lateral side and above, 
about half an inch. It pouches upward under the quadriceps femoris for a distance 
of two or three inches, a pad of fat separating the capsule from the muscle. Be- 
low the patella it is separated from the patellar ligaments by a thick pad of fat, 
but inferiorly it is in contact with the femoro-tibial capsules. The joint cavity is 
the most extensive in the body. It usually communicates with the medial sac of 
the femoro-tibial joint cavity by a slit-like opening situated at the lowest part of 
the medial ridge of the trochlea. A similar, usually smaller, communication with 
the lateral sac of the femoro-tibial capsule is often found at the lowest part of the 
lateral ridge. 

The medial communication is rarely absent in adult horses, but is liable to be overlooked 
on account of the fact that it is covered by a valvrilar fold of the synovial membrane. It is about 

1 This is also commonly called the pubo-femoral ligament. 



THE STIFLE JOINT 



233 



half an incli wide, and lies under the narrow articular area which connects the trochlea and medial 
condyle. The lateral communication occurs in 18 to 25 per cent, of cases, according to Baum; in 
rare cases it is larger than the inner one. It is instructive to distend this capsule and thus obtain 
an idea of its potential capacity and relations (Fig. 246). 

Ligaments. — The femoro-patellar ligaments, lateral and medial (Lig. feinoro- 
patellare fibulare, tibiale), are two thin bands which reinforce the capsule on either 



Femur — 



Accessory cartilage of 
patella 



Medial ridge of trochlea 
Medial patellar ligament 

Medial epicomli/l, 

Medial femoro-l ihml 
ligament 

Medial meni>:iii-: 
Medial condyle of tibia 



Tuberosity of tibia 




Patella 



Biceps feinoris 

Lateral patellar ligament 



Lateral femoro-tibial 
ligament 



Lateral meniscus 



Lateral condyle of tibia 



Fig. 245. — Left Stifle Joint of Horse; r 
1, Middle patellar ligament; 2, stump of fascia lata: 3. s 



Interosseous space 

Fibula 

Interosseous ligamenl 



The Capsules are Removed. 

tendon of extensor longus and peroneus 



side. The lateral ligament is fairly distinct ; it arises from the lateral epicondyle of 
the femur just above the lateral femoro-tibial ligament, and ends on the lateral 
border of the patella. The medial ligament i.s thinner and is not distinct from the 
capsule; it arises above the medial epicondyle, and ends on the patellar fibro-car- 
tilage. 

The patellar ligaments (Ligg. patellae)' are three very strong bands which at- 

' They are also termed the straight ligaments of the patella. This terra seems objectionable 
since they are all oblique in direction. 



234 



THE ARTICULATIONS OF THE HORSE 



tach the patella to the tuberosity of the tibia. The lateral patellar ligament ex- 
tends from the lateral part of the anterior surface of the patella to the lateral part 
of the tuberosity of the tibia. It receives a strong tendon from the biceps femoris 
muscle and also part of the fascia lata. The middle patellar ligament extends 
from the front of the apex of the patella to the distal part of the groove on the 
tuberosity of the tibia; a bursa is interposed between the ligament and the upper 
part of the groove, and a smaller one occurs between the upper part of the ligament 
and the apex of the patella. The medial patellar ligament is attached above to the 



Proximnl ertd of 
Shaft femoro-pdtcllar 

of capsule 



Lateral head of gastrocnemius 

Lateral femoro-patellar ligament 

AUachmeiit of joint capsule 
Lateral condyle of femur 
Lateral femoro-tibial ligament- 
Popliteus 



Deep digital flexor 




Base of patella 



f-Distal end of capstde 
Middle patellar ligament 
Medial patellar ligament 

Lateral patellar ligament 
{slump) 



Tuberosity of tibia 

Tibialis anterior 



Long extensor 



Lateral extensor 



Fig. 246. — Right Stifle Joint of Horse; Lateral View. 
The femoro-patollar c.ipsule was filled with plaster-of-Paris and then removed after the cast was set. The femoro- 
tibial capsule and most of the lateral patellar ligament are removed. M, Lateral meniscus. 



patellar fibro-cartilage, and ends on the tuberosity of the tibia at the medial side of 
the groove. It is joined by the common aponeurosis of the gracilis and sartorius, 
and its proximal part furnishes insertion to fibers of the vastus medialis. These 
so-callctl ligaments are, in reality, the tendons of insertion of the quadriceps 
femoris and biceps femoris muscles, and transmit the action of the latter to the 
tibia; they also function similarly for the other muscles attached to them as noted 
above. 

It \vill be noticed that the proximal attachments are further apart than the distal ones, so 
that the ligaments converge below. The medial ligament is especially oblique. The middle 
ligament is more deeply placed than the others, and therefore cannot usually be felt so distinctly 
in the living animal. The lateral hgament is very largely the tendon of the anterior part of the 



THE STIFLE JOINT 



235 



biceps femoris, but it also furnishes insertion to the tensor fasciae latse by means of the fascia 
lata, which blends with it. 

The femoro-tibial articulation (Articulatio femoro-tibialis) is formed between 
tlie condyles of the femur, the ])roximal end of the tibia, antl tlie interposed articular 
menisci or semilunar cartilages. 

Articular Surfaces. — The condyles of the femur are slightly oblique in direc- 
tion. The articular surface of the lateral one is more strongly curved than that of 
the medial one; the latter is confluent below with the medial ridge of the trochlea, 



Medial condyle of 
femur 
Medial fcinoro-tihial 
ligament 
Medial meniscus 

Medial condyle of 
tibia 




Base of palella 



iccessory cartilage 



Medial ridge of trochlea 



Medial patellar liga- 
ment 



cuddle patellar liga- 
ment 



Tuberosity of tibia 



247. — Left Stifle Joint of Hobse: 



while the narrow ridge which connects the lateral condyle with the trochlea is 
usually non-articular. The saddle-shaped surfaces of the condyles of the tibia are 
not adapted to the femoral condyles, and are in contact with only a small part of 
them. 

The menisci, lateral antl medial (Meniscus lateralis, medialis),' are two C- 
shaped or crescentic plates of fibro-cartilage which produce congruence in the ar- 
ticular surfaces. Each has a proximal concave surface adapted to the condyle of 
the femur, and a distal surface which fits the corresponding condyle of the tibia. 
' These are also commonly termed the semilunar cartilages, although they are not so shaped. 



236 



THE ARTICULATIONS OF THE HORSE 



The lateral meniscus does not cover the lateral and posterior part of the tibial con- 
dyle, over which the tendon of origin of the popliteus muscle plays. The peripheral 
border is thick and convex, the central one very thin and concave. The fibrous 
ends or ligaments are attached to the tibia in front of and behind the spine. The 
lateral meniscus has a third attachment by means of an oblique band (Ligamentum 
femorale menisci lateralis) which passes from the posterior end to the posterior 
part of the intercondyloid fossa of the femur. 



Base of paldla 



Medial ridge of 
trochlea 



Lateral patellar liga- 
ment 



Middle patellar liga- 
ment 



Lateral femoro-patellar 



Tiiherosif;/ of lihia 



Fia. 248. — Left Stif 
1, Stump of tendon of origin of ext 




Lateral femoro-tibial 
ligatiwtbl 



Lateral meniscus 



Lateral condyle of 
tibia 



: Joint of Horse; Latf.ral Vie',v. The Capsules are Removed. 
i3or longus and peroneus tertiua; 2, stump of fascia lata; 3, patellar attachment of 
biceps femoria and lateral patellar ligament. 



The ligaments of the medial meniscus (Ligamenta tibialia anterius et posterius meni.sci medi- 
alis) are attached iu front of and behind the medial eminence of the spine. The anterior hgameiit 
of the lateral meniscus (Ligamentum tibiale anterius menisci lateralis) is attached in front of the 
lateral eminence of the spine. The posterior one bifurcates; the lower branch (Ligamentum tibiale 
posterius menisci lateralis) is inserted at the pophteal notch, the upper (Ligamentum femorale 
menisci lateralis) in a small fossa in the extreme posterior part of the intercondyloid fossa. 

The joint capsule is attached to the margin of the tibial articular surface, 
but on the femur the line of attachment is for the greater part about half an inch 
(ca. 1 cm.) from the articular margin. It is also attached to the convex borders of 
the menisci and to the cruciate ligaments. It is thin in front, where it consists 



THE STIFLE JOINT 



237 



practically of the synovial layer only. It is much stronger posteriorly: here it 
is reinforced by what might be regarded as a posterior ligament. This is a 
strong, flat band which arises from the femur just lateral to the origin of the medial 
head of the gastrocnemius, and extends down to the posterior border of the medial 
condyle of the tibia; it is wider below than above. There are two synovial sacs, 
corresponding to the double nature of the articular surfaces; they do not usually 
communicate, and each is partially divided into an upper and a lower compartment 
by the meniscus. The medial sac pouches upward about half an inch over the con- 



Laleral condyle of 
femur 



Lntcral femoro- .° 
tibial ligament 
Stump of p<ij)- 
liteus tendon 
Lateral meniscus 



Lateral condyle of ^ '|^ 
tibia 'i m 



Head of fil 



Interosseous space 




Medial femoro- 
tibial ligament 



Medial condyle of 
femur 



Medial meniscus 



Medial condyle of 
tibia 



Fig. 249. — Left Stifle Joint of Horse 
1, Femoral ligament of lateral meniscus; 2, posterior ligament of lateral i 
posterior cruciate ligament. 



Capsule is Removed. 

3, anterior cruciate ligament; 4, 



dyle of the femur. The lateral sac invests the tendon of origin of the popliteus 
muscle, and also pouches downward about three inches (ca. 7.5 cm.) beneath the 
peroneus tertius and extensor longus muscles. As stated above, the lateral sac 
sometimes communicates with the femoro-patellar joint cavity, and the medial 
sac usually does so in the adult. 

Ligaments. — There are four of these — two collateral and two cruciate. 

The medial ligament (Lig. collateral tibiale) is attached above to the prom- 
inent medial epicondyle of the femur, and below to a rough area below the margin 
of the medial condyle of the tibia. 



238 



THE ARTICULATIONS OF THE HORSE 



The lateral ligament (Lig. coUaterale fibulare) is somewhat thicker; it arises from 
the upper depression on the lateral epicondyle, and ends on the head of the fibula. 

Lateral patellar 
ligament 



Medial patellar 
ligament 



Medial condyle 




Medial meniscus 



Fig. 250. — Proximal End of Right Tibia with Menisci, Etc. 
1, 2, Anterior and posterior cruciate ligaments: 3, posterior ligament of medial meniscus; 4, femoral ligament of 
lateral meniscus; 5, 5', anterior ligaments of menisci; 6, groove for popliteus tendon; 7, spine of tibia; 8, 9, medial 
and lateral femoro-tibial ligaments. 



It covers the tendon of the origin of the popliteus muscle, a bursa being interposed 

between the two; another bursa is present 
between the lower part of the ligament and 
the margin of the lateral condyle of the tibia. 
The cruciate ligaments are two strong 
rounded bands situated mainly in the inter- 
condyloid fossa of the femur, between the two 
synovial sacs. They cross each other some- 
what in the form of an X, and are named ac- 
cording to their tibial attachments. The 
anterior cruciate ligament (Lig. cruciatum an- 
terius) arises in the central fossa on the tiljial 
spine, extends upward and backward, and ends 
on the lateral wall of the intercondyloid fossa. 
The posterior cruciate ligament (Lig. crucia- 
tum posterius) is medial to the preceding, and 
is somewhat larger. It is attached to an emi- 
nence at the popliteal notch of the tibia, is 
1, 2, Medial and lateral patellar ligaments; ^Yivecied upward and forward, and cncls in the 

3, 4, anterior ligaments of menisci; a, 7, anterior " ^ ' ^ 

and posterior cruciate ligaments; G, posterior ailteriOr part of the interCOllclA'loicl foSSa of 

ligament of medial meniscus. tll6 femUt' 

It may be added that these ligaments do not lie in a sagittal plane, but are somewhat twisted 
across each other; outward rotation of the leg untwists and slackens them. 

Movements. — The principal movements of the stifle joint as a whole are 




Fig. 251. — Proximal End of Right Tibia of 
Horse, with Areas of Ligamentous At- 



TIBIO-FIBULAR ARTICULATION — THE HOCK JOINT 239 

flexion and extension. In the ordinary standing position the articular angle 
(l)ehind) is about 140° to 150°. Flexion is limited only by contact of the leg with 
the thigh, if the hock is also flexed. Extension is incomplete, i. e., the femur anil 
tibia cannot be brought into the same straight line. Rotation is limited, and is 
freest during semiflexion. The patella glides on the femoral trochlea upward in 
extension, downward in flexion. 

Extension is checked mainly by tension of the cruciate and collateral ligaments. In extreme 
extension, which is accompanied by slight outward rotation of the leg, the patella can be pushed 
upward and inward so that its fibro-cartilage hooks over the upper end of the medial ridge of the 
trochlea, but it will not remain there unless held in position. When pressure is removed, the base 
of the patella tips forward and the cartilage lies upon the most prominent part of the trochlear 
ridge. During flexion, which is accompanied by slight inward rotation of the leg, the condyles 
of the femm' and the menisci glide backward on the tibia; the movement of the lateral condyle 
and meniscus is greater than that of the medial one. In extreme flexion the patellar and posterior 
cruciate ligaments are tense; the other ligaments are relaxed. The movement of the patella is 
gliding with coaptation, i. e., different parts of the opposing articular surfaces come into contact 
successively. Only a narrow transverse strip (ca. 1.5-2 cm. wide) of the patella is in contact 
with the trochlea at a time. 

TIBIO-FIBULAR ARTICULATION 

This joint (Articulatio tibiofibularis) is formed bj' the head of the fibula ar- 
ticulating with a crescentic facet just l^elow the outer margin of the lateral condyle 
of the tibia. The joint capsule is strong and close. The shaft of the fibula is at- 
tacheil to the lateral bortler of the tibia by the interosseous membrane of the leg 
(Membrana interossea cruris) ; this is perforated about an inch from its proximal 
end b>' an opening which transmits the anterior tibial vessels to the front of the tibia. 
A fibrous cord usually extends from the distal end of the shaft of the fibula to the 
lateral malleolus. The latter is the distal end of the fibula which has fused with the 
tibia. No appreciable movement occurs in this joint. 



THE HOCK JOINT 

This is a composite joint made up of a numl^er of articulations (Artie ulationes 
tarsi). These are: (1) The tibio-tarsal articulation; (2) the intertarsal articula- 
tions; (3) the tarso-metatarsal articulation. 

The tibio-tarsal articulation (Articulatio talocruralis) is a typical ginglymus 
formed bj' the trochlea of tlie tibial tarsal bone and the corresponding surface of the 
distal end of the tibia. The ridges and grooves of these surfaces are directed ob- 
liquelj' forward and outward at an angle of about 12° to 15° with a sagittal plane. 
The trochlear surface is about twice as extensive as that on the tibia, and its ridges 
have a spiral curvature. The other articulations are arthrodia, which have joint 
surfaces and ligaments of such a nature as to allow onl\' a minimal amount of glid- 
ing motion. 

As in the case of the carpal joints, it is convenient to describe first the common 
capsule and ligaments, which are the more important practically, and then to 
consider very briefly the .special ligaments. 

The filsrous part of the joint capsule is attached around the margin of the 
tibial-- articular surface above and the metatarsal surfaces below; it is also attached 
in part to the surfaces of the bones which it covers, and blends with the collateral 
ligaments. Its dorsal part (anterior ligament) is rather thin; in distention of the 
capsule, as in "bog-spavin," its antero-medial part, which is not bound down by 
the tendons passing over the joint, forms a fluctuating swelling over the medial 
ridge of the trochlea. The plantar part (posterior and tarso-metatarsal ligaments) 
is verj' thick below, and is intimately attached to the tarsal bones. It is in part 
cartilaginous, and forms a smooth surface for the deep flexor tendon. The proximal 
part pouches upward behind the distal end of the tibia for a distance of about two 



240 



THE ARTICULATIONS OF THE HORSE 



inches (ca. 5 cm.); here it is thin. It is continued downward to form the sub- 
tarsal or check ligament, which unites with the deep flexor tendon a))out the mid- 
dle of the metatarsus. 

There are four synovial sacs: 1. Tlie tibio-tarsal sac lul^ricates the proximal 
joint, and is much the largest and most important.' 2. The proximal intertarsal 
sac lines the joints formed by the tibial and fibular tarsal bones aljove, and the cen- 
tral and fourth tarsals l)elow; it communicates in front with the tiliio-tarsal sac. 
3. The distal intertarsal sac lubricates the joints formed between the central tarsal 
and the bones below and on either side. 4. The tarso-metatarsal sac lubricates 




Medial malleolus 

Long medial ligament \ 
Trochlea of tibial tarsal bom; ' 



Dorsal ligament 




^ i - - — • Plantar ligament 



I 



Mt. II 




Fig. 252. — Right Hock Joint of Horse; Medial View. The Capsule is Removed. 

1, 2, Branches of short part of medial ligament; 3, tarso-metatarsal ligament; -4, proximal tuberosity of tibial tarsal 

bone; 5, sustentaculum; 6, groove for deep flexor tendon; Mt. II, Mt. Ill, metatarsal bones. 



the joints formed between the tarsal and metatarsal l)ones, those between the 
proximal ends of the metatarsal bones, and tliose formetl by the third tarsal with 
the bones on either side. 

Common Ligaments. — The lateral ligament (Lig. collaterale filiulare) consists 
of two distinct bands which cross each other. The long lateral ligament (Lig. 
collaterale laterale longum) is superficial ; it arises on the posterior part of the lateral 
malleolus, is directed almost straight downward, and is attached to the fibular and 
fourth tarsal liones and the large and lateral small metatarsal bones. It forms a 
canal for the lateral extensor tendon. The short lateral ligament (Lig. collaterale 

' It is this part of the capsule which is cliiefly involved in distention by excess of fluid in the 
joint cavity (as in "bog-.spavin"). 



THE HOCK JOINT 



241 



laterale breve) is deeper; it arises on the anterior part of the lateral malleolus, is 
directed chiefly backward, and ends on the rough excavation on the lateral surface 
of the tibial tarsal and the adjacent surface of the fibular tarsal bone. 

The medial ligament (Lig. coUaterale tibiale) also consists of two parts which 
cross each other. The long medial ligament (Lig. collaterale mediale longum) 
is superficial ; it arises on the posterior part of the medial malleolus, becomes wider 
below, and is attached on the distal tuberosity of the til)ial tarsal, the large and 
medial small metatarsal l^ones, and the surface of the lower tarsal bones which it 



Tuber calcis 



Plantar ligament 



Mt.IV 



Fig. 253.— Right Hoc: 




Short lateral ligament 
Long lateral liganie7it 



C-^psuLE IS Removed. 

of fibular tarsal bone: 2, groove for 



1, Ligament connecting lateral ridge of tibial tarsal with processus cochlei 
lateral extensor tendon: T. /., lateral ridge of trochlea of tibial tarsal bone; T. c, central tarsal bone; T. 3, third tarsal 
bone: Mt. Ill, ML IV, metatar.sal bones. 



covers. The short medial ligament (Lig. collaterale mediale breve) lies largely 
under cover of the long one. It extends from the anterior part of the medial malleo- 
lus, runs backward and somewhat downward, and divides into two branches; one 
of these ends on the proximal tuberosity on the medial surface of the tibial tarsal 
bone, the other on the sustentaculum tali. 

The plantar ligament (Lig. tarsi plantare)' is a very strong, flat band which 
covers the outer part of the plantar surface of the tarsus. It is attached to the 
plantar surface of the filndar antl fourth tarsal bones and the proximal end of the 
lateral metatarsal bone. 

The dorsal ligament (Lig. tarsi dorsale)- is a triangular sheet which is attached 

' Also termed the calcaneo-metatarsal ligament. - Also known a3 the oblique ligament. 

16 



242 



THE ARTICULATIONS OF THE HORSE 



above to the distal tuberosity on the medial face of the tibial tarsal bone, and 
spreads out below on the central and third tarsal bones, and the proximal ends of 
the large and outer small metatarsal bones, to all of which it is attached. 

Special Ligaments. — A considerable number of short bands which connect 
adjacent bones of the tarsus and metatarsus are described by various authors; 
some of these are quite distinct; others are difficult to isolate. Most of them are 
not of sufficient importance to justify detailed description. 



Lateral malleolus 



Short, lateral ligament 



Trochlea of tibial tarsal 
hone 



ML IV 




Short medial ligaments 



ligament 



FROM THE FrOXT AN'D SlIGHTLV LaTERAL 

> Long Collateral Ligaments. 



■ After Removal of 



Fig. 254. — Right Hock Joint or Horse. Vi 
Joint Capsui 

T. t.. Tibial tarsal bone (distal tuberosity): T. c, central tarsal bone; T. 3, ridge of third tarsal bone; T.f., fibular tarsal 
bono (distal end); T. 4* fourtti tarsal bone; Mt. Ill, Mt. IV, metatarsal bones. Arrow points to vascular canal. 



(1) The tibial and fibular tarsal bones are united by four bands (astragalo-calcaneal liga- 
ments). The medial ligament extends from the sustentaculum taU to the adjacent part of the 
tibial tarsal, Ijlcndinj? «itli the short collateral ligament. The lateral ligament extends from the 
cochlear process of the fibular tarsal to the adjacent part of the lateral ridge of the trochlea. 
The proximal ligament extends from the posterior margin of the trochlea to the fibular tarsal. 
The interosseous ligament is deeply placed in the sinus tarsi between the two bones, and is at- 
tached in the rough areas of the opposed surfaces. 

(2) The smaller bones are attached to each other as follows: The central and third tarsal are 
united by an interosseous and an obUque dorsal ligament (scaphoido-cunean ligaments). The 
central and fourth tarsal are united by an interosseous and a lateral transverse hgament (cuboido- 
scaphoid Ugament). The third and fourth tarsals are similarly connected (cuboido-cunean Uga- 
ments). The third tarsal is joined by an interosseous (intercunean) ligament to the (fused) first 
and second tarsals; the latter are connected with the fourth tarsal by a plantar transverse liga- 
ment. 

(3) The smaller bones are connected with the proximal row as follows: The central is 



THE HOCK JOINT 



243 



attached to the tibial by plantar and interosseous (astragalo-scaphoid) hgaments, and to the fibular 
tarsal by a short oblique (calcaneo-scaphoid) band. The fourth is attached to the fibular tarsal 
by interosseous and plantar (calcaneo-cuboid) ligaments. The (fused) first and second tarsals 
are connected with the fibular tarsal by a plantar (calcaneo-cunean) ligament. 

(4) The distal tarsal bones are connected with the metatarsus liy tarso-metatarsal ligaments, 
which are not distinct from the common Ugaments, except in the case of the interosseous ligament 
between the third tarsal and metatarsal bones. 

Movements. — These are flexion and extension, which take place at the tibio- 
tarsal joint. The movements between the tarsal liones, and between the latter 
and the metatarsus, are so limited as to be negligible so far as the action of the joint 
as a whole is concernetl. In the standing position the articular angle (in front) 



Superficial flexor tendon 

Gastrocnemius tendon 

Tarsal tendon of 
biceps femoris 

Calcanean bursa 

Gastrocnemius 
bursa 

Tuber calcis 

Upper pouch of 
joint capsule 

Tibial tarsal bone 



Interosseous ligament 

Plantar ligament 

Fourth tarsal bone 

Interosseous ligament 
Large metatarsal bone 

Suspensory ligament 
Check ligament 




Tibialis anterior 



Per one us tertius 



Tibio-tarsal joint cavity 
Joint capsule 
Centred tarsal bone 
Third tarsal bone 

Distal annular ligament 



Fig. 255. — Sagittal Section of Hock of Horse. 
The section is cut so far laterally that the deep flexor tendon does not show. 



is about 150° to 160°. Complete extension is prevented by tension of the collateral 
ligaments. Flexion is checked only by contact of the metatarsus with the leg, 
provided the stifle joint is also flexed. Owing to the fact that the axis of motion 
is slightly oblique, the lower part of the limb deviates somewhat outward during 
flexion. The long collateral ligaments are tense in extension, the short ones in 
flexion, of the joint. The movements of the hock joint nmst correspond with those 
of the stifle on account of the tendinous bands in front and behind (peroneus tertius 
and flexor superficialis), which ex-tend from the lower part of the femur to the tarsus 
and metatarsus. 

The remaining joints differ in no material respect from those of the thoracic 
limb. 



244 



COMPARATIVE ARTHROLOGY 



COMPARATIVE ARTHROLOGY i 
Joints and Ligaments of the Vertebra 

Ox. — The ligamentuni nuchse is better developed than in tlie horse. The 
funicular part is clearly divided into two lateral halves, which are round at their 
occipital attachment, Imt from the axis backward become rapidly wider and flat. 
This wide portion is almost sagittal, lies on either side of the vertebral spines, and 
is coveretl by the trapezius and rhomboideus muscles. From the highest part of 
the withers (third thoracic spine) it gradually diminishes in size and fades out in 
the lumbar region. The lamellar part is thick, and consists of anterior and pos- 
terior parts. The anterior part is double; its fibers proceed from the funicular 
part to the second, third, and fourth cervical spines. The posterior part is single; 
its fibers extend from the first thoracic spine to the fifth, sixth, and seventh cervical 
spines. 

The ventral longitudiual ligament is very strong in the Imubar region. 




Funicular part; 6, its 



Fir,. 25fi. T.TnAMENTTTM NtTCH.E OF Ox. 

dde portion; r, (/, lamellar part; e, interspinous ligament ; 7, spinous process of first thoracic 
vertebra; 2, axis (Ellenberger-Baum, Anat. d. Haustiere.) 



The intervertebral fibro-cartilages are thicker than in the horse. 

The interspinous ligaments of the back and loins consist largely of elastic 
tissue. 

There are no intertransverse joints in the lumbar region. 

Pig. — The ligamentuni nucha is represented by a fibrous raphe and thin 
layers of elastic tissue which extend between the cervical spines. 

The atlanto-occipital and atlanto-axial joints resemble those of the dog. 

Tlie interspinous ligaments of the neck are elastic. 

Dog. — The ligamentum nuchte consists of a small fibrous band which extends 
from the spine of the axis to the anterior thoracic spines; it may be regarded as a 
mere fibrous raphe between the right and left muscles. 

There are interspinous muscles instead of ligaments in the neck. 

There are three ligaments in connection with the dens of the axis. The two 
alar ligaments (Ligg. alaria) arise on either side of the dens, diverge, and end on 

' This section consists necessarily only of a brief statement of the most important differences 
in the joints of the other animals. 



ARTICULATIONS OF THE THORACIC LIMB 245 

either side of the foramen magnum. The transverse ligament of the atlas (Lig. 
transversum atlantis) stretches across the dorsal surface of tlie dens and binds it 
down on the ventral arch of the atlas, a bursa being interposed. It is attached on 
either side to the lateral mass of the atlas. 

The two capsules of the atlanto-occipital joint communicate with each other, 
and usually with the capsule of the atlanto-axial joint also. 



Articulations of the Thorax 

Ox. — The second to the eleventh costo-chondral joints inclusive are diarthroses 
with close capsules, reinforced externally. (They are synchondroses in the sheep.) 
The upper parts of the cartilages are attached to each other by distinct elastic liga- 
ments (Ligg. intercostalia) . 

The first pair of chondro-sternal joints are separate from each other; inter- 
crossing filjers unite the costo-chondral junctions above the joints. 

The first segment of the sternum forms with the body a diarthrodial interstemal 
joint (Articulatio intersternaHs). The anterior joint surface is concave, the pos- 
terior convex. The joint is surrounded by a close capsule, and the joint surfaces 
are attached to each by a small inter-articular ligament. Limited lateral move- 
ment is possible. (In the sheep the joint is a synchondrosis.) Both surfaces of the 
sternum are covered by a layer of fibrous tissue (Membrana sterni). 

Pig. — The second to the fifth or sixth costo-chondral joints are diarthroses. 
The intersternal articulation antl tjie sternal ligaments resemble those of the ox. 

Dog. — The first chondro-sternal joints do not coalesce. The internal sternal 
ligament divides into three bands. 



TEMPORO-MANDIBULAR ARTICULATION 

Ox. — The articular surfaces are of such a character as to permit more extensive 
transverse movement than in the horse {vide Osteology). The posterior ligament 
is absent. 

Pig. — The considerable longitudinal diameter of the temporal articular sur- 
faces and the very small size of the postglenoid process allow great freedom of 
protraction and retraction of the lower jaw. Transverse movement is limited. 
The posterior ligament is absent. 

Dog. — The articular surfaces allow extremely little transverse or gliding move- 
ment. They are cylindrical in curvature, and the interarticular disc is very thin. 
The posterior ligament is absent. 

The other articulations of the skull are sufficiently described in the Osteology. 



Articulations of the Thoracic Limb 
shoulder joint 

Ox. — The articular angle is about 100°. 

Pig and Dog. — The joint capsule communicates so freely with the bicipital 
bursa that the latter may well be regarded as a pouch of the capsule. There is a 
rudimentary marginal cartilage around the rim of the glenoid cavity. In the pig 
the front of the capsule is reinforced by cruciate bands. In the dog there is usu- 
ally a strong band extending from the acromion to the lateral part of the capsule; 
another band (Ligamentum coraco-acromiale) often stretches between the scapular 
tuberosity and the acromion. 



246 COMPARATIVE AKTHROLOGY 

ELBOW JOINT 

Ox. — No important differences exist. The upper part of the interosseous 
raclio-ulnar ligament is conunonlj' ossified in the adult. 

Pig. — There are no important differences. The radius and ulna are so firmly 
united by the interosseous ligament as to prevent any appreciable movement be- 
tween them. 

Dog. — The joint capsule is reinforced in front by an oblique ligament which 
arises on the front of the lateral condyle of the humerus above the joint surface, 
and joins the terminal part of the biceps and brachialis below. There is a strong 
reinforcement of the postero-medial part of the capsule, which extends obliquely 
from the medial side of the olecranon fossa to the ulna, just above the processus an- 
coneus. The lateral ligament is much stronger than the medial one. It is attached 
above to the lateral epicondyle of the humerus, and below chiefiy to the eminence 
distal to the neck of the radius ; but part of it inclines backward and is attached to 
the ulna. The middle part of the ligament is wide and forms a sort of cap over the 
proximal tuberosity of the radius. From this part a band, the annular ligament 
of the radius (Lig. annulare radii), extends across the front of the proximal end of 
the radius and ends on the ulna; although incorporated in the joint capsule it is 
easily defined. The medial ligament is more slender. It arises from the medial 
epicondyle of the hmnerus and passes deeplj' into the proximal part of the inter- 
osseous space, ending chiefly on the posterior surface of the radius a little medial to 
the attachment of the lateral ligament; there is also a small attachment to the 
interosseous border of the ulna. This ligament is very oblique. An elastic band 
(Ligamentum olecrani) extends from the lateral surface of the medial epicondyle 
to the anterior border of the ulna. 

There are two radio-ulnar joints. The proximal radio-ulnar joint (Articulatio 
radioulnaris proximalis)is included in the capsule of the elbow, but is provided with 
an annular ligament, as described above. The distal radio-ulnar joint (Articulatio 
radioulnaris tlistalis) is formed by a concave facet on the radius and a convex one on 
the ulna, and is surrounded by a tight capsule. The interosseous membrane unites 
the shafts of the two bones; its proximal part is specially strong and is attached to 
prominences on both bones. The movements consist of limited rotation of the 
radius (ca. 20°), carrying the paw ^\'ith it. The ordinary position is termed prona- 
tion; outward rotation is supination.' 



THE CARPAL JOINTS 

These have the same general arrangement as in the horse. Numerous minor 
differences naturally exist, but must be excluded from this brief account, which 
contains only important special features. 

The lateral and medial movements are freer, especially in the dog, but flexion is 
not so complete : the anatomical explanation of these facts lies in the nature of the 
articular surfaces and certain ligamentous differences. The collateral ligaments are 
much weaker, the long lateral one being especially small in the ox. Two oblique, 
somewhat elastic bands cross the front of the radio-carjjal and intercai-pal joints. 
The proximal one is attached to the distal end of the radius and passes downward 
and outward to the ulnar carpal bone; the other one connects the radial and fourth 
carpal bones in a similar fashion. 

In the ox the short collateral ligaments are well defined; a ligament connects 
the accessory carpal with the distal end of the ulna, and strong volar bands connect 

' These movements are best seen in man, in whom the back of the hand may be turned for- 
ward (pronation) or backward (supination). In tlie dog the rotation is nmch restricted and is 
freest when the elbow is flexed. 



INTERMETACARPAL JOINTS — METACARPO-PHALANGEAL JOINTS 



247 



the distal bones with the metacarpus 
uhiar carpal bone with the meta- 
carpus. 

The dorsal, volar, and interos- 
seous carpal ligaments vary with the 
number of carpal bones present in 
the different species. 

In the dog there are sL\ dorsal 
and six volar ligaments. The inter- 
osseous ligaments are not inter- 
ordinal. The accessory carpal bone 
is attached by ligaments to the ulna, 
the radio-intermediate, and the 
third, fourth, and fifth metacarpal 
bones. The distal carpal bones are 
attached to the metacarpal bones by 
dorsal and volar ligaments. 

INTERMETACARPAL JOINTS 
In the ox the small (fifth) meta- 
carpal bone articulates with the large 
metacarpal, but not with the carpus. 
The joint cavity is connected with 
that of the carpo-metacarpal sac. 
The proximal end of the small meta- 
carpal bone is attached by a ligament 
to the fourth carpal, and another 
band extends from its distal part 
to the side of the large metacarpal. 
There is also an interosseous liga- 
ment, which is permanent and allows 
a small amount of movement. 

The chief metacarpal bones of 
the pig, and the second to the fifth of 
the dog, articulate with each other 
at their proximal ends, and are con- 
nected by interosseous ligaments, 
which do not, however, unite them 
closely, as in the horse. There are 
feeble dorsal and volar ligaments 
(Ligg. basium) which unite the 
proximal ends of the metacarpal 
bones in the dog. 



A strong oblique ligament connects the 




Fig. 257.— Distal J 
AND Tendons. 
LAR Part ( 



I OF Ox, Showing 

AND C'ORRESPOND 



Ligaments 
NO Articu- 



One D 
' Metacarpal Bone are Removed. 
a. Suspensory ligament: a', branch of a to superficial flexor 
tendon: a", a'", lateral and central branches of a; 6, deep flexor 
tendon: b', branch of b to digit removed: c, c, superficial flexor 
tendon: rf, d', intersesamoid ligament (cut): e, interdigital col- 
lateral ligament of fetlock joint; /, tendon of commoji extensor; 

METACARPO-PHALANGEAL JOINTS " """"'"'"' •""■-'^""'"' i—""""'- '■ 'i""t»i »'"■"' 

Ox. — There are two joints, one 
for each digit. The volar parts of 
the two joint capsules communicate. 
The two interdigital collateral liga- 
ments (Ligg. collateralia interdigi- 
talia) result from the bifurcation of a 

band which arises in the furrow between the divisions of the distal end of the large 
metacarpal bone; they spread out and end on the proximal ends of the first pha- 



g, proximal interdigital Hgament; h, digital annular ligament; 
i, posterior annular ligament of fetlock; ^•, collateral ligament 
of pastern joint; /, distal interdigital ligament; m, cruciate inter- 
digital ligament (cut); m', m", attachments of m to second pha- 
lanx and distal sesamoid bone; n. suspensory ligament of distal 
sesamoid; o, dorsal elastic hgament: p, lateral volar ligament 
of pastern joint; I, metacarpus, sawn off at 1'; 3, first phalanx; 
S, second phalanx; 4. third phalanx. (Ellenberger-Baum, Anat. 
d. Haustiere.) 



248 COMPARATIVE ARTHROLOGY 

langes. The other collateral ligaments are arranged like those of the horse. A strong 
interdigital ligament (Lig. interdigitale), consisting of short intercrossing fibers, 
unites the middles of the interdigital surfaces of the first phalanges of the chief digits. 
It prevents untlue divergence of the phalanges. It is not present in the sheep. 

Cruciate ligaments (Ligg. phalango-sesamoidese) connect the proximal sesamoids 
with the proximal end of the opposite first phalanx. 

The intersesamoid ligament connects all four sesamoids, and extends upward 
much less than in the horse. 

The laterate and medial sesamoidean ligaments end chiefly on the first phalanges, 
but also detach a small part to the large metacarpal bone. 

The superficial or straight distal sesamoidean ligament is absent. The middle 
distal sesamoidean ligaments of each digit are two short, strong bands which extend 
from the distal margins of the proximal sesamoids to the proximal ends of the first 
phalanges. The deep distal sesamoidean ligaments are strong and distinctly 
cruciate. 

The suspensory ligament or interosseus tendon contains more muscular 
tissue than in the horse — indeed, in the young animal it consists almost entirely of 
muscular tissue. At the distal third of the metacarpus it divides into three branches. 
These give rise to five subdivisions, either by bifurcation of the lateral and medial 
branches or trifurcation of the middle branch. The two lateral and two medial 
bands end on the proximal sesamoid bones and the distal end of the large meta- 
carpal bone, and detach slips to the extensor tendons. The middle band passes 
through the groove between the two divisions of the distal end of the metacarpus, 
and divides into two branches which join the tendons of the proper extensors of the 
digits; it sends fibers also to the interdigital collateral ligaments and to the central 
sesamoids. About the middle of the metacarpus the suspensory ligament detaches 
a band which unites lower clown with the superficial flexor tendon, thus inclosing 
the tendon of the deep flexor of the digit; it also l^Iends with the thick fascia of the 
region. The latter gives off a band on either side to the accessory digits, and a ten-, 
dinous laand descends from each accessory digit to the third phalanx and distal sesa- 
moid bone, blending with the tendon of the corresponding proper extensor. 

Pig. — There are four metacarpo-phalangeal joints, each of which has a capsule, 
collateral, intersesamoidean, and cruciate sesamoidean ligaments. Since distinct 
interosseous muscles are present, there are, of course, no suspensory ligaments. 

Dog. — There are five metacarpo-phalangeal joints, each having its own capsule 
and indistinct collateral ligaments. A small sesamoid bone occurs in the anterior 
part of each capsule, over which the corresponding extensor tendon plays. The 
intersesamoidean ligaments do not extend above the sesamoids. The cruciate 
ligaments are present, as well as a fibrous layer which attaches the distal margins 
of the sesamoids to the posterior surface of the jDroximal end of the first phalamx. 



INTERPHALANGEAL JOINTS 

Ox. — The two proximal joints have separate capsules, and broad, but rather 
inchstinct, collateral hgaments. Each joint has also central and collateral volar 
ligaments. The central ligaments are largely fused to form a strong band which is 
attached by two branches to the distal end of the first phalanx and to the depression 
on the volar surface of the proximal end of the second phalanx. The collateral ones 
extend from the borders of the first phalanx to the proximal end of the second 
phalanx; those on the interdigital side are weak and indistinct. 

The distal interphalangeal joints have, in arldition to the capsules and collateral 
ligaments, bands which reinforce them on either side. The interdigital pair arise 
in the depressions on the distal ends of the first phalanges, receive fibers from the 
second phalanges, and end on the interdigital surfaces of the third phalanges at the 



INTERPHALANGEAL JOINTS 



249 



margin of the articular surface. The abaxial pair have a similar course, but are 
thinner, and end on the corresponding third sesamoid. An elastic band crosses the 
front of the second phalanx ol)liciuely, from the distal end of the first phalanx to the 
extensor process of the third phalanx. 

The cruciate or distal interdigital ligaments (Ligg. cruciata interdigitalia) are 
two strong bands which limit the separation of tlie digits. They are attached above 
to the abaxial eminences on the proximal ends of the secontl phalanges (blending 
with the collateral ligaments), cross the deep flexor tendon obliquely, and reach the 





Fio. 258. — LiGA 



Pia; 



Volar Vi 



a. Superficial flexor tendon; b, deep flexor tendon; b', 
branches of 6 to accessory digits: c. c', annular ligaments; 
d-d"\ ligaments of accessor>" digits: e, cruciate interdigital 
ligaments: /, /', spiral band around the flexor tendons of 
the accessory digits; g, abductor of accessory digit. (EUen- 
berger-Baum, Anat. d. Haustiere.) 



Fig. 259. — Ligaments and Tendons of Digits of 
Dog, Hind Limb; Volar View. 
a, a', Superficial flexor tendon; b, tendon to 
large pad; c, lumbricales muscles; d, interossei 
muscles; e, /, annular ligaments at metatarso- 
phalangeal joints: g, suspensory ligament of large 
pad; h, digital annular ligaments: i. deep flexor 
tendon: k, distal sesamoid: I, suspensory ligament 
of k; m, suspensory ligament of digital pad: n, 
digital pads. (EIlenberger-Baum, Anat. d. Haus- 
tiere.) 



interdigital space, where they intercross and blend. Most of the fibers end on the 
distal sesamoid of the opposite side, but some are attached to the interdigital as- 
pect of the second phalanx and the distal sesamoid of the same side. In the sheep 
there is, instead of the foregoing, a transverse ligament which is attached on either 
side to the interdigital surfaces of the second and third phalanges and the distal sesa- 
moid bone. It is related below to the skin, above to a pad of fat. 

Pig. — The interphalangeal joints of the chief digits resemble in general those 
of the ox. The distal interdigital ligament resembles, however, that of the sheep, 
and is intimately adherent to the skin. There is, besides, a remarkable arrange- 



250 COMPARATIVE ARTHROLOGY 

ment of ligaments which connect the small digits with each other and with the 
chief digits (Fig. 258). 

This apparatus is somewhat complex, but its chief features are as follows: A proximal inter- 
digital ligament is attached on either side to the third phalanges of the small cUgits, while centrally 
it blends with the annular ligaments of the flexor tendons behind the metacarpo-phalangeal 
joints of the chief chgits. Two bands (central longitudinal interdigital ligaments) arise on the 
bases of the small digits, cross the flexor tendons obliquely downward and centrally, pass through 
the proximal interdigital ligament, and blend below with the distal interdigital ligament. Two 
collateral bands (collateral longitudinal interdigital ligaments) are attached in common with the 
proximal interdigital Ugaments to the tliird phalanges of the small digits, and blend below with 
the outer part of the distal interdigital ligament. 

Dog. — Each joint has a capsule and two collateral ligaments. The distal 
joints have also two elastic dorsal ligaments (Ligg. dorsaha), which extend from 
the proximal end of the second jjhalanx to the ridge at the base of the third 
phalanx. They produce dorsal flexion of the joint, and thus raise or retract the 
claws when the flexor muscles relax. The distal sesamoids are represented by 
complementary cartilages attached to the volar margins of the articular surfaces 
of the third phalanges. 

Three interdigital ligaments restrict the spreading apart of the digits (Fig. 259). 
Two of these cross the volar surface of the proximal parts of the chief digits, i. e., 
one for the second and third, the other for the fourth and fifth ; they blend with the 
annular ligaments on either side. The third ligament is attached on either side to 
the foregoing ligaments and the annular ligaments of the third and fourth digits, 
and curves downward centrally, ending in the large pad on the paw. 



Articulations of the Pelvic Limb 

SACRO-ILIAC joint 

This joint and the pelvic ligaments present no very .striking diff'erences in the 
other animals except that the sacro-sciatic ligament in the dog is a narrow but 
strong banil which extends from the posterior part of the lateral margin of the 
sacrum to the tuljer ischii; it is the homologue of the ligamentum sacro-tuberosum 
of man. 

HIP JOINT 

Ox. — The shallowness of the acetabulum is compensated by the greater size 
of the marginal cartilage, which is specially large laterally. The head of the femur 
has a smaller radius of curvature than that of the horse, and the articular surface 
extends a consideral)le distance outward on the upper surface of the neck. The 
round ligament is entirely intra-articular; it is small, and sometimes absent. The 
accessory ligament is alnsent. 

There are no important differences in the other animals. 

STIFLE JOINT 

Ox. — There is a considerable connnunication between the femoro-patellar 
and medial femoro-tibial joint cavities; this is situated as in the horse, but is wider. 
A small communication with the lateral femoro-tibial capsule sometimes occurs. 
The two femoro-tibial capsules usually communicate. The middle patellar liga- 
ment is not sunken, as there is no groove on the tuberosity of the tibia where it is 
attached. The lateral patellar ligament fuses completely with the tendon of in- 
sertion of the biceps femoris, and a large synovial bursa is interposed between them 
and the lateral condyle of the femur. 

Pig. — The femoro-patellar capsule is strongly reinforced on both sides by bands 



TIBIO-FIBTJLAR JOINTS — HOCK JOINT 251 

which blend with the collateral femoro-tibial ligaments. The cavit^v is continuous 
below with that of the femoro-tibial joint. A sagittal synovial fold (rudimentum 
septi) extends up a short distance from the anterior cruciate ligament. The supra- 
patellar pouch extends an inch or more (ca. 2-3 cm.) above the trochlea; from this 
a pouch extends up beneath the quadriceps femoris almost an inch and communi- 
cates through a large round opening with the joint cavity. There is a strong 
ligamentum patellte, which has a bursa under its distal part. The tendon of the 
biceps femoris takes the place of the lateral patellar ligament. A small ligamentum 
transversum connects the anterior faces of the menisci. 

Dog. — The joint in general resembles that of the pig. The posterior part of 
the capsule contains two sesamoid bones, which are imbedded in the origin of the 
gastrocnemius. 

TIBIO-FIBULAR JOINTS 

Ox. — The proximal end of the fibula fuses with the lateral condyle of the 
tibia. The distal end remains separate, and forms an arthrosis with the distal end 
of the tibia; the movement here is imperceptible, as the two bones are closely 
united by strong peripheral fibers. 

Pig. — The i:)roxunal joint is provided with a capsule which is reinforced in 
front and behind l^y fibrous tissue. The interosseous ligament attaches the shaft 
of the fibula to the lateral border of the tibia. The distal joint is included in the 
capsule of the hock joint, and is strengthened by dorsal and plantar ligaments 
(Lig. malleoli lateralis dorsalis, plantaris), which extend ahnost transversely from 
one bone to the other. There is also an interosseous ligament. 

Dog. — The arrangement is essentially the same as in the pig, but there is no 
interosseous ligament in the distal joint. Not miconunonly the distal part of the 
shaft of the fibula and tibia are ankylosed. 



HOCK JOINT 

Ox. — There is very consideralilc mobility at the proximal intertarsal joint, the 
capsule of which is correspondingly roomy. The short lateral ligament is attached 
distally on the tibial tarsal only. A strong transverse ligament attaches the lateral 
malleolus (distal end of the fibula) to the back of the tibial tarsal bone. The dorsal 
ligament is narrow and thin. 

Pig. — The arrangement in general resembles that of the ox. The medial liga- 
ment consists of a thin superficial part which extends almost vertically from malleo- 
lus to metatarsus, and a very strong deep part, which runs from the malleolus back- 
ward and dowmward to the sustentaculum and tibial tarsal. The lateral ligament 
also consists of two parts. The small superficial part extends from the malleolus 
down to the lateral face of the body of the fibular tarsal bone. The stronger deep 
part arises from the anterior part of the malleolus, passes cheifly backward, widens, 
and ends on a ridge on the lateral surface of the fiJDular tarsal. A strong band ex- 
tends from the lateral face of the medial malleolus to a depression on the medial 
surface of the proximal part of the tibial tarsal bone. An oblique dorsal band con- 
nects the central and fourth tarsal bones. 

Dog. — The long collateral ligaments are very small, and the short ones double. 
The plantar ligament is weak, and ends on the fourth metacarpal bone. No dis- 
tinct dorsal ligament is present, unless we regard as such a ligament which extends 
from the neck of the tibial tarsal to the fourth tarsal and third metatarsal bones. 

The remaining joints resemble those of the thoracic limb. 



MYOLOGY 

Myology deals with the muscles and their accessory structures. The muscles 
(Musculi) are highly specialized organs, which are characterized ])y their property 
of contracting in a definite manner when stimulated. They are the active organs 
of motion. The contractile ]>art of the muscle is the muscular tissue. Three kinds 
of muscular tissue are recognized, viz.: (1) Striated or striped; (2) non-striated, 
unstriped or smooth; (3) cardiac, which may be regarded as a specialized variety 
of striated muscle. Only the first of these will be considered in this section. The 
striated muscles are for the most part connected directly or indirectly with the 
skeleton, upon which they act, and are hence often designated as skeletal muscles 
(Musculi skeleti), in distinction from non-striated muscle, which is often spoken 
of as visceral. The striated muscles cover the greater part of the skeleton, and play 
an important part in determining the form of the animal. They are red in color, 
the shade varying in different muscles and under various conditions. Some are in- 
timately associated with and attached to the skin, and are called cutaneous mus- 
cles (Musculi cutanei). The muscular part of each is composed of Ijundles of con- 
tractile fibers surrounded by a thin sheath of connective tissue, the perimysium. 

The description of the muscles may be arranged under the followng heads: (1) 
Name; (2) shape and position; (3) attachments; (4) action; (5) structure; (6) 
relations; (7) blood and nerve supply. 

(1) The name is determined by various considerations, e. g., the action, at- 
tachments, shape, position, direction, etc. In most cases two or more of these are 
combined to produce the name, e. g., flexor carpi radialis, longus colli, ol^liquus 
externus abdominis. 

A satisfactory comparative nomenclature is exceedingly difficult to work out, and much 
confusion exists in this respect. This is due in great part to the lack of a uniform l^asis for the 
formation of names and the difficulty in determining homologies in various species. 

(2) The shape is in many cases sufficiently definite and regular to allow the 
use of such terms as triangular, quadrilateral, fan-shaped, fusiform, etc. Some 
muscles are characterized as long, broad, short, etc. Orbicular or ring-like muscles 
circumscribe openings; since the contraction of such a muscle closes the orifice, it is 
often termed a sphincter. The position and direction are usually stated with refer- 
ence to the region occupied and to adjacent structures which may be presumed to be 
already known. 

(3) The attachments are in most cases to bone, but many muscles are attached 
to cartilage, ligaments, fascia, or the skin. As a matter of convenience, the term 
origin (Origo) is applied to the attachment which always or more commonly re- 
mains stationary when the muscle contracts; the more movable attachment is 
termed the insertion (Insertio). Such a distinction is often quite arbitrary, and 
cannot always be made, as the action may be reversible or both attachments may be 
freely movable. With respect to the muscles of the limbs, the proximal attachment 
is regarded as the origin and the distal one as the insertion. In all cases the attach- 
ment is made by fibrous tissue, the muscular tissue not coming into direct relation 
with the i^oint of attachment. But when the intermediate fibrous tissue is not evi- 
dent to the naked eye, it is customary to speak of a "fleshy attachment." The 
term "tendinous attachment" is applied to those cases in which the intermediate 
fibrous tissue — tendon or aponeurosis — is evident. A tendon (Tendo) is a band of 

252 



MYOLOGY 2o3 

dense white fibrous tissue by means of which a muscle is attached; an aponeurosis 
is a broad fibrous sheet which fulfils a similar function. 

(4) The action l^elongs rather to physiological study, but the main points are 
usually given in anatomical descriptions. In some cases "the action is simple, in 
others, complex. Muscles which concur in action are termed synergists; those 
which have oi:)posite actions are antagonists. 

(5) The consideration of structure includes the direction of the muscular fibers, 
the arrangement of the tendons, the synovial membranes, and any other accessory 
structures. The terms fieshy and tendinous are sometimes used to indicate the 
relative amounts of muscular and tendinous tissue. In the case of the long muscles 
of the limbs, the origin is termed the head (Caput), and when the muscle is fusi- 
form, the large fleshy part is often called the belly (Venter) of the muscle. Some 
muscles have two or more heads, and are hence designated as biceps, triceps, etc. A 
digastric muscle is one having two bellies and an intermediate tendon. In most 
muscles the muscle-fibers join the tendon at an acute angle, like the relation of the 
barbs of a feather to its shaft; hence the term peimate is applied to such an arrange- 
ment. When the fibers are so arranged on one side of the tendon the muscle is 
imipennate (M. unijiennatus); while one in which this arrangement exists on both 
sides is bipennate (Tvl. hipcnnatus). The structure may be still more complex, re- 
sulting in a multipennate muscle. The structure of many muscles is much more 
complex than a superficial examination would lead one to suppose. Frequent Ij- 

Mesotendm Fibrous sheath. 
^g^^^iLlf^^^^^ ^ynos/tal sheath 




A B 

260. — Diagrams of Cross-sections of Synovial Bursa (A) and Synovial Sheath (B) ; T, Tendon. 
In both the synovial sac is represented for the sake of clearness as though somewhat distended. 



they are intersected by tendinous layers or bands, knowai as tendinous intersec- 
tions. Intersecting bands or tracts wliich apjiear on the surface — usually as zig- 
zag lines — are termed tendinous inscriptions (Inscriptiones tendinese). 

(6) The relations constitute a very important part of anatomical topography, 
and a knowledge of them is fundamental to further study in this respect. 

(7) The blood and nerve supply are, of course, important on clinical grounds. 
The nerve supply is often of value in the determination of homologies. As might 
be expected, the muscles have a large blood supply. They are also provided with 
lymph-vessels. The nerves to the muscles are motor, sensory, and vasomotor m 
fimction. 

The accessory structures associated with the muscles are the sj-novial mem- 
branes and the fasciae. 

The synovial membranes are thin-walled sacs, similar to the sjmovial mem- 
branes of the joints, and having a similar function. Two forms are recognized. 
A synovial bursa (Bursa synovialis) is a simple sac which is interposed at a point of 
unusual jiressurc between a tendon or muscle and some underlying structure, com- 
monly a prominence of the skeleton. A s3movial sheath (Vagina sjTiovialis ten- 
dinis) differs from a bursa in the fact that the sac is folded around the tendon so that 
two layers can Ije distinguished: the inner one is adherent to the tendon, while the 
outer one lines the canal in ^\hich the tendon lies. The two layers are continuous 
along a fold termed the mesotendon. The arrangement is showTi in the annexed 
diagrams. The synovial membranes of joints in some places form extra-articular 



254 FASCIA AND MUSCLES OF THE HORSE 

pouches which act as Isursse. The synovial sheath is not to be confused with the 
fibrous sheath of a tendon (Vagina fibrosa tendinis) . 

The student will note in dissection that intermediate forms of these sacs occur. A synovial 
sheath may belong to two or more tendons in common; in such cases the synovial membrane is 
reflected from one tendon to the other, forming a secondary mesotendon. In the normal state 
these sacs cannot be recognized on external examination of the subject. It is only when they are 
distended that their presence is evident. 

The fasciae are sheets of connective tissue, composed mainly of bundles of white 
fibers, with a greater or less admixture of elastic fillers in some cases. At least two 
layers may usually be distinguished. The superficial fascia (Fascia superficialis) 
is subcutaneous, and is composed of loose connective tissue which usually contains 
more or less fat. The deep fascia is composed of one or more layers of dense fibrous 
tissue. Its deep face maj- be very slightly adherent to the underlying structures, 
but in many places it is attached to the skeleton, ligaments, and tendons. In many 
places laminae are given off from the deep face of the fascia, pass between muscles, 
and are attached to bones or ligaments; such layers are termed intermuscular septa 
(Septa intermuscularia). The groove in which a tendon lies is convert etl into a 
canal by a band or fascial sheet kno\vn as a vaginal or annular ligament (Lig. 
vaginale). Many fasciae furnish origin or insertion to muscles and thus act as 
tendons; such are tendinous in structure, so as to render the distinction between 
fascia and aponeurosis in these cases arbitrary. Burste occur in certain situations 
between the fascia and underlying structures, and are distinguished as subfascial 
bursas. Those between the fascia and the skin are subcutaneous bursae. 



FASCIA AND MUSCLES OF THE HORSE 

The cutaneous muscle or panniculus camosus (Musculus cutaneus) is a thin 
muscular layer developed in the superficial fascia. It is intimately adherent in 
great part to the skin, but has very little attachment to the skeleton. It does not 
cover the entire body, and may be conveniently divided into facial, cervical, omo- 
brachial, and abdominal parts. 

The facial part, m. cutaneus faciei, consists of a thin and usually incomplete 
muscular layer, which extends over the mandibular space and the masseter muscle. 
A distinct branch of it passes forward to the angle of the mouth and blends ^\dth the 
orbicularis oris. This part, the m. cutaneus labiorum, retracts the angle of the 
mouth, and has therefore been termed the retractor anguli oris. 

The cervical part, m. cutaneus coUi, is situated on the ventral region of the neck. 
It arises from the cariniform cartilage and a median fibrous raphe. The fibers are 
directed forward and diverge from the raphe to the sides of the neck in pennate 
fashion. It is thick at its sternal origin, but thins out in front and laterally. On 
the side of the neck it is attached to the cervical fascia, which acts as its aponeurosis. 
It is related deeply to the sterno-cephalicus, the brachio-cephalicus (in part) and 
the jugular vein. Some bundles extend uj^on the jiarotid gland, and in well- 
developed subjects it is continuous with the facia! part. 

The omo-brachial part, m. cutaneus omo-brachialis, covers the lateral surface 
of the shoulder and arm. Its fibers begin over the upper part of the scapula and 
extend to the proximal part of the forearm. Most of its fibers are vertical, but 
posteriorly they become oblique and are continued by the al:)dominal part. 

The abdominal part, m. cutaneus tnuici, covers a large part of the body be- 
hind the shoulder and arm. Its fibers are largely longitudinal. It is continuous 
in front with the omo-brachial part, and a tendinous layer from it passes forward 



THE FASCIA AND MUSCLES OF THE HEAD 255 

with the posterior deep pectoral muscle to the medial tuberosity of the humerus. 
Posteriorly it forms a fold, which, covered by the skin, forms the fold of the flank, 
and ends on the fascia above the stifle. The dorsal limit of the muscle corresponds 
approximately with a line drawn from the posterior angle of the scapula to the fold 
of the flank. Ventrally the two muscles are about a handbreadth apart in the um- 
bilical region. Further forward they diverge, so as to overlap the posterior deep 
pectoral muscle only to a small extent. Here the cutaneous muscle is closely ad- 
herent to the pectoral and contains the external thoracic vein. Posteriorly they 
diverge to the fold of the flank. 

The muscle is in general closely adherent to the skin and its contraction twitches 
the skin, thus getting rid of insects or other irritants. 



The Fasciae and Muscles of the Head 

The muscles of the head (]Mm. capitis) may be divided into three groups, viz.: 
(1) Superficial muscles, including the cutaneous muscle and those of the lips, cheeks, 
nostrils, eyelids, and exiernal ear; (2) the orbital muscles; (3) the mandibular 
muscles; (4) the hyoid muscles. 

The superficial fascia forms an almost continuous layer, but is very scanty 
around the natural orifices. It contains a niunber of the thin superficial muscles, 
so that care must lae exercised in removing the skin. Over the frontal and nasal 
bones the fascia blends with the periosteum. 

The deep fascia is of special interest in three regions. The temporal fascia 
(Fascia temporalis) covers the temporalis muscle, and is attached to the parietal 
and frontal crests medially, and to the zygomatic arch laterally. The buccal fascia 
(F. buccalis) covers the buccinator muscle and the free part of the outer surface of 
the ramus of the mandible. It is attached to the facial crest, and posteriorly it 
forms a band (Raphe pterygomandibulare) which stretches from the hamulus of the 
pterygoid bone to the mandible behind the last molar tooth. It is directly continu- 
ous with the pharyngeal fascia (F. pharyngea), which is attached to the great and 
thyroid cornua of the hyoid bone and the thyroid cartilage of the larynx; it covers 
the lateral walls of the pharynx, and blends dorsally wnth the median raphe of the 
constrictor muscles of the latter. 

Cutaneus faciei. — This has been described (p. 2.54). 

MUSCLES OF THE LIPS AND CHEEKS 

1. Orbicularis oris. — Thi.s is the sphincter muscle of the mouth; it is con- 
tinuous with the other muscles which converge to the lips. It lies between the 
skin and the mucous membrane of the lips, and is intimately adherent to the 
former. Most of the fibers run parallel to the free edges of the lips and have no 
direct attachment to the skeleton. 

Action. — It closes the lips. 

Blood-supply — Palato-labial, facial, and mental arteries. 

Nerve-supply. — Facial nerve. 

2. Levator nasolabialis.' — This thin muscle lies directly under the skin, and 
chiefly on the lateral surface of the nasal region. 

Origin. — The frontal and nasal bones. 

Insertion. — (1) The upper lip and the lateral wing of the nostril; (2) the com- 
missure of the lips. 

Action. — (1) To elevate the upper lip and the commissure; (2) to dilate the 
nostril. 

'Also termed the levator labii superioris alaeque nasi. 



256 



FASCIA AND MUSCLES OF THE HORSE 



Structure. — The muscle arises by a thin aponeurosis. The belly is also thin, 
and divides into two branches, between which the lateral dilator of the nostril passes. 
The dorsal branch reaches the nostril and upper lip, blending with the lateral di- 
lator; the ventral one is much smaller, and blends at the labial commissure with 
the orbicularis and buccinator. 

Relatiotm. — Superficially, the skin, fascia, and lateral dilator (in part) ; deeply, 




Fig. 261. — Muscles of Head of Horse; Lateral View. The M. ctttaneus is Removed. 
a, Levator labii superioris proprius; b, levator nasolabialis; c, brachiocephalicus; d, sterno-cephalicus; d', 
tendon of d; c, omo-hyoideus; /, dilatator naris lateralis; g, zygomaticus; li, buccinator; )'. depressor labii inferioris; 
k, orbicularis oris; t, lateralis nasi, dorsal part; m, masseter; n, parotido-auricularis; o, zygomatico-auricularis; p, 
interscutularis; p', fronto-scutularis, pars temporalis; q, cervico-auricularis profundus major; r, cervico-auricularis 
auperficialis; s, obliquus capitis anterior; i, splenius; r. occipito-mandibularis; y, mastoid tendon of brachiocephalicus; 
:&, posterior, 3, anterior, border of external ear; 5, scutiform cartilage; 5, zygomatic arch; iO, orbital fat; i 5, temporo- 
mandibular articulation; 27, facial crest; 30', angle of jaw; 37, external maxillary vein; 38, jugular vein; 39, facial 
vein; 40, parotid duct; 41, transverse facial vein; 4^, masseteric vein; 43, facial nerve; 44, parotid gland; 4d, chin; 
z, wing of atlas. By an oversight the superior buccal branch of the facial nerve is shown crossing over instead of under 
the zygomaticus. (After EUenberger-Baum, Anat. fiir Kiinstler.) 



the levator labii superioris proprius, lateral dilator (in part), buccinator, branches 
of the facial vessels and nerve, and the infraorbital arterj' and nerve. 

Blood-supplij. — Facial and palato-labial arteries. 

Nerve-sup pi [I . — Facial nerve. 

3. Levator labii superioris proprius. — This lies on. the dorso-lateral aspect of 
the face, partly covered by the pi-eceding muscle. 

Origin. — The lacrimal, malar, and maxillary bones at their junction. 



MUSCLES OF THE LIPS AND CHEEKS 



257 



Insertion. — The upper lip, by a common tendon with its fellow. 

Action. — Acting with its fellow, to elevate the upper lip. This action, if 
carried to the fullest extent, results in eversion of the lip. In unilateral action the 
lip is drawn upward and to the side of 
the muscle acting. 

Structure. — The muscle has a short, 
thin tendon of origin. The belly is at 
first flattened, but becomes narrower 
and thicker, then tapers over the nasal 
diverticulum, to terminate in a tendon. 
The tendons of the two muscles unite 
over the alar cartilages of the nostrils, 
forming an expansion which spreads 
out in the substance of the upper 
lip.i 

Relations. — Superficially, the skin, 
the levator nasolabialis, and the angu- 
lar vessels of the eye; deeply, the later- 
alis nasi, the transversus nasi, and the 
infraorbital artery and nerve. 

Blood-supply. — Facial artery. 

Nerve-supply. — Facial nerve. 

4. Zygomaticus. — This verj' thin 
muscle lies immediatelj' under the skin 
of the cheek. 

Origin. — The fascia covering the 
masseter muscle below the facial 
crest. 

Insertion. — The commissure of the 
lips, blending with the buccinator. 

Action. — To retract and raise the 
angle of the mouth. 

Structure. — Fleshy, with a thin 
aponeurotic origin. 

Relations. — Superficially, the skin; 
deeply, the buccinator. 

Blood- supply . — Facial artery. 

Nerve-supply. — Facial nerve. 

5. Incisivus superior. — This lies 
under the mucous memlirane of the 
upper lip. 

Origin. — The alveolar border of 
the premaxilla from the second incisor 
to the first cheek tooth. 

Insertion. — The upper lip. 

Action. — To depress the upper 
lip. 

6. Incisivus inferior. — This is ar- 
ranged in the lower lip like the pre- 
ceding muscle in the upper one. 

Origin. — The alveolar border of the mandible from the second incisor to a 
point near the first cheek tooth. 

1 In rare cases a branch is given off from the ventral border of the muscle. It passes forward 
and ends in the subcutaneous tissue at the posterior end of the diverticulum nasi. 
17 




Fig. 262. — Mttscles of Head op Horse; Dorsal View. 
The M. cctaneus is Removed. 
a. Levator labii superioris proprius; a', common 
tendon of a with opposite muscle; h. levator nasolabialis; 
/, dilatator naris lateralis ; g, zygomaticus ; I, lateralis 
nasi; n, parotido-auricularis; o", scutulo-auricularis super- 
ficialis superior; p, interscutularis ; p', fronto-scutularis, 
pars temporalis; r, cervico-auricularis superficialis; «, 
corrugator supercilii ; x, transversus nasi ; 2, posterior, 
3, anterior, border of external ear; S, scutiform cartilage; 
5, zygomatic arch; 10, supraorbital depression; 5-5, medial 
wing of nostril, containing lamina of alar cartilage; 39, 
facial vein. (After Ellenberger-Baum, Anat. fiir Kiinstler.) 



258 FASCIvE AND MUSCLES OF THE HORSE 

Insertion. — The alveolar border of the mandible from the second incisor to a 
point near the first cheek tooth. 

Insertion. — The skin of the lower lip and the prominence of the chin. 
Action. — To raise the lower lip. 

7. Mentalis.' — This is situated in the prominence of the chin. Its fibers arise 
from each side of the body of the mandible and are inserted into the skin of the 
chin. It is mingled with fat and strands of connective tissue, in which the roots 
of the tactile hairs are embedded. It raises and corrugates the skin to which it is 
attached. 

8. Depressor labii inferioris. — This muscle lies on the lateral surface of the 
ramus of the mandible, along the ventral border of the buccinator. 

Origin. — The alveolar border of the mandible near the coronoid process and 
the maxillary tuberosity, in common with the buccinator. 

Insertion. — The lower lip. 

Action. — To depress and retract the lower lip. 

Structure. — The tendon of origin and the belly are fused with the buccinator 
as far forward as the first cheek tooth. From this point forward the belly is dis- 
tinct and rounded, terminating in a tendon which spreads out in the lower lip, 
blending with the orbicularis and the muscle of the opposite side. 

Relations. — Superficially, the skin, masseter, facial vessels, and parotid duct; 
deeply, the mandible and inferior labial artery. 

Blood-supply. — Facial artery. 

Nerve-supphj. — Facial nerve. 

9. Buccinator. — This muscle lies in the lateral wall of the mouth, extending 
from the angle of the mouth to the maxillary tuberosity. 

Origin. — The lateral surface of the maxilla above the interalveolar space and 
the molar teeth; the alveolar border of the mandible at the interalveolar space and 
also posteriorly where it turns upward to the coronoid process; the pterygo-mandib- 
ular raphe. 

Insertion. — The angle of the mouth, blending with the orbicularis oris. 

Action. — To flatten the cheeks, thus pressing the food between the teeth; 
also to retract the angle of the mouth. 

Structure. — Two layers may be recognized. The superficial layer (Pars buc- 
calis) extends from the angle of the mouth to the masseter. It is incompletely pen- 
nate, having a longitudinal raphe on which most of the muscle-fibers converge. 
The upper fibers are directed chiefly downward and backward, the lower ones up- 
ward and backward. The deep layer (Pars molaris) consists mainly of longitudinal 
fibers. It blends in part with the superficial layer of the orbicularis; it has a 
small tendinous attachment to the coronoid process behind, and is united ventrally 
with the depressor labii inferioris. 

Relations. — Superficially, the skin and fascia, the zygomaticus, levator naso- 
labialis, lateral dilator of the nostril, the superior buccal glands, the parotid duct, 
the facial vessels, and branches of the facial nerve ; deeply, the mucous membrane 
of the mouth and the inferior buccal glands. 

Blood-supply. — Facial and buccinator arteries. 

Nerve-supply. — Facial nerve. 

MUSCLES OF THE NOSTRILS 

1. Levator nasolabialis. — This has been described (p. 2.55). 

2. Dilatator naris lateralis (M. caninus). — This thin, triangular muscle lies 
on the lateral nasal region, and passes between the two branches of the levator 

nasolabialis. 

' Also known as the levator nienti. 



MUSCLES OF THE NOSTRILS 



259 



Origin. — The maxilla, close to the anterior extremitj' of the facial crest. 

Insertion. — The lateral wing of the nostril. 

Action. — To dilate the nostril. 

Structure. — The muscle has a flat tendon of origin, passes between the two 
branches of the levator nasolabialis, and spreads out in the lateral wing of the 
nostril. The lower fibers blend with the orbicularis oris. 

Relations. — Superficially, the skin, fascia, and the labial branch of the levator 
nasolabialis; deeply, the maxilla and the nasal branch of the levator nasolabialis. 

Blood-supply. — Facial artery. 

Nerve-supply. — Facial nerve. 

3. Transversus nasi.' — This is an unpaired, quadrilateral muscle, which lies 
between the nostrils. It consists of two layers. 




Fig. 263. — Nasal and Sdperior Labial Muscles of Horse. 
Transversus nasi; b, levator labii superioris proprius; b' , tendon of h: b' 



levatorea labii superioris proprii; c, c', c", d, ventral part of lateral! 
bicularis oris; g, levator nasolabialis, a portion of whicii is removed: ) 
whicli is removed); i, cornu of alar cartilage: k, nostril; k', uppei 
naaal bone. (After Ellenberger-Baum, Top. Anat. d. Pferdes.) 



tendon of two 
nasi; e, dorsal part of lateralis nasi; /, or- 
dilatator naris lateralis (the terminal part of 
of nostril; /, nasal diverticulum; m. 



Attachments. — Superficial layer, the superficial faces of the laminte of the alar 
cartilages; deep layer, the convex edges of the cornua of the same. 

Action. — To dilate the nostrils. 

Structure.— \t is composed of transverse fleshy fibers, which blend below with 
the orbicularis. 

Relations. — Superficially, the skin, fascia, and tendinous expansion of the 
levator labii superioris proprius; deeply, the alar cartilages, the extremity of the 
septum nasi, and the palato-labial artery. 

Blood-supply. — Palato-labial artery. 

Nerve-supply. — Facial nerve. 

Lateralis nasi. — This is situated along the margins of the naso-maxillary notch, 
and may Ije regarded as consisting of dorsal and ventral parts. 

The dorsal part (Pars dorsalis m. lateralis nasi}- is a thin layer which lies along 

* Also called the dilatator naris transversus. ^ Also known as the dilatator naris superior. 



260 FASCIA AND MUSCLES OF THE HORSE 

the dorsal border of the naso-maxillary notch. Its fibers arise from the nasal bone 
and pass outward and doAviiward to the parietal cartilage and the adjacent part of 
the soft lateral wall of the nasal cavity. 

The ventral part (Pars ventralis m. lateralis nasi)^ is much thicker and lies 
along the ventral border of the notch. It arises from the nasal process of the pre- 
maxilla and the adjacent part of the maxilla, and its fibers curve inward to end on 
the cartilaginous prolongations of the turbinate bones (chiefiy the ventral one) and 
on the lateral wall of the vestibule of the nasal cavity. A few bundles pass from 
the cornu of the alar cartilage to the lateral wing of the nostril. 

Action. — To dilate the vestibule of the nasal cavity, to rotate the turbinal car- 
tilages outward, and to assist in dilating the nostril. 

Relations. — Superficially, the skin, fascia, nasal diverticulum, the levator labii 
superioris proprius, the levator nasolabialis, and the lateral nasal arteiy; deeply, 
the nasal bone, the parietal cartilage, the maxilla, the premaxilla, the nasal mucous 
membrane, and the anterior nasal branch of the infraorbital nerve. 

Blood-supply. — Facial and palato-labial arteries. 

Nerve-supply. — Facial nerve. 

The preceding muscle does not dilate the so-called "false nostril" or nasal diverticulum, as 
is commonly stated. Both act on the lateral wall of the vestibule of the nasal cavity so as to draw 
it out wardjthus tending to constrict, rather than dilate, the nasal diverticulum. The thick part 
of the ventral muscle which is attached to the cartilage of the tvu-binate bone has a similar effect. 
When the nostril is fully dilated, the so-called "false nostril," i. e., the entrance to the nasal diver- 
ticulum, is closed. The newer term seems preferable. 



MUSCLES OF THE EYELffiS 

1. Orbicularis oculi. — This is a flat, elliptical, sphincter muscle, situated in and 
around the eyelids, the portion in the upper lid being much broader than that in 
the lower. The chief attachment is to the skin of the lids, but some bundles are 
attached to the palpebral ligament at the medial canthus and to the lacrimal bone. 
Its action is to close the lids. 

2. Corrugator supercilii. — This is a very thin, small muscle, which arises over 
the root of the supraorl^ital process and spreads out in the upper eyelid, blending 
with the orbicularis oculi (Fig. 262). Its action is to assist in raising the upper lid 
or, especially in pathological conditions, to wrinkle the skin. 

3. Malaris. — This is a very thin muscle, which varies much in different sub- 
jects. It extends from the fascia in front- of the orbit to the lower lid. Its action 
is to depress the lower lid. 

The foregoing muscles receive their blood-supply from the facial, transverse 
facial, supraorbital, and infraorbital arteries; the nerve-supply is derived from the 
facial nerve. 

4. Levator palpebrae superioris. — This slender, flat muscle is almost entirely 
within the orbit (Fig. 561). It arises on the pterygoid crest, passes forward above 
the rectus oculi superior and below the lacrimal gland, and terminates in a thin ten- 
don in the upper lid. 

Aciion. — To elevate the upper lid. 
Blood-supply. — Ophthalmic artery. 
Nerve-supply. — Oculomotor nerve. 

MANDIBULAR MUSCLES 
The muscles of this group (Mm. mandibulse) are six in number in the horse. 
They arise from the upper jaw and the cranium, and are all inserted into the man- 
dible. 

' Also known as the dilatator naris inferior. 



MANDIBULAR MUSCLES 2G1 

1. Masseter.^ — This muscle extends from the zygomatic arch and facial crest 
over the broad part of the mandibular ramus. It is semi-elliptical in outline. 

Origin. — By a strong tendon from the zygomatic arch and the facial crest. 

Insertion. — The lateral surface of the broad part of the ramus of the mandible. 

Action. — Its action is to bring the jaws together. Acting singly, it also carries 
the lower jaw toward the side of the contracting muscle. 

Structure. — The superficial face of the muscle in its upper part is covered by a 
strong, glistening aponeurosis, and several tendinous intersections partially divide 
the muscle into layers. The fibers of the superficial layer take origin from the 
malar and maxilla only, and diverge somewhat to their insertion close to the thick 
ventral border of the lower jaw. The fibers of the deep layer arise from the entire 
area of origin, and pass straight to the border of the mandible; it will be noted that 
a small part, near the temporo-mandibular joint, is not covered by the superficial 
layer. The two layers are separable only above and behind; elsewhere they are 
fused. 

Relations.- — Superficially, the skin and cutaneus, the parotid gland, the 
transverse facial and masseteric vessels, and the facial nerve; deeply, the ramus of 
the mandible, the liuccinator and depressor labii inferioris muscles, the superior 
buccal glands, the buccinator vessels and nerve, and the vena reflexa, which joins 
the facial vein at the anterior etlge of the muscle. The facial vessels and parotid 
duct run along the anterior edge of the muscle; the duct, however, bends for- 
ward about the middle of the border and leaves the muscle. 

Blood-supply. — Transverse facial and masseteric arteries. 

Nerve-supply. — Mandibular nerve. 

2. Temporalis. — This muscle occupies the temporal fossa. 

Origin. — The rough part of the temporal fossa and the crests which limit it. 

Insertion. — The coronoid process of the mandible, which it envelops. 

Action. — Chiefly to raise the lower jaw, acting with the masseter and medial 
pterygoid muscles. 

Structure. — The surface of the muscle is covered with a glistening aponeurosis, 
and strong tendinous intersections are found in its substance. The medial edge of 
the muscle is quite thin, but as the fibers converge toward the much smaller area 
of insertion, the muscle becomes nearly an inch thick. It fuses partly ■R'ith the 
masseter. 

Relations. — Superficially, the scutiform cartilage, the anterior nmscles of the 
external ear, and the auricular and orbital fat; deeply, the temporal fossa and the 
deep temporal vessels and nerves. 

Blood-supply. — Superficial and deep temporal, and posterior meningeal arteries. 

Nerve-supply. — Mandibular nerve. 

3. Pterygoideus medialis (s. internus). — This muscle occupies a position on 
the medial surface of the ramus of the mandible similar to that of the masseter 
laterally. 

Oi-igin. — The crest formed by the pterygoid process of the sphenoid and the 
palatine bone. 

Insertion. — The concave medial surface of the broad part of the ramus of the 
mandible and the medial lip of the ventral border. 

Action. — Acting together, to raise the lower jaw; acting singly, to produce also 
lateral movement of the jaw. 

Striicture. — The muscle is capable of division into two parts. The principal 
part is superficial (medial), and its fibers are, for the most part, vertical in direc- 
tion. It contains much tendinous tissue (septa). The smaller portion is lateral 
to the foregoing, and its fibers are directed downward and backward. 

Relations. — Laterally, the ramus of the mandible, the lateral pterygoid muscle, 
the inferior alveolar vessels and nerve, and the lingual and mylo-hyoid nerves; 



262 



FASCIA AND MUSCLES OF THE HORSE 



medially, the great cornu of the hyoid hone, the pharj'nx, the larynx, the tensor 
palati, mylo-hyoideus, digastricus, and stylo-hyoideus muscles, the guttural pouch, 
the external maxillary vessels, the ninth and twelfth nerves, the mandibular salivary 
gland, the mandibular and parotid ducts, and the mandibular and pharyngeal lymph- 
elands. 

Blood-supply. — Internal maxillary, masseteric, and inferior alveolar arteries. 

Nerve-supply. — Mandibular nerve. 

4. Pterygoideus lateralis (s. externus). — This muscle is considerably smaller 
than the jorcceding one, and is situated lateral to its upper part. 

Origin. — The lateral surface of the pterj^goid process of the sphenoid bone. 

Insertion. — The medial surface of the neck, the medial part of the anterior 
border of the condyle of the mandible and the articular disc. 

Action. — Acting together, to draw the lower jaw forward; acting singly, to 



/ Ethmo- 

turbinates 
Dorsal meatus 
Dorsal turbinate 
Middle meatus 
Ventral turbinate 
Ventral meatus 




Fig. 264. — Sagittal Sectiox of H 



Region and Nas.i 



OF Horse, Showing Deep Pterygo-m 
Cranial Cavities. 
1. Cerebral compartment of cranial ca\-ity; 2, cerebellar compartment of same; 5, tentorium ( 
torium cerebelli; 5, sphenoidal sinus; (?. hamulus of pterygoid bone-tendon of tensor palati cut off short at anterior 
border of hamulus; 7, myio-glossus. The olfactory mucous membrane is shaded. 



move the jaw also toward the side opposite to the muscle acting. The latter action 
is due to the fact that the origin is nearer to the median plane than the insertion. 

Structure. — The muscle is almost entirely fleshy, and the fibers are almost 
longitudinal in direction. Some of them are inserted into the edge of the articular 
disc. 

Relatiojis. — Laterally, the temporo-mandibular articulation and the temporalis 
muscle; medially, the medial pterygoid and tensor palati muscles. The internal 
maxillary artery crosses the ventral face of the muscle and dips in between it and 
the tensor palati. The mandibular nerve lies on the ventral surface, and the buc- 
cinator nerve perforates the origin of the muscle. 

Blood-supply. — Internal maxillary and inferior alveolar arteries. 

Nerrc-supply. — INIandibular nerve. 

5. Occipito-mandibularis^ (M. jugulomandibularis). — This is a short, fusiform 

' Tliis muscle is also known as the stylo-maxillaris, stylo-mandibularis, etc. 



MANDIBULAR MUSCLES 



263 



muscle extending from the paramastoid process of the occipital bone to the posterior 
border of the lower jaw; it is covered by the parotid gland. 




Fig. 265. — Mandibular and Laryngeal Regions of Horse, after Removal of Skin and CuTANEtrs. 
c, Brachiocephalicus; d, sterno-cephalicus; e. orao-hyoideus and sterno-hyoideus; h, buccinator; t, depressor 
labii inferioris; m, masseter; v, occipito-mandibularis; u\ mylo-hyoideus; 2, posterior, 3, anterior, border of external 
ear; 30', angle of jaw; 36, mandibular lymph-giands; 37, external maxillary vein; 39, facial continuation of 57,- 
40, parotid duct; 44, parotid gland; 4o, prominence of chin; x, wing of atlas. (After EUenberger-Baum, Anat. fiir 
Kiinstler.) 



Origin. — The paramastoid process of the occipital bone, in common with the 
posterior belly of the digastricus. 

Insertion. — The posterior border of the ramus of the mandible. 
Action. — To depress the lower jaw and open the mouth. 



264 FASCIvE AND MUSCLES OF THE HORSE 

Structure. — The muscle contains a good deal of tendinous tissue. It blends 
with the posterior belly of the digastricus. 

Relations. — Superficialh^, the parotid gland, the tendon of the sterno-cephalicus, 
and the fibrous expansion which connects it with the tendon of the brachiocephali- 
cus; deeply, the guttural pouch, the external carotid artery, the ninth and twelfth 
nerves, the pharynx, and the mandibular salivary gland. 

Blood-supply. — External carotid artery. 

Nerve-supply. — Facial nerve. 

G. Digastricus. — This muscle is composed of two fusiform, flattened bellies, 
united by a round tendon. 

Origin. — The paramastoid process of the occipital bone, in common with the 
preceding muscle. 

Insertion. — The medial surface of the ventral border of the molar part of the 
ramus of the mandible. 

Action. — It assists in depressing the lower jaw and opening the mouth. If the 
mandible be fixed and both bellies contract, the hyoid bone and the base of the 
tongue are raised, as in the first phase of deglutition. 

Structure. — The posterior belly has the appearance of a branch detached from 
the medial surface of the occipito-mandibularis. It passes do\vnward and forward, 
and is succeeded by a small rounded tendon. The latter perforates the tendon of 
insertion of the stylo-hyoideus, and is provided with a synovial sheath. The an- 
terior belly is larger and terminates by thin, tendinous bundles. 

Relations. — The posterior belly has practically the same relations as the oc- 
cipito-mandibularis. The intermediate tendon is in contact laterally with the me- 
dial pterygoid muscle, the mandibular glanil and duct, and the external maxillary 
artery. The anterior belly lies in the mandibular space between the ramus of the 
jaw and the mylo-hyoideus muscle; the sublingual vessels run along its dorsal 
border. 

Blood-supply. — External carotid and sublingual arteries. 

Nerve-supply. — Facial and mandibular nerves. 

THE HYOID MUSCLES 

This group consists of eight muscles (I\Im. ossis hvoidei), one of which, the 
hyoideus transversus, is unpaired. 

1. Mylo-hyoideus.' — This muscle, together with its fellow, forms a sort of 
sling between the rami of the mandible, in which the tongue is supported. 

Origin. — The medial surface of the alveolar border of the mandible. 

Insertion. — (1) A median fibrous raphe extending from the symphysis to the 
hyoid bone ; (2) the lingual process, body, and thyroid cornu of the hyoid bone. 

Action. — It raises the floor of the mouth, the tongue, and the hyoid bone. 

Structure. — Each muscle consists of a thin curved sheet, the fibers passing 
ventrally from their origin and then curving toward the median raphe. It is 
chiefly fleshy, and is thickest behind. There is a tendinous intersection between this 
muscle and the omo-hyoideus, to which both muscles are attached. The anterior 
superficial part of the muscle is termed the mylo-glossus. 

Relations. — On the superficial surface of the muscles are the ramus, the medial 
pterygoid and digastricus muscles, and the mandibular lymph-glands. The deep 
surface is in contact with the mucous membrane of the mouth, the st.ylo-glossus, 
hyo-glossus, and genio-hyoideus muscles, the sublingual gland and vessels, the 
mandibular duct, and the lingual and hypoglossal nerves. The sublingual vein 
passes through the jjosterior part. 

Blood-supply. — Sublingual artery. 

' Also known as the transversus mandibulae. 



THE HYOID MUSCLES 265 

Nerve-sjtpply. — Mylo-hyoid branch of the mandibular nerve. 

2. Stylo-hyoideus. — This is a slender, fusiform muscle, having a direction 
nearly parallel to that of the great cornu of the hyoid bone (Fig. 559) . 

Origin. — The muscular angle of the dorsal extremity of the great cornu of the 
hyoid bone. 

Insertion. — The anterior part of the thyroid cornu of the hyoid bone. 

Action. — It draws the base of the tongue and the larynx upward and backward. 

Structure. — It arises by a thin, short tendon, and has a fusiform belly. The 
tendon of insertion is jjerforatcd for the passage of the intermediate tendon of the 
digastricus, and at this point there is a small synovial sheath. 

Relations. — Superficially, the medial pterygoid muscle and the parotid gland; 
deeply, the guttural pouch, the pharynx, the external carotid and maxillary arteries, 
and the hypoglossal nerve. 

Blood-supply. — External carotid artery. 

Nerve-supply. — Facial nerve (stylo-hyoid branch). 

In rare cases an anomalous arrangement is present in which the stylo-hyoideus is not at- 
tached to the thyroid cornu but is continuous with the intermediate tendon of the digastricus, 
and no fibrous ring is formed. The posterior belly of the digastricus is inserted chiefly on the 
thyroid cornu, but also sends a delicate tendinous slip to the intermediate tendon. 

3. Occipito-hyoideus (M. jugulo-hyoideus). — This is a small triangular muscle, 
which lies in the space between the paramastoid process and the great cornu of the 
hyoid bone. 

Origin. — The paramastoid process of the occipital bone. 

Insertion. — The dorsal extremity and ventral edge of the great cornu of the 
hyoid bone. 

Action. — It carries the ventral extremity of the great cornu backward. 

Structure. — The muscle is somewhat triangular, its fibers being longer as the 
ventral border is approached. It blends with the posterior belly of the digastricus. 

Relations. — Superficially, the parotid gland; deeply, the guttural pouch. 

Blood-supply. — Occipital artery. 

Nerve-supply. — Facial nerve. 

4. Genio-hyoideus. — This is a long, spindle-shaped muscle, which lies under 
the tongue in contact with its fellow of the opposite side (Fig. 330). 

Origin. — A small depression on the medial surface of the ramus of the mandible, 
close to the symphysis. 

Insertion. — The extremity of the lingual process of the hyoid bone. 

Action. — It draws the hyoid bone and tongue forward. 

Structure. — The muscle arises by a short tendon, which is succeeded by the 
belly, composed of long bundles of parallel fibers. 

Relatio7is. — Ventrally, the mylo-hyoideus; dorsally, the hyo-glossus, stylo- 
glossus, genio-glossus, the sublingual gland, mandibular duct, and the lingual nerve. 

Blood-supply. — Sublingual artery. 

Nerve-supply. — Hypoglossal nerve. 

5. Kerato-hyoideus. — This small triangular muscle lies in the space between 
the thyroid and small cornu, under cover of the hyo-glossus (Fig. 331). 

Origin. — The posterior edge of the small cornu and the adjacent part of the 
ventral border of the great cornu. 

■ Insertion. — The dorsal edge of the thyroid cornu. 
Action. — It raises the thyroid cornu and the larynx. 
Relations. — The muscle is crossed laterally by the lingual artery. 
Blood-supply. — Lingual artery. 
Nerve-supply. — Glosso-pharyngeal nerve. 

6. Hyoideus transversus. — This is a small, unpaired muscle, which extends 
transversely Ijetween the two small cornua of the hyoid bone. 



266 FASCIA AND MUSCLES OF THE HORSE 

Attachments. — The small cornua close to the junction with the great cornua. 
Action. — When relaxed, its dorsal surface is concave; when it contracts, it 
elevates the root of the tongue. 

Structure. — Fleshy, composed of parallel transverse bundles. 
Blood-mpply. — Lingual artery. 
Nerve-supply. — Glosso-pharyngeal nerve. 

7. Stemo-thyro-hyoideus, and 

8. Om.o-hyoideus. — These are tlescribed with the muscles on the ventral sur- 
face of the neck (p. 268). 



The Fasciae and Muscles of the Neck 

It is convenient to divide the nmscles of the neck (Mm. colli) into ventral and 
lateral groups, the two lateral groups being separated from each other b}' the liga- 
mentum nuchae. 

THE FASCIA OF THE NECK 

The superficial fascia is in part two-layered, and contains the cervical cutaneous 
muscle. The fasciae of the right and left sides are attached along the dorsal line 
of the neck to the ligamentum nuchse, while along the ventral line they meet in a 
fibrous raphe. A deep layer is detached which passes underneath the cutaneous 
muscle, bridges over the jugular furrow, and crosses over the deep face of the brachio- 
cephalicus and omo-hyoideus to join the superficial layer. It again separates to 
pass under the cervical trapezius, and become attached to the ligamentum nuchse. 
Along the ventral line a septum is detached which separates the sterno-cephalici. 
Two other layers in front of the shoulder enclose the prescapular lymph-glands. 

The deep fascia also forms two layers. The superficial layer is attached to 
the wing of the atlas and the ventral edge of the longissimus capitis et atlantis and 
scalenus. Passing downward it encloses the trachea, and, together M'ith the deep 
layer, furnishes sheaths for the vagus and sympathetic nerves and the carotid 
artery. Passing upward it detaches septa between the extensor muscles of the spine. 
Anteriorly it covers the thyroid gland, the guttural pouch, the adjacent vessels and 
nerves, and the larynx, and is attached to the mastoid process of the temporal bone 
and the thyroid cornu of the hyoid bone. Posteriorly it is attached to the first 
rib and the cariniform cartilage of the sternum. The deep layer (prevertebral 
fascia) covers the ventral surface of the longus colli, and encloses the trachea and 
oesophagus. Anteriorly it forms, with the corresponding laj^er of the opposite 
side, a septum between the guttural pouches; posteriorly it becomes continuous 
with the endothoracic fascia. A fascia propria forms a tubular sheath around the 
trachea, enclosing also the recurrent nerves. 



VENTRAL CERVICAL MUSCLES 
This group consists of twelve pairs of muscles which lie ventral and lateral to 
the vertebrie. 

1. Cutaneus colli. — This has been described (p. 2.54). 

2. Brachiocephalicus. — This is described on p. 294. 

3. Stemo-cephalicus.' — This is a long, narrow muscle which extends along the 
ventral and lateral aspects of the trachea from the sternum to the angle of the jaw. 
It forms the ventral boundary of the jugular furrow. 

' This muscle is probably the homologue of the sternal part of the sterno-cleido-mastoid 
of man. On account of the differences in its insertion in the various animals, it seems desirable 
to adopt the name sterno-cephalicus. It is also known as the sterno-mandibularis or sterno- 
maxillaris. 



VENTRAL CERVICAL MUSCLES 



267 



Origin. — The cariniform cartilage of the sternum. 
Insertion. — The posterior border of the ramus of the mandible. 
Action. — Acting together, to fiex the head and neck; acting singly, to incline 
the head and neck to the side of the muscle contracting. 

Structure. — The two nmscles are fused at their origin, which is fleshy. Near 





Fig. 266. — Antero-l-^teral View of Muscles and Skeleton of Horse. 
a, Trapezius; c, brachiocephalicus; d, sterno-cephalicus; /, long head of triceps; /', lateral head of triceps; 
ff, anterior superficial pectoral muscle; ff', posterior superficial pectoral; //.anterior deep pectoral; r, cutaneus colli; 
z, supraspinatus; 29, omo-hyoideus; SO, sterno-thyro-hyoideus; 31, jugular vein; S3, cephalic vein; 1, scapula; 
^', cartilage of scapula; 5, spine of scapula; 4. shaft of humerus; 4' lateral epicondyle; 5, lateral tuberosity of humerus; 
£?, deltoid tuberosity: 74, ventral border ("keel") of sternum; i-^', cariniform cartilage; i.K., first rib. C.\fter EUen- 
berger-Baum, Anat. fur Kiinstler.) 



the middle of the neck they separate, and, becoming narrower and thinner, each 
muscle passes under the parotid gland and terminates by a flat tendon. The latter 
is connected by a thin aponeurosis with that of the brachiocephalicus. 

Relations. — Superficially, the cutaneous muscle; deeply, the sterno-thyro- 
hyoideus and omo-hyoideus muscles. The dorsal edge of the muscle is related to 
the jugular vein, which lies m the jugular furrow. The carotid artery, the vagus, 



268 FASCIA AND MUSCLES OF THE HORSE 

sympathetic, and recurrent nerves also lie along the upper edge at the root of the 
neck. The tendon passes under the external maxillarj' vein and the parotid gland, 
having the mandibular gland and occipito-mandibularis muscle on its medial side. 

Blood-supphj. — Carotid artery. 

Nerve-supply. — Ventral branch of the spinal accessor}^ nerve. 

4. Stemo-thyro-hyoideus (Sterno-thyreoideus et sterno-hyoideus). — This is a 
long, slender, digastric muscle, applied to the ventral surface of the trachea and 
its fellow of the opposite side. 

Origin. — The cariniform cartilage of the sternum. 

Insertion. — (1) A prominence on the posterior border of the lamina of the thy- 
roid cartilage of the larynx at the ventral end of the oblique line; (2) the body 
and lingual process of the hyoid bone. 

Action. — To retract and depress the hyoid iDone, the base of the tongue, and 
the larynx, as in deglutition. It maj' also fix the hyoid bone when the depressors 
of the tongue are acting, as in sucking. 

Structure. — The origin of the muscle is fleshy, and as far as the middle of the 
neck, it blends with its fellow. The common belly is then interrupted by a tendon, 
or sometimes two tendons, from which arise three or four fleshy bands. The lat- 
eral small bands (Sterno-thyroidei) diverge to reach their insertion into the thy- 
roid cartilage by a delicate tendon; while the medial and larger bands (Sterno- 
hyoidei), closely applied to each other and blending with the omo-hyoideus, pass 
straight forward to reach the ventral surface of the hyoid bone. 

Relations. — At the root of the neck the common belly is related ventrally to 
the sterno-cephalicus, and the carotid arteries and recurrent nerves dorsally. 
Further forward the trachea becomes the dorsal relation, and near the head the 
omo-hyoideus, skin and fascia, the ventral one. 

Blood-supply . — Carotid artery. 

Nerve-supply. — Ventral branches of the first and second cervical nerves. 

5. Omo-hyoideus. 1 — This is a thin, ribbon-like muscle, almost entirely flesh}', 
which crosses the trachea verj' obliquely. 

Origin. — The subscapular fascia close to the shoulder joint. 

Insertion. — The body and adjacent part of the lingual process of the hyoid 
bone, in common with the hyoid branch of the preceding muscle. 

Action. — To retract the hyoid bone and the root of the tongue. 

Structure. — The muscle is composed of parallel fleshy fibers, except at its origin, 
where it has a thin tendon. 

Relations. — The posterior part of the muscle is related laterally to the supra- 
spinatus, anterior deep pectoral, and brachiocephalicus and the prescapular lymph- 
glands; and medially to the scalenus. It is intimately adherent to the brachio- 
cephalicus. In the middle of the neck it is related superficially to the brachio- 
cephalicus, sterno-cephalicus, and the jugular vein; deepl}', to the rectus capitis 
ventralis major, the carotid artery, the vagus, sympatb.etic, and recurrent nerves, 
the trachea, and, on the left side, the oesophagus. In its anterior part the muscle 
blends with the sterno-hyoideus, the two covering the sterno-thyroideus, the thy- 
roid gland in part, and the ventral face of the larynx. 

Blood-supply. — Carotid and inferior cervical arteries. 

Nerve-supply. — Ventral branch of the first cervical nerve. 

6. Scalenus (M. scalenus primaj costs). — This muscle is deeply situated on 
the side of the posterior half of the neck. It is composed of two parts, between 
which the cervical roots of the l^rachial plexus of nerves emerge. 

Origin. — The anterior border and lateral surface of the first rib. 
Insertion. — (1) The dorsal (smaller) part (M. scalenus dorsalis) is attached to 
the transverse process cf the seventh cervical vertebra; (2) the ventral part (M. 
1 Also termed the subscapulo-hyoideus. 



VENTRAL CERVICAL MUSCLES 269 

scalenus ventralis) is attached to the transverse processes of the sixth, fifth, and 
fourth cervical vertebrae. 

Action. — The necli is flexed or inclined laterally, according as the muscles act 
together or singly. If the neck be the fixed point, the muscle may have a respira- 
tory action by pulling forward or fixing the first rib. 

Structure. — The dorsal part is composed of several small fleshy bundles. The 
ventral portion, which is much larger, is almost entirely fleshy, and not so divided. 

Relations. — Superficially, the anterior deep pectoral, brachiocephalicus, and 
omo-hyoideus muscles, the phrenic nerve, and branches of the brachial plexus; 
deeply, the vertebrae, the longus colli and intertransversales muscles, the oesoph- 
agus (on the left side), the trachea (on the right side), the vertebral vessels, 
the vagus, sympathetic, and recurrent nerves. The roots of the brachial plexus 
form a flat anastomosis, which lies between the two parts of the muscle. The 
brachial vessels cross the venti-al edge close to the first rib. 

Blood-supply. — Carotid, vertebral, and inferior cervical arteries. 

Nerve-supply. — \'entral branches of the cervical nerves. 

7. Cervicalis ascendens.' — This muscle is the cervical continuation of the 
longissimus costarum, antl is sometimes regarded as a part of the scalenus, with 
which it is partially united. It consists of three or four bundles which are attached 
to the transverse processes of the last three or four cervical vertebrae and the first 
rib. 

Action. — To extend the neck or to flex it laterally. 

Relations. — Superficially, the brachiocephalicus and anterior deep pectoral; 
deeply, the scalenus and intertransversales. 
Blood-supply. — Vertebral artery. 
Nerve-supply. — Cervical nerves. 

8. Rectus capitis ventralis major (M. longus capitis). — This is the largest 
of the three sijecial flexors of the head, and lies along the ventro-lateral surface 
of the anterior cervical vertebrae and the base of the cranium. 

Origin. — The transverse processes of the fifth, fourth, and third cervical ver- 
tebrae. 

Insertion. — The tubercles at the junction of the basilar part of the occipital 
bone ^vith the body of the sphenoid. 

Action. — Acting together, to flex the head; acting singly, to incline it to the 
same side also. 

Structure. — The origin of the muscle is by fleshy digitations. The belly in- 
creases in size by the union of these digitations, reaching its maximum at the axis. 
It then diminishes, passes toward the median plane, and terminates on a rounded 
tendon. 

Relations. — Superficially, the brachiocephalicus and omo-hyoideus, the mandib- 
ular gland, the carotid artery (which lies along the ventral bortler), the occipital 
and internal carotid arteries, and the tenth, eleventh, and sympathetic nerves; 
deeply, the vertebrae, the longus colli, intertransversales, and the rectus capitis 
ventralis minor. The terminal part of the muscle lies in contact with its fellow 
above the pharynx and between the guttural pouches. 

Blood-supply. — Carotid, vertebral, and occipital arteries. 

Nerve-supphj. — ^\^ntral branches of the cervical nerves. 

9. Rectus capitis ventralis minor (M. rectus capitis ventralis). — This is a small 
muscle which lies dorsal to and under cover of the preceding one. 

Origin. — The ventral arch of the atlas. 

Insertion. — The basilar part of the occipital bone, close to the preceding muscle. 

Action. — To flex the atlanto-occipital articulation. 

Structure. — Fleshy. 

1 This muscle is also known as the ilio-costalis cervicis. 



270 FASCI.E AND MUSCLES OF THE HORSE 

Relations. — Ventrally, to the preceding muscle; dorsally, to the atlas, atlanto- 
occipital articulation, and the basilar part of the occipital bone; laterally, to the 
rectus capitis lateralis and the guttural pouch. 

Blood-supply. — Occipital artery. 

Nerve-supply. — Ventral branch of the first cervical nerve. 

10. Rectus capitis lateralis. — This is a still smaller muscle, which lies for the 
most part under the oliliquus capitis anterior. 

Origin. — The atlas, lateral to the preceding muscle. 
Insertion. — The paramastoid process of the occipital bone. 
Action. — The same as the preceding muscle. 
Structure. — Fleshy. 

Relations. — Superficially, the obliquus capitis anterior, the occipital vessels, 
and the ventral branch of the first cervical nerve. 
Blood-supply. — Occipital artery. 
Nerve-supply. — Ventral branch of the first cervical nerve. 

11. Longus colli. — This muscle covers the ventral surfaces of the vertebrae, 
from the sixth thoracic to the atlas, and is united -with its fellow. It consists of 
two parts, thoracic and cervical. 

Origin. — (1) Thoracic part, the bodies of the first six thoracic vertebrae; (2) 
cervical part, the transverse processes of the cervical vertebrae. 

Insertion. — (1) Thoracic part, the bodies and transverse processes of the last 
two cervical vertebrae; (2) cervical part, the bodies of the cervical vertebrae and 
the ventral tubercle of the atlas. 

Action. — To flex the neck. 

Structure. — The muscle is composed of a succession of bundles. The largest 
of these constitute the thoracic part of the muscle, which has a strong tendon in- 
serted into the last two cervical vertebrae. A bursa is interposed between the ten- 
don and the spine at the first costo-vertebral articulation. The cervical part con- 
sists of a number of smaller bundles, each of which passes from its origin on the 
transverse process of one vertebra forward and mediallj' to its insertion into a ver- 
tebra further forward. The most anterior bundle is inserted by a strong tendon into 
the ventral tubercle of the atlas. 

Relations. — The principal relations of the two muscles in the thorax are: 
ventrally, the pleura, and, further forward, the trachea and oesophagus; dorsally, 
the vertebrae and the costo-vertebral joints; laterally, the dorsal,, deep cervical, 
anrl vertebral vessels, the sympathetic nerve, and the thoracic roots of the brachial 
plexus. In the neck important relations are: ventrally, the trachea and oesophagus, 
the carotid artery, the vagus, sympathetic, and recurrent nerves; dorsally, the 
vertebrae and, in the middle third of the neck, the intertransversales muscles; lat- 
erally, the scalenus, the rectus capitis ventralis major, and the intertransversales 
(in the anterior third). The terminal part of the muscle is separated from the 
trachea by the oesophagus, which is here median in position. 

Blood-supply. — Subcostal and vertebral arteries. 

Nerve-supply. — Ventral branches of the spinal nerves. 

12. Intertransversales colli (Mm. intertransversarii cervicis). — These are six 
fasciculi which occupy the spaces between the lateral aspects of the vertebrae and 
the transverse and articular processes. There is thus a bundle for each inter- 
vertebral articulation except the first. Each bundle consists of a dorsal and ven- 
tral part. 

Attachments. — The dorsalv,bundles pass from transverse process to articular 
process; the ventral bundles extend between adjacent transverse processes. 
Action. — To flex the neck laterally. 
Structure. — They contain strong tendinous intersections. 
Relations. — Superficially, the brachiocephalicus, rectus capitis ventralis ma- 



LATERAL CERVICAL MUSCLES 271 

jor, obliquus capitis posterior, complexus, longissimus capitis et atlantis, splenius, 
scalenus, and longissimus tlorsi et costarum muscles; deeply, the vertebrae, the 
longus colli muscle, and the vertebral vessels. The muscles are perforated by 
branches of these vessels and by the primary branches of the cervical nerves. 

Blood-supply. — Vertebral artery. 

Nerve-supply. — The cervical nerves. 



LATERAL CERVICAL MUSCLES 
This group consists of twelve pairs of muscles arranged in layers. 

First Layer 

1. Trapezius cervicalis. — Described on p. 293. 

Second Layer 

2. Rhomboideus cervicalis. — Described on p. 293. 

3. Serratus cervicis. — Described on p. 297. 

Third Layer 

4. Splenius. — This is an extensive, flat, triangular muscle, partly covered by 
the preceding three muscles. 

Origin. — The second, third, and fourth thoracic spines by means of the dorso- 
scapular ligament and the funicular part of the ligamentum nuchae. 

Insertion. — The nuchal crest, the mastoid process, the wing of the atlas, 
and the transverse processes of the third, fourth, and fifth cervical vertebrae. 

Action. — Acting together, to elevate the head and neck; acting singly, to in- 
cline the head and neck to the side of the muscle acting. 

Structure. — The muscle arises in the withers from the anterior part of the 
dorso-scapular ligament, which also affords attachment to the rhomboideus, ser- 
ratus dorsalis, and complexus muscles. The fibers pass upward and forward 
toward the head and the first cervical vertebra. The insertion on the occipital 
bone and the mastoid process is by means of a thin aponeurosis common to the 
splenius and longissimus capitis et atlantis. The atlantal insertion is by a strong, 
flat tendon, also in common wth these muscles and the brachiocephalicus. The 
remaining insertions are fleshy digitations. 

Relations. — Superficially, the skin and fascia, the trapezius, rhomboideus 
cervicalis, serratus ventralis, and posterior auricular muscles" deeply the com- 
plexus and longissimus dorsi muscles. 

Blood-supply. — Deep cervical and dorsal arteries. 

Nerve-supply. — Dorsal branches of the last six cervical nerves. 

Fourth Layer 

5. Longissimus capitis et atlantis.' — This muscle consists of two parallel, fusi- 
form portions. It lies between the deep face of the splenius and the ventral part 
of the complexus. 

Origin. — (1) The transverse processes of the first two thoracic vertebrae; (2) 
the articular processes of the cervical vertebrae. 

Insertion. — (1) The mastoid process; (2) the wing of the atlas. 

Action. — Acting together, to extend the head and neck; acting singly, to flex 
the head and neck laterally or to rotate the atlas. 

Structure. — The origin from the thoracic vertebrae is by aponeurotic slips 
which blend with the complexus. The succeeding fleshy part, in passing along 
'Also termed the trachelo-mastoideus. 



272 



FASCI.E AND MUSCLES OF THE HORSE 



the neck, receives fasciculi from each of the cervical vertebrae except the 
first two. The dorsal division of the muscle (M. longissimus capitis) is 
inserted into the mastoid process by a flat tendon which fuses with that of 
the splenius; the ventral division (M. longissimus atlantis) is inserted into the 




LATERAL CERVICAL MUSCLES 273 

wing of the atlas by a ribbon-like tendon in common with the splenius and 
brachiocephalicus. 

Relations. — Superficially, the splenius muscle and dorsal branches of the 
cervical nerves; deeply, the com plexus, the spinalis colli, and the oblique muscles 
of the head. The deep cervical vessels cross the deep face of the muscle obliquely 
at the level of the sixth and seventh cervical vertebrae. 

Blood-supply. — Vertebral and deep cervical arteries. 

Nerve-supply. — Dorsal branches of the last six cervical nerves. 

6. Complexus (M. semispinalis capitis). — This is a large triangular muscle 
which lies chiefly on the ligamentum nuchse, under cover of the splenius. 

Origin. — (1) The second, third, and fourth thoracic spines, in common with 
the splenius and serratus dorsalis; (2) the transverse processes of the first six or 
seven thoracic vertebrse ; (3) the articular processes of the cervical vertebrae. 

Insertion. — A rough area on the occipital bone just ventral to the nuchal crest. 

Action. — It is the chief extensor of the head and neck. Acting singly, the 
muscle inclines the head to the same side. 

Structure. — The origin of the muscle at the withers is aponeurotic. In the 
neck the bundles arising from the articular processes run obliquely upward 
and forward, giving the lower part of the muscle a distinct pennate character. 
The dorsal part of the belly is crossed obliquely by four or five tendinous 
intersections. The insertion is by a strong tendon. 

Relations. — Superficially, the rhomboideus, serratus ventralis, splenius, and 
longissimus capitis et atlantis; deeply, the ligamentum nuchse, the multifidus 
cervicis, longissimus dorsi, and the oblique and dorsal straight muscles of the head, 
the deep cervical vessels, and the dorsal cutaneous branches of the cervical nerves. 

Blood-supply. — Deep cervical, vertebral, and occipital arteries. 

Nerve-supply. — Dorsal branches of the last six cervical nerves. 

7. Multifidus cervicis. — This muscle lies on the arches of the last five cervical 
vertebrse. It consists of five or six segments. 

Origin. — The articular processes of the last four or five cervical and the first 
thoracic vertebrae. 

Insertion. — The spinous and articular processes of the cervical vertebrae. 

Action. — Acting together, to extend the neck; acting singly, to flex the neck on 
the side of the muscle contracting and to rotate the neck to the opposite side. 

Structure. — The muscle is composed of two sets of bundles. The superficial 
bundles are directed obliquely forward and inward, each passing from an articular 
process to the spine of the preceding vertebra. The deep bundles arc shorter and 
run straight from an articular process to that of the preceding vertebra. 

Relations. — Superficially, the complexus, longissimi, and obliquus capitis poster- 
ior; deeply, the spinalis, the ligamentum nuchae, and the arches of the vertebrse. 

Blood-supply. — Deep cervical and vertebral arteries. 

Nerve-supply. — Dorsal branches of the last six cervical nerves. 

8. Spinalis. — Described with the longissimus on p. 278. 

9. Obliquus capitis posterior (s. caudalis). — This is a strong, quadrilateral 
muscle, which covers the dorso-lateral aspect of the atlas and axis. 

Origin. — The side of the spine and the posterior articular process of the axis. 

Insertion. — The dorsal surface of the wing of the atlas. 

Action. — Chiefly to rotate the atlas, and with it the head, to the same side; 
also to assist in extending and fixing the atlanto-axial joint. 

Structure. — The muscle is composed almost entirely of parallel fleshy fibers 
directed obliquely forward and outward. It is covered by a special fascia. 

Relations. — Superficially, the splenius, complexus, longissimus capitis, and 
brachiocephalicus muscles; deeply, the arch and spine of the axis, the wing of 
the atlas, the atlantoaxial joint, the rectus capitis dorsalis minor, the occipital and 
18 



274 



FASCIA AND MUSCLES OF THE HORSE 



vertebral vessels, and the first and second cervical nerves. The terminal part of 
the vertelsral artery joins the posterior branch of the occipital artery under cover 
of tlie muscle. 

Blood-supply. — Occipital and vertebral arteries. 




LATERAL CERVICAL MUSCLES 



275 



Nerve-svpphj. — Dorsal liranch of the second cervical nerve. 

10. Obliquus capitis anterior (s. cranialis). — This short, thick, quadrilateral 
muscle lies on the side of the atlantooccipital articulation. 

Origin. — The anterior edge and ventral surface of the wng of the atlas. 

Insertion. — The paramastoid process and nuchal crest of the occipital bone 
and the mastoid process. 

Action. — Acting together, to extend the head on the atlas; acting singly, to 
fiex the head laterally. 

Striicture. — The muscle contains a good deal of tendinous tissue. The direction 
of its fibers is forward, upward, antl inward. 




Fig. 269. — Deepest Later of Muscles of Neck of Horse. 
a, Obliquus capitis anterior; 6, obliquus capitis posterior; c, rectus capitis lateralis; d, rectus capitis ventralis 
minor; e, rectus capitis ventralis major; /, longus colli; g, g', scalenus; h, longissimus costarum; i, longissimus dorsi; 
/:, spinalis et semispinalis; /, multifidus dorsi; m, multifidus cervicis; n, intertransversales; o, o', rectus capitis dorsalis 
major; p, rectus capitis dorsalis minor; q, tendon of insertion of complexus; I, lamellar part, /', funicular part of liga- 
mentum nuchfe; 2, nuchal crest; 3, paramastoid process; 4. edge of wing of atlas; J, transverse, and 6, articular, 
processes of cervical vertebrse; 7, nerves of brachial plexus (cut) ; S, first rib. (Ellenberger-Baum, .\nat. d. Haustiere.) 



Relations. — Superficially, the complexus, the aponeurosis of the splenius, longus 
capitis, and brachiocephalicus, overlying which are the posterior auricular muscles, 
artery, and nerve, and the parotid gland; deeply', the dorsal straight muscles, 
the occipito-hyoideus, the atlanto-occipital articulation, the posterior meningeal 
artery, and a branch of the occipital nerve. 

Blood-supply. — Occipital artery. 

Nerve-supply. — Dorsal Ijranch of the first cervical nerve. 

11. Rectus capitis dorsalis major. — This muscle extends from the axis to the 
occipital bone, in contact with the ligamentum nuchse. 

Origin. — The edge of the spinous process of the axis. 



276 FASCIAE AND MUSCLES OF THE HORSE 

Insertion. — The occipital bone, below the complexus; the tendon of insertion 
of the complexus. 

Action. — To extend the head. 

Structure. — The muscle is fleshy and may be divided into two parallel parts, 
superficial and deep. The former blends somewhat with the terminal part of the 
complexus. The deep part may be termed the rectus capitis dorsalis medius. 
Bundles frequently arise from the fascia over the obliquus capitis posterior. 

Relations. — Superficially, the obliquus capitis anterior, splenius, and com- 
plexus; medially, the ligamentum nuchse; deeply, the atlas, the atlanto-occipital 
articulation, and the rectus capitis dorsalis minor. The dorsal branch of the first 
cervical nerve appears between this muscle and the obliquus capitis anterior. 

Blood-supply. — Occipital artery. 

Nerve-supply. — Dorsal branch of the first cervical nerve. 

12. Rectus capitis dorsalis minor. — This small muscle lies under cover of the 
preceding. 

Origin. — The dorsal surface of the atlas. 

Insertion. — The occipital bone beneath the preceding muscle and lateral to the 
funicular part of the ligamentum nuchse. 

Action. — To assist the preceding muscle. 

Structure. — It is fleshy and varies a good deal in volume, being sometimes 
small and difficult to recognize.' On the other hand, it is sometimes double. 

Relations. — Superficially, the preceding muscle and the obliquus capitis an- 
terior; deeply, the atlas and the atlanto-occipital articulation. 
_ Blood-supply. — Occipital artery. 

Nerve-supply. — Dorsal branch of the first cervical nerve. 



The Fascle and Muscles of the Back and Loins 
(fascle et musculi dorsi et lumborum) 

The superficial fascia presents no special features. The lumbo-dorsal fascia 
(Fascia lumbo-dorsalis) closely invests the muscles, but is easily stripped off the 
longissimus. It is attached medially to the supraspinous ligament and the spinous 
processes of the vertebrae; it divides laterally into two layers. The superficial 
layer is practically the aponeurosis of the latissimus dorsi. The deep layer gives 
origin to the serratus dorsalis, the lumbar part of the obliquus abdominis externus, 
the transversus abdominis, and the retractor costae. Its lateral edge curves under 
the longissimus and is attached to the ribs and lumbar transverse processes. Pos- 
teriorly it is continuous with the gluteal fascia. At the withers it forms an impor- 
tant structure, the dorso-scapular ligament. This is a strong tendinous sheet, 
attached to the third, fourth, and fifth thoracic spines. Its upper part is very 
thick and gives origin by its superficial surface to the rhomboideus thoracalis, by 
its anterior part to the splenius. The lower part is thin and elastic, and furnishes 
numerous lamellae which intersect the scapular part of the serratus ventralis and 
are attached to the scapula. Three lamelliE are detached from the ligament. 
The deepest of these passes between the longissimus and spinalis and is attached to 
the transverse processes of the first seven thoracic vertebrae; it gives attachment 
to the complexus. The middle one dips in between the longissimus dorsi and 
longissimus costarum. The superficial one gives origin to the serratus dorsalis. 
A strong fascial layer, the ilio-lumbar ligament, extends from the last rib to the 
tuber coxae. 

There are nine pairs of muscles in this region, arranged in four layers. 

' This seems due to pressure produced by pathological changes in the supra-atloid bursa, 
which are frequently extensive in dissecting-room subjects. 



the fascia and muscles of the back and loins 277 

First Layer 

1. Trapezius thora calls. 

2. Latlsslmus dorsi. 

Second Layer 

3. Rhomboideus thoracalls. 

The foregoing are described with the other muscles which attach the thoracic 
Hmb to the trunk (p. 293). 

4. Serratus dorsalls anterior (s. cranialis). — This is a thin quadrilateral muscle, 
named from its serrated ventral border. It lies under cover of the rhomboideus, 
serratus ventralis, and latissimus dorsi. 

Origin. — The lumbo-dorsal fascia and dorso-scapular ligament. 

Insertion. — The lateral surfaces of the fifth or sixth to the eleventh or twelfth 
ribs inclusive. 

Action. — To draw the ribs on which it is inserted forward and outward, thus 
assisting in inspiration. 

Structure. — The muscle arises by means of a thin aponeurosis. The muscle- 
fibers pass ventrally and backward to be attached to the ribs by seven or eight 
digitations below the lateral edge of the longissimus costarum. 

Relations. — Superficially, the rhomboideus, serratus ventralis, latissimus dorsi, 
and serratus dorsalis posterior; deeply, the longissimus dorsi, longissimus costarum, 
external intercostal muscles, and the ribs. 

Blood-supply. — Intercostal arteries. 

Nerve-supply. — Thoracic nerves. 

5. Serratus dorsalis posterior (s. caudalis). — This muscle resembles the pre- 
ceding one, which it partly covers. 

Origin. — The lumbo-dorsal fascia. 

Insertion. — The lateral surfaces of the last seven or eight ribs. 

Action. — To draw the ribs backward, thus assisting in expiration. 

Structure. — Similar to the preceding muscle. The fibers are directed ventrally 
and forward and terminate in seven or eight digitations, one or two of which cover 
the posterior teeth of the anterior muscle. The aponeurosis blends with that of 
the latissimus dorsi. 

Relations. — Superficially, the latissimus dorsi and external oblique; deeply, 
the longissimus dorsi, longissimus costarum, external intercostals, serratus dorsalis 
anterior, and the ribs. 

Blood-supply. — Intercostal and lumbar arteries. 

Nerve-supply. — Thoracic nerves. 

Third Lay'er 

6. Longissimus costarum.' — This long, segmental muscle extends across the 
series of ribs, in contact with the outer edge of the longissimus dorsi. 

Origin. — (1) The deep layer of the lumbo-dorsal fascia as far back as the third 
or fourth lumbar transverse process. (2) The anterior borders and lateral surface 
of the last fifteen ribs.- 

Insertion. — The posterior borders of the ribs and the transverse processes of 
the last cervical vertebra. 

Action. — Chiefly to depress and retract the ribs and so help in exjjiration. 

1 This muscle is also known as the long costal, ilio-costalis, or transversalis costarum. The 
name given above was introduced by the International Commission for the Reform of Myological 
Nomenclature and appears worthy of general adoption. 

2 The lumbar part of this muscle is subject to variation. It may, in quite exceptional cases, 
extend as far as the ilium, and sometimes, on the other hand, it does not arise quite as far back as 
given above. In some subjects the origin can be traced distinctly to the tips of lumbar transverse 
processes. 



278 



FASCI.E AND IICSCLES OF THE HORSE 



Acting together, they may assist in extending the spine, acting singly in inclining 
it laterally. 

Structwe. — This muscle presents a distinct segmental arrangement. It is 
composed of a series of bundles, the fibers of which are directed forward and a little 
ventro-laterally. From these are detached two sets of tendons. The superficial 
tendons spring from the lateral edge of the muscle. They are flat and are about 
half an inch in width. Each crosses two or three intercostal spaces, to be inserted 
on the posterior border of a rib. The deep tendons are detached from the dorsal 
part of the deep face of the muscle. Each passes backward across one or two inter- 
costal spaces to its origin on the anterior border or lateral surface of a rib. Small 

bursse may be found between the ribs and 
tendons. 

Relations. — Superficially, the dorsal and 
ventral serrati; deeply, the external inter- 
costals and the ribs. The lumbar origin is 
covered by the longissimus dorsi. The deep 
cervical and dorsal vessels cross the surface of 
the muscle at the first and second intercostal 
spaces respectively, and branches of the in- 
tercostal vessels and nerves emerge between 
it and the longissimus dorsi; here a fascial 
layer dips in between the two. 

Blood-supply. — Intercostal arteries. 
^^ „ ., , n 4 1 \\\ Nerve-supply. — Dorsal branches of the 

^^^ZI^ r w>A ' ** \l\ thoracic nerves. 

7. Longissimus dorsi.' — This is the 
largest and longest muscle in the body. It 
extends from the sacrum and ilium to the 
neck, filling up the space between the spinous 
processes medially and the lumbar trans- 
verse processes and the upper ends of the 
ribs ventralh' ; consequently it has the form 
of a three-sided prism. 

Origin. — (1) The tubera, crest, and ad- 
jacent part of the ventral surface of the ilium ; 
(2) the first three sacral spines; (3) the lum- 
bar and thoracic spines and the supraspinous 
ligament. 

Insertion. — (1) The lumbar transverse 
and articular processes; (2) the thoracic 
transverse processes; (3) the spinous and 
transverse processes of the last four cer- 
vical vertebfffi; (4) the lateral surfaces of the ribs, except the first. 

Action. — Acting with its fellow, it is the most powerful extensor of the back 
and loins; by its cervical attachment it assists in extending the neck. By its costal 
attachment it may also assist in expiration. Acting singly, it flexes the spine 
laterally. 

Structure. — This is quite complex. The posterior part of the muscle is greatly 
developed and constitutes the common mass of the loins. This is covered by a 
strong aponeurosis which blends with the supraspinous and sacro-iliac ligaments, 
and is attached to the crest and sacral angle of the ilium and the first and second 
sacral spines; it furnishes origin to the lumbar portion of the middle gluteus. In 

' The muscle as here described includes the longissimus dorsi et cervicis and the spinalis and 
semispinalis components, as the separation of these is largely artificial in the horse. 




Fig. 270. — Right Portion of Cross-sectiox of 
Back of Horse. Section- is Cut Through 
Seventh Thoracic Vertebra. 
a, Ligamentum nuchie; 6, trapezius mus- 
cle: c, cartilage of scapuJa: d, latissimus dorsi; e, 
cutaneus; /, rhomboideus thoracalis; g, ser- 
ratus ventralis; h, serratus dorsalis; h'. lumbo- 
dorsal fascia, which diWdes below into three 
layers; i, longissimus costarum; k. levator costae; 
k', internal intercostal muscle: /. longissimus dorsi; 
m, m', seventh thoracic vertebra: ", head of 
eighth thoracic vertebra: o, head of eighth rib; 
p, seventh rib; r, intercostal arterj- and nerve: .1, 
skin. The fasciae are indicated by dotted lines. 
(After Ellenberger. in Leisering's Atlas.) 



THE FASCLE AND MUSCLES OF THE TAIL 279 

its course further forwai'd the muscle receives fasciculi from the lumbar and thoracic 
spines, but diminishes somewhat in volume. About the twelfth thoracic vertebra 
it divides into two parts. The dorsal division (m. spinalis et semispinalis), rein- 
forced by bundles from the first four thoracic spines, passes forward under the com- 
plexus to be inserted into the spines of the last four cervical vertebrae. The ventral 
division passes forward and downward underneath the serratus ventralis to be in- 
serted into the ribs and the transverse processes of the last four cervical vertebrae. 
Three sets of fasciculi may be distinguished, viz.: (1) spinal, which are superficial 
and medial; (2) transverse, attached to the transverse and articular processes, 
which are medial antl deep; (3) costal, which are lateral. 

Relations. — Superficially, the middle gluteus, the lumbo-dorsal fascia, the 
latissimus dorsi, serrati dorsales, serratus ventralis, and complexus; deeply, the 
multifidus, intertransversales, external intercostals, levatores costarum, the liga- 
mentum nuchfe, and its fellow of the opposite side (in the neck). 

Blood-supply. — Dorsal, deep cervical, intercostal, and lumbar arteries. 

Nerre-supply. — Dorsal branches of the thoracic antl lumbar nerves. 

8. Multifidus dorsi. — This is a long segmental muscle which lies along the sides 
of the spinous processes of the vertebrae from the sacrum to the neck. 

Origin. — (1) The lateral part of the sacrmn; (2) the articular processes of 
the lumbar vertebrae; (3) the transverse processes of the thoracic vertebrae. 

Insertion. — The spinous processes of the first two sacral, the lumbar, thoracic, 
antl last cervical vertebrae. 

Action. — Acting with its fellow, it is an extensor of the spine; acting singly, 
it flexes it laterally. 

Structure. — It is composed of a series of bundles which are directed oliliquely 
forward and upward. Each fasciculus passes over several vertebrte to its insertion. 
In the posterior part of the series the bundles cross two or three vertebrae and are 
inserted into the summits of the spines. Anteriorly the bundles have a more 
horizontal direction, cross three to five vertebrae, and are inserted into the sides 
of the spines considerably below their summits. A further complication consists 
in the fusion of several bundles into a common insertion. 

Relations. — Superficially, the longissimus dorsi; deeply, the vertebral spines. 

Blood-supply. — Intercostal and lumbar arteries. 

A'erre-supply. — Dorsal branches of the thoracic and lumbar nerves. 

9. Intertransversales lumbonim. — These are very thin muscular and tendin- 
ous strata, which occupy the spaces between the transverse processes of the lumbar 
vertebriB except the fifth and sixth. 

Action. — To assist in flexing the loins laterally or in rendering the region rigid. 
Relations. — Superficially, the longissimus dorsi; deeply, the quadratus Imii- 
borum. 

Blood-supply. — Lumbar arteries. 
Nerve-supply. — Lumbar nerves. 



The Fascia and Muscles of the Tail 

(FASCIA et MUSCULI CAUD^) 

The muscles of the tail are inclosed in the strong coccygeal fascia, which is 
continuous in front with the gluteal fascia and blends with the lateral sacro-iliac 
ligament. At the root of the tail it is loosely attached to the subjacent muscles, 
but further back it is intimately adherent to them. From its deep face are de- 
tached septa which pass between the muscles to become attached to the vertebrae. 

1. Coccygeus.' — This is a flat, triangular muscle which lies chiefly between the 
sacro-sciatic ligament and the rectum. 

' Also termed the ischio-coceygeus or compressor coccygis. 



280 



FASCIA AND MUSCLES OF THE HORSE 



Origin. — The pelvic surface of the sacro-sciatic ligament near the ischiatic spine. 

Insertion. — The first four coccygeal vertebrae and the coccygeal fascia. 

Action. — Acting together, to de- 
press (flex) the tail, compressing it 
over the perineum; acting singly, 
to depress and incline it to the 
same side. 

Structure. — The origin of the 
muscle is aponeurotic. Becoming 
fleshy, its fibers pass upward and 
backward and divide into two 
layers. The lateral layer is at- 
tached to the vertebrae, the medial 
to the fascia; included between 
the two lie the intertransversales. 
When the tail is raised, the ventral 
edges of the muscles produce a dis- 
tinct ridge at either side of the anus. 
Relations. — Laterally, the 
sacro-sciatic ligament and the semi- 
membranosus ; medially, the rectum 
and the sacro-coccygeus ventralis 
muscle. The internal pudic artery 
crosses the origin of the muscle, 
sacrococcygeus dorsalis medialis).' — This 




Fig. 271. — Cross-section of Tail of H 
1. 2, Branches of lateral coccygeal vessels and n 
die coccygeal artery: 4, sacro-coccygeus dorsalis; 4' 
geus lateralis: 5, 5', intertransversales; 6, sacro-coccygeus ven 
trails; 7, recto-coccygeus; 8, coccygeal fascia; 9, fibro-cartilagi 
between fourth and fifth coccygeal vertebrse. The veins are black 



3, niid- 



2. Sacro-coccygeus dorsalis (M. 
muscle lies along the dorso-median aspect of the tail, in contact with its fellow 

Origin. — The last three sac- 
ral spines and some of the coccy- 
geal spines. 

Insertion. — The dorsal sur- 
face of the coccygeal vertebrae. 

Action. — Acting together, to 
elevate (extend) the tail; acting 
singly, to elevate and incline it 
laterally. 

Structiire. — The muscle has 
a strong rounded belly. It is in- 
serted by means of short tendons 
which fuse with those of the next 
muscle. 

Relations. — Superficially, the 
coccygeal fascia; medially, its 
fellow; laterally, the sacro-coccy- 
geus lateralis; deeply, the verte- 
brae. 

3. Sacro-coccygeus lateralis 
(M . sacro-coccygeus dorsalis later- 
ahs).- — This muscle lies immedi- 
ately lateral to the preceding. 

Origin. — The sides of the 




1 Also termed the erector coccy- 
gis. 

■ Also known as the curvator 
coccygis. 



Fig. 272. — Muscles of Perineum of Horse. 
a, Coccygeus; b, retractor ani; c, c' , sphincter ani externusr 
d, recto-coccygeus; e, sacro-coccygeus ventralis lateralis; /, retrac- 
tor penis; g, bulbo-cavernosus; h, ischio-cavernosus; i. internal 
pudic artery; k, anus; /, penis. (After EUenberger-Baum, Top. 
Anat. d. Pferdes.) 



THE MUSCLES OF THE THORAX 281 

sacral spines, with the multifidus, and the transverse processes of the sacral and 
coccygeal vertebrae. 

Insertion. — The lateral surface of the coccygeal vertebree, except the first four. 

Action. — Acting with its fellow, to assist the preceding muscle in elevating the 
tail; acting singlj-, to inchne it to the same side. 

Structure. — This muscle appears to be a direct continuation of the multifidus 
dorsi. The belly is fusiform and receives reinforcing fasciculi from the transverse 
processes of the sacrum. This is succeeded by bundles of tendons, as many as four 
lying alongside of each other. 

Relations. — Superficially, the lateral sacro-iliac ligament and the coccygeal 
fascia; dorsally, the sacro-coccygeus dorsalis; ventrally, the intertransversales; 
deeply, the vertebrae and a branch of the lateral coccygeal artery and accompanying 
vein and nerve. 

4. Intertransversales caudae (Mm. intertransversarii caudae). — These con- 
sist of muscular bundles which lie on the lateral aspect of the tail, between the 
preceding muscle and the sacro-coccygeus ventralis. They begin on the lateral 
edge of the sacrum and occupy the spaces between the transverse processes, to which 
they are attached. They are, however, not arranged in a strict segmental manner. 

Action. — Acting together, to fix the coccygeal vertebrae; acting singly, to assist 
in lateral flexion. 

5. Sacro-coccygeus ventralis (Mm. sacro-coccygei ventrales).' — This muscle 
lies on the ventral aspect of the sacrum and coccyx. It is composed of two parts, 
described by Bourgelat and the German anatomists as separate muscles. 

(a) The lateral part (M. coccygeus ventralis lateralis) is much the larger of 
the two. It arises from the lateral part of the ventral surface of the sacrum, about 
as far forward as the third foramen, and is inserted into the transverse processes 
and ventral surface of the coccygeal vertebrae. 

(6) The medial part (M. sacro-coccygeus ventralis medialis) arises from the 
ventral surface of the sacrum medial to the preceding muscle and the first eight 
coccygeal vertebrae, and is inserted into the ventral surfaces of the coccygeal ver- 
tebrae. 

Action. — Acting together, to depress (flex) the tail; acting singly, to incline 
it laterally also. 

Structure. — The lateral part has a somewhat compressed belly, and receives 
bundles from the transverse processes of the coccygeal vertebrae. The medial part 
is much smaller and shorter, reaching only about to the middle of the tail. 

Relations. — Ventrally, the pelvic and coccygeal fasciae; dorsally, the sacrum, 
coccygeal vertebrae, and the intertransversales; laterally, the sacro-sciatic liga- 
ment, the coccygeus, and the coccygeal fascia; medially, its fellow, the recto- 
coccygeus, and the middle coccygeal vessels. Branches of the lateral coccygeal 
vessels and nerves lie between the lateral division of the muscle and the intertrans- 
versales. 

Blood-supply. — Middle and lateral coccygeal arteries. 

Nerve-supply. — Coccygeal nerves. 



The Muscles of the Thorax 
(musculi thoracis) 

These consists of seven muscles or sets of muscles, which are attached to the 
thoracic vertebrae, to the ribs and their cartilages, and to the sternum. They are 
muscles of respiration. 

1. Levatores costarum. — These constitute a series of small muscles which oc- 
cupy and overlie the dorsal ends of the intercostal spaces. 
' Also known as the depressor coccygis. 



282 



FASCLE AND MUSCLES OF THE HORSE 



Origin. — The transverse processes of the thoracic vertebrae. 

Insertion. — The lateral surfaces of the upper ends of the ribs posterior to the 
vertebral origin. 

Action. — To draw the ribs forward in inspiration. 

Structure. — Arising by tendinous fibers, each muscle passes backward and out- 
ward and expands at its insertion. Some fibers pass over one rib and are inserted 



iicventh cervical vertebra-' 



First thoracic vertebra 
% 



Section of scapula 



Levatorcs coslarum 




Intertransverse ligaments 
Ilio-l u nibar liga m c nt 



Lateral border of Ion- 
gissimus dorsi 



0^^^^ - Tuber coxa^ 



Fig. 273. — Deep Di'^sectiov of Dor'^\l and Litmbar Regions of Horse Dorsal View. (After Schmaltz, Atla 

d. Anat. d. Pferdes.J 



on a succeeding one. At the beginning and end of the series the muscle cannot be 
distinguished from the external intercostal, of which it is in reality only a specially 
developed part. 

Relations. — Superficially, the longissimus tlorsi; deeply, the ribs, internal in- 
tercostal muscles, and the intercostal vessels and nerves. 

Blood-supply. — Intercostal arteries. 



THE MUSCLES OF THE THORAX 283 

Nerve-supply. — Intercostal nerves. 

2. External intercostals (Mm. intercostales externi). — Each of these occupies 
an intercostal space, from the levatores to the sternal extremity of the rib. They 
do not occupy the intercartilaginous spaces. 

Origin. — The posterior borders of the ribs. 

Insertion. — The anterior borders and lateral surfaces of the succeeding ribs. 

Action. — To draw the ribs forward in inspiration. 

Structure. — The fibers are directed downward and backward. There is a 
considerable admixture of tendinous tissue. The thickness of the muscles grad- 
ually diminishes toward the lower ends of the spaces. 

Relations. — Superficially, the serratus ventralis, latissimus dorsi, serratus 
dorsalis, longissimus dorsi, longissimus costarum, rectus thoracis, deep pectoral, 
obliquus abdominis externus, and cutaneous muscles; deeply, the internal inter- 
costals and (in the upper part of the spaces) the intercostal vessels and nerves. 

Blood-supply. — Intercostal and internal thoracic arteries. 

Nerve-supply. — Intercostal nerves. 

3. Internal intercostals (Mm. intercostales interni). — These extend the en- 
tire length of the intercostal spaces, including their interchondral portion. 

Origin. — The anterior borders of the ribs and their cartilages. 

Insertion. — The posterior borders of the preceding ribs and cartilages. 

Action. — To draw the ribs backward in expiration. It seems probable, how- 
ever, that the intercartilaginous portion is inspiratory.' 

Structure. — The direction of the fibers is oblique downward and forward. 
There is a smaller amount of tendinous tissue than in the external set, and the 
thickness diminishes dorsally. In the upper part of the spaces fibers sometimes 
cross a rib in a fashion similar to the subcostals of man. A thin fascia separates 
the internal from the external intercostal muscle in each space. 

Relations. — Superficially, the levatores costarum and the external intercostals; 
deeply, the endothoracic fascia and pleura, the transversus thoracis, diaphragm, 
transversus abdominis, and the internal thoracic 8.nd musculo-phrenic vessels. 
In the upper part of the intercostal spaces the intercostal vessels and nerves lie 
between the internal and external intercostal muscle, but below they lie chiefly on 
the deep face of the internal muscle. 

Blood-supply. — Intercostal and internal thoracic arteries. 

Nerve-supply. — Intercostal nerves. 

The muscles in connection with the costal cartilages are sometimes distinguished as Mm. 
interoartilaginei; tlieir direction is similar to that of the internal intercostal, and they cover the 
cartilages of the asternal ribs more or less. At the ventral ends of some of the intercostal spaces 
there is a layer of longitudinal muscle. 

4. Retractor costae. — This is a small triangular muscle which lies Ijehind the 
last rib, chiefly unck'r cover of the serratus dorsalis. 

Origin. — The transverse processes of the first three or four lumbar vertebrse 
by means of the Imiibar fascia. 

hisertion. — The posterior border of the last rib. 

Action. — To retract the last rib. 

Structure. — The muscle arises by a thin aponeurosis. Its fibers are parallel 
to those of the adjacent internal oblique. 

Relations. — Superficially, the serratus dorsalis antl external olilique; deeply*, 
the transversus abdominis. 

Blood-supply. — Lumbar arteries. 

Nerve-supply. — Lumbar nerves. 

5. Rectus thoracis.- — This is a thin muscle which lies under cover of the deep 

'The function of the intercostal muscles is still a subject of much discussion. The state- 
ments made above seem to represent the view most commonly held in regard to their action. 
^ Also known as the transversus costarum or lateralis sterni. 



284 



FASCLE AND MUSCLES OF THE HORSE 



pectoral muscles. It is directed obliquely backward and downward, and crosses 
the lower part of the first three intercostal spaces. 

Origin. — The lateral surface of the first rib, below the scalenus. 

Insertion. — The cartilage of the fourth rib. The aponeurosis usually joins the 
rectus abdominis. It may reach the fifth rib or the sternum. 



Cariniform cartilage 



Sternal ligament 



First rib 
Internal thoracic vessels 



Internal intercostal muscle 




Costal part of 

diaphragm Sternal Transver.sus 

[cut edge) part of abdominis 

diaphragm {cut) 

Fig. 274. — Dissection op Floor of Thorax of Horse. 
The ribs have been sawn off near their sternal ends and the diaphragm and transversus abdominis cut off close to their 

attachment. 
1, Eighth rib; 2, 3, cartilages of ninth and tenth ribs; 4, xiphoid cartilage: 5, apex of pericardium. 



Action. — It may assist in inspiration or concur with the rectus abdominis. 
Relations. — Superficially, the deep pectoral muscles; deeply, the intercostal 
muscles and the ribs. 

Blood-supply. — Internal and external thoracic arteries. 
Nerve-supply. — Intercostal nerves. 



THE MUSCLES OF THE THORAX 285 

6. Transversus thoracis. — This is a flat muscle situated on the thoracic sur- 
face of the sternum and the cartilages of the sternal ribs. 

Origin. — The sternal ligament, meeting the opposite muscle. 

Insertion. — The cartilages of the ril)s, from the second to the eighth inclusive, 
and the adjacent part of some of the ribs. 

Action. — It draws the ribs and costal cartilages inward and backward, thus 
assisting in expiration. 

Structure. — Each muscle has the form of a scalene triangle, of which the base 
is the strongly serrated lateral border. The muscle contains a good deal of ten- 
dinous tissue. The anterior bundles are directed forward and outward; the poste- 
rior, backward and outward. 

Relations. — Dorsally, the endothoracic fascia and pleura; ventrally, the 
costal cartilages, the internal intercostal muscles, and the internal thoracic vessels. 

Blood-supply. — Internal thoracic arterj\ 

Nerve-supply. — The intercostal nerves. 

7. Diaphragm. — This is a broad, unpaired muscle which forms a partition be- 
tween the thoracic and abdominal cavities.' In outline it has some resemblance to 
a palm-leaf fan. In form it is dome-shaped, compressed laterally. On a median 
section it is seen to have a general direction downward and forward from the lumbar 
vertebrae to the xiphoid cartilage. The thoracic surface is strongly convex, and 
is covered by the pleura. The abdominal surface is deeply concave, and is covered 
for the most part by the peritoneum. The muscle consists of a fleshy rim which 
may be subdivided into costal and sternal parts; a lumbar part, composed of two 
crura; and a tendinous center. 

Attachments. — (1) Costal part (Pars costalis): The cartilages of the eighth, 
ninth, and tenth ribs, and behind this to the ribs at an increasing distance from their 
sternal ends. 

(2) Sternal part (Pars sternalis) : The upper surface of the xiphoid cartilage. 

(3) Lumbar part (Pars lumbalis): (a) The right cms (Crus dextrum) is at- 
tached to the ventral longitudinal ligament, and by this means to the first four or 
five lumbar vertebrae, (b) The left crus (Crus sinistrum) is attached in a similar 
fashion to the first and second lumbar vertebrae. 

Action. — It is the principal muscle of inspiration and increases the longitu- 
dinal diameter of the chest. The contraction produces a general lessening of the 
curvature of the diaphragm. In the expiratory phase the costal part and crura lie 
almost entirelj' on the body walls, so that the bases of the lungs are in contact with 
the tendinous center almost exclusively. In ordinary inspiration the fleshy rim 
recedes from the chest-wall, so that the bases of the lungs move backward to a line 
about parallel with the costal arches, and about four or five inches (ca. 10-12 ctii.) 
therefrom. 

It is stated that the inspiratory movement affects the tendinous center much less than the 
fleshy part, and that the foramen vense cavEc scarcely moves at all, since the posterior vena cava 
is firmly attached to it. It should be noted, however, that the direction of the thoracic part of 
the vena cava in the expiratory phase is oblique upward and backward. Thus it would seem that 
there is no anatomical reason why the diaphragm should not move as a whole in ordinary inspira- 
tion at least; examination of formaUn-hardened subjects in wliich the diaphragm appears to be 
fixed in the inspiratory phase indicates that such is the case. 

Structure. — The costal part consists of a series of digitations which meet, or 
are separated by a very narrow interval from, the transversus abdominis; between 
the two are the musculo-jjlirenic vessels. From the tenth rib backward the at- 
tachments to the ribs are at an increasing distance above the costo-chondral junc- 
tions. Thus at the last rib the upper limit of the attachment is four to five inches 
(10-12 cm.) from the ventral end. Anteriorly the origin extends along the eighth 

1 It should be noted, however, that in the embryo the diaphragm appears as a paired struc- 
ture, extending from the lateral walls of the coelom to fuse with the septum transversum. 



286 



FASCI.E AND MUSCLES OF THE HORSE 



and ninth costal cartilages to the xiphoid cartilage. From these points of origin 
the fibers curve inward and forward to join the tendinous center.' The right cms 
is about twice as thick as the left one and is also longer. It arises by a strong tendon 



Longissitnus dorsi 
Lumbar transverse 




Costal arch 
Musculo-phrenic 

artery 
Transversus 

abdoininaUs (cut 

edge) 
Xiphoid cartilage 



OF Horse; Abdominal Surface. 
Ventral longitudinal ligament; 2, 2', tendons of crura; 3, lumbar sympathetic trunks; J,, external spermatic 
a, 5, great splanchnic nerves; 6, eisterna chyli (opened); 7, 7, oesophageal continuations of vagus nerves; 
; 9. coronary ligament of liver (cut) ; W, right lateral ligament of liver (cut) ; 11, left lateral ligament of 
falciform ligament of liver (cut); A.I., lumbo-costal arch; N.i., intercostal nerve; C.d., right crus; 



S, lymph-gland 
liver (cut); 12 
C.S., left crus; 
Schmaltz, Atla 



.4, aorta: Ca, cceliac artery; Oe., CEsophagus; 
! d. Anat. d. Pferdes.) 



posterior vena ( 



T'.p., phre: 



(Aftei 



which blends with the ventral longitudinal ligament. The tendon is succeeded by 
a rounded belly which leaves the vertebral column at the last thoracic vertebra. 

1 It is interesting to note that when a nineteenth rib is present (even when it is well developed) 
the diaphragm has no connection with it, but ends on the eighteenth rib at a point a little more 
ventral than usual. 



THE ABDOMINAL FASCIA AND MUSCLES 287 

Passing downward and forward, its fibers spread out and join the tendinous center. 
The left cms arises by a thin tendon from the ventral longitudinal ligament at the 
first and second lumbar vertebrae. This is succeeded by a triangular belly which 
joins the central tendon. Between the crura and the attachment to the last rib 
the edge of the muscle crosses the ventral surface of the psoas muscles without at- 
tachment, forming the .so-called lumbo-costal arch (Arcus lumbocostalis) ; here the 
thoracic and abdominal cavities arc separated only by the serous membranes and 
some areolar tissue. The tendinous center (Centrum tendineum) resembles the 
periphery in outline, but is more elongated. It is partially divided into right and 
left parts by the descent of the crura into it. It is composed largely of radiating 
fibers, but many interlace in various directions; this is specially evident around the 
foramen venae cavae, which is encircled by fibers. A strong tendinous layer extends 
across below the hiatus oescphageus. 

Schmaltz and others describe the lumbar part as consisting of four crura, two medial and two 
lateral. On this basis the left crus of the preceding description becomes the crus lalerale sinistrum, 
and the corresponding part of the right side is the crus laterale dextrum. The central part is di\i( led 
by the hiatus oesophageus and the slit which extends from it dorsally into a crus mediale dextrum 
and a crus mediale sinistrum. Both modes of division are in part artificial. 

The diaphragm is pierced by three foramina. (1) The hiatus aorticus is an 
interval between the two crura and below the last thoracic vertebra. It contains 
the aorta, vena azygos, and cisterna chyli. (2) The hiatus oesophageus^ perforates 
the right crus near its junction with the tendinous center. It is situated a little to 
the left of the median plane and about a hand breadth ventral to the thirteenth 
and fourteenth thoracic vertebrte. It transmits the oesophagus, the vagus nerves, 
and the oesophageal branch of the gastric artery. (3) The foramen venae cavae- 
pierces the tendinous center about an inch (ca. 2-3 cm.) to the right of the median 
plane, and about six to eight inches (ca. 15-20 cm.) below the eleventh and 
twelfth thoracic vertebrae. The vena cava is firmly attached to the margin of the 
opening.'' 

Relations. — The thoracic surface is related to the endothoracic fascia, pleurae, 
pericardium, the bases of the lungs, and the ribs in part. The abdominal surface 
is in great part covered by the peritoneum, and is related chiefly to the liver, stom- 
ach, intestine, spleen, pancreas, kidneys, and adrenals. The sympathetic trunk and 
splanchnic nerve pass between the crus and the psoas muscles on each side. The 
musculo-phrenic vessels perforate the edge of the muscle at the ninth costo-chondral 
joint. 

Blood-supply. — Phrenic and musculo-phrenic arteries. 

■Nerve-supply. — Phrenic nerves. 



The Abdominal Fascia and Muscles 
(fascia et musculi abdominis) 

The superficial fascia of the abdomen is in part fused dorsally with the lumbo- 
dorsal fascia; in front it is continuous with the superficial fascia of the shoulder and 
arm, behind with that of the gluteal region. In the inguinal region it forms part 
of the fascia of the penis or of the mammary glands. At the lower part of the flank 
it forms a fold which is continuous with the fascia of the thigh near the stifle joint. 

1 Formerly termed the foramen sinistrum. ^ Formerly termed the foramen dextrum. 

' In order to get a clear idea of the relative positions of these foramina and of the form of 
the diaphragm, the thoracic surface of the latter should be examined in properly preserved sub- 
jects while the abdominal \'iscera remain in situ. It will be observed that the distances of the 
hiatus oesophageus and foramen vena> cavse from the vertebral column vary according to the ful- 
ness of the abdominal viscera and the degree of contraction of the diaphragm. The statement.s 
given above are averages. 



288 FASCI.E AND MUSCLES OF THE HORSE 

In this fold are the prefemoral lymph-glands. Medially it blends with the linea 
alba. It contains the abdominal cutaneous muscle (described on p. 254). 

The deep fascia is represented chiefly by the abdominal tunic (Tunica flava 
abdominis) . This is a sheet of elastic tissue which assists the muscles in supporting 
the great weight of the abdominal viscera. It is practically coextensive with the 
obliquus externus, which it covers. Ventrally it is thick, and is intimately ad- 
herent to the aponeurosis of the muscle. Laterally it becomes thinner and is more 
easily separated, although fibers from it dip in between the muscle-bundles. It is 
continued for some distance upon the intercostals and serratus ventralis. Traced 
forward, it passes as a thin layer beneath the posterior deep pectoral muscle. Pos- 
teriorly it is attached to the tuber cox£e. In the inguinal region it forms the deep 
fascia of the prepuce or of the mammary glands. 

The linea alba is a median fibrous raphe which extends from the xiphoid car- 
tilage to the prepubic tendon. It is formed chiefly by the junction of the aponeu- 
roses of the oblique and transverse muscles, but partly by longitudinal fibers. A 
little behind its middle (about in a transverse plane tangent to the last pair of ribs) 
is a cicatrix, the lunbilicus, which indicates the position of the umbilical opening 
of the foetus. 

1. Obliquus abdominis extemus. — This is the most extensive of the abdominal 
muscles. It is a broad sheet, irregularly triangular in shape, widest behind. Its 
fibers are directed chiefly downward and backward. 

Origin. — (1) The lateral surfaces of the last fourteen ribs, and the fascia over 
the external intercostal muscles; (2) the lumbo-dorsal fascia. 

Insertion. — (1) The linea alba and the prepubic tendon; (2) the tul:)er coxse and 
shaft of the ilium; (3) the medial femoral fascia. 

Action. — (1) To compress the al)dominal viscera, as in defecation, micturition, 
parturition, and expiration; (2) to flex the trunk (arch the back) ; (3) acting singly, 
to flex the trunk laterally. 

Structure. — The muscle is composed of a muscular part and an aponeurosis. 
The muscular part lies on the lateral wall of the thorax and abdomen. It arises 
by a series of digitations, the anterior four of which alternate with those of the ser- 
ratus ventralis. The origin may be indicated by a slightly curved line (concave 
dorsally) drawn from the lower part of the fifth rib to the tuber coxae. The fibers 
are directed downward and backward and terminate on the aponeurosis, except in 
the upper part of the flank, where they are less oblique in direction and end on the 
tuber coxffi. The line of junction is a curve (concave dorsally) extending from the 
upper edge of the posterior deep pectoral muscle toward the point of the hip. The 
aponeurosis is intimately attached to the abdominal tunic, and its fibers are largely 
interwoven ventrally with those of the aponeurosis of the internal oblique. By 
this fusion is formecl the outer sheath of the rectus abdominis, which blends at the 
linea alba vnth that of the opposite side. In the inguinal region the aponeurosis 
divides into two chief layers; one of these curves dorsally and backward and is in- 
serted into the tuber coxse and the prepubic tendon. Between these points the 
aponeurosis is much strengthened and is called the inguinal ligament (Ligamentum 
inguinale).' This curves upward and somewhat forward, becomes thin, and blends 
with the iliac fascia. It forms the posterior wall of the inguinal canal. About an 
inch (ca. 2 to 3 cm.) in front of the pubis and about two inches (ca. 4 to 5 cm.) 
from the median plane the aponeurosis is pierced by a slit-like opening, the 
subcutaneous or external inguinal ring (Annulus inguinalis subcutaneus) .- This is 

' Also commonly known as Poupart's ligament. — based on a false historical allusion. It is 
in no proper sense a ligament, but is the inguinal part of the aponeurosis of the obliquus externus; 
it might therefore well be termed the lamina inguinahs. 

- It is narrow and slit-like in the natural condition, but may appear oval in the dissecting- 
room, especially if the hind hmb is drawn back and abducted. 



THE ABDOMINAL FASCIA AND MUSCLES 



289 



the external orifice of the inguinal canal. Its long axis is directed outward, for- 
ward, and somewhat ventrally, and is four to five inches (ca. 10-12 cm.) in length. 




t^ I s 



.2 6 



■g iT E 



The medial angle is rounded and is well defined by the junction of the aponeurosis 
with the prepubic tendon, but the lateral angle is not so sharply defined. The bor- 
ders or crura are constituted by arciform fibers of the aponeurosis (Crus mediale, 



290 FASCIA AND MUSCLES OF THE HORSE 

laterale). The femoral lamina of the aponeurosis (Lamina femoralis) passes on 
to the medial surface of the thigh, where it blends with the femoral fascia. A 
thin iliac lamina (Lamina iliaca) passes over the lateral margin of the iliacus and 
is attached to the lateral border of the ilium. 

Relations. — Superficially, the skin, the abdominal cutaneus, the abdominal 
tunic, and the posterior deep pectoral muscle; deeply, the ribs and their cartilages, 
the intercostal muscles, the obliquus abdominis internus, the contents of the inguinal 
canal, and the sartorius and gracilis. 

Blood-supply. — Intercostal and limibar arteries. 

Nerve-supply. — Intercostal and lumbar nerves. 

2. Obliquus abdominis internus. — This muscle is situated under the preceding 
one. Its fibers are directed do^viiward, forward, and inward. It forms a triangular 
curved sheet with the base behind. 

Origin. — The tuber coxae and the adjacent part of the inguinal ligament. 

In.sertion. — (1) The cartilages of the last four or five ribs; (2) the linea alba 
and the prepubic tendon. 

Action. — Similar to that of the preceding muscle. 

Structure. — Like the external oblique, it is composed of a fleshy portion and 
an aponeurosis. The muscular part is fan-shaped, and is situated chiefly in the 
flank. At its iliac origin it is covered by a glistening aponeurosis. Traced medially 
and ventrally along the abdominal surface of the inguinal ligament, the muscular 
origin is found to become much thinner, and also becomes loosely attached to the 
ligament. This medial part of the muscle forms the anterior wall of the inguinal 
canal. The abdominal orifice of the canal, the abdominal or internal inguinal 
ring' (Annulus inguinalis abdominalis) , is found here, ft is normally a narrow 
slit, bounded in front by the edge of the internal oblique, and behind by the in- 
guinal ligament. Near the last rib the muscle divides into two parts. The small 
dorsal part is inserted by four or five thin tendinous strips to the medial surface of 
the last four or five costal cartilages. The aponeurosis of the large ventral part 
is to a great extent blended with that of the external oblique, being, indeed, consider- 
ably interwoven with it ventrally. Where it covers the rectus abdominis it is at- 
tached to the tendinous inscriptions of that muscle. It may be noted that the dor- 
sal margin of the aponeurosis varies in different subjects in the fact that it may 
cover the costal arch or lie ventral to it. 

Relations. — Superficially, the obliquus externus; deeply, the rectus abdominis, 
transversus abdominis, and the peritoneum. 

Blood-supply. — Circumflex iliac, lumbar, and intercostal arteries. 

Nerre-supphj. — Ventral branches of the lumbar nerves. 

3. Rectus abdominis. — This muscle is confined to the ventral part of the ab- 
dominal wall; it extends from the steriial region to the pubis. 

Origin. — The cartilages of the fourth or fifth to the ninth ribs inclusive, and the 
adjacent surface of the sternum. 

Insertion. — The pubis, by means of the prepubic tendon. 

Action. — Similar to that of the oblique muscles. It is especially adapted to 
flex the lumbo-sacral joints and the lumbar and thoracic parts of the spine. 

Structure. — The fibers of the muscle are directed longitudinally. Nine to 
eleven transverse bands of fibrous tissue extend in an irregular manner across the 

' It must be admitted that the term "ring" is rather misleading as appUed to the abdomi- 
nal opening of the canal, since normally it is a mere dilatable slit. The ring-like constriction 
which exists here in the male is constituted by the peritoneum, wliich descends into the canal 
to form the tunica vaginalis. This peritoneal ring is termed the vaginal ring (.\nnulus vagi- 
nalis), and must not be confused with the subperitoneal ring, i. e., the abdominal or internal 
inguinal ring. The internal inguinal ring is six or seven inches (ca. 16 cm.) in length. Its 
direction corresponds approximately to a line from the lateral margin of the prepubic tendon to the 
ventral part of the tuber coxae. 



THE ABDOMINAL FASCIA AND MUSCLES 291 

muscle. These are termed inscriptiones tendineae. They strengthen the muscle 
and serve to prevent separation of its fibers. The width of the muscle is greatest 
about its middle. The anterior part blends with the rectus thoracis. 

Relations. — Superficially, the aponeuroses of the oblique muscles (which con- 
stitute the external rectus sheath) and the posterior deep pectoral; deeply, the 
transversus abdominis, intercostals, the cartilages of the ribs, and the sternum. 
The posterior abdominal artery runs along the lateral edge of the muscle posteriorly, 
and the anterior abdominal artery on or in its anterior part. 

Blood-supply. — Anterior and posterior abdominal arteries. 

Nerve-supply. — Intercostal and lumbar nerves. 

4. Transversus abdominis. — This muscle, named from the general direction 
of its fibers, is a triangular curved sheet. Its lateral part is muscular, its ventral 
aponeurotic. 

Origin. — (1) The medial surfaces of the cUstal ends or the cartilages of the 
asternal ribs, meeting the costal attachment of the diaphragm; (2) the transverse 
processes of the lumbar vertebrte, by means of the deep layer of the lumbo-dorsal 
fascia. 

Insertion. — The xiphoid cartilage and the linea alba. 

Action. — Similar to that of the oblique muscles. 

Structure. — The muscular part is a sheet of parallel bundles of fibers, directed 
ventro-medially. It is thickest along the cartilages of the ribs, and from here it 
thins out greatly toward the aponeurosis and the lumbar region. The fibers of the 
aponeurosis directly continue those of the fleshy part. Posteriorly it becomes ex- 
tremely thin and fades out without reaching the pelvis. It covers the deep face 
of the rectus, so forming the internal rectus sheath. 

Relations. — Superficially, the oblique and straight muscles, the retractor costae, 
the cartilages of the asternal ribs, and the internal intercostal muscles ; deeplj', the 
fascia transversalis and the peritoneum. The fascia transversalis is little de- 
veloped in the horse, and is very thin in emaciated subjects, but in animals in good 
condition it contains a good deal of fat. It blends with the iliac fascia and de- 
scends into the inguinal canal. The musculo-phrenic artery runs along the inter- 
val Between the origin of the transversus ancl the costal part of the diaphragm. 
The intercostal nerves pass down over the lateral surface of the muscle, to which 
they give branches. Branches of the first three lumbar nerves are similarly dis- 
posed further back. 

Blood-supply. — Intercostal, lumbar, and musculo-phrenic arteries. 

Nerve-supply. — Intercostal and lumbar nerves. 

5. Cremaster extemus. — This small muscle may be regarded as a detached 
portion of the obliquus al:)dominis internus, with which it blends at its origin (Figs. 
370, 575). 

Origin. — The iliac fascia, near the origin of the sartorius. 

Insertion. — The tunica vaginalis communis. 

Action. — To raise the tunica vaginalis, and with it the testicle. 

Structure. — The muscle arises by a thin aponeurosis which is succeeded by a 
flat muscular belly about two inches (ca. 5 cm.) in width in the stallion.^ It passes 
down the inguinal canal on the postero-lateral surface of the tunica vaginalis, to 
which it is very loosely attached. On reaching the point where the tunic is reflected 
on to the tail of the epididymis, the muscle is inserted into the outer surface of the 
tunic by short tendinous fibers. 

Relations. — The muscle lies between the peritoneum and the fascia trans- 
versalis in front and the iliac fascia and inguinal ligament behind. On reaching 

1 As might be expected, the cremaster usually undergoes more or less atrophy and is paler 
in the castrated subject. In the mare the muscle is very small, and ends in the connective tissue 
in the inguinal canal. 



292 FASCIA AND MUSCLES OF THE HORSE 

the abdominal ring it descends the inguinal canal on the postero-lateral surface of 
the tunica vaginalis communis. 

Blood-supply. — External spermatic artery. 

Nerve-supply. — External spermatic nerve. 

The Inguinal Canal. — This term (Canalis inguinalis) is applied to an oblique 
passage through the posterior part of the abdominal wall.' It begins at the ab- 
dominal inguinal ring, and extends obliquely ventro-medially, and somewhat for- 
ward, to end at the subcutaneous inguinal ring. Its anterior wall is formed by the 
fleshy posterior part of the internal oblique muscle, and the posterior wall by the 
strong tendinous inguinal ligament. The average length of the canal, measured 
along the spermatic cord, is about four inches (ca. 10 cm.). The abdominal or 
internal inguinal ring (Annulus inguinalis abdominalis) is the internal opening of 
the canal ; it is bounded in front by the thin margin of the internal oblique muscle, 
and behind by the inguinal ligament. It is directed from the edge of the prepubic 
tendon approximately toward the tuber coxae. Its length is about six or seven 
inches (ca. 15-17.5 cm.). The edge of the muscle is attached to the surface of the 
ligament here })y delicate connective tissue, except where structures intervene be- 
tween the walls of the canal. The lateral limit of the ring is determined by the 
muscle becoming firmly attached to the ligament, i. e., actually arising from the 
latter. The subcutaneous or external inguinal ring (Annulus inguinalis subcutan- 
eus) is a well-defined slit in the aponeurosis of the external oblique muscle, lateral 
to the prepubic tendon. Its long axis is directed from the edge of the prepubic 
tendon outward, forward, and slightly ventrally, and its length is about four or five 
inches (ca. 10-12 cm.). The canal contains in the male the spermatic cord, the 
tunica vaginalis, the external cremaster muscle, the external pudic artery (and in- 
constantly a small satellite vein), and the inguinal lymph vessels and nerves. In 
the female it contains the mammary vessels and nerves; in the bitch it also lodges 
the round ligament of the uterus, enclosed in a tubular process of peritoneum. 

The two rings do not correspond in direction, but diverge laterally, so that the length of the 
canal varies greatly when measured at different points. The medial angles of the two rings are 
separated only by a distance equal to the thickness of the prepubic tendon (about a centimeter), 
but the lateral angles are about seven inches (ca. 17.5 cm.) apart. The distance measured along 
the spermatic cord is about four inches (ca. 10 cm.). The medial angle of the subcutaneous ring 
is well defined and distinctly palpable at the side of the prepubic tendon; from here the direction 
of the ring is tracealjle. 

The Prepubic Tendon. — The prepubic tendon (Tendo prtepubicus) is essentially 
the tendon iif insertion of the two recti abtlominis, but also furnishes attachment to 
the obliqui, the graciles, antl the pectinei. It is attached to the anterior borders of 
the pubic bones, including the ilio-pectineal eminences. It has the form of a very 
strong thick band, with concave lateral borders which form the medial boundaries 
of the subcutaneous inguinal rings. Its direction is oblique upward and backward. - 
Its structure is somewhat complex. Most of the fibers of the posterior part extend 
from one ilio-pectineal eminence to the other. The fibers which belong to the recti 
curve in to the mechan line. The aponeuroses of the internal oblique muscles are 
inserted into its abdominal surface, and the inguinal ligaments are attached to and 
continue across it in arciform fashion. The anterior part of the tendon of origin 
of the gracilis is fused with it ventrally, and many of the fibers of the pcctineus 
arise from it. It gives off on either side a strong round band, the so-called accessory 
ligament, which is inserted into the fovea of the head of the femur with the round 

' The term canal is somewhat misleading; it is rather a slit-like passage or space between 
the two obUque muscles, since the inguinal ligament is that part of the aponeurosis of the exter- 
nal oblique muscle which stretches between the tuber coxse and the prepubic tendon. 

- The obliquity of the tendon and the angle which it forms with the pelvic floor are of clinical 
importance in regard to manipulation of the foetus in obstetrical cases. The slope varies in 
different subjects. In some cases the tendon forms about a right angle with the pubic bones. 



THE MUSCLES OF THE THORACIC LIMB 293 

ligament (vide hip joint). A band from the ventral surface extends backward and 
blends with the tendon of origin of the gracilis on each side. 



The Muscles of the Thoracic Limb 

I. the muscles of the shoulder girdle (Figs. 266, 267, 268, 276) 

This group (Mm. cinguli extremitatis thoracalis) consists of those muscles 
which connect the thoracic limb with the head, neck, and trunk. It may be re- 
garded as consisting of two divisions — dorsal and ventral.' 

A. Dorsal Division 

This division consists of two layers which overlie the proper muscles of the 
neck and back. 

First Layer 

1. Trapezius. — This is a flat, triangular muscle, the base of which extends 
along the supraspinous ligament. It is divided by an aponeurotic portion into two 
parts : 

(a) Trapezius cervicalis. — Origin. — The funicular part of the ligamentum 
nuchse, from the second cervical to the third thoracic vertebra. 

Insertion. — The spine of the scapula and the fascia of the shoulder and arm. 

(b) Trapezius thoracalis (s. dorsalis). — Origin. — The supraspinous ligament, 
from the third to the tenth thoracic vertebra. 

Insertion. — The tuber spinse of the scapula. 

Action. — Acting as a whole, to elevate the shoulder; the cervical part draws 
the scapula forward ami upward and the thoracic part draws it backward and up- 
ward. 

Structure. — The muscle arises by a narrow, thin aponeurosis, from which the 
fibers of the flat fleshy part converge to the spine of the scapula and the aponeurosis 
which separates the two portions. The cervical fascia joins the ventral edge of the 
cervical portion to the brachioceplialicus, or the two muscles may unite or overlap 
here. 

Relations. — Superficially, the skin and fascia; deeply, the rhomboideus, 
latissimus dorsi, supraspinatus, infraspinatus, deltoid, splenius, serratus ventralis, 
and anterior deep pectoral muscles, and the cartilage of the scapula. 

Blood-supply. — Deep cervical and intercostal arteries. 

Nerve-supply. — Spinal accessory nerve. 

Second Layer 
This consists of three muscles — the rhomboideus, latissimus dorsi, and brachio- 
cephalicus. 

2. Rhomboideus. — This consists of two parts: 

(a) Rhomboideus cervicalis. — Origin. — The funicular part of the ligamentum 
nuchse, from the second cervical to the second thoracic vertebra. 

Insertion. — The medial surface of the cartilage of the scapula. 

(b) Rhomboideus thoracalis (s. dorsalis). — Origin. — The spinous processes of 
the second to the seventh thoracic vertebra by means of the dorso-scapular liga- 
ment. 

Insertion. — The medial surface of the cartilage of the scapula. 
Action. — To draw the scapula upward and forward. When the limb is fixed 
the cervical part will elevate the neck. 

' The terms dorsal and ventral are here used in the topographic and not in the morpho- 
logical sense; all the muscles of the group are ventral in the latter sense. 



294 FASCIA AND MUSCLES OF THE HORSE 

Structure. — The cervical part is narrow, pointed at its anterior extremity, and 
lies along the funicular part of the ligamentum nuchse, to which it is attached by- 
short tendon bundles. The fibers are directed for the most part longitudinally. 
The thoracic part is quadrilateral in shape, and its fibers are nearly vertical. Its 
deep face is intimately attached to the dorso-scapular ligament. 

Relations. — Superficially, the skin and fascia (over a small area in front), the 
trapezius, and the cartilage of the scapula; deeply, the dorso-scapular ligament, 
the splenius, complexus, longissimus dorsi, and serratus dorsalis. 

Blood-supply. — Dorsal and deep cervical arteries. 

Nerve-supply. — Sixth and seventh cervical nerves. 

3. Latissimus dorsi. — This is a \vide muscle which has the form of a right- 
angled triangle. It lies for the most part under the skin and cutaneous muscle, 
on the lateral wall of the thorax, from the spine to the arm. 

Origin. — The lumbo-dorsal fascia — and by this means from the Imnbar and 
thoracic spines as far forward as the highest point of the withers. 

Insertion. — The teres tubercle of the humerus, in common with the teres 
major. 

Action. — To draw the humerus upward and backward and flex the shoulder- 
joint. If the limb is advanced and fixed, it draws the trunk forward. 

Structure. — The muscle arises by a wide aponeurosis, which fuses with that 
of the serratus dorsalis and with the lumbo-dorsal fascia. The muscular part 
is at first rather thin, but by the convergence of its fibers becomes thicker as it 
approaches the arm. The anterior fibers pass almost vertically downward over 
the dorsal angle of the scapula and its cartilage. The posterior fibers are directed 
downward and forward. The thick belly formed by the convergence of these 
passes under the triceps to end on the flat tendon of insertion, which is common 
to this muscle and the teres major. The tendon of insertion furnishes origin to the 
anterior part of the tensor fascije antibrachii. 

Relations. — Superficially, the superficial fascia, skin, cutaneus, trapezius, 
and triceps; deeply, the cartilage of the scapula, the rhomboideus, the serrati, the 
external intercostals, and the lumbo-dorsal fascia. 

Blood-supply. — Subscapular, intercostal, and lumbar arteries. 

Nerve-s apply . — Thoraco-dorsal nerve . 

B. Ventral DmsioN 

1. Brachiocephalicus.' — This muscle extends along the side of the neck from 
the head to the arm. It is incompletely divisible into two portions. 

Origin. — (1) The mastoid process of the temporal bone and the nuchal crest; 
(2) the wing of the atlas and the transverse processes of the second, third, and 
fourth cervical vertebrs. 

Insertion. — The deltoid tuberosity, the curved rough line which extends from 
this almost to the distal extremity of the humerus, and the fascia of the shoulder 
and arm. 

Action. — When the head and neck are fixed, to draw the limb forward, ex- 
tending the shoulder joint. When the limb is fixed, to extend the head and neck, 
if the muscles act together; acting separately, to incline the head and neck to 
the same side. By means of its attachment to the strong fascia which extends 
from the deltoid tuberosity to the outer face of the elbow the muscle also acts as 
an extensor of the elbow joint (e. g., in standing). 

Structure. — As already mentioned, the muscle is capable of incomplete di- 
vision into two parts, the line of division being indicated by the emergence of sup- 
erficial branches of the ventral divisions of the cervical nerves. The mastoid part 

' This muscle is also called the mastoido-humeralis, humero-mastoideus, dero-brachialis and 
levator humeri. 



THE MUSCLES OF THE SHOULDER GIRDLE 295 

(M. cleido-mastoideus) partly overlaps the other (M. cleido-transversarius), which 
lies dorsal to it. The former is attached to the mastoid process and the occipital 
bone by a broad tendon which fuses at its terminal part with that of the splenius 
and longissimus capitis et atlantis; it is also attached to the tendon of insertion of 
the sterno-cephalicus by aponeurosis. The dorsal part is attached to the transverse 
processes by four fleshy digitations. The belly of the muscle is adherent superfi- 
cially to the cervical fascia and the cutaneous muscle, and deeply to the omo- 
hyoideus. In front of the shoulder its deep face may present a tendinous inter- 
section of variable development.' Here the muscle becomes wider, covers the 
shoulder joint, passes between the brachialis and biceps, and is inserted by means 
of a wide tendon which it shares with the superficial pectoral muscle. 

Relations. — Superficially, the skin, cervical fascia, the parotid gland, the cuta- 
neus, the brachialis, and branches of the cervical nerves; deeply, the splenius, 
longissimus capitis et atlantis, rectus capitis ventralis major, omo-hyoideus, ser- 
ratus ventralis, anterior deep pectoral and biceps muscles, the inferior cervical 
artery, the prescapular lymph glands, and branches of the cervical nerves. The ven- 
tral edge of the muscle forms the dorsal boundary of the jugular furrow. The 
dorsal border may be in contact with the cervical trapezius, or be separated from 
it by a variable interval. 

Blood-supply. — Inferior cervical, carotid, and vertebral arteries. 

Nerve-supply. — Si:)inal accessory, cervical, and axillary nerves. 

The pectoral fascia is a thin membrane covering the surface of the pectoral 
muscles, to which it is, for the most part, closely attached. It detaches a layer 
which passes between the superficial and deep pectorals. At the posterior edge of 
the triceps another layer is given off, which passes on the lateral surface of this 
muscle to blend with the scapular fascia; the deeper layer becomes continuous with 
the subscapular and cervical fasciae. 

The pectoral muscles form a large fleshy mass which occupies the space be- 
tween the ventral part of the chest-wall and the shoulder and arm. They are 
clearly divisible into a superficial and a deep layer. The superficial layer may be 
subdivided into two parts by careful dissection; the deep layer is clearly made up 
of two muscles. 

2. Superficial pectoral muscle (M. pectoralis superficialis) . 

(a) Anterior superficial pectoral muscle (pars descendens) .- — This is a short, 
thick, somewhat rounded muscle, which extends from the manubrium sterni to 
the front of the arm. It forms a tlistinct prominence on the front of the breast, 
which is easilj' recognized in the living animal. 

Origin. — The cariniform cartilage of the sternum. 

Insertion. — (1) The curved line of the humerus with the brachiocephalicus; (2) 
the fascia of the arm. 

Action. — To adduct and advance the limb. 

Structure. — The belly of the muscle is convex on its superficial face, but deeply 
it is flattened where it overlaps the posterior superficial pectoral. Here the two 
muscles are usuallj' closely attached to each other, and care must be exercised in 
making the separation. The tendon of insertion blends with that of the brachio- 
cephalicus and with the fascia of the arm. At the middle line of the breast a fur- 
row occurs between the two muscles; laterally, another furrow, containing the 
cephalic vein, lies between the muscle and the brachiocephalicus. 

Relations. — Superficially, the skin, fascia, and panniculus; deeply, the pos- 

' This is regarded as a vestige of the clavicle. On this basis the portion of the muscle from 
the vestige to the arm represents the clavicular part of the deltoid and perhaps the clavicular part 
of the pectoralis major of man. 

^ Also termed the pectoralis anticus or pars clavicularis. 



296 FASCliE AND MUSCLES OF THE HORSE 

terior division, the deep pectoral, and the biceps. The cephalic vein lies in the 
groove between this muscle and the brachiocephalicus. 

(b) Posterior superjScial pectoral muscle (pars transversa).' — This is a wide 
muscular sheet which extends from the ventral edge of the sternum to the medial 
surface of the elbow. 

Origin. — (1) The ventral edge of the sternum as far back as the sixth car- 
tilage; (2) a fibrous raphe common to the two muscles. 

Insertion. — (1) The fascia on the proximal third of the forearm; (2) the 
curved line of the humerus with the preceding muscle. 

Action. — To adduct the limb and to tense the fascia of the forearm. 

Structure. — It is thin and pale, and mixed with a good deal of fibrous tissue. 
The right and left muscles fuse at a median fibrous raphe. The tendon of inser- 
tion unites with the fascia on the medial side of the forearm for the most part; 
only a small part in front, about an inch in ^vidth, is attached to the humerus. 

Relations. — Superficially, the skin, fascia, and the preceding muscle; deeply, 
the deep pectoral, the biceps, and the Israchialis; at the elbow, the median vessels 
and nerve, and the medial and mitldle flexors of the carpus. 

3. Deep pectoral muscle (M. pcctoralis profundus). — This muscle is much 
thicker antl more extensive in the horse than the superficial pectoral. It consists 
of two distinct parts. 

(a) Anterior deep pectoral muscle (pars scapularis).^ — This is prismatic and 
extends from the anterior part of the lateral surface of the sternum to the cervical 
angle of the scapula. 

Origin. — The anterior half of the lateral surface of the sternum and the car- 
tilages of the first four ribs. 

Insertion. — The aponeurosis which covers the supraspinatus at its dorsal 
end, and the scapular fascia. 

Action. — To adduct and retract the limb; when the limb is advanced and 
fixed, to draw the trunk forward. 

Structure. — The muscle is almost entirely fleshy. It describes a curve (con- 
vex anteriorly), passing at first forward, then upward over the front of the shoulder, 
a little to its medial side, and finally inclines somewhat backward along the anterior 
border of the supraspinatus. It is loosely attached to the latter muscle, and 
terminates in a pointed end which becomes more firmly attached near the cer- 
vical angle of the scapula. ' 

Relations. — Superficially, the skin and fascia, the cutaneus, superficial pec- 
toral, trapezius, and brachiocephalicus muscles, the cephalic vein, and the in- 
ferior cervical artery; deeply, the posterior deep pectoral, biceps, supraspinatus, 
omo-hyoideus, and serratus ventralis muscles, the brachial vessels, and the branches 
of the l^rachial plexus of nerves. 

(b) Posterior deep pectoral muscle (pars himieralis s. ascendens).^ — This is 
much the largest of the pectoral group in the horse. It is somewhat triangular or 
fan-shaped. 

Origin. — (1) The abdominal tunic; (2) the xiphoid cartilage and ventral 
aspect of the sternum ; (3) the cartilages of the fourth to the ninth ribs. 

Insertion. — (1) The posterior part of the medial tuberosity of the humerus; (2) 
the anterior part of the lateral tuberosity of the humerus; (3) the tendon of origin 
of the coraco-brachialis. 

Action. — To adduct and retract the limb; if the limb is advanced and fixed, 
to draw the trunk forward. 

Structure. — This muscle is almost entirely fleshy. Its posterior part is wide 

' Also termed the pectoralis transversus or pars sternocostalis. 
' Also termed the pectoralis parvu.s or pars prsescapularis. 
' Also known as the pectoralis magnus. 



THE MUSCLES OF THE SHOULDER GIRDLE 297 

and thin, Ijut as the muscle is traced forward, it becomes narrower and much 
thicker. It passes forward and shghtly upward in a gentle curve to its insertion. 
The humeral insertion is just below that of the medial division of the supraspinatus. 
Part of the fibers are inserted by means of a tendinous band which binds down the 
tendon of the biceps and is attached to the lateral lip of the intertuberal or bicipital 
groove, and a small part is attached to the tendon of origin of the coraco-brachialis. 

Relations. — Superficially, the skin, cutaneus, and superficial pectoral; deeply, 
the abdominal tunic, the external oblique, the rectus abdominis et thoracis, the 
brachial ves-sels, and branches of the brachial plexus of nerves. The external 
thoracic vein lies along the lateral border. 

Blood-supply. — Internal and external thoracic, inferior cervical, anterior 
circumflex, and intercostal arteries. 

Nerve-supply. — Pectoral nerves, from the brachial plexus. 

3. Serratus ventralis' (Figs. 267, 268). — This is a large, fan-shaped muscle, 
situated on the lateral surface of the neck and thorax. It derives its name from 
the serrated ventral edge of its thoracic portion. It consists of cervical and tho- 
racic parts. 

(a) Serratus cervicis. 

Origin. — The transverse processes of the last four or five cervical vertebrae. 
Insertion. — The anterior triangular area on the costal surface of the scapula 
(facies serrata) and the adjacent part of the cartilage. 

(b) Serratus thoracis. 

Origin. — The lateral surfaces of the first eight or nine ribs. 

Insertion. — The posterior triangular area on the costal surface of the scapula 
(facies serrata) and the adjacent part of the cartilage. 

Action. — The two muscles form an elastic support, which suspends the trunk be- 
tween the two scapulae.- Contracting together, they raise the thorax; contracting 
singly, the weight is shifted to the limb on the side of the muscle acting. The two 
parts can act separately and are antagonistic in their effect on the scapula. The 
cervical part draws the liase of the scapula toward the neck, while the thoracic 
part has the opposite action; these effects concur in the backward and forward 
swing of the limb respectively. With the limb fixed, the cervical part extends 
(raises) the neck or inclines it laterally. The thoracic part may act as a muscle of 
forced inspiration. 

Structure. — In the domesticated animals there is no such clear division of 
the muscle as is found in man and the apes. On account of the difference in action, 
however, it seems desirable to distinguish the two portions. The serratus cervicis is 
thick and almost entirely fleshy. The serratus thoracis has on its superficial face a 
thick, tendinous layer which may sustain the weight of the trunk when the muscle 
substance relaxes. The ventral edge presents distinct digitations, the last four of 
which alternate with those of the obliciuus ext-ernus abdominis, and are covered by 
the abdominal tunic. The fourth and fifth digitations extend nearly to the sternal 
ends of the ribs. The ninth digitation is small and may be absent. Exceptionally, 
additional digitations may be attached to the tenth or eleventh rib or to the fascia 
over the intercostal muscles. The fibers converge to the insertion, which is thick 
and is intersected by elastic lamellae derived from the dorso-scapular ligament. 

Relations. — Superficially, the brachiocephahcus, trapezius, deep pectoral, 
subscapularis, teres major, latissimus dorsi, cutaneus, the abdominal tunic, the 
brachial vessels, and the long thoracic nerve; deeply, the splenius, complexus, 

' Formerly termed the serratus magnus. 

- It has been commonly stated that these muscles form a sort of sling in which the trunk is 
suspended. This is not quite correct as the two muscles do not meet ventrally. The arrange- 
ment is admirable, since the pull of the thorax on the muscles presses the scapula; against the body 
wall. 



298 FASCIA AND MUSCLES OF THE HORSE 

serratus dorsalis, longissimi, the ribs and external intercostal muscles, and branches 
of the deep cervical and dorsal arteries. 

Blood-supply. — Deep cervical, dorsal, vertebral, and intercostal arteries. 

Nerve-supply. — Fifth to eighth cervical nerves. 



n. THE MUSCLES OF THE SHOULDER 

The muscles of this group (Mm. omi) arise on the scapula and end on the arm; 
they may be divided into two groups — one covering the lateral, the other the costal, 
surface of the scapula. 

The superficial fascia of the shoulder and arm contains the cutaneous muscle 
of this region {vide p. 254), and may be considered to be continued on the medial 
side of the limb by the subscapular fascia. 

The deep fascia of the shoulder and arm (Fascia omobrachialis) is strong and 
tendinous, and is intimately adherent to the muscles on the lateral surface of the 
scapula, between which it detaches intermuscular septa, which are attached to the 
spine and borders of the scapula. The brachial portion is, for the most part, only 
loosely attached to the underlying muscles, for which it forms sheaths; it is attached 
to the proximal and deltoid tuberosities of the humerus. A specially strong part 
extends from the deltoid tuberosity to the lateral surface of the elbow; it furnishes 
insertion to part of the brachiocephalicus and gives origin to fibers of the lateral 
head of the triceps and of the extensor carpi radialis. The fascia blends distally 
with the tendon of insertion of the biceps, and is continued by the antibrachial 
fascia. 

A. Lateral Group (Pies. 267, 268) 

1. Deltoideus. — This lies partly on the triceps in the angle between the scap- 
ula and humerus, partly on the infraspinatus and teres minor. 

Origin. — (1) The upper part of the posterior border of the scapula; (2) the 
spine of the scapula, by means of the strong aponeurosis which covers the infra- 
spinatus. 

Insertion. — The deltoid tuberosity of the humerus. 

Action. — To flex the shoulder joint and abduct the arm. 

Structure. — The origin of the muscle is partly aponeurotic, partly fleshy. 
The aponeurosis fuses with that which covers the infraspinatus; the posterior part 
is attached to the scapula immediately in front of the origin of the long head of the 
triceps. The belly of the muscle lies for the most part in a cavity formed in the 
triceps. It is widest about its middle. 

Relations. — Superficially, the skin, fascia, cutaneus, and brachiocephalicus; 
deeply, the infraspinatus, teres minor> triceps, and brachialis muscles, and branches 
of the posterior circumflex artery and axillary nerve. 

Blood-supply. — SulDScapular artery (chiefly through the posterior circumflex). 

N erve-fmpphj . — Axillary nerve. 

2. Supraspinatus. — This muscle occupies the supraspinous fossa, which it 
fills, and beyond which it extends, thus coming in contact with the subscapularis. 

Origin. — The supraspinous fossa, the spine, and the lower part of the car- 
tilage of the scapula. 

Insertion. — The anterior parts of the proximal tuberosities of the humerus. 

Action. — To extend the shoulder joint. It also assists in preventing dislo- 
cation. 

Structure. — The surface of the muscle is covered by a strong aponeurosis, 
from the deep face of which many fibers arise. The muscle is thin at its origin 
from the cartilage, but becomes considerably thicker distally. At the neck of the 
scapula it divides into two branches, between which the tendon of origin of the 



THE MUSCLES OF THE SHOULDER 299 

biceps emerges. These branches, fleshy superficially, tendinous deeply, are united 
by a fibrous membrane already mentioned in connection with the deep pectoral 
muscle ; some fibers are attached to this membrane and the capsule of the shoulder 
joint. A bursa is often present under the muscle at the tuber scapulte. 

Relations. — Superficially, the skin, fascia, cutaneus, trapezius, and brachio- 
cephalicus; deeply, the scapula and its cartilage, the subscapularis muscle, and the 
suprascapular vessels and nerve; in front, the anterior deep pectoral muscle; be- 
hind, the spine of the scapula and infraspinatus muscle. 

Blood-supply. — Suprascapular and posterior circumflex arteries. 

Nerve-supply. — Suprascapular nerve. 

3. Infraspinatus. — This muscle occupies the greater part of the infraspinous 
fossa and extends beyond it posteriorly. 

Origin. — The infraspinous fossa and the scapular cartilage. 

Insertion. — (1) The lateral tulserosity of the humerus, distal to the lateral 
insertion of the supraspinatus ; (2) the posterior eminence of the lateral tuberosity. 

Action. — To abduct the arm and rotate it outward.' It also acts as a lateral 
ligament. 

Structure. — This muscle is also covered by a strong aponeurosis, from which 
many fibers arise, and by means of which the deltoid is attached to the spine of 
the scapula. A thick tendinous layer partially divides the muscle into two strata, 
and, coming to the surface at the shoulder joint, constitutes the chief means of in- 
sertion. This tendon, an inch or more (3 cm.) in width, passes over the posterior 
eminence of the lateral tuberosity of the humerus; it is bound down by a fibrous 
sheet, and a synovial bursa is interposed between the tendon and the bone. The 
portion of the tendon which crosses the lateral tuberosity is in part cartilagi- 
nous. When the long insertion is cut and reflected, the short insertion, partly 
tendinous, partly fleshy, is exposed. 

Relations. — Superficially, the skin, fascia, cutaneus, trapezius, and deltoid; 
deeply, the scapula and its cartilage, the shoulder joint and capsule, the long head 
of the triceps, the teres minor, and branches of the posterior circmnflex artery of the 
scapula. 

Blood-supply. — Subscapular artery. 

Nerve-supply. — Suprascapular nerve. 

4. Teres minor. — This is a much smaller muscle than the foregoing. It 
lies chiefly on the triceps, under cover of the deltoid and infraspinatus. 

Origin. — (1) The rough lines on the distal and posterior part of the infra- 
spinous fossa; (2) a small part of the posterior border of the scapula, about its 
middle; (3) a tubercle near the rim of the glenoid cavity. 

Insertion. — The deltoid tuberosity and a small area just above it. 

Action. — To flex the shoulder joint and to abduct the arm; also to assist in 
outward rotation. 

Structure. — The muscle is not rounded, but flat and triangular in the horse. 
Its origin from the posterior border of the scapula is by means of a fascicular aponeu- 
rosis which also gives origin to fibers of the infraspinatus and triceps. The short, 
deep part of the muscle which lies on the joint capsule behind the lateral tuberosity 
of the humerus is covered at its origin by the distal edge of the tendon of origin of 
the long head of the triceps. A bursa is commonly found between the terminal 
part of the muscle and the capsule of the shoulder joint, and is often continuous 
with that of the infraspinatus. 

Relations. — Superficially, the deltoid and infraspinatus muscles; deeply, the 
scapula, the shoulder joint, and the triceps muscle. 

Blood-supply. — Subscapular artery. 

Nerve-supply. — Axillary nerve. 

' Giinther states that this muscle assists in extension or flexion according to the position 
of the head of the humerus relative to the glenoid cavity. 



300 FASCIA AND MUSCLES OF THE HORSE 



B. Medial Group 

1 . Subscapularis. — This muscle occupies the subscapular fossa, beyond which, 
however, it extends both before and behind. 

Origin. — The subscapular fossa. 

Insertion. — The posterior eminence of the medial tuberosity of the humerus. 

Action.— To adduct the humerus. 

Structure.— The muscle is flat and triangular. The base is thin and inter- 
digitates with the scapular attachments of the serratus ventralis. Distally the 
belly thickens and becomes narrower. It is covered by an aponeurosis, and con- 
tains a considerable amount of tendinous tissue. The tendon of insertion is crossed 
by the tendon of origin of the coraco-brachialis ; it is intimately adherent to the cap- 
sule of the shoulder joint, and may be regarded as replacing the medial ligament of 
the latter. A small bursa usually is present between the tendon and the tuberosity 
of the humerus. 

Relations. — Superficially, the scapula and shoulder joint, the supraspinatus, 
triceps, and teres major muscles; deeply, the serratus ventralis muscle, the bra- 
chial vessels, and the chief branches of the brachial plexus. The subscapular 
vessels run along or near the posterior edge of the muscle. 

Blood-supply. — Subscapular artery. 

Nerve-supply. — Subscapular nerves. 

2. Teres major. — This muscle is flat, widest about its middle, and lies chiefly 
on the medial face of the triceps. 

Origin. — The dorsal angle and the adjacent part of the posterior border of 
the scapula. 

Insertion. — The teres tubercle of the humerus, in common with the latissimus 
dorsi. 

Action. — To flex the shoulder joint and adduct the arm. 

Structure. — It is for the most part fleshy, but the origin consists of an apo- 
neurosis which blends with that of the tensor fasciae antibrachii. The insertion 
is by a flat tendon which fuses with that of the latissimus dorsi. 

Relations. — Laterally, the triceps; medially, the serratus ventralis. The sub- 
scapular vessels lie in a groove between the anterior edge of this muscle and the 
posterior border of the subscapularis; near the shoulder joint the posterior cir- 
cumflex artery and the axillary nerve emerge between the two muscles. The 
medial face of the muscle is crossed by the thoracic branches of the brachial plexus, 
and by the artery which supplies the latissimus dorsi. 

Blood-supply. — Subscapular artery. 

Nerve-supply. — Axillary nerve. 

3. Coraco-brachialis.^ — This muscle lies on the medial surface of the shoulder 
joint and the arm. 

Origin. — The coracoid process of the scapula. 

Insertion. — (1) A small area above the teres tubercle of the humerus; (2) the 
middle third of the anterior surface of the humerus. 

Action. — To adduct the arm and to flex the shoulder joint. 

Structure. — The long tendon of origin emerges between the subscapularis and 
the medial branch of the supraspinatus. It passes over the terminal part of the 
subscapularis and is provided with a synovial sheath. The belly spreads out and 
divides into two parts. The small, short part is inserted into the proximal third of 
the medial surface of the shaft of the humerus; the large, long part is inserted into 
the middle third of the humerus, in front of the teres tubercle and the medial head of 
the triceps. 

' Also termed the coraco-humeralis. 



THE MUSCLES OF THE SHOULDER 



301 



Relations. — Laterally, the subscapularis, the brachialis, the tendon of insertion 
of the latissimus dorsi, and the humerus; medially, the deep pectoral; in front, 
the biceps brachii. The anterior circumflex artery and the nerve to the biceps 
pass between the two parts, or between the muscle and the bone, and the brachial 
vessels lie along the posterior border of the muscle. 



Teres major 



Tensor fasciw antibrtichit. 



Deep fascia of forearm 



Subscapularis 

1 nterior deep pectoral 




Extensor carpi radiali. 

Brachialis 

Long medial ligameid of elbow 



Fig. 277. — Muscles of Shoulder and Arm of Horse; Medial View. 
1, Long head of triceps brachii; 2, medial head of triceps; 3, distal end of humerus. 



Blood-supply. — Anterior circumflex artery. 
Nerve-supply. — Musculo-cutaneous nerve. 

4. Capsularis.' — This is a very small muscle, which lies on the flexion surface 
of the capsule of the shoulder joint. 

' Also known as the scapulo-humeralis posticus s. gracilis. 



302 FASCIA AND MUSCLES OF THE HORSE 

Origin. — The scapula, close to the rim of the glenoid cavity. 

Insertion. — The posterior surface of the shaft of the humerus, a short distance 
below the head. 

Action. — It has been held that it tenses the capsule of the shoulder joint and 
prevents its being pinched during flexion, but there does not appear to be any 
attachment of the muscle to the joint capsule. 

Structure. — It is fleshy and usually about the breadth of a finger. It may, 
however, consist of only a few bundles of fibers ; sometimes it is double. It passes 
through the brachialis muscle to reach its insertion. 

Relations. — Laterally, the teres minor and triceps muscles; medially, the teres 
major and subscapularis muscles, and the capsule of the joint. 

Blood-supply. — Posterior circumflex artery. 

Nerve-supply. — Axillary nerve. 

m. THE MUSCLES OF THE ARM 

This group consists of five muscles (Mm. brachii) which are grouped around the 
humerus. They arise from the scapula and the humerus, and are inserted into the 
forearm. They act on the elbow joint and the fascia of the forearm. 

1. Biceps brachii.' — This is a strong fusiform muscle, which lies on the anterior 
surface of the humerus (Fig. 277). 

Origin. — The tuber scapulae. 

Insertion. — (1) The radial tuberosity; (2) the medial ligament of the elbow 
joint; (3) the fascia of the forearm and the tendon of the extensor carpi radialis. 

Action.- — To flex the elbow joint; to fix the shoulder, elbow, and carpus in 
stancUng; to assist the extensor carpi radialis, and to tense the fascia of the fore- 
arm. 

Structure. — The muscle is inclosed in a double sheath of fascia, which is attached 
to the tuberosities and the deltoid ridge of the humerus. The tendon of origin 
is molded on the intertuberal or bicipital groove; it is very strong and dense and 
is partly cartilaginous. Its play over the groove is facilitated by the large inter- 
tuberal or bicipital bursa (Bursa intertubercularis).- The synovial membrane 
covers not onlj^ the deep face of the tendon, but extends somewhat around the edges 
to the superficial face. A well-marked tendinous intersection runs through the belly 
of the muscle and divides distally into two portions. Of these, the short, thick 
one is inserted into the radial tuberosity and detaches fibers to the medial collat- 
eral ligament of the elbow joint. The long tendon (Lacertus fibrosus) is thinner, 
blends with the fascia of tlie forearm, and ends by fusing with the tendon of the 
extensor carpi radialis; thus the action is continued to the metacarpus. 

Relations. — Laterally, the brachiocephalicus and brachialis muscles; medially, 
the posterior deep pectoral antl the superficial pectoral muscles; in front, the an- 
terior deep pectoral muscle; behind, the humerus, the coraco-brachialis muscle, 
the anterior circumflex and anterior radial vessels, and the musculo-cutaneous 
nerve. 

Blood-supply. — Branches of the brachial and anterior radial arteries. 

Nerve-supply. — Musculo-cutaneous nerve. 

2. Brachialis.' — This muscle occupies the musculo-spiral groove of the humerus. 
Origin. — The proximal third of the posterior surface of the humerus. 
Insertion. — The medial surface of the neck of the radius (under cover of the 

long collateral ligament) and the transverse radio-ulnar ligament. 
Action. — To flex the elbow joint. 

' Also known as the coraco-radialis or flexor brachii. 

- In some cases the bursa communicates with the cavity of the shoulder joint. 

' Also known as the humeralis obliquus s. externus and as the brachialis anticus. 



THE MUSCLES OF THE ARM 303 

Structure. — The peculiar spiral course of this muscle gave rise to the name 
often applied to it — humeralis obliquus. Beginning on the posterior surface of the 
shaft, close to the heafl of the humerus, it mnds over the lateral surface, crosses the 
biceps very obliquely, and finally reaches the medial side of the forearm by passing 
between the biceps and the extensor carpi. It is entirely fleshy, with the exception 
of its relatively slejider tendon of insertion. Some fibers at the proximal end are 
attached to the capsule of the shoulder joint, which may thereby be tensed during 
flexion. 

Relations. — Laterally, the skin and fascia, the teres minor, deltoid, triceps 
(lateral head), and brachiocephalicus muscles. Deeply, the teres major, the bi- 
ceps, and the humerus. The anterior radial artery crosses the deep face of the 
muscle in its distal third, and the radial nerve accompanies the muscle in the distal 
half of the musculo-spiral groove. 

Blood-supply. — Brachial artery. 

Nerve-supphj. — Musculo-cutaneous nerve; frequently radial nerve also. 

3. Tensor fasciae antibrachii (Fig. 277).' — This is a thin muscle which lies 
chiefly on the medial surface of the triceps. 

Origin. — The tendon of insertion of the latissimus dorsi and the posterior 
border of the scapula. 

Insertion. — (1) The deep fascia of the forearm; (2) the olecranon. 

Action. — (1) To tense the fascia of the forearm and to extend the elbow joint. 

Structure. — The origin consists of a very thin aponeurosis which blends with 
those of the caput longum and the latissimus dorsi. In most cases there is a dis- 
tinct division into anterior and posterior heads. The muscular portion is thin in 
its anterior part, somewhat thicker behind, and is narrower than the aponeurotic 
origin. It is succeeded by an aponeurotic insertion, which ends chiefly by blending 
^vith the fascia of the forearm a little below the elbow. There is, however, a small 
but constant tendinous attachment to the olecranon. 

Relations. — Laterally, the eutaneus, triceps (long and medial heads), the medial 
and middle flexors of the carpus, and the ulnar vessels and nerve; medially, the 
latissimus dorsi, serratus ventralis, and posterior pectoral muscles. 

Blood- supply. — Subscapular, ulnar, and deep brachial arteries. 

Nerve-supply. — Radial nerve. 

4. Triceps brachii (Figs. 267, 268, 277). — This, together with the preceding 
muscle, constitutes the large muscular mass which fills the angle between the pos- 
terior Ijorder of the scapula and the humerus. It is clearly divisible into three 
heads. 

(a) Long head (Caput longum tricipitis).- — This, the largest and longest of 
the three heads, is a powerful, thick, triangular nauscle, which extends from the 
posterior border of the scapula to the olecranon. 

Origin. — The posterior border of the scapula. 

Insertion. — The lateral and posterior part of the summit of the olecranon. 

Action. — (1) To extend the elbow joint; (2) to flex the shoulder joint. 

Structure. — The muscle arises by a wide, strong aponeurosis from the posterior 
border of the scapula. From this the bundles of the fleshy portion converge to 
the short, strong tendon of insertion. A careful examination will show that the 
muscle is penetrated by a tendinous intersection from which many fibers take origin 
obliquely. The superficial face is covered by an aponeurosis which is specially 
developed at its distal part. A small bursa occurs under the tendon of insertion. 

' M'Fadyean and Vaughan term tliis muscle the scapulo-ulnaris, while Arloing and Lesbre 
term it "Ancone accessoire du grand dorsal." The above name seems to agree best with the 
chief insertion and action, although it certainly arises largely from the tendon of insertion of the 
latissimus dorsi. 

^ Also known .as the anconseus longus or caput magnum. 



30-t FASCIA AND MUSCLES OF THE HORSE 

Relations. — Laterally, the cutaneus, deltoid, infraspinatus, teres minor, and 
the lateral head; medially, the tensor fascise antibrachii, teres major, latissimus dorsi 
and posterior deep pectoral muscles, and the subscapular vessels; in front, the 
brachialis and the medial head, the deep brachial and posterior circumflex vessels, 
and the axillary and radial nerves; behind, the skin and fascia. 

Blood-supply. — Subscapular and deep brachial arteries. 

Nerve-sxipply. — Radial nerve. 

(b) Lateral head (Caput laterale tricipitis).' — This is a strong, quadrilateral 
muscle, which lies on the lateral surface of the arm. Its proximal third is covered 
by the deltoid and teres minor muscles, the remainder only by the thin cutaneous 
muscle and the skin. 

Origin. — (1) The deltoid tuberosity and the curved rough line which extends 
from it to the neck of the humerus; (2) the strong fascia which extends from the 
deltoid tuberosity to the lateral surface of the elbow joint. 

Insertion. — (1) A small prominent area on the lateral surface of the olecranon; 
(2) the tendon of the long head. 

Action. — To extend the elbow joint. 

Structure. — The origin consists of short tendinous fibers. The belly is thick, 
and is composed of parallel bundles which are directed obliquely downward and 
backward. They are inserted partly into the tendon of the long head and partly 
into the olecranon below and in front of that tendon. 

Relations. — Laterally, the deltoid, teres minor, and cutaneus muscles; medially, 
the long and medial heads and the brachialis muscle. Branches of the circumflex 
vessels and axillary nerve emerge between the posterior edge of the muscle and the 
long head. The deep face of the muscle is related to the branches of the deep Ijra- 
chial artery and of the radial nerve. 

Blood-supply. — Posterior circumflex and deep brachial arteries. 

Nerre-supply. — Radial nerve. 

(c) Medial head (Caput mediate tricipitis) (Fig. 277).^ — This is much the small- 
est of the three heads. It is situated on the medial surface of the arm, and extends 
from the middle third of the humerus to the olecranon. 

Origin. — The middle third of the medial surface of the shaft of the humerus, 
behind and below the teres tubercle. 

Insertion. — The medial and anterior part of the summit of the olecranon, be- 
tween the insertion of the long head and the origin of the ulnar head of the deep 
digital flexor. 

Action. — To extend the elbow joint. 

Structure. — The muscle is fleshy except at its insertion, where it has a flat ten- 
don, under which a small bursa may be found. 

Relations. — Laterally, the humerus, brachialis, anconeus, and the lateral head; 
medially, the posterior deep pectoral, coraco-brachialis, teres major, latissimus dorsi, 
and tensor fascite antibrachii muscles, the brachial and deep brachial vessels, and 
the median and ulnar nerves; behind, the long head, branches of the deep brachial 
vessels, and the radial nerve. 

Blood-supply. — Deep brachial and ulnar arteries. 

Nerve-supply. — Radial nerve. 

5. Anconeus. — This is a small muscle which covers the olecranon fossa and 
is covered by the triceps. It is somewhat difficult to separate from the lateral head 

Origin. — The distal third of the posterior surface of the humerus. 

Insertion. — The lateral surface of the olecranon. 

Action. — To extend the elbow joint, and to raise the capsule of the joint andi 
prevent its being pinched during extension. 

' Also known as the anconaeus lateralis s. externus or caput medium. 
^ Also known as the anconaeus mediaUs s. internus or caput parvum. 



fascijE and muscles of the forearm and manus 



305 



Structure. — It is almost entirely fleshy. The deep face is adherent to the joint 
capsule. 

Relations.— Superficially, the triceps muscle; deeply, the humerus and the 
elbow joint. 

Blood-supply. — Deep brachial artery. 

Nerve-supply. — Radial nerve. 



Deep flexor tendon 

Distal end of .small metacarpal bone 
'Suspensory ligament 



Branch of superficial flexor tendon 
Distal digital annular ligament 
Upper border of cartilage 
of third phalanx 



rV. FASCIiE AND MUSCLES OF THE FOREARM AND MANUS 
(FASCI.E ET MUSCULI ANTIBRACHD ET MANUS) 

The forearm is covered on three sides by the muscles of this group, leaving 
the medial surface of the radius for the most part subcutaneous. The extensors of 
the carpus and digit lie on the 
dorsal and lateral parts of the 
region, while the flexors oc- 
cupy the volar surface. 

The fascia of the fore- 
arm (Fascia antibrachii) 
forms a very strong and com- 
plete investment for all the 
muscles of the region. The 
superficial fascia is thin, and 
blends at the carpus with the 
deep fascia ; it furnishes inser- 
tion to the posterior super- 
ficial pectoral muscle. The 
deep fascia is very strong and 
tendinous in character. It 
furnishes insertion at its 
proximal and medial part to 
the tensor fasciae antibrachii 
muscle ; at its proximal anter- 
ior and lateral part to the 
brachiocephalicus and biceps. 
It is attached at the elbow to 
the lateral tuberosities of the 
humerus and radius, to the 
ulna, and to the collateral 
ligaments. On [ the medial 
surface of the forearm it 
blends with the periosteum 
on the subcutaneous surface 

of the radius. It is closely adherent to the surface of the extensor muscles, but is 
rather loosely attached to the flexors; near the carpus it blends with the tendons 
attached to the accessory carpal bone. From its deep face are detached intermus- 
cular septa, which form sheaths for the muscles and are attached to the underlying 
bones. The principal septa are: (a) One which passes between the common digital 
extensor and the lateral extensor and ulnaris lateralis; (6) one between the com- 
mon extensor and the extensor carpi radialis; (c) one between the medial and middle 
flexors of the carpus. 

The carpal fascia (Fascia carpi) is a direct continuation of that of the forearm. 
It is attached chiefly to the tuberosities at the distal end of the radius, to the ac- 
cessory carpal bone', and to the carpal collateral ligaments. In front it forms the 
so-called dorsal annular ligament of the carpus (Lig. carpi dorsale), bridging over 
20 




Fig. 278.— Di 
14., Deep flexor tendon 
nular ligament of fetlock; 
ment; 11, cartilage of third phalanx 
berger-Baum, Anat. fur Kiinstler.) 



OF Horse; Volak View. 
superficial flexor tendon; 16, volar i 



proximal digital annular < 
^4. digital cushion. 



: vaginal liga- 
C.\fter Ellen- 



■306 FASCIA AND MUSCLES OF THE HORSE 

the grooves and binding down the extensor tendons and their synovial sheaths. Be- 
hind it is greatly thickened and forms the volar annular or transverse ligament of 
the carpus (Lig. carpi transversum). This stretches across from the accessory car- 
pal bone to the medial collateral ligament and the proximal extremity of the medial 
metacarpal bone. It thus completes the carpal canal (Canalis carpi), in which lie 
the flexor tendons, the carpal synovial sheath, the common digital artery, and 
the medial volar nerve. 

The superficial fascia of the metacarpus and digit presents no special features, 
but the deep fascia (Fascia metacarpea et digitalis) is complicated by the existence 
of several annular ligaments. In the metacarpus it is hardly distinguishable from 
the periosteum in front. On the proximal part of the volar surface it forms a strong 
and close sheath for the flexor tendons, and is attached to the metacarpal bone 
on each side. Lower down and between the annular ligaments it is thin. On the 
flexion surface of the fetlock joint it is much thickened by fibers passing transversely 
from one sesamoid bone to the other, forming the volar aimular ligament of the fet- 
lock, which binds down the flexor tendons in the sesamoid groove and converts the 
latter into a canal. Distal to this is a second thick quadrilateral sheet, the prox- 
imal digital annular ligament (Lig. vaginale), which covers and is adherent to the 
tendon of the superficial flexor. It is attached on either side by two bands to the 
ends of the borders of the first phalanx, thus firmly binding down the flexor tendons. 
A little further down a crescentic fibro-elastic sheet, the distal digital annular liga- 
ment, covers the terminal expansion of the deep flexor tendon. It is attached 
on either side by a strong band to the side of the first phalanx about its middle ; its 
superficial face is largely covered by the digital cushion and its deep surface is in 
great part adherent to the deep flexor tendon. It is also connected with the so- 
called tendon or ligament of the ergot (Fig. 572). This is a thin and narrow 
fibrous band, which begins in the fibrous basis of the ergot, as the mass of horn at the 
fetlock is called. It descends to the side of the pastern joint, crossing over the 
digital artery and nerve; here it \\'idens out and blends with the fibro-elastic sheet 
just described. 

A. Extensor Division 

1. Extensor carpi radialis (M. radialis dorsalis).^ — This is the largest muscle 
of the extensor division, and lies on the dorsal surface of the radius. 

Origin. — (1) The lateral condyloid crest of the humerus; (2) the coronoid 
fossa; (3) the deep fascia of the arm and forearm and the intermuscular septum 
between this muscle and the common extensor. 

Insertion. — The metacarpal tuberosity. 

Action. — To extend and fix the carpal joint and to flex the elbow joint. 

Structure. — The tendon of origin blends with that of the common extensor 
and is adherent to the capsule of the elbow joint. The belly of the muscle is rounded 
and runs out to a point at the distal third of the forearm. The tendon, which runs 
nearly the whole length of the fleshy portion, appears on the surface of the latter 
about its middle; here the muscle shows a distinctly pennate arrangement. The 
tendon passes through the middle groove at the distal extremity of the radius and 
over the capsule of the carpal joint, bound down by the dorsal annular ligament and 
invested with a S3movial sheath. The latter begins three to four inches (ca. 8- 
10 cm.) above the carpus and extends to the middle of the carpus. Distal to this 
the tendon is attached to the joint capsule, but there is usually a small bursa at the 
level of the third carpal bone. In the tlistal half of the forearm the deep fascia 
blends with the tendon, and here the latter is joined by the long tendon of the biceps. 

Relations. — Superficially, the skin, fascia, and the oblique extensor; deeply, 
the capsule of the elbow joint, the short biceps tendon, the radius, the carpal joint 

'■ Also commonly termed the extensor metacarpi magnus. 



EXTENSOR DIVISION 307 

capsule, the anterior radial artery, and the radial nerve; laterally, the common ex- 
tensor; medially, at the elbow, the brachialis and biceps. 

Blood-supply. — Anterior radial artery. 

Nerve-supply. — Ratlial nerve. 

2. Common digital extensor (M. extensor digitalis communis).' — This muscle 
lies lateral to the foregoing, which it resembles in general form, although less bulky. 

Origin. — (1) The front of the distal extremity of the humerus, in antl lateral 
to the coronoid fossa; (2) the lateral tuberosity on the proximal extremity of the 
radius, the lateral ligament of the elbow, and the lateral border of the radius at the 
junction of its proximal and middle thirds; (3) the lateral surface of the shaft of 
the ulna; (4) the fascia of the forearm. 

Insertion. — (1) The extensor process of the third phalanx; (2) the dorsal sur- 
face of the proximal extremities of the first antl second phalanges. 

Action. — To extend the digital and carpal joints, and to flex the elbow joint. 

Structure. — The muscle is a compound one, representing the common extensor, 
together \n\h vestiges of the proper extensors of the digits. Usually at least two 
heads may be distinguished, although the tlivision is always more or less artificial 
so far as the muscular part is concerned. The humeral head (Caput humerale), 
which constitutes the bulk of the muscle, arises from the front of the lateral epi- 
condyle of the humerus in common with the extensor carpi; the tendon of origin 
is adherent to the capsule of the elbow joint. Its belly is fusiform, and terminates 
in a point near the distal third of the radius. The tendon appears on the surface 
of the muscle about the midtUe of the belly, the arrangement being pennate. The 
tendon passes downward through the outer of the two large grooves on the front of 
the distal end of the radius, and over the capsule of the carpal joint. Passing down 
over the front of the metacarpus, it gradually inclines medially, reaching the middle 
line of the limb near the fetlock. A little below the middle of the first phalanx it 
is joined by the branches of the suspensory ligament, and the tendon thus becomes 
much wider. Two synovial membranes facilitate the play of the tendon. The 
proximal one is a synovial sheath which begins about three inches (ca. 7-8 cm.) 
above the carpus, and terminates at the proximal end of the metacarpus. At the 
fetlock a bursa occurs between the tendon and the joint capsule, but other\\'ise 
the two are adherent. The smaller head, arising chiefly from the radius and ulna, 
is often divisible into two parts (Fig. 568). The larger of these is the radial head 
(Caput radiale) ;- it arises from the lateral tuberosity and border of the radius, and 
from the lateral ligament of the elbow joint. The flat belly is succeeded by a deli- 
cate tendon, which accompanies the principal tendon over the carpus (included in 
the same sheath), and then passes outward to fuse \vith the tendon of the lateral 
extensor, or it may continue downward between the common and lateral extensor 
tendons to the fetlock. Usually a slip is detached which is inserted on the prox- 
imal extremity of the first jihalanx, or ends in the fascia here. The smaller and 
deeper division is the ulnar head (Caput ulnare);^ it is usually somewhat difficult 
to isolate. It arises from the ulna close to the interosseous space. It has a small 
rounded belly and is provitled with a delicate tendon which may fuse with the 
principal tendon or may be inserted into the joint capsule and the fascia in front of 
the fetlock joint. 

Relations. — The chief relations of the belly of the muscle are: superficially, the 
skin and fascia; deeply, the elljow joint, the radius and ulna, the extensor carpi 
obliquus, and the anterior radial vessels and radial nerve; in front and medially, 

'■ Termed also the anterior extensor of the phalanges or extensor pedis. 

- This (formerly called the muscle of Phillips) is considered to represent the part of the 
common extensor for the fourth and fifth digits. ' 

' Martin considers that this muscle (formerly termed the muscle of Thiernesse) represents 
the extensor indicis proprius and the part of the comnxon extensor for the second digit. 



308 



FASCIA AND MUSCLES OF THE HORSE 



the extensor carpi radialis; behind, the lateral extensor and the interosseous 
vessels. 

Blood-supply. — Radial and interosseous arteries. 

Nerve-supply. — Radial nerve. 

Lesbre reports that he has found in one case a brachioradialis muscle in the horse. It 
was a delicate fleshy bundle, superposed on the medial border of the common extensor, and ex- 
tended from the lateral condyloid crest to the cUstal part of the medial border of the racUus. 



Extensor carpi obliqvus 



Metacarpal tuberosity -^ 



Tendon from common to lateral extensor 



Lateral stnall metacarpal bo7ie 




Olecranon 



Ulnar head of deep flexor 



Lateral extensor 
Deep flexor (humeral head) 



Tendon of ulnaris lateralis 
Accessory carpal bone 



Check ligament 

Suspensory ligament 
Flexor tendons 



Branch of suspensory ligamen 
extensor tendon 



gament to ^ I ^^y 






Flexor tendons 
Cartilage of third phalanx 



Fig. 279. — Muscles of Left Thoracic Limb or Horse from Elbow Downwakd; Lateral View. 
a, Extensor carpi radialis; g, brachialis; g', anterior superficial pectoral; c, common digital extensor; e, ulnar 
eralis. (After Ellenberger-Baum, Anat. fiir Kiinstler.) 



3. Lateral digital extensor (M. extensor digitalis lateralis s. tligiti quinti pro- 
prius).^ — This muscle is much smaller than the preceding, behind which it is situated. 
Origin. — The lateral tuberosity of the radius and the lateral ligament of the 
' Also known as the lateral extensor of the phalanges. 



EXTENSOR DIVISION 



309 



elbow joint, the shaft of the uhia, the lateral border of the radius, and the inter- 
muscular septum. 

Insertion. — An eminence on the front of the proximal extremity of the first 
phalanx. 

Action. — To extend the digit and carpus. 

Structure. — The muscle is pennate, and is enclosed in a sheath formed by the 
deep fascia, from which many fibers arise. The belly is thin and fusiform and 
terminates at the distal third of the forearm. From here the tendon (at first 
small and round) passes downward through the groove on the lateral tuberosity 
of the distal end of the radius, then over the carpus, and, gradually inclining toward 



Intermuscular septu 



Common digital extensor 

Extensor carpi obliquus 

Intermuscular septum 

Lateral digital extensor 
Intermuscular septuin 



Deep digital flexor 
(humeral head) 

Ulnaris lateralis 




Extensor carpi radialis 



Cutaneous branch of mus- 

cido-cutaneous nerve 
Cephalic vein 



Median nerve 
Flexor carpi radialis 



Flexor carpi ulnaris 



Deep digital flexor 
{ulnar head) 



Ulnar vessels and nerve c> ^ • i j ■ -^ r ^ 

buperflcial digital flexor 

Fig. 280. — Choss-section of Left Forearm of Horse. 

Section is cut a little above middle of region and the figure is a proximal view. 

1, Median artery and satellite veins; 2, 3, branches of deep brachial and anterior radial vessels; 4, dorsal interosseous 

vessels. 



the front, but not reaching the middle line of the limb, it passes over the meta- 
carpus and fetlock to its insertion. Two synovial membranes occur in connection 
with the tendon. A synovial sheath envelops the tendon, begiiming about three 
inches (ca. 6-8 cm.) above the carpus, and reaching to the proximal end of the 
metacarpus. At the fetlock a small bursa lies between the tendon and the joint 
capsule, but otherwise the tendon is adherent to the capsule. The tendon becomes 
flat and much larger below the carpus, having received the tendon of the radial 
head of the common extensor and a strong band from the accessory carpal bone. 

Relations. — Superficially, the skin and fascia; deeply, the lateral face of the 
radius and ulna; in front, the common extensor, the oblique extensor, and the 



310 FASCIA AND MUSCLES OF THE HORSE 

interosseous artery; behind, the lateral flexor of the carpus and the deep flexor of 
the digit. 

Blood-supply. — Interosseous artery. 

Nerve-nupply. — Radial nerve. 

4. Extensor carpi obliquus (M. abductor pollicis longus et extensor pollicis 
brevis).' — This is a small muscle which curves obliquely over the distal half of the 
radius and the carpus. 

Origin. — The lateral border and adjacent part, of the dorsal surface of the 
radius (the attachment area beginning at a point above the middle of the bone and 
extenchng down to its distal fourth). 

Insertion. — The head of the medial (second) metacarpal bone. 

Action. — To extend the carpal joint. 

Structure. — The muscle is pennate and has a flat belly which curves downward, 
forward, and medially over the distal part of the radius. The tendon continues 
the direction of the muscle, and passes over the tendon of the extensor carpi radialis ; 
it then occupies the oblicjue groove at the distal end of the radius, and crosses the 
medial face of the carpus. It is provided with a synovial sheath. 

Relations. — Superficially, the skin and fascia, the lateral extensor, and the 
common extensor; deeply, the radius, the extensor carpi radialis, the carpal joint 
capsule, and the medial ligament of the carpus. 

Blood-supply. — Interosseous and anterior radial arteries. 

Nerve-supply. — Radial nerve. 

B. Flexor Division 

1. Flexor carpi radialis (or medial flexor of the carpus).- — This muscle lies on 
the medial surface of the forearm, behind the border of the radius. 

Origin. — The medial epicondyle of the humerus, below antl behind the col- 
lateral ligament. 

Insertion. — The proximal end of the medial (second) metacarpal bone. 

Action. — To flex the carpal joint and to extend the elbow. 

Structu7-e. — The muscle has a short tendon of origin, which is succeeded by a 
somewhat flattened, fusiform bell.y. The tendon of insertion begins near the distal 
fourth of the radius and descends in a canal in the transverse carpal ligament. It 
is provided with a synovial sheath which begins two or three inches (ca. 5-8 cm.) 
above the carpus and extends almost to the insertion of the tendon. 

Relations. — Superficially, the skin and fascia, the posterior superficial pectoral, 
and the tensor fasciae antil)rachii; deeply, the elbow joint, the radius, the deep 
flexor, the flexor carpi ulnaris, the median vessels, and the median nerve. At the 
elbow the artery and nerve lie in front .of the muscle, but below they dip beneath it. 

Blood-supply. — Median artery. 

Nerve-supply. — Median nerve. 

On removing the deep fascia on tlie medial surface of the elliow the student may notice a 
small muscle lying along the collateral ligament. This .is the pronator teres, which is usually 
not present or a mere vestige in the horse. It arises by a small, flat tendon from the medial epi- 
condyle of the humerus, and is inserted into the medial ligament of the elbow. On account of its 
small size and the fact that the forearm is fixed in the position of pronation, the muscle can have 
no appreciable function. It is usually represented by a tendinous band. 

2. Flexor carpi ulnaris (or middle flexor of the carpus).' — This muscle lies on the 
medial and posterior aspect of the forearm, partly under, partly behind, the preced- 
ing muscle. It arises by two heads — humeral and ulnar. 

' Also known as the extensor metacarpi obliquus. 

- Also known as the flexor carpi s. metacarpi internus or radialis volaris. 

2 Also known as the flexor carpi (s. metacarpi) medius or ulnaris medialis. 



FLEXOR DIVISION 



311 



Origin.- — (1) The medial epicondyle of the humerus just behind the preceding 
muscle; (2) the medial surface and posterior border of the olecranon. 



Long head of triceps 
Medial head, of triceps 

Olecranon 
Ulnar head of deep flexor 



Flexor carpi ulnaris 
Flexor carpi radialis 



Accesf<ory carpal bone 
Medial ligament of carpus 

Superficial flexor tendon 

Deep flexor tendon 

Suspensory ligament 

Distal end of Mc. II 
Annular ligament 

Superficial flexor tendon 
Deep flexor tendon 




Biceps hrachii 



Extensor carpi radialis 

Long tendon of biceps 

Brachialis 

~ Long medial ligament 



Tendon of cxtctisor carpi 
ohliquus 



Metacarpal tuberosity 



Fetlock joint 

Extensor branch of suspensory 
ligament . 

Common extensor tendon 
Pastern joint 
Cartilage of third phalatix 



Fig, 281. — Mttscles of Left Thoracic Limb of Horse from Elbow Downward; Medial View. 
The fascia and the ulnar head of the flexor carpi ulnaris have been removed. 1, Distal end of humerus; 2, median 

vessels and nerve. 

Insertion. — The proximal edge of the accessory carpal bone. 
Action. — To flex the carpal joint and to extend the elbow. 



312 



FASCIA AND MUSCLES OF THE HORSE 



Structure. — The humeral head is much the larger, constituting, in fact, the 
bulk of the muscle. It is flattened, curved, and tapers at both ends. The ulnar 
head, much smaller and very thin, is covered by an aponeurosis from which many of 
its fibers arise. It joins the large head a little above the middle of the forearm. 



Ulnar head of deep flexor 
Stump of flexor carpi radialis 

Stump of flexor carpi idnaris 



Superficial digital flexor 
Deep digital flexor 

Tendon of ulnar head 

Radial head of superficial flexor 

Insertion of fiexor carpi ulnaris 

Accessory carpal banc 




Deep flexor tendon j 

Superficial flexor tendon -~~Ji\ 

Check ligament — 

Suspensory ligament 



Annular ligament 



Deep flexor tendon 
Cartilage of third phalanx 




Biceps brachii 

Brachialis 

Long medial ligament 

Extensor carpi radialis 



Radius 



Tendon of flexor carpi radialis 
/pi — Tendon of extensor carpi obliquus 

n 



Mc. Ill 



Fetlock joint 

Extensor branch of suspeiisory 
ligament 



Fig. 282. — Muscles of Left Thoracic Limb of Horse, from Elbow Downward; Medial View. 
Parts of superficial muscles have been removed, carpal canal opened up, and flexor tendons drawn backward. 



The tendon of insertion is short and strong; it blends with the posterior annular 
ligament of the carpus. 

Relations. — Superficially, the tensor fasciae antibrachii, superficial pectoral, and 
flexor carpi radialis, the skin and fascia, and cutaneous branches of the ulnar 
nerve; deeply, the superficial and deep flexors of the digit. In the distal half of 



FLEXOR DIVISION 313 

the forearm the ulnar vessels and nerve lie between the lateral edge of this muscle 
and the lateral flexor of the carpus. 

Blood-supply. — Ulnar and median arteries. 

Nerve-supply. — Ulnar and median nerves. 

3. Ulnaris lateralis (or lateral flexor of the carpus).^ — This muscle lies on the 
lateral face of the forearm, behinil the lateral extensor of the digit. 

Origin. — The lateral epicondylc of the humerus, behind and below the lateral 
ligament. 

Insertion. — (1) The lateral surface and proximal border of the accessory carpal 
bone; (2) the proximal extremity of the lateral (fourth) metacarpal bone. 

Action. — To flex the carpal joint and to extend the elbow. 

Structure. — The belly of the muscle is flattened and is intersected by a good 
deal of tendinous tissue. There are two tendons of insertion. The short tendon 
is insertetl into the accessory carpal bone. The long tendon is detached just above 
the carpus; it is smaller and rounded; it passes downward and a little forward 
through a groove on the lateral surface of the accessory carpal bone, enveloped by 
a synovial sheath, to reach its insertion on the lateral metacarpal bone. A synovial 
pouch lies under the origin of the muscle at the elbow joint, with the cavity of 
which it communicates. 

Relations. — Superficially, the skin, fascia, and cutaneous branches of the ulnar 
nerve; deeply, the elbow joint, the ulna, and the flexors of the digit; in front, the 
lateral extensor of the digit; behind, the middle flexor of the carpus, the ulnar head 
of the deep flexor, and the ulnar vessels and nerve. 

Blood-supply. — Interosseous, ulnar, and median arteries. 

Nerve-supply. — Radial nerve. 

4. Superficial digital flexor^ (M. flexor digitalis superficialis). — This muscle is 
situated in the middle of the flexor group, chiefly under cover of the middle flexor 
of the carpus. 

Origin. — (1) The medial epicondyle of the humerus; (2) a ridge on the pos- 
terior surface of the radius, below its middle and near the medial border. 

Insertion. — (1) The eminences on the proximal extremity of the second phalanx, 
behind the collateral ligaments; (2) the distal extremity of the first phalanx, also 
behind the collateral ligaments. 

Action. — To flex the digit and carpus and to extend the elliow. 

Structure. — The fleshy part of the muscle is the humeral head ( Caput humerale) ; 
it takes origin from the humerus. The radial head (Caput tendincum) consists of 
a strong fibrous band, usually termed the radial or superior check ligament, which 
fuses with the tendon near the carpus. The belly of the muscle is intersected by 
tendinous strands, and fuses more or less with that of the deep flexor, from which 
it is therefore somewhat difficult to separate. Near the carpus it is succeeded by a 
strong, thick tendon which passes dowm through the carpal canal and is envelopetl 
by a synovial sheath, in common with the deep flexor. This, the carpal sheath 
(Vagina carpea), begins three or four inches (8-10 cm.) above the carpus, and ex- 
tends downward nearly to the middle of the metacarpus. Below the carpus the 
tendon becomes flattened and broader and at the fetlock it widens greatly. Near 
the fetlock it forms a ring through which the tendon of the deep flexor passes (Fig. 
286). Here the two tendons are bound down in the sesamoid groove by the volar 
annular ligament, which fuses more or less with the superficial flexor tendon. At 
the distal end of the first phalanx the tendon divides into two branches which di- 
verge to reach their points of insertion, and between these branches the tendon of 

' Also known as the flexor carpi (s. metacarpi) externus or extensor carpi ulnaris. Morpho- 
logically it belongs to the extensor group. 

^ Also commonly known as the flexor perforatus or superficial flexor of the phalanges. 



314 



FASCIA AND MUSCLES OF THE HORSE 



the deep flexor emerges (Fig. 278). A second synovial membrane, the digital 
synovial sheath (Vagina digitalis), begins at the distal fourth of the metacarpus, 




Fig. 2S3.— Synovial Sheaths and Burs.e of Distal Fig. 2S4.— Synov 

Part of Right Fore Limb 
View. View. 

The synovial sheatha (colored yellow) and the joint capsules (colored pink) 




; injected. 



a, Sheath of extensor carpi obliquus; 6, sheath 
of flexor carpi radialis; c, carpal sheath; d, d', d", d'", 
digital sheath; e, bursa under common extensor ten- 
don; /, capsule of fetlock joint; 1, extensor carpi ra- 
dialis; 2, tendon of extensor carpi obliquus; 3, flexor 
carpi radialis; 4t flexor carpi ulnaris; 5, superficial 
flexor tendon; 6, deep flexor tendon; 7, suspensory liga- 
ment; S, small metacarpal bone; 9, large metacarpal 
bone; 10, volar annular ligament of fetlock; 11, 
proximal digital annular ligament; 12, radius; IS, 
radiocarpal joint; 1^, fetlock joint; 15, cartilage of 
third phalanx; 16, band from first phalanx to cartilage. 
(After Ellenberger, in Leisering's Atlas.) 



a. Sheath of extensor carpi radialis; b, sheath 
01 common extensor; c, sheath of lateral extensor; d, 
sheath of outer tendon of ulnaris lateralis; e, e', carpal 
sheath; /, /', /", digital sheath; g, bursa under com- 
mon extensor tendon; h, bursa under lateral extensor 
tendon; i. capsule of fetlock joint; 1, extensor carpi 
radialis; 2, common digital extensor; 3, lateral digital 
extensor; 4. ulnaris lateralis; 4'. 4", tendons of 4>' 5» 
superficial flexor tendon; 6, deep flexor tendon; 7, 
suspensory Hgament; S, lateral metacarpal bone; 9, 
large metacarpal bone; 10, volar annular ligament 
of fetlock; 11, digital annular Hgament; 12, fetlock 
joint; 13, cartilage of third phalanx; 14, band from 
first phalanx to cartilage. (After Ellenberger, in 
Leisering's Atlas.) 



two or three inches (ca. 5-8 cm.) above the fetlock, and extends to the middle of 
the second phalanx. 

Relations. — The belly, of the muscle is related superficially to the ulnar head 
of the deep flexor, the flexor carpi ulnaris, and, at its origin, to the ulnar vessels 



FLEXOR DIVISION 



315 



and nerve; deeply, to the humeral head of the deep flexor. The tendon is re- 
lated superficially to the skin and fascia; deeply, to the deep flexor tendon. 

Blood-supply. — Median artery. 

Nerve-supply. — Ulnar and median nerves. 

5. Deep digital flexor' (M. flexor digitalis profundus). — The fleshy part of 
this muscle lies on the posterior surface of the radius, and is almost entirely under 
cover of the preceding muscles. It is the largest muscle of the flexor group. 

Origin. — (1) The medial epicondyle of the humerus; (2) the medial surface of 
the olecranon; (3) the midtUe of the posterior surface of the radius and a small ad- 
jacent area of the ulna. 

Insertion. — The semilunar crest and the adjacent surface of the cartilage of 
the third phalanx. 

Action. — To flex the digit and carpus and to ex-tend the cIIdow. 

Structure. — This muscle consists of three heads. The humeral head (Caput 
humerale) constitutes the bulk of the muscle. It is marked liy tendinous inter- 
sections, and is separable into three secondary heads. A synovial pouch from the 
elbow joint descends under its 

origin about two inches. The Tendon of Tendon of 

ulnar head (Caput ulnare) is lateral extensor conunon extensor 

much smaller, and is at first \ 

superficially situated between 
the lateral and middle flexors 
of the carpus. The radial head 
(Caput radiale) is the smallest, 
and is not always present; it 
is situated on the distal two- 
thirds of the posterior surface 
of the radius, under the humer- 
al head. Each of these heads 
is provided with a tendon. The 
principal tendon — that of the 
humeral head — begins about 
three or four inches (8-10 
cm.) above the carpus and is 
joined at the carpus by the 
tendons of the other two heads. 
The conjoined tendon passes 
tlownward through the carpal 

canal, being included in the carpal sjmovial sheath -ndth the superficial flexor ten- 
tlon, as previously described. The tendon is at flrst broad and three-sided, but 
liecomes narrower and rounded below. Continuing downward, it is joined about 
the middle of the metacarpus by a strong fibrous band, the so-called inferior or 
subcarpal check ligament (Caput carpale s. tendineum).- This is a direct continua- 
tion of the posterior ligament of the carpus. Below this the tendon passes through 
the ring formed by the superficial flexor tendon, then in succession over the sesa- 
moid groove, the distal sesamoidean ligaments, and the flexor surface of the distal 
sesamoid, to its insertion (Figs. 241 and 242). At the fetlock it widens consider- 
ably, narrows again in the middle of the digital region, again widens at the pulley 




Tendon of supcijicial fleioi 



Digital vein 
Digital artery 
Digital nerve 



Ti ndon of deep flexor 



-Cross-sectiox of Distal Paht of Left Me 
Horse, Just Above Sesamoids. 



' Also commonl}' known tis the flexor perforans or deep flexor of the phalanges. 

-This might appropriately be termed the carpal head (caput carpale) or tendinous head 
(caput tendineum). At its upper end it is broad, occupying the entire width of the space between 
the small metacarpal bones; below it becomes narrower and thicker. It is related in front to 
the suspensory ligament, and its posterior face, wliich is related to the deep flexor tendon, is 
covered by the deep layer of the carpal sheath. 



316 



FASCIA AND MUSCLES OF THE HORSE 



of the second phalanx, and forms a terminal fan-like expansion. At the pulleys 
of the digit the tendon contains cartilage and is thickened. From the distal fourth 
of the metacarpus to the distal end of the second phalanx it is inclosed in the dig- 
ital synovial sheath described in connection with the superficial flexor. The bursa 
podotrochlearis or navicular bursa is found between the tendon and the distal sesa- 
moid or navicular bone. Tlie terminal part of the tendon is bound down by the 
distal digital annular ligament described with the fascia. 

Relations. — The belly of the muscle is related posteriorly to the superficial 



Extensor tendon 



Proximal end of capsule of fetlock 
joint 

Bursa 

Collateral ligament of fetlock joint 
Fascia 



Branch of suspensory ligament 



Lateral volar ligament of pastem 

joint IH'j' 



Suspensory ligament of navicular 
bone 
Ba ml from cartilage to extensoi 
tendon 
Collateral ligament of coffin joint -^ 




Superficial flexor tendon 
Deep flexor tendon 
Suspensory ligament 
Lateral interosseus tendon 

Proximal end of digital sheath 
Ring of superficial flexor tendon 
Intersesamoidean ligament 
Posterior annular ligament (cut) 



Collateral sesainoidean ligament 
Superficial distal sesatnoidean 

ligament 
Middle distal sesamoidean ligament 

Attachments of proximal digital 
annular ligament 



Pouch of digital sheath 

Distal digital annular ligament 
Cartilage 



Fig. 286. — Ligaments and Tendons of Distal Part op Limb of Horse. 
. in, Large metacarpal bone; Ph. L first phalanx; Ph. IL second phalanx; Ph. IIL third phalanx: L deep flexor 
tendon; 2, band from first phalanx to digital cushion, (.\fter Schmaltz, Atlas d. ,\nat. d. Pferdes.) 



flexor and to the middle flexor of the carpus; medially, to the flexor carpi radialis, 
the radial check ligament, and the median vessels and nerve; laterally, to the 
ulnaris lateralis; anteriorly, to the radius and ulna and branches of the median 
artery and nerve. Below the carpus the tendon is accompanied by the vessels and 
nerves of the digit. It may also be noted that the muscle is not entirely covered 
by the other flexors; it comes in contact with the skin and fascia on the postero- 
lateral aspect of the proximal half of the forearm, and also on the lateral aspect of 
the distal fourth. 

Blood-supply. — Median and ulnar arteries. 



FASCIAE AND MUSCLES OF THE PELVIC LIMB THE FASCIA 317 

Nerve-supply. — Median and ulnar nerves. 

The five muscles of the metacarpus and digit are either reduced to vestiges or 
modified greatly in structure. 

1, 2. Lumbricales (medialis et lateralis). — These are two verj- slender fusiform 
muscles which lie on either side of the flexor tendons above the fetlock. They arise 
from the deep flexor tendon, and end in the fibrous tissue which lies under the nod- 
ule of horn at the fetlock which is known as the ergot (Fig. 572). Their action is 
inappreciable. The size of these muscles is subject to much variation. Often very 
little muscular tissue can be found, but the small tendon is constantly present. 

Blood-supphj . — Metacarpal arteries. 

Nerve-supply. — Median and ulnar nerves. 

3, 4, 5. Interossei. — These are three in number in the horse, and are situated 
chiefly in the metacarpal groove. Two, the medialis antl lateralis, are very small 
muscles, each of which arises from the corresponding small metacarpal bone near 
its proximal extremity, and is provided with a delicate tendon which is usually lost 
in the fascia at the fetlock (Fig. 240). They have no appreciable action. Their 
blood- and nerve-supply is the same as that of the preceding muscles. 

The interosseus medius is so much modified that it is usually termed the 
suspensory or superior sesamoidean ligament. It contains little muscular tissue, 
being transformed very largely into a strong tendinous band (Tendo interosseus), 
bifurcate below, and having for its chief function the supporting of the fetlock. It 
has been described, in deference to common usage, with the ligaments. 



Fascle and Muscles of the Pelvic Limb 
The Fascia 

The iliac fascia (Fascia iliaca) covers the ventral surface of the iliacus and psoas 
muscles, over which it is tightly stretched (Fig. 575). It is attached medially to 
the tendon of the psoas minor; laterally it is attached to the tuber coxae and blends 
wth the deep layer of the lumbo-dorsal fascia. Its anterior part is thin. Pos- 
teriorly it is continuous with the inguinal ligament and the pelvic fascia. It fur- 
nishes surfaces of origin for the sartorius, cremaster externus, and transversus ab- 
dominis muscles. 

The pelvic fascia (Fascia pelvis) lines the cavity as the parietal layer and 
at the pelvic outlet is reflected on the viscera to form the visceral layer. Laminse 
are detached from it to strengthen the various peritoneal folds. 

The superficial fascia of the gluteal region is thin and is closely adherent to 
the deep fascia. A subcutaneous bursa may be found on the tuber coxae. The 
gluteal fascia (Fascia glutca) covers the superficial muscles of the region, and de- 
taches intermuscular septa, which pass between the muscles. It is attached to the 
sacral spines, the dorsal sacro-iliac ligament, and the tubera of the ilium, and is con- 
tinuous in front with the lumbo-dorsal fascia, behind with the coccygeal fascia. 
Its deep face gives origin to fibers of the superficial and middle glutei, the biceps 
femoris, and the semitendinosus, so that care is necessary in dissecting it oif these 
muscles. The chief intermuscular septa are: (1) One which passes between the 
superficial gluteus and the biceps femoris; (2) one between the biceps and semi- 
tendinosus, from which a lamella is detached which passes between the middle and 
posterior parts of the biceps and is attached to the tuber ischii ; (3) one between the 
semitendinosus and semimembranosus, which is attached to the sacro-sciatic liga- 
ment and tuber ischii; it furnishes origin for fibers of the long head of the semi- 
membranosus. 

The superficial fascia of the thigh presents no exceptional features, but the deep 



318 FASCIA AND MUSCLES OF THE HORSE 

fascia is very thick and strong on the front and lateral surface. This part, the 
fascia lata (Fig. 267), is continuous with the gluteal fascia; it is tenchnous in char- 
acter, and easily separable from the underlying muscles. It furnishes insertion to 
the tensor fasciae latse and to the biceps femoris (in part), by both of which it is 
tensed. At the stifle it is attached to the patella and the lateral and medial patellar 
ligaments. Medially it is continuous with the inedial femoral fascia. It furnishes 
the following intermuscular septa: (1) One which passes between the vastus lat- 
eralis and biceps femoris to be attached to the third trochanter of the femur; (2) 
two which pass between the three branches of the biceps femoris; (3) a fourth be- 
tween the biceps femoris and semitendinosus. The medial femoral fascia (Fascia 
femoralis medialis) covers the superficial muscles on tlie medial surface of the thigh. 
At its upper part it is joined by the femoral lamina of the aponeurosis of the external 
ol)liciue nmscle (Fig. 575). The posterior part is thin. It is continuous with the 
fascia lata in front and the fascia cruris below. At the stifle it fuses with the ten- 
dons of the sartorius and gracilis. 

The fascia cruris, or fascia of ttie leg, consists of three layers. Two of these 
invest the entire region and may, therefore, be termed the common fasciae. The 
superficial layer is a continuation of that of the thigh, while the second layer may be 
regarded chiefly as a continuation of the tendons of the superficial muscles of the 
hip and thigh (biceps femoris, semitendinosus, tensor fasciae latse, sartorius, and 
gracilis). The two layers frequently fuse, and are attached chiefly to the medial 
and' lateral patellar ligaments and the crest and medial surface of the tibia. About 
the middle of the leg the two layers unite behind the deep flexor of the digit and 
form a strong band which passes downward in front of the tendons of the gastroc- 
nemius and superficial flexor, to be attached with the latter to the anterior and 
medial part of the tuber calcis. This constitutes a tarsal tendon of insertion of the 
biceps femoris and semitendinosus. A strong band, about two inches in ■width, 
arises from the lateral supracondyloid crest, descends over the lateral head of the 
gastrocnemius, and blends with the foregoing and the superficial flexor tendon. 
The third layer forms sheaths for the muscles, furnishing origin in part to their 
fibers. Two important intermuscular septa are detached, viz.: (1) One which 
passes between the long and lateral digital extensors to be attached to the fibula 
and the lateral border of the tibia; (2) one between the lateral digital extensor and 
the deep digital flexor. 

The tarsal fascia (Fascia tarsi) fuses with the ligaments and bony prominences 
of the region. It is strong and tendinous in front, and joins the tendon of the long 
extensor below the joint. On the sides it is tliin and fuses with the ligaments. 
Posteriorly it is very thick and strong, forming an annular ligament which stretches 
from the medial ligament to the fibular tarsal bone and the plantar ligament. This, 
converts the groove at the back of the hock into a canal, in which are the deep flexor 
tendon with its synovial sheath and the plantar vessels and nerves. In this vicinity 
there are three annular ligaments (Ligamenta transversa). The proximal one binds 
down the tendons of the long extensor, peroneus tertius, and tibialis anterior on 
the distal end of the shaft of the tibia. The middle one stretches from the fibular 
tarsal bone to the lateral tendon of the peroneus tertius, forming a loop around the 
tendon of the long extensor. The distal band stretches across the "proximal ex- 
tremity of the large metatarsal bone and incloses the tendons (and sheaths) of the 
two extensors of the digit. 

The metatarsal and digital fasciae do not differ materiallj' from those of the 
corresponding regions of the thoracic limb. 



THE MUSCLES THE SUBLUMBAR MUSCLES 319 

The Muscles 1 

I. THE SUBLUMBAR MUSCLES (Figs. 287, 575) 

The muscles of this group are not confined to the sublumbar region, but ex- 
tend beyond it both before and behind. Their chief function is to fiex the hip 
joint. Two, however, — the psoas minor and the quadratus lumborum, — have not 
this action. 

1. Psoas minor. — This is a fusiform, flattened, pennate muscle, which lies 
along the ventro-lateral aspect of the bodies of the last three thoracic and the 
lumbar vertebrae. 

Origin. — The bodies of the last three thoracic and first four or five lumbar 
vertebrse, and the vertebral ends of the sixteenth and seventeenth ribs. 

Insertion. — The psoas tubercle on the shaft of the ilium. 

Action. — To flex the pelvis on the loins, or to incline it laterally. 

Structure. — The muscle arises by a series of digitations which pass backward 
and outward to join the tendon at an acute angle. The latter lies along the lateral 
border of the fleshy portion and is flattened. It appears on the surface of the mus- 
cle at the third lumbar process and increases gradually in width until it reaches the 
pelvic inlet, where it becomes narrower. 

Relations. — The ventral surface of the thoracic part of the muscle is related 
to the pleura, crura of the diaphragm, and sympathetic and splanchnic nerves. 
In the abdomen the chief ventral relations are the peritoneum, the vena cava 
(right side), the aorta and left kidney (left side), the sympathetic nerves, and the 
ureters. Dorsally, the chief relations are the vertebrse, the psoas major, aufl lum- 
bar nerves. The lumbar arteries pass through the medial edge. Near its insertion 
the tendon is crossed medially by the external iliac artery, and laterally by the fem- 
oral nerve. 

Blood-supply. — Intercostal and lumbar arteries. 

Nerve-supply. — Lumbar nerves. 

2. Psoas major. — This is much larger than the preceding muscle, by which it 
is partly covered. It is triangular, vfiih the base anterior. 

Origin. — The ventral surfaces of the transverse processes of the lumbar ver- 
tebrae and the last two ribs. 

Insertion. — The trochanter minor of the femur, by a common tendon with 
the iliacus. 

Action. — To flex the hijj joint antl to rotate the thigh outward. 

Structure. — The origin of the muscle is fleshy, the belly being in general flat- 
tened, thick in its mitldle, thin at its edges. The thoracic part is small, the abdom- 
inal part much thicker antl wider, extending laterally beyond the extremities of the 
lumbar transverse processes. From the lumbo-sacral articulation it lies in a deep 
groove formed in the iliacus (with which it is partly united), becomes smaller and 
rounded, and passes downward and backward to terminate by a strong tendon 
common to it and the iliacus. On account of the intimate union between the psoas 
major and iliacus they are frequently considered a single muscle, to which the name 
ilio-psoas is applied ; some anatomists include the psoas minor also under this term. 

Relations. — Dorsally, the last two ribs and thoracic vertebrse, the lumbar 
vertebrse, the internal intercostals, quadratus lumborum, longissimus dorsi, and 
iliacus, and the lumbar vessel^ and nerves; ventrally, the pleura and peritoneum, 
the iliac fascia, inguinal ligament, the diaphragm, psoas minor and sartorius, 
and the circumflex iliac vessels. 

' On account of the very slight mobility of the sacro-ihac articulation, the muscle.s of the 
peK-ic girdle are much reduced, and almost all of those which might be included in this group 
extend to the femur or even to the leg. It seems undesirable, therefore, to attempt a morpho- 
logical grouping. 



320 FASCIA AND MUSCLES OF THE HORSE 

Blood-supply. — Lumbar and circumflex iliac arteries. 
Nerve-supply. — Lumbar and femoral nerves. 

3. Iliacus. — This muscle covers the ventral surface of the ilium lateral to the 
sacro-iliac articulation, and e.xtends beyond the lateral border of the bone, under- 
neath the middle gluteus. 

Origin. — The ventral surface of the ilium lateral to the ilio-pectineal line, the 
ventral sacro-iliac ligament, the wing of the sacrum, and the tendon of the psoas 
minor. 

Insertion. — The trochanter minor of the femur, by a common tendon with 
the psoas major. 

Action. — To flex the hip joint and to rotate the thigh outward. 

Structure. — The belly of the muscle is so deeply grooved for the psoas major 
as to give the appearance of being completely divided into medial and lateral parts. 
AVhen the psoas is removed, it is seen, however, that the two heads are not entirely 
separated. The lateral, larger head arises from the wing of the ilium chiefly; the 
medial, smaller head arises chiefly from a small area on the shaft of the ilium, be- 
tween the psoas tubercle and the depression for the medial tendon of the rectus 
femoris, and from the tendon of the psoas minor. The two parts inclose the psoas 
major in front of the hip joint. 

Relations. — Dorsally, the ilium, sacrum, sacro-iliac articulation, the gluteus 
medius, the ilio-lumbar and external circumflex vessels; ventrally, the iliac fascia, 
inguinal ligament, the psoas major, sartorius, and abdominal muscles. At the 
level of the hip joint the chief relations are: medially, the femoral vessels, the fem- 
oral nerve, and the sartorius muscle; laterally, the rectus femoris and tensor fasciffi 
latse; in front, the abdominal muscles; behind, tl\e hip joint. 

Blood-supply. — Lumbar, circumflex iliac, and deep femoral arteries. 

Nerve-supply. — Lumbar and femoral nerves. 

4. Quadratus lumborum. — This thin muscle lies on the lateral part of "the ven- 
tral surfaces of the lumbar transverse processes. 

Origin. — The ventral surface of the upper part of the last two ribs and the 
lumbar transverse processes. 

Insertion. — The ventral surface of the wng of the sacrum and the ventral 
sacro-iliac ligament. 

Action. — Acting together, to fix the last two ribs and the lumbar vertebrae; 
acting singly, to produce lateral flexion of the loins. 

Structure. — The muscle is pennate, and is curved with the convexity lateral. 
It is thiiV largely mixed with tendinous fibers, and is, in general, little developed in 
the horse in comparison with some of the other animals (e. g., clog, sheep). 

Relations. — Ventrally, the psoas major and the last thoracic and first three 
lumbar nerves; dorsally, the last two ribs, the lumbar transverse processes, and 
the lateral branches of the lumbar arteries. 

Blood-supply. — Lumbar arteries. 

Nerve-supply. — Lumbar nerves. 

5. Intertransversales lumborum. — (See p. 279.) 

U. THE LATERAL MUSCLES OF THE HIP AND THIGH 

Under this head the muscles of the lateral surface of the pelvis and thigh, and 
those which form the posterior contour of the latter, will be described. 

1. Tensor fasciae latae (Fig. 267). — This is the most anterior muscle of the 
superficial layer. It is triangular in form, with its apex at the tuber coxse. 

Origin. — The tuber coxse. 

Insertion. — The fascia lata and thus indirectly to the patella, the lateral patel- 
lar ligament, and the crest of the tibia. 



THE LATERAL MUSCLES OF THE HIP AND THIGH 321 

Action. — To tense the fascia lata, flex the hip joint, and extend the stifle joint. 
. Structure. — The muscle arises by a rather small head, about two inches (ca. 
5 cm.) wide, on the antero-inferior eminence of the tuber coxae. Below this the 
belly spreads out and terminates in the aponeurosis about midway between the 
point of the hip and the stifle. Many fibers arise from an intermuscular septum 
between this muscle and the superficial gluteus; this septum is attached to the lat- 
eral border of the ilium. The aponeurosis fuses with the fascia lata, which may be 
regarded practically as the tendon of insertion; it detaches a lamina which passes 
with the tendon of insertion of the superficial gluteus to the lateral border of the 
femur. 

Relations. — Laterally, the skin and fascia; medially, the obliquus abdominis 
externus, the iliacus, superficial gluteus, rectus femoris, and vastus lateralis, branches 
of the circumflex iliac, ilio-lumljar, and iliaco-femoral arteries, and the anterior 
gluteal nerve; anteriorly, the prefemoral lymph-glands. A considerable quantity 
of connective tissue is found between the deep face of the muscle and the abdominal 
wall. 

Blood-supply. — Circumflex iliac, ilio-lumlmr, and iliaco-femoral arteries. 

Nerve-siipply. — Anterior gluteal nerve. 

2. Gluteus superficialis (Fig. 267). — This muscle lies behind and partly 
underneath the tensor fascice latse. It is triangular and consists of an anterior and 
a posterior head united by the gluteal fascia. 

Origin. — (1) The tuber coxae and the adjacent part of the lateral border of 
the ilium; (2) the gluteal fascia. 

Insertion. — The third trochanter of the femur. 

Action. — To abduct the limb, flex the hip joint, and tense the gluteal fascia. 

Structure. — The anterior head of the muscle is not completely separable (ex- 
cept artificially) from the tensor fasciae latse, since both muscles are attached to an 
intermuscular septum. The attachment to the border of the ilium is by means of 
an intermuscular septum, which passes beneath the thick lateral border of the 
gluteus medius and furnishes origin to fibers of both muscles. The posterior heatl 
arises from the deep face of the gluteal fascia, and so indirectly from the dorsal 
sacro-iliac ligament. The two heads unite and terminate on a strong flat tendon, 
which is inserted into the edge of the third trochanter of the femur, under cover of 
the biceps femoris. 

Relations. — Superficially, the skin, fascia, and biceps femoris; deeply, the 
gluteus medius, iliacus, rectus femoris, and branches of the iliaco-femoral vessels; 
in front, the tensor fasciae latse; behind, the biceps femoris. 

Blood-supply. — Gluteal and iliaco-femoral arteries. 

Nerve-supply. — Anterior gluteal nerve. 

3. Gluteus medius (Figs. 268, 580). — This is a very large muscle which covers 
the gluteal surface of the ilium and the greater part of the lateral wall of the pelvis, 
and extends forward also on the lumbar part of the longissimus dorsi. 

Origin. — (1) The aponeurosis of the longissimus dorsi, as far forward as the 
first lumbar vertebra; (2) the gluteal surface and tubera of the ilium; (3) the dorsal 
and lateral sacro-iliac and sacro-sciatic ligaments, and the gluteal fascia. 

Insertion. — (1) The summit of the trochanter major of the femur; (2) the crest 
below the trochanter; (3) the lateral aspect of the trochanteric ridge. 

Action. — To extend the hip joint and abduct the limb. By its connection 
with the longissimus a muscular mass is formed which is one of the chief factors in 
rearing, kicking, and propulsion. 

Structure. — The anterior extremity of the muscle is narrow and thin, and lies 

in a tlepression on the surface of the longissimus, from the strong aponeurosis of 

which the fibers take origin. The pelvic portion of the muscle is very voluminous, 

and forms the bulk of the muscular mass which gives the haunch its rounded con- 

21 



322 FASCIA AND MUSCLES OF THE HORSE 

tour. This part of the muscle is intersected by several tendinous sheets. One of 
these is particularly distinct, and is attached to the gluteal line on the ilium. This 
divides the muscle incompletely into superficial and deep strata. The superficial 
part is inserted by a strong tendon into the summit of the great trochanter, and 
by a pointed fleshy mass with a tendinous border into the lateral surface of the 
trochanteric ridge. The deep part is termed the gluteus accessorius ; it is smaller, 
and arises entirely from the ilium between the gluteal line and the tuber coxae (Fig. 
580). It has a strong flat tendon which passes over the anterior part or convexity 
of the trochanter to be inserted into the crest below it. The trochanter is covered 
here with cartilage, and the trochanteric bursa (Bursa trochanterica) is interposed 
between the tendon and the cartilage.' 

Relations. — Superficially, the skin, lumbo-dorsal and gluteal fasciae, the tensor 
fasciae latae, gluteus superficialis, and biceps femoris; deeply, the longissimus, the 
ilium, sacro-iliac and sacro-sciatic ligaments, the gluteus profundus, iliacus and 
rectus femoris, the iliaco-femoral vessels, the gluteal and internal pudic vessels and 
nerves, and the great sciatic nerve. 

Blood-supply. — Gluteal, ilio-lumbar, lumbar, and iliaco-femoral arteries. 

Nerve-supply. — Gluteal nerves. 

4. Gluteus profundus.- — This much smaller quadrilateral muscle lies under 
the posterior part of the preceding muscle, and extends over the hip joint, from the 
superior ischiatic spine to the anterior part of the trochanter major (Fig. 580). 

Origin. — The superior ischiatic spine and the adjacent part of the shaft of the 
ilium. 

Insertion. — The edge of the anterior part or convexity of the trochanter major 
of the femur. 

Action. — To abduct the thigh and to rotate it inward. 

Structure. — The muscle is short and thick and contains numerous tendinous 
intersections. The fibers are directed almost transversely outward over the capsule 
of the hip joint and converge at the convexitj^ of the trochanter. 

Relations. — Superficially, the gluteus medius and branches of the gluteal vessels 
and nerves; deeply, the shaft of the ilium, the hip joint, and the rectus femoris 
and capsularis. 

Blood-supply. — Gluteal artery. 

Nerve-supply. — Anterior gluteal nerve. 

5. Biceps femoris.^ — This large muscle lies behind and in part upon the super- 
ficial and middle glutei. It extends in a curved direction from the sacral and 
coccygeal spines to the lateral surface of the stifle and leg (Figs. 267, 292, 580). 

Origin. — (1) The dorsal and lateral sacro-iliac ligaments, the gluteal and 
coccygeal fasciae, and the intermuscular septum between this muscle and the semi- 
tendinosus; (2) the tuber ischii. 

Insertion. — (1) A rough eminence oh the posterior surface of the femur near 
the trochanter tertius; (2) the free (anterior) surface of the patella and the lateral 
patellar ligament; (3) the tibial crest; (4) the crural fascia and the tuber calcis. 

Action. — The action is somewhat complex, because the muscle is composed 
of three parts, has several points of insertion, and acts on all the joints of the 
limb except those of the digit. The general action is to extend Hie limb, as in pro- 
pelling the body, rearing or kicking, and to abduct it. The anterior part, by its 
attachment to the posterior surface of the femur and to the patella, would extend 

' By most anatomists the portion inserted into the crest is termed the gluteus accessorius, 
but Lesbre considers this to be the deep gluteus, homologous with the gluteus minimus of man. 
The portion inserted into the trochanteric ridge apparently represents the piriformis of man. 

' Lesbre considers this to be the scansorius. 

^ Apparently the muscle represents the biceps, together with part of the gluteus super- 
ficiaUs of man. Hence the names, gluteo-biceps and paramero-biceps have been suggested. 



THE LATERAL MUSCLES OF THE HIP AND THIGH 323 

the stifle and hip joints and abduct the limb. The middle part, being inserted 
chiefly on the tibial crest and the lateral patellar ligament, would extend the hip, 
and may, with the semitendinosus, flex the stifle. The posterior part, by virtue 
of its attachment to the tuber calcis, assists in extending the hock. It is to be noted, 
however, that extension of the hock joint can occur only when the stifle is also ex- 
tended, and vice versa. 

Structure. — The muscle has two heads of origin. The long or vertebral head 
arises chiefly from the dorsal and lateral sacro-iliac ligaments, the coccygeal fascia, 
and the intermuscular septum. There is often a large bursa between this head and 
the trochanter major. The short or ischiatic head arises by a strong tendon from 
the ventral spine on the tuber ischii, which also furmshes origin to part of the semi- 
tendinosus. They unite, and a short tendon, detached from the deep face of the 
muscle, is inserted into the posterior surface of the femur near the third trochanter; 
here a bursa is interposed between the tendon and the bone. The muscle then 
divides into three parts, which terminate on a strong aponeurosis over the 
junction of the thigh and leg. The anterior part is directed toward the patella, 
the middle one toward the tibial crest, while the posterior one assists in the forma- 
tion of the posterior contour of the limb. The aponeurosis blends with the deep 
layer of the fascia cruris, as already described. A sj'novial bursa occurs under the 
patellar insertion, and in some cases there is also one between the muscle and the 
third trochanter. 

Relations. — Superficially, the sldn and fascia; deeply, the sacro-iliac and sacro- 
sciatic ligaments, the coccygeal fascia, the femur, the gluteus medius, obturator, 
gemellus, quadratus femoris, adductor, semimembranosus, vastus lateralis, and 
gastrocnemius muscles, branches of the lateral sacral, gluteal, obturator, femoral 
and deep femoral vessels, the great sciatic, tibial, peroneal, and posterior gluteal 
nerves; in front, the superficial and middle glutei; behind and medially, the semi- 
tendinosus. 

Blood-supply. — Gluteal, obturator, and posterior femoral arteries. 

Nerve-supply. — Posterior gluteal and great sciatic nerves. 

6. Semitendinosus. — This is a long muscle which extends from the first two 
coccygeal vertebra to the proximal third of the medial surface of the tibia. It lies 
at first behind the biceps, then passes downward on the back of the thigh, between 
that muscle and the semimembranosus (Figs. 268, 288, 580). It has two heads of 
origin. 

Origin. — (1) The transverse processes of the first and second coccygeal ver- 
tebra, the coccygeal fascia, and the intermuscular septum between this muscle and 
the biceps femoris; (2) the ventral surface of the tuber ischii. 

Insertion. — (1) The tibial crest; (2) the crural fascia and the tuber calcis. 

Action. — To extend the hip and hock joints, acting with the biceps and semi- 
membranosus in propulsion of the trunk, rearing, etc. ; also to flex the stifle and ro- 
tate the leg inward.' 

Structure. — The long or vertebral head is small at its origin, but becomes larger 
by the accession of fibers arising on the intermuscular septum. Below the tuber 
ischii it unites with the short head, which arises partly by fleshy fibers, partly by a 
common tendon with the biceps. The muscle then passes downward on the back 
of the thigh, and terminates on a wide tendon on the medial surface of the proximal 
third of the leg. A cUstinct band passes forward to be inserted on the tibial crest 
(a bursa lying between the tendon and the tibia) , part fuses with the fascia of the 
leg, while the remainder joins the biceps tendon and concurs in the formation of the 
tendinous band, which, as before described, terminates on the tuber calcis (Fig. 
583). A bursa may occur under the long head where it passes over the tuber ischii. 

' It should be remembered, however, that the stifle can be flexed only when the hock is also 
flexed and vice versd. 



324 



FASCIA AND MUSCLES OF THE HORSE 



Relations. — Laterally, the skin and fascia, the biceps, and the medial head 
of the gastrocnemius; medially, the coccygeal fascia, the sacro-sciatic ligament, 
the semimembranosus; anteriorly, the biceps femoris, branches of the femoral 
artery, and the great sciatic nerve. 

Blood-supply. — Posterior gluteal, obturator, and posterior femoral arteries. 

Nerve-supply. — Posterior gluteal and great sciatic nerves. 



Origin nf nhliqunx ah- 
fioniini.^ iidirinix 
Inguinal liyamcitt (part 
removed) 

Iliacus 

Tensor faciw latce 

Rectus femoris 



Vastus medialis 
Sartorius 




Medial patellar ligaint nl 
Tendon of sartor in 



i.scia cruris 



Fig. 2S7. — Muscles of Pelvis axd Thiuh of Young Horse. Right .Side: Medi.vl View. 
1, Psoas minor, and 1', its insertion; 2, psoas major; 3, 3', heads of obturator internus; 4, sacro-coccygeus ven- 
tralis; 5. coccygeus; fi, retractor am (cut) ; 7. sacro-sciatic ligament; S, lesser sciatic foramen; 9, semimembranosus; 
10, lumbo-sacral plexus; H, obturator nerve and vessels (cut); 12, femoral vessels (origin) ; 13, pubis; 14, prepubic 
tendon; IS, deep inguinal lymph glands; 16, opening for external pudic vein. Vertebra are numbered by regions. 



7. Semimembranosus^ (Figs. 276, 287, 288, 576).— This very large, three- 
sided muscle lies on the medial surface of the preceding muscle and the gastroc- 
nemius, and has two heads of origin. 

Origin. — (1) The posterior border of the sacro-sciatic ligament; (2) the ventral 
surface of the tulDcr ischii. 

' This muscle was incorrectly designated the adductor magnus by Percivall and Strange- 
ways. Its name, however, is not at all descriptive of its structure in the domesticated animals. 



THE MEDIAL MUSCLES OF THE THIGH 325 

Insertion. — The medial epicondyle of the femur, behind the eollateral hgament. 

Action. — To extend the hip joint and to adduct the liml). 

Structure. — The long head, small and pointed above, extends toward the root 
of the tail, fusing with the sacro-sciatic ligament. Passing dowaiward, it becomes 
larger and covers in part the posterior aspect of tlie tuber ischii. A bursa may be 
found here. Below this it joins the short head, which is larger. The large belly 
so formed passes downward and forward, covered in great part by the gracilis, and 
terminates on a short, flat tendon of insertion at the distal end of the femur. 

Relations. — The upper part of the muscle concurs with the sacro-sciatic liga- 
ment in forming the lateral boundary of the pelvic outlet. It is related posteriorly 
and laterally to the skin and fascia and the semitendinosus ; metlially, to the anus 
and its muscles, the vulva in the female, and the internal pudic artery and nerve 
(Figs. 577, 578). Below the pelvis the chief relations are: laterally, the semi- 
tendinosus, biceps, and gastrocnemius, branches of the obturator, femoral, and 
posterior femoral arteries, and the great sciatic nerve and its chief branches; 
medially, the crus penis and ischio-cavernosus muscle (in the male) and the 
gracilis; in front, the adductor and the femoral vessels; behind, the skin and fascia. 

Blood-supply. — Obturator and femoral arteries. 

Nerve-supply. — Great sciatic nerve. 



m. THE MEDIAL MUSCLES OF THE THIGH 
The muscles of this group are arranged in three layers. 

First Layer 

1. Sartorius (Figs. 287, 288, 576). — This long and rather narrow muscle is the 
most anterior one of the first layer. It extends from the posterior part of the sub- 
lumbar region to the lower and medial part of the stifle, and is directed downward 
and somewhat backward. 

Origin. — The iliac fascia and the tendon of the psoas minor. 

Insertion. — The medial patellar ligament and the tuberosity of the tibia. 

Action. — To flex the hip joint and adduct the limb. 

Structure. — The muscle is thin at its origin, but becomes thicker, narrower, 
and three sided distally. It terminates near the stifle joint on an aponeurosis which 
blends with that of the gracilis and with the fascia of the leg. 

Relations. — Medially, the inguinal ligament, the abdominal muscles, the skin 
and fascia; laterally, the ilio-psoas, quadriceps femoris, and femoral nerve. It 
forms the anterior boundary of the femoral canal, in which the femoral artery and 
vein and the deep inguinal lymph glands are situated (Fig. 576). 

Blood-supply. — Femoral artery. 

Nerve-supply. — Saphenous nerve. 

A rare variation is the existence of a small accessory head which arises from the anterior 
border of the pubis or from the prepubic tendon and joins the normal muscle near the middle of 
the thigh. 

2. Gracilis (Figs. 276, 287, 575).— This is a wide, quadrilateral muscle, 
which is situated behind the sartorius, and covers the greater part of the metlial 
surface of the thigh. 

Origin. — The middle third of the pelvic symphysis, the prepubic tendon and 
accessory ligament, and the ventral sm-face of the pubis behind the prepuliic ten- 
don. 

Insertion. — The medial patellar ligament, the medial surface of the tibia in 
front of the medial femoro-tibial ligament, and the crural fascia. 

Action. — To adduct the limb. 

Structure. — The muscle arises by a strong tendon, chiefly in common with the 



326 FASCI.E AND MUSCLES OF THE HORSE 

opposite muscle. Its direct attachment to the ventral surface of the pelvis is not 
so extensive as a superficial inspection would suggest. The tendon of origin pre- 
sents anteriorly a foramen for the passage of the external pudic vein. The belly 
is composed of parallel bundles, and is marked by a superficial furrow which, how- 
ever, does not indicate a muscular division. It terminates on the medial surface 
of the stifle on a thin wide tendon which blends in front with that of the sartorius, 
below \vith the crural fascia. 

Relations. — Superficially, the skin and fascia, the penis or mammary gland, 
and the saphenous vessels and nerve; deeply, the pectineus, adductor, semimem- 
branosus and semitendinosus, and, at the middle of the femur, the femoral vessels; 
anteriorly, the sartorius. In the proximal third of the thigh the sartorius and gracili 
are separated by a triangular interval (femoral triangle), in which lie the deep in- 
guinal lymph glands and the femoral vessels. 

Blood-supply. — Femoral and deep femoral arteries. 

Nerve-supply. — Obturator nerve. 

Second Layer 

1. Pectineus (Figs. 276, 288, 576). — This muscle is fusiform and extends from 
the anterior border of the pubis to the middle of the medial border of the femur. 

Origin. — The prepubic tendon, the accessory ligament, and the anterior border 
of the pubis. 

Insertion. — The middle of the medial border of the femur, near the nutrient 
foramen. 

Action. — To adduct the limb and flex the hip joint. 

Structure. — The belly is cylindrical and contains little fibrous tissue. Its 
origin is perforated by the accessory ligament — from which many fibers arise — 
and is thus divided into two unequal parts. The large upper part arises largely 
from the prepubic tendon — only a small part gaining direct attachment to the 
puliis. The small lower part does not reach the bone. The insertion is pointed 
and tendinous. 

Relations. — Medially, the gracilis; laterally, the femur, the vastus medialis, 
the terminal part of the psoas major and iliacus, and the deep femoral artery; an- 
teriorly', the sartorius, the femoral vessels, the saphenous nerve, and the deep in- 
guinal lymph glands; posteriorly, the adductor and obturator externus, and the 
obturator nerve (anterior division). 

Blood-supply. — Femoral and deep femoral arteries. 

Nerve-supply. — Obturator nerve. 

The femoral canal is exposed in the dissection of the preceding muscles (Figs. 
288, 290). It is bounded anteriorly by the sartorius, posteriorly by the pectineus, 
and laterally by the ilio-psoas and vastus medialis. Its medial wall is formed by 
the femoral fascia and the gracilis. Its upper or abdominal opening, the femoral 
ring (Lacuna vasorum), lies behind the medial part of the internal inguinal ring and 
is bounded anteriorly by the inguinal ligament, posteriorly by the anterior border 
of the pubis, and laterally by the tendon of the psoas minor. The canal termi- 
nates below at the insertion of the pectineus. It contains the deep inguinal lymph 
glands, the femoral artery and vein, and the saphenous nerve. 

2. Adductor! (Figs. 276, 288, 576).— This fleshy, prismatic muscle lies behind 
the pectineus and vastus medialis. It extends downward and forward from the 
ventral surface of the pelvis to the medial epicondyle of the femur. 

Origin. — The ventral surface of the pubis and ischium and the tendon of ori- 
gin of the gracilis. 

1 It has been customary to describe two adductors — a parvus or breWs, and a longus or 
niagnus. This division is partly artificial, and has been abandoned in the new nomenclature — 
a return to the views of Bourgelat and Girard. 



THE MEDIAL MUSCLES OF THE THIGH 



327 



Insertion. — (1) The posterior surface of the femur from the level of the third 
trochanter to the groove for the femoral vessels; (2) the medial epicondyle of the 
femur and the medial ligament of the stifle joint. 

Action. — To adduct the limb and extend the hip joint. It also rotates the fe- 
mur inward. 

Structure. — It is almost entirely fleshy, antl is composed of parallel bundles 



Psoas minor 
Sartorius {origin) 

Iliopsoas 

Tensor fasciw latce 

Rectus femoris 




Semimembranosus 
Adductor 



Vastus medialis 



Patella 



Middle patellar ligament ^^y^. 
Medial patellar ligament -—"^ 
Tendon of sartorius (cut) -^""^ 

Tendon of gracilis (cut) 



Tibial insertion of semitendinosus 



Semiterulinosus 



Medial head of gastroc- 
nemius 
Tibial nerve 



Fig. 288.— Muscles of Pelvis and Thigh of Hor.se, Right Side; Me 

Figure represents deeper dissection of specimen shown in preceding figure. 
1. Tendon of insertion of psoas minor; 2, lumbo-sacral plexus; 3, 3', heads of obturator internus; 4, sacro-coccy- 
geus ventralis; 5, coccygeus: 6, retractor ani (origin) ; 7, sacro-sciatic Ugament; 8, lesser sciatic foramen; 9. femoral 
nerve; 10, femoral ves.sels; 11, 11, pectineus; 12, accessory ligament; 13, external pudic vein; 14, pubis; 15, femoro- 
patellar joint capsule; 16, distal end of femur; 17, medial meniscus; 18, medial ligament of stifle joint; 19, medial 
femoro-patellar ligament. 



united rather loosely. It is usually possible to separate from the principal mass a 
small anterior short part,' which is inserted into the femur behind the pectineus. 
The principal mass- is perforated just below the insertion of the pectineus by an 
opening for the femoral vessels (hiatus adductorius), and is thus divided into two 

1 This ha.s been termed by various authors the adductor parvus or brevis. 
^ Termed by various authors the adductor magnus or longus. 



328 FASCIA AND MUSCLES OF THE HORSE 

branches. The lateral branch is inserted into the back of the femur with the short 
portion, while the medial branch is attached to the medial epicondyle and col- 
lateral ligament. There is often a superficial slip which ends partly on the femoro- 
patellar joint capsule and may reach the accessory cartilage or medial ligament of 
the patella. Some fibers pass under the collateral ligament and end on the tendon 
of the semimembranosus. 

Relations. — Medially, the gracilis, and l^ranches of the femoral artery and 
of the obturator nerve; laterally, the femur, the obturator extern us, quadratus 
femoris, biceps femoris, and the femoral, deep femoral, and obturator arteries ; an- 
teriorly, the pectineus, vastus medialis, and a large branch of the obturator nerve; 
posteriorly, the semimembranosus and the great sciatic nerve. 

Blood-supply. — Femoral, deep femoral, and obturator arteries. 

Nerve-supply. — (31.iturator nerve. 

3. Semimembranosus. — Described on p. 324. 

Third Layer 

1. Quadratus femoris.' — This is a narrow, three-sided muscle, which lies under 
cover of the upper part of the adductor (Fig. 581). 

Origin. — The ventral surface of the ischimn, just in front of the semimembrano- 
sus. 

Insertion. — An oblique line on the posterior surface of the femur, near the 
lower part of the trochanter minor. 

Action. — To extend the hip joint and to adduct the thigh. 

Structure. — It is composed of parallel Innidles of fibers directed dowTiwarfl, 
forward, and outward. 

Relations. — Fostero-medially, the adductor, semimemljranosus, and the ob- 
turator vessels; antero-laterally, the obturator externus and biceps femoris, the 
deep femoral vessels, and the great sciatic nerve. 

Blood-supply. — Deep femoral and obturator arteries. 

Nerve-supply. — Great sciatic nerve. 

2. Obturator externus (Fig. 581). — This is a pyramidal itiuscle which extends' 
across the liack of the hip joint from the ventral surface of the pelvis around the 
obturator foramen to the trochanteric fossa. 

Origin. — The ventral surface of the pubis and ischium, and the margin of the 
obturator foramen. 

Insertion. — The trochanteric fossa. 

Action. — To adduct the thigh and to rotate it outward. 

Structure. — It is almost entirely fleshy, the muscle-bundles being rather loosely 
connected. The insertion is pointed, flattened, and partly tendinous. The origin 
is perforated by the obturator vessels and. nerve. 

Relations. — Medially, the adductor and quadratus femoris and the deep 
femoral vessels; laterally, the gemellus, the tendon of the obturator internus, the 
biceps femoris, and the great sciatic nerve; anteriorly, the hip joint, the pectineus, 
and the external pudic vein. 

Blood-supply. — Deep femoral and obturator arteries. 

Nerve-supply. — Obturator nerve. 

3. Obturator internus (Fig. 288). — This arises Avithin the pelvic cavity by two 
heads, the tendon emerging through the lesser sciatic foramen. 

Origin. — (1) The pelvic surface of the pubis and ischium around the obturator 
foramen; (2) the pelvic surface of the shaft of the ilium and the wing of the sacrum. 
Insertion. — The trochanteric fossa. 
Action. — To rotate the femur outward. 

' Also known as the iscliio-femoralis. 



ANTERIOR MUSCLES OF THE THIGH 329 

Structure. — The ischio-pubic head lies on the pelvic floor and covers the ob- 
turator foramen. It is thin and fan-shaped. The iliac head extends along the 
lateral wall of the pelvis, and is pennate, with a central tendon throughout. Both 
terminate on a flat tendon which passes outward through the lesser sciatic fora- 
men to be inserted into the trochanteric fossa. The tendon furnishes insertion to 
fibers of the gemellus. A synovial bursa facilitates the play of the tendon over the 
lateral border of the ischium. ^ 

Relations. — The pelvic surface is covered by the pelvic fascia and in part by 
the peritoneum. The obturator vessels and nerve lie between the two heafls, and 
the internal pudic vessels and nerve lie along the dorsal edge of the iliac head. The 
tendon is crossed by the great sciatic nerve. 

Blood-supply. — Obturator and internal pudic arteries. 

Nerve-supply. — Great sciatic nerve. 

4. Gemellus'- (Fig. 580). — This is a thin, triangular muscle, which extends 
from the lateral border of the ischium to the trochanteric fossa and ridge. 

Origin. — The lateral border of the ischium near the ischiatic spine. 

Insertion. — The trochanteric fossa and ridge. 

Action. — To rotate the femur outward. 

Structure. — The thin tendon of origin is attached to a line on the lateral border 
of the ischium, which begins just l^elow the posterior end of the superior ischiatic 
spine. Many superficial fibers are inserted into the tendon of the obturator in- 
ternus. 

Relations. — Superficially, the biceps femoris, the tendon of the obturator in- 
ternus, the gluteus medius, and the great sciatic nerve; deeply, the obturator ex- 
ternus and the hip joint. 

Blood-supply. — Obturator artery. 

Nerve-supply. — Great sciatic nerve. 



IV. ANTERIOR MUSCLES OF THE THIGH 

This group consists of the sartorius, quadricejjs femoris, and capsularis. 

1. Sartorius. — This is described on p. 325. 

2. Quadriceps femoris (Figs. 268, 289, 291). — This constitutes the large mus- 
cular mass which covers the front and sides of the femur. It has four heads, one 
of which, the rectus, arises from the ilium; the other three arise from the femur. 
All are inserted into the patella. 

( 1 ) Rectus femoris. — This is fusiform and rounded. It arises bj' two tendons. 

Origin. — Two depressions on the shaft of the ilium above and in front of the 
acetabulum. 

Insertion. — The base and anterior surface of the patella. 

Action. — To extend the stifle joint and to flex the hip joint. 

Structure. — It has two short strong tendons of origin; beneath the lateral one 
is a bursa. The belly is rounded and rests in a groove formed by the other portions 
of the quadriceps. Its sides are covered by a strong tendinous layer which fur- 

' The iliac head has been described as a separate muscle, and termed the piriformis. This 
does not seem desirable, especially since it is probable that the homologue of the piriformis of 
man is that portion of the middle gluteus which is inserted into the trochanteric ridge. 

- The name is based on the arrangement in man, in whom the muscle usually consists of two 
fascicvili forming a groove between them for the tendon of the obturator internus. In the horse 
it is usually undivided at its origin, but toward the insertion the upper part is separated from the 
rest of the muscle or is readilj' isolated. The muscle is subject to much variation in size. When 
well developed, the insertion extends from the proximal end of the trochanteric fossa to a point 
just above the femoral attachment of the biceps femoris; in such cases the upper part, which 
occupies the space behind the liip joint between the gluteus profundus and obturator externus, 
is much thicker than the remainder, which covers the latter muscle. The gemellus may be re- 
garded as the extrapelvic head of the obturator internus (Gegenbaur). 



330 



FASCIA AND MUSCLES OF THE HORSE 



nishes insertion to fibers of the vasti. The tendon of insertion is formed by the 
union of these tendinous layers on the lower part of the muscle. The lower portion 
of the muscle is pennate, the fibers on either side converging on the tendon at an 
acute angle. 

Relations. — Medially, the iliacus, sartorius, and vastus medialis; laterally, 
the tensor fasciae latae, glutei, and vastus lateralis; posteriorly, the hip joint and 
the vastus intermedius; anteriorly, the fascia lata and the skin. The anterior 
femoral artery and branches of the femoral nerve descend into the interspace be- 



Shaft of ilium 



\ , Medial tendon of origin 
'' of rectus femoris 



Gluteus profundus 




Prepubic tendon {in 
median section) 
Obturator exlcrnus 

Iliopsoas [insertion) 
Adductor 

Vastus mediulis 



Medial femoro-tibial ligament 
-Medial meniscus 



Lateral patellar ligament 



Tuberosity of tibia 



Fig. 289. — Muscles of Right Thigh of Horse, Deep Dissectio.m. The Preparation is Vi: 
AND Some 



> FROM IN Front 



1, Acceasory ligament of hip joint: 2. transverse ligament of same; 3, head of femur; 4, patella; 5, trochlea of femur; 
6, 7, middle and medial patellar ligaments. 



tween the upper part of the rectus and the vastus medialis; similarly, the iliaco- 
femoral artery dips in between the rectus femoris and vastus lateralis. 

Blood-supply. — Femoral and iliaco-femoral arteries. 

Nerve-supply. — Femoral nerve. 

(2) Vastus lateralis. — This lies on the lateral surface of the femur, extending 
from the great trochanter to the patella. It is wide in its middle, smaller at each end. 

Origin. — The lateral border and surface of the femur, from the trochanter 
major to the supracondyloid fossa. 



ANTERIOR MUSCLES OF THE THIGH 



331 



Insertion. — (1) The lateral part of the anterior surface of the patella; (2) the 
tendon of the rectus femoris. 

Action. — To extend the stifle joint. 

Structure. — The fibers are directed downward and forward, many being in- 
serted into the tendinous sheet which covers the side of the rectus. A bursa is 
usually present between the distal end and the patella. 

Relations. — Laterally, the fascia lata and skin, tensor fasciae latae, superficial 



Fold of flank 
Tctisor fascia: latoe 



Vujstus mcdiali 

Sartorius 

Saphenous vein 

Saphenous nerae 

Femoral artery 

Gracilis 

Adductor 

Peroneal nern 
Tibial neri'e 



Semimem- 
branosus 



Semilendinosus 




Fio. 290. — Cross-section op Middle of Right Thigh 



gluteus, and biceps femoris; medially, the femur and femoro-patellar joint capsule, 
the rectus femoris, vastus intermedius, and the iliaco-femoral artery. 

Blood-supply. — Iliaco-femoral artery. 

Nerve-supply. — Femoral nerve. 

(3) Vastus medialis. — This resembles the preceding muscle, and lies in a sim- 
ilar position on the medial side of the femur. 

Origin. — The medial surface of the femur, from the neck to the distal third. 

Insertion. — (1) The medial border of the patella and its cartilage, and the 



332 



FASCI/B AND MUSCLES OF THE HORSE 



proximal part of the medial patellar ligament. (2) The tendon of the rectus 
femoris. 

Actio7i. — To extend the stifle joint. 

Structure. — This is very similar to that of the vastus lateralis. It is, how- 
ever, more difficult to separate from the intermedins, because many fibers of the 
latter arise on the tendinous sheet which covers the contact surface' of the medial 



Shaft of femur 



Gluteus profundus 



Trochanter major 
(anterior part) 



Vastus lateralis 

Vastus inlermedius 

Rectus femoris 

Vastus lateralis 

Biceps femoris 

Paldhi 



Lateral femoro-tibiid 
ligament 
Lateral patellar ligament 



Prepuhic tendon 
Obturator externus 




Medial femoro-tibial ligament 
Medial meniscus 

Middle patellar ligament 



Tuberosity of tibia 



Fig. 291. — Muscles of Right Thigh of Horse; Deep Dissection. 
The preparation is viewed from the front and somewhat medially. Most of rectus femoris and vastu.s lateralis 
has been removed. 1, Stump of origin of rectus femoris; 2, capsularis; 3, accessory ligament; 4, cotyloid ligament; 
5, head of femur; 6, trochlea of femur. 



vastus. Its insertion into the patella is chiefly by means of a broad, strong tendon. 
From the deep face fleshy fibers are inserted also into the femoro-patellar joint cap- 
sule. 

Relations. — Medially, the skin and fascia, the iliacus, sartorius, pectineus, and 
adductor, the femoral vessels, and saphenous nerve ; laterally, the femur, femoro- 
patellar joint capsule, rectus femoris, and vastus intermedins, the anterior femoral 
artery, and branches of the femoral nerve. 



THE MUSCLES OF THE LEG AND FOOT 333 

Blood-supply. — Femoral and anterior femoral arteries. 

Nerve-supply. — Femoral nerve. 

(4) Vastus intermedius. — This muscle is deeply situated on the anterior face 
of the femur, and is entirely covered by the preceding heads. 

Origin. — (1) The anterior surface of the femur, from the proximal to the distal 
fourth; (2) the tendinous covering of the vastus medialis. 

Insertion. — (1) The base of the patella; (2) the femoro-patellar joint capsule. 

Action. — (1) To extend the stifle joint; (2) to tense (raise) the femoro-patellar 
capsule during extension of the joint. 

Structure. — The muscle is usually quite difficult to isolate from the other vasti, 
so that many since Giinther have declared it an artefact.' It is entirely fleshy, and 
is small at its proximal end, but when traced downward increases in bulk by the 
accession of fibers arising on the femur and the tendinous covering of the vastus 
medialis. The terminal part is intimately adherent to the femoro-patellar joint 
capsule, where the latter bulges above the level of the patella. 

Relations. — Medially, the vastus medialis; laterally, the vastus lateralis; 
anteriorly, the rectus; posteriorly, the femur and femoro-patellar capsule. 

Blood-supply. — Iliaco-femoral and anterior femoral arteries. 

Nerve-supply. — Femoral nerve. 

The patellar ligaments are to be regarded as tendons of the quadriceps which communicate 
the action of the latter to the tibia, the patella being intercalated as a sesamoid bone. 

3. Capsularis (Fig. 291).- — This is a small fusiform muscle (scarcely as large 
as one's finger), which arises by a thin tendon on the ilium immediately above the 
outer tendon of the rectus femoris. Its delicate tendon of insertion dips in between 
the vastus intermedius and lateralis and is attached to the proximal third of the 
anterior surface of the femur. It passes over the outer side of the hip joint, to the 
capsule of which some fibers are attached. Sometimes the muscle has two dis- 
tinct heads, in which case the additional head arises between the two tendons of 
origin of the rectus femoris. Its action may be to raise the capsule during flexion 
of the joint. It is related laterally to the gluteus profundus and vastus lateralis, 
medially to the rectus femoris and vastus intermedius and the hip joint. 



V. THE MUSCLES OF THE LEG AND FOOT 
The muscles of this region cover almost all of the tibia except its medial face, 
which is largely subcutaneous. As in the forearm, the muscles fall into two groups, 
a dorso-lateral and a plantar. The muscles of the first group are extensors of the 
digit and flexors of the hock, those of the second have the opposite action. 

A. Dorso-lateral Group 

1. Long digital extensor (M. extensor digitalis longus).^ — This muscle is sit- 
uated superficially on the dorso-lateral aspect of the leg, and is provided with a long 
tendon which passes down over the front of the tarsus, metatarsus, and digit. 

Origin. — The extensor fossa of the femur. 

Insertion. — (1) The extensor process of the third phalanx; (2) the dorsal sur- 
face of the proximal extremities of the first and second phalanges. 

Action. — To extend the digit and flex the hock. It also assists in fixing the 
stifle joint. 

'While it is true that the separation of the intermedius is never entirely a natural one in the 
horse, it varies in individual cases, and is usually clear on cross-sections. In some subjects it is 
possible to separate another slip which may represent the articularis genu of man. 

- Also known as the rectus parvus. 

2 Also termed the extensor pedis or the anterior extensor of the phalanges. 



334 



FASCIA AND MUSCLES OF THE HORSE 



Structure. — The origin is by means of a strong tendon in common with the 
peroneus tertius, on which also many fibers arise. The common tendon passes 
downward in the groove between the lateral condyle and the tuberosity of the tibia, 



Crest of tibia 

Long digital extensor 
Lateral digital extensor 



Proximal annular ligament 
Lateral malleolus 



Gastrocne7nius, lateral head 

Suleus 

Tendon of gastrocnejnius 
Tarsal tendon of biceps fetnoris 

Deep flexor 



Superficial 
flexor tendon 



Middle annular ligament 

Distal annular ligament 
Tendon of long extensor -- 
Tendon of lateral extensor-- 



Branch of suspensory ligament to 
extensor tendon 




Superficial flexor 
tendon 



Deep flexor tendon 



Suspensory 
ligament 



Fig. 292. — Muscles of Lower Part op Thigh, Leg, and Foot op Horse; Lateral View. 
, Fascia lata; g, q', q", biceps feraoris; r, semitendinosus; ;?/', lateral condyle of tibia. The extensor brevis is visible 
in the angle between the long and lateral extensor tendons, but by an oversight it i 
berger-Baum, Anat. fiir Kiinstler.) 



) not marked. (.After EUen- 



where a pouch from the femoro-tibial capsule descends three or four inches (ca. 
7.5 to 10 cm.) beneath the tendon. The belly is fusiform and somewhat flattened. 
The long tendon of insertion begins in the belly about its middle, and is clear of the 



THE MUSCLES OF THE LEG AND FOOT 335 

fleshy part near the tarsus. It passes downward over the front of the hock, t)ound 
down by the three annular ligaments already described (see tarsal fascia), and en- 
veloped by a synovial sheath which begins a little above the level of the lateral 
malleolus, and extends nearly to the junction with the lateral extensor tendon. 
This union occurs usually about a hand's breadth below the tarsus. In the angle 
of union the extensor brevis also joins the principal tendon. Beyond this point 
the arrangement is the same as in the fore limb. 

Relations. — Superficially, the skin and fascia; deeply, the femoro-tibial joint, 
peroneus tertius, and tibialis anterior; behind, the lateral extensor and the super- 
ficial and deep peroneal nerves. In front of the tarsus the anterior tibial artery 
crosses the deep face of the tendon (Fig. 585). 

Blood-supply. — Anterior tiljial artery. 

Nerve-supply. — Peroneal nerve. 

2. Lateral digital extensor (M. extensor digitalis lateralis).' — This muscle lies 
on the lateral surface of the leg, behind the preceding one. 

Origin. — The lateral ligament of the stifle joint, the fibula, the lateral border 
of the tibia, and the interosseous ligament. 

Insertion. — The tendon of the long extensor, alsout a third of the way down 
the metatarsus. 

Action. — To assist the long extensor. 

Structure. — The belly is fusiform, flattened, and pennate. The tendon runs 
through the entire length of the belly and becomes free from it at the distal fourth 
of the tibia. It descends through the groove on the lateral malleolus, bound doAvn 
by an annular ligament, and, inclining forward, blends (usually) with the tendon 
of the long extensor. It is provided with a S3movial sheath, which begins about 
an inch (ca. 2 to 3 cm.) above the lateral malleolus antl ends about one and one- 
half inches (ca. 3 to 4 cm.) above the junction. Sometimes the fusion does not 
occur; the tendon then descends alongside of that of the long extensor, and is in- 
serted into the first phalanx like the corresponding muscle of the thoracic limb. 

Relations. — Laterally, the skin and fascia and the superficial peroneal nerve; 
medially, the tibia and fibula; anteriorly, the intermuscular septum, the long 
extensor, and the tibialis anterior; posteriorly, the deep digital flexor and the soleus. 
" Blood-supply. — Anterior tibial artery. 

Nerve-supply. — Peroneal nerve. 

3. Peroneus tertius (Tendo f emoro-metatarseus) .- — This consists in the horse 
of a strong tendon which lies between the long extensor and the tibialis anterior. 

Origin. — The extensor fossa (between the lateral condyle and the trochlea 
of the femur), in common with the long extensor. 

Insertion. — (1) The proximal extremity of the large (third) metatarsal bone 
and the third tarsal bone; (2) the fibular and fourth tarsal bones. 

Action. — Mechanically to flex the hock when the stifle joint is flexed. 

Structure. — It is entirely tendinous. The proximal end and the underlying 
prolongation of the synovial membrane of the femoro-tibial joint have been men- 
tioned in the description of the long extensor. The superflcial face gives origin 
to fibers of the long extensor in the upper part of the leg, and the deep face is fused 
with the tibialis anterior except at either end of the region. At the distal end of the 
tibia the tendon is perforated for the emergence of the tendon of the tibialis anterior 
and divides into two branches. The anterior branch is attached to the third tarsal 
and third metatarsal bones, while the lateral one curves outward, bifurcates, and 

' Also known as the peroneus or the lateral extensor of the phalanges. Lesbre considers it 
to be the homologue of the peroneus bre\'is of man and other pentadactyls. 

^ It seems inadvisable to retain the old term, tendinous part of the flexor metatarsi, since it 
is inappUcable to other domesticated animals in which the muscle is well developed (e. g., pig). 
Schmaltz uses the term tendo femoro-tarseus, and Varaldi and Lesbre designate it the femoro- 
metatarsal cord. The name peroneus anterior has also been proposed. 



336 



FASCIA AND MUSCLES OF THE HORSE 



is inserted into the fibular and fourth tarsal bones. The lateral terdon gives off 
a branch which forms a loop around the long extensor tendon (Fig. 293). 

Relations. — Superficially, the long extensor ; deeply, the tibialis anterior. The 
anterior tibial vessels cross the deep face of the outer branch. 



Lateral ridge of trochlea of femur 
Lateral femoro-libial ligament 

Lateral meuiscus 
Lateral condyle of tibia 

Long extensor (stump) 

Peroneus tertiiis 
Tibialis anterior 
Lateral extensor 



Tendinous loop -j 

Extensor breeis 

Tendon of lateral extensor 
Tendon of long extensor 




Medial ridge of trochlea of femur 



Medial me7iiscus 

Medial femoro-tibial ligament 



Tendon of long extensor 
Annular ligament 
Peroneus tertius 



^<SC—Anter> 



MedUd tendon, of tibialis anterior 



or tendon of tibialis anterior 
Anterior tendon of peroneus tertius 

Annular ligament 
Mt. Ill 



Fig. 29.3.— Muscles of liiuHT Leo of Horse; Fhokt View. 
The greater part of the long extensor has been removed. 1, 2, .3, .Stumps of patellar ligaments; 4, tuberosity of tibia. 



4. Tibialis anterior.' — This lies on the dorso-lateral face of the tibia; it is wide 
and flattened above, pointed below. 

Origin. — The lateral condyle and border of the tibia and a small area on the 
lateral surface of the tuberosity. 

' Thi.s is also known as the muscular part of the flexor metatarsi. 



THE MUSCLES OF THE LEG AND FOOT 



337 



Insertion. — (1) The ridge on the front of the proximal end of the large meta- 
tarsal bone; (2) the first and second tarsal bones. 

Action. — To flex the hock joint. 

Structure. — The origin is fleshy, and forms a groove in which lie the common 
tendon of the long extensor and peroneus tertius and a synovial pouch which de- 
scends from the femoro-tibial joint. Many superficial fibers arise from the deep 
fascia at the proximal part of the leg and thus from the tibial crest. Passing down- 
ward on the tibia, the belly is united by tendinous and fleshy fibers with the per- 
oneus tertius, and terminates close to the tarsus in a point on the tendon of inser- 




FiG.- 294. — Injected Synovial Sheaths 
OF Tarsal Region of Horse; Medi/ 



VD BURS.E 

View. 



a, Synovial sheath of peroneus tertius and tibialis 
anterior; /). bursa under medial (cunean) tendon of 
tibialis anterior ; c, synovial sheath of flexor longus ; 
d, tarsal sheath of deep flexor; e, e', bursa under 
superficial flexor tendon; /, /', tibio-tarsal joint capsule; 
J, long extensor; 3, tibialis anterior; 2', medial (cun- 
ean) tendon of 3; 3, flexor longus; 4. deep digital 
flexor; 5, superficial flexor tendon; G, gastrocnemius 
tendon; 7, tibia; S, tarsus; 9, tuber calcis; 10, large 
metatarsal bone ; 11, medial small metatarsal bone ; 
12, 12', fascial bands. (After Ellenberger, in Leisering's 
Atlas.) 




Fig. 295. — Injected Synovial Sheaths and Burs.*: 
OF Tarsal Region of Horse; Lateral View. 
a. Synovial sheath of long digital extensor; 6, 
synovial sheath of lateral digital extensor; c, c' , bursa 
under superficial flexor tendon; d, capsule of hock joint; 
1. long extensor; 2, lateral extensor; 5, 3, 3, annular 
ligaments; 4, deep digital flexor; 5, tendon of gastroc- 
nemius; 6, superficial flexor tendon; 7, tibia; S, t9,rsus; 
9, tuber calcis; 10, metatarsus. (After Ellenberger, 
in Leisering's Atlas.) 



tion. The latter emerges between the branches of the peroneus tertius and bi- 
furcates, the anterior branch being inserted into the large metatarsal bone, the 
medial one into the first tarsal bone. The tendon is provided with a synovial sheath 
at its emergence, and a bursa is interposed between the medial l^ranch and the 
medial ligament of the hock.^ 

Relatioyis. — Superficially, the long and lateral extensors, the peroneus tertius, 
and the deep peroneal nerve; deeply, the tibia, the deep flexor, and the anterior 
tibial vessels. 

^ In surgical works the medial branch is termed the cunean tendon; it is sometimes resected 
for the relief of l>one spavin. 



338 



FASCIA AND MUSCLES OF THE HORSE 



Blood-supply .- 
Nerve-supply.- 



-Anterior tibial artery. 
-Peroneal nerve. 



Shaft of femu: 



Faiscial band 



B. Plantar Group 
1. Gastrocnemius (Figs. 268, 292, 296). — This muscle extends from the distal 
third of the fenmr to the point of the hock. It arises by two heads. 

Origin. — (1) Lateral head, 
from the lateral supracondy- 
loid crest (margin of the supra- 
condyloid fossa); (2) medial 
head, from the medial supra- 
condyloid crest. 

Insertion. — The posterior 
part of the tuber calcis. 

Action. — To extend the 
hock and to flex the stifle 
joint; these two actions, how- 
ever, cannot occur simulta- 
neously. 

Structure. — The two bel- 
lies are thick, fusiform, and 
somewhat flattened. They 
are covered by a strong apo- 
neurosis and contain tendinous 
intersections. They terminate 
toward the middle of the leg 
on a common tendon, which at 
first lies posterior to that of the 
superficial flexor, jjut, by a 
twist in both, comes to lie in 
front of the latter. The deep 
fascia blends with the tendon 
throughout its length, and the 
soleus muscle is inserted into 
its anterior edge.- A small 
bursa (Bursa tendinis m. gas- 
trocnemii) lies in front of the 
insertion on the tuber calcis, 
and a large bursa (calcanea 
subtendinea) is interposed be- 
tween the two tendons from 
the twist do\\iiward to the 
middle of the hock. The super- 
ficial digital flexor lies between 
the two heads and is adherent 
to the lateral one (Fig. 582). 
The term tendo calcaneus or 
tendo Achillis is a convenient 
designation for the aggregated 
tendons in the distal part of the 
leg which are attached to the 
tuber calcis. 
Relations. — Anteriorly, the stifle joint, the superficial digital flexor, popliteus, 
deep digital flexor, popliteal vessels, and tibial nerve; medially (above), the semi- 




Tibialis paste 
rior 



Joint capsule.. 

Medial malle- 
olus 



Flcro/- hallucis 



Tendon of gas 
trocneiiiius 



Superficial 
flexor tendon 



Tendon of long 
digital flexor 



0^1 

Tendon of deep flexor 



Fig. 296. — Muscles of Right Leg of Hor 



THE MUSCLES OF THE LEG AND FOOT 339 

tendinosus, semimembranosus, and adductor, (below) the fascia and skin; laterally 
(above), the biceps femoris and peroneal nerve, (below) the fascia and skin. The 
popliteal lymph lands lie on the upper part of the muscle. 

Blood-supply. — Popliteal artery. 

Nerve-supply. — Tibial nerve. 

2. Soleus (Fig. 296). — This muscle is very small in the horse. It lies along 
the lateral border of the gastrocnemius under the common deep fascia, on the prox- 
imal half of the lateral surface of the leg. 

Origin. — The head of the fibula. 

Insertion. — The tendon of the gastrocnemius, about the middle of the leg. 

Action. — To assist the gastrocnemius. 

Structure. — It is a thin, fleshy band, usually about an inch (ca. 2 to 3 cm.) in 
width, and terminates on a thin tendon which fuses with that of the gastrocnemius.^ 

Relations. — Superficially, the skin, fascia, and peroneal nerve; deeply, the 
lateral extensor and deep flexor. 

Blood-supply. — Posterior tibial artery. 

Nerve-supphj. — Til>ial nerve. 

3. Superficial digital flexor (M. flexor digitahs pedis superficialis) (Figs. 292, 
296, 297).- — The proximal part of this muscle lies between antl under cover of 
the two heads of the gastrocnemius. It consists almost entirely of a strong tendon, 
the belly being very little developed. 

Origin. — The supracondyloid fossa of the femur. 

Insertion. — (1) The tuber calcis; (2) the eminences on each side of the prox- 
imal extremity of the second phalanx, and the distal extremity of the first phalanx 
behind the collateral ligaments of the pastern joint. 

Action. — To flex the digit and extend the hock joint. On account of the ex- 
ceedingly small amount of muscular tissue the action is to be regarded chiefly as a 
mechanical effect which results from the action of other muscles on the stifle joint. 

Structure. — The origin is by means of a strong round tendon which is incom- 
pletely covered with fleshy fibers as far as the upper third of the leg. Here it is 
intimately attached to the gastrocnemius, especially to the lateral head. At the 
distal third of the tibia it winds around the medial surface of the gastrocnemius 
tendon, and then occupies a position behind the latter. At the point of the hock 
it widens out, forming a sort of cap over the tuber calcis, and detaches on either side 
a strong band which is inserted into the tuber calcis with the tarsal tendons of the 
biceps and semitendinosus. It then passes downward over the plantar ligament, 
becomes narrower, and is arranged distally as in the thoracic limb. A large syno- 
vial bursa (B. calcanea subtendinea) lies under the tendon from the distal fourth of 
tlic tibia to the middle of the tarsus. A subcutaneous bursa (B. calcanea subcu- 
tanea) is sometimes present on the wide part of the tendon at the point of the hock. 

Relations. — Posteriorly, the gastrocnemius, fascia, and skin; anteriorly, the 
femoro-patellar capsule, the popliteus, the deep flexor, and the popliteal vessels; 
medially, the tibial nerve. 

Blood-supply. — Posterior femoral artery. 

Nerve-supply. — Tiljial nerve. 

4. Deep digital flexor (M. flexor digitalis pedis profundus) (Figs. 292, 298).^ — 
The belly of this muscle lies on the posterior surface of the tibia, and is divisible 
into three heads, which, however, finally unite on a common tendon of insertion. 

Origin. — (1) The posterior edge of the lateral condyle of the tibia; (2) the 
border of the lateral condyle of the tibia, just behind the facet for the fibula; (3) 

' The soleus is sometimes included with the two heads of the gastrocnemius under the 
name triceps sur». 

' This is also known as the flexor pedis perforatus or superficial flexor of the phalanges. 
' This muscle is also commonly termed the flexor pedis perforans. 



340 



FASCIA AND MUSCLES OF THE HORSE 



the middle third of the posterior surface and the upper part of the lateral border of 
the tibia, the posterior border of the fibula, and the interosseous ligament. 

Insertion. — The semilunar crest and the adjacent surface of the cartilage of 
the third phalanx. 

Action. — To flex the digit and to extend the hock joint. 

Structure. — (1) The medial head is termed the long digital flexor (M. flexor 
digitalis longus s. flexor accessorius) ; it is easily isolated (Figs. 298, 584). It has a 
fusiform belly, which crosses the leg obliquely and lies in a groove formed by the 



Peroneus terlius 



Long digital 
extensor 



Superficial peroneal pyfr^H 

7ierve fJflJS 

. MSB 



Intermuscular. 

septum 

Lateral digital. 

extensor 




Tiljinlis anterior 



Cutaneous branch of 
saphenous nerve 



Lateral head of gastroc- 
nemius 



Recurrent tarsal vein 



'( Saphenous vessels 
and nerve 

Popliteus 



Flexor digitalis longus 



Tibial nerve 

Sii perficial digital flexor 

Medial head of gastroc- 
nemius 



Fig. 297.— Cross- 

The section is cut about the junction of the proximal and middle thirds of the region. 
2, deep peroneal nerve; 3, fibula; 4, posterior tibial vessels; 5, recurrent tibial vessels, 
saphenous nerve is shown medial to the popliteus, but is not marked. 



1, .\nterior tibial vessels; 
A cutaneous branch of the 



other heads and the popliteus. This terminates near the lower third of the tibia 
on a round tendon which descends in a canal in the medial ligament of the hock, 
and joins the common tendon about a third of the way down the metatarsus. In 
its course over the medial surface of the hock the tendon is provided with a syno- 
vial sheath which extends from the distal fourth of the tibia to the junction with 
the principal tendon. (2) The superficial head is the tibiaUs posterior (M. tibialis 
posterior) ; it is only partially separable from the deep heatl. It has a flattened 
belly, terminating near the distal third of the tibia on a flat tendon which soon fuses 



THE MUSCLES OF THE LEG AND FOOT 



341 



with the principal tendon. (3) The deep head, the flexor hallucis (M. flexor 
halhicis longus), is much the largest. It lies on the posterior surface of the tibia, 
from the popliteal line outward and downward. The belly contains much tendi- 
nous tissue, and terminates behind the distal enrl of the tibia on a strong round ttn- 



Shaft of femur- 
Medial head of gastrocnemius 
Medial condyle of femur 

^Aledial femoro-lihial ligament 

Medial meniscus 

Medial comhjle nf tibia 

Popliteus 
Flexor digitalis longus 



Flexor liaUucis 



Pouch of Joint capsule 



Deep flexor tendon . 
Tendon of flexor digitalis longui 




Lateral head of gaslrncncinius 
Superficial digital flexor 

Lateral condyle of femur 

Lateral femoro-titnal ligament 
Lateral comlyle of tibia 



Tibialis posterior 
Lateral digital extensor 

— Tendon of gastrocnemius 
Stipcrjicial flexor tendon 



Fig. 298. — Muscles of Right Leg of Horse, Deep Dissection; Posterior View. 

don. The latter receives the tendon of the tibialis posterior, descends in the tarsal 
groove, bound down by the strong plantar annular ligament (Ligamentum lacini- 
atum) and enveloped in a synovial sheath, receives the tendon of the metlial head 
below the hock, and, a little further down, the so-called check ligament (Caput 
tendinemu). The tendon is partly cartilaginous where it plays over the fibular 



342 



FASCIA AND MUSCLES OF THE HORSE 



tarsal bone. The tarsal sheath (Vagina tarsea) begins two to three inches (ca. 
5 to 7.5 cm.) above the level of the medial malleolus, and extends about one-fourth 
of the way down the metatarsus. The check ligament resembles that of the fore 
limb, except that it is longer and very much weaker; it may be alasent.' The re- 
mainder of the tendon is arranged like that of the thoracic limb. 



Tibialis 
anterior 




Tendon of 
gastrocnemius 

SuperfiHnl 
flexor tendon 

Calcanean 
bursa 

- Tuber calcis 

Subcutaneous 
thickening 



/:-— ' —Plantar liga- 
ji I ment 

T>eep flexor 

tendon 

== Tarsal sheath 



Tibial tarsal bone 



Superficial flexor 
tendon 
Annular ligament 



Joint capsule (tarso- 
metatarsal ligament) 

Fourth tarsal 
Perforating tarsal vein 

ck ligament 
Suspensory ligament 



Fin. 299. — Sagittal Section of Right Hock o 
The section passes through the middle of the groove of the trochlea of the tibial tarsal bone. 1. 2, Proximal ends 
of cavity of hock joint; 3, thick part of joint capsule over which deep flexor tendon plays; 4, fibular tarsal bone (sus- 
tentaculum). A large vein crosses the upper part of the joint capsule (in front of 1). 



Relations. — Anteriorly, the tibia and fibula, the popliteus, lateral extensor, 
tibialis anterior, and the tibial vessels; posteriorly, the gastrocnemius, superficial 
flexor, and the tibial nerve; laterally, the fascia, skin, and the soleus; medially, 
the fascia and skin. 

' This might well be called the tarsal (tendinous) head of the deep flexor. 



MUSCLES OF THE METATARSUS AND DIGIT 343 

Blood-supphj. — Posterior tibial artery. 

Nerve-siipply. — Tiiiial nerve. 

5. Popliteus (Fig. 298). — This thick, triangular muscle lies on the posterior 
surface of the tibia above the popliteal line. 

Origin. — A small depression on the lateral epicondyle of the femur, close to 
the articular surface and under the lateral ligament. 

Insertion. — A triangular area on the posterior surface of the til^ia, proximal and 
medial to the popliteal line; also the proximal half of the medial border and a 
narrow adjacent part of the medial surface of the tibia. 

Action. — To flex the femoro-tibial joint and to rotate the leg inward. 

Structure. — The strong tendon of origin lies at first under the lateral ligament, 
and curves backward and inward over the lateral contlyle of the tibia in contact 
with the lateral meniscus; it is invested by a reflection of the synovial membrane 
of the joint (Fig. 584). The tendon is succeeded by a thick triangular belly, the 
fibers of which are directed metlially in the proximal part, but incline downward 
below. 

Relations. — Superficially, the fascia and skin, semitendinosus, gastrocnemius, 
superficial flexor; deeply, the femoro-tibial joint, the tibia, the popliteal vessels 
and their divisions. The saphenous vessels and nerve lie along the medial border 
of the muscle, separated from it, however, by the deep fascia. 

Blood-supply. — Popliteal and posterior tibial arteries. 

Nerve-supply. — Tibial nerve. 

MUSCLES OF THE METATARSUS AND DIGIT 

Extensor digitalis brevis. — This small muscle lies in the angle of union of the 
tendons of the long and lateral extensors of the digit. (Fig. 293.) 

Origin. — The lateral tendon of the peroneus tertius, the middle annular liga- 
ment, and the lateral ligament of the hock. 

Insertion. — The tendon of the long extensor. 

Action. — To assist the long extensor. 

Structure. — It is principally fleshy, having a superficial origin from the annular 
ligament, and a deep one (by a thin tendon) from the lateral tendon of the peroneus 
tertius. The insertion is by a thin tendon. 

Relations. — Superficially, the skin and fascia and the tendons of the long and 
lateral extensors; deeply, the tarsal joint capsule, the great metatarsal artery, and 
the deep peroneal nerve. 

Blood-supply. — Great metatarsal artery. 

Nerve-supply. — Deep peroneal nerve. 

The interossei and lumbricales are arranged like those of the thoracic limb, 
the only noticeable difference being the greater development of the lumbricales in 
the pelvic limb. 



THE MUSCLES OF THE OX 
Muscles of the Face 

The cutaneus is much more developed than in the horse, presenting as a special 
feature the extensive frontalis muscle, which covers the frontal and nasal regions. 

The orbicularis oris does not form a complete ring, the defect being in the 
middle of the upper lip. 

The levator nasolabialis is extensive, thin, and not very distinct from the 



344 



THE MUSCLES OF THE OX 



frontalis; it divides into two layers, between which the levator labii superioris 
proprius and the lateral dilator of the nostril pass. The superficial layer ends in 
the nostril and upper lip, the deep layer on the accessory (lateral) nasal cartilages 
and on the nasal process of the premaxilla. 

The levator labii superioris proprius arises on and before the facial tuberosity 
and terminates by several tendons in the muzzle. It passes between the two layers 
of the preceding muscle, blending in part with the deep layer. 

The zygomaticus is much stronger than in the horse. It arises on the masse- 
teric fascia, and ends chiefly in the upper lip. 




Fig. .'300.— Muscles of Head c 
a, Levator labii superioris proprius; b, levator nasolabialis; c 
cephalicus; e, omo-layoideus; /, dilatator naris lateralis; g, zygomati 
inferioris; k, orbicularis oris; m, masseter; n, parotido-auricularis; 
superficialis inferior; o", scutulo-auricularis superfieialis superior; 
p, p', scutularis; u, frontalis; w, mylo-hyoideus; 1, concha;- £, 3, posterior and anterior borders of 1; 8, scutiform 
cartilage; 5, zygomatic arch; 3S\ ramus of mandible; 37, external maxillary vein; 38, jugular vein; 39, facial vein; 
44, parotid gland; 50, 51', submaxillary gland; dotted line at oO indicates position of atlantal lymph gland, and the 
parotid lymph gland lies partly under parotid gland, just in front of 44i ^8, medial palpebral ligament; 59, laryngeal 
prominence. (After Ellenberger-Baum, Anat. fiir Kiinatler.J 



Ox; Lateral View. 
c, trapezius; c', brachiocephalicus; d, d' , sterno- 
; q' , malaris; h, buccinator: i, depressor labii 
zygomatico-auricularis and scutulo-auricularis 
, scutulo-auricularis superficialis 



The depressor labii superioris arises just in front of the facial tuberosity, and 
divides usually into two Ijranchcs, which terminate in a number of tendons that 
form a network in the muzzle and upper lip. 

The incisivus inferior is a small, rounded muscle, which arises on the body of 
the mandible below the second and third incisors, and ends in the lower lip, blending 
with the orbicularis. 

The depressor labii inferioris is thin, and does not extend as far backward 
as in the horse; only the anterior end is distinct from the buccinator. 



MUSCLES OF THE FACE 345 

The buccinator shows no marked variation, liut its superficial layer is well 
developed. 

The dilatator naris lateralis arises in front of the facial tuberosity, passes for- 
ward between the branches of the levator nasolabialis, and terminates in the lat- 
eral wing of the nostril. 

The dilatator naris apicalis is situated in the muzzle and joins its fellow at a 
metlian raphe. It arises on the border and upper surface of the body of the pre- 




FiG. 301. — MuscLE.s OF Head of Ox; Dorsal View. 
a, a'. Levator labii superioria proprius; b, levator nasolabialis; /, dilatator naris lateralis; o', malaris; o, zygo- 
matico-auricularis and scutulo-auricnlaris superficialis inferior; o", scutulo-auricularis superficialis superior; o'", 
scutulo-auricularis superficialis accessorius; p, scutularig; u, frontalis; 2, orbicularis oculi; i, concave surface of 
concha; 3, 2, anterior and posterior borders of concha; S, scutiform cartilage; 34, parietal cartilage; 39, facial vein; 
IfS, muzzle; 58, medial palpebral ligament. (After EUenberger-Baum, Anat. fiir Kiinstler.) 

maxilla, the fibers passing obliquely upwartl and outward to the medial wing of the 
nostril. 

The dorsal part of the lateralis nasi arises frona the alar cartilage of the nostril 
and ends in the medial wing of the nostril. 

The ventral part of the lateralis nasi consists of two layers which arise on the 
nasal process of the premaxilla and the lateral nasal cartilage and end in the lateral 
wing of the nostril. 

The orbicularis oculi is well developed. 

The corrugator supercilii is not present as a separate muscle, its place and 
function being taken by the frontalis. 

The malaris is broad, and spreads out below on the fascia over the buccinator 
and masseter; it is divided into two parts. 



346 



THE MUSCLES OF THE OX 



MANDIBULAR MUSCLES 

The masseter is not so large as in the horse; a considerable part of it arises 
on the facial tuberosity and is directed obliquely backward and downward, so that 
it would draw the lower jaw forward as well as upward. 

The temporalis conforms to the temporal fossa, and is therefore longer and 
entirely lateral in position. 

The pterygoideus medialis arises from the lateral surface of the perpendicular 
part of the palatine bone aiad from the pterygoid jDrocess. Since the origin is nearer 




Fig. 302. — Muscles of Head of O.x; Ventbal View. 
d, d', Sterno-cephalicus; e. omo-hyoideus; g, zygomaticu3: A, buccinator; i, depressor I.abii inferioris; t. orbicularis 
oris; m, masseter: n. parotido-auricularis; o', zygomatico-auricularia; w, mylo-hyoideus; I, concha, convex surface; 
£, anterior border of concha: 30', angle of jaw; 30, facial vein; 44, parotid gland; 4o, lower lip; 4S, angle of mouth; 
SO, 50', mandibular gland; 59, larynx; X. w-ing of atlas. (After Ellenberger-Baum, Anat. fur Kiinstler.) 



the median plane and the insertion further from it than in the horse, the muscle pro- 
duces more marked lateral movement of the mandible. 

The pterygoideus lateralis is flattened transversely, wide and thin in front, 
narrower and thicker behintl. It has an extensive origin in the pterygo-palatine 
fossa, where it is pai'tly covered t:)y the pterygoideus medialis. 

The occipito-mandibularis is absent. 

The digastricus has a tendinous origin on the paramastoid process of the 
occipital bone ; its l)ellies are short and thick. The intermediate tendon is round and 
thick ; it does not perforate the stylo-hyoideus. The anterior bellies are connected 
beneath the root of the tongue by a layer of transverse muscle-fibers termed the 
transversus mandibulae. 



MUSCLES OF THE NECK VENTRAL GROUP LATERAL GROUP 347 



HYOID MUSCLES 

The mylo-hyoideus is thicker and more extensive than in the horse. 

The stylo-hyoideus has a long, slender tendon of origin which is attached to the 
muf?cular angle of the great cornu of the hyoid bone. The insertion is fleshy and 
is not perforated Ijy the digastricus. 

The genio-hyoideus is much more developed than in the horse. 

The kerato-hyoideus has an additional attachment on the middle cornu of the 
hyoid bone. 

The hyoideus transversus is bifid. 

The stemo-thyro-hyoideus has no intermediate tendon and is thicker. 

The omo-hyoideus arises as a thin band from the fascia over the third and 
fourth cervical vertebrae. It blends here with the rectus capitis ventralis major. 

The occipito-hyoideus is thick. Its large lateral part entirely covers the para- 
mastoid process (from which it arises) and is inserted into the muscular angle of 
the great cornu. The smaller medial part arises from the ventral end of the para- 
mastoid process and ends on the medial face of the great cornu below the dorsal 
end. 



Muscles of the Neck 

A. ventral group 

The cervical cutaneus is absent. 

The stemo-cephalicus consists of two muscles. They arise from the manu- 
brium sterni and first rib. The superficial muscle is the stemo-mandibularis ; it 
is insertetl on the anterior border of the masseter, the ramus of the mandible, and 
the buccal fascia. The deep muscle is the stemo-mastoideus ; it crosses under the 
preceding and ends on the mastoid processes, the mandiljle, and, in common with 
the rectus capitis ventralis major, on the liasilar jiart of the occipital bone. 

There are two scaleni. The scalenus ventralis (s. prima costse) arises from 
the transverse processes of the third to the seventh cervical vertebree and ends on 
the first rib. It is traversed Isy the roots of the brachial plexus, which divide it 
into bundles. The emerging brachial artery separates a narrow part below from 
the main mass. The scalenus dorsalis (s. supracostalis) arises usually on the 
transverse processes of the fourth, fifth, and sixth cervical vertebrae. Its •ndde 
posterior part lies on the ventral part of the serratus thoracis; it is attached to the 
third rib and to the serratus thoracis. 

The rectus capitis ventralis major arises on the third to the sixth cervical 
transverse processes, and Ijlends at its insertion with the stemo-mastoideus and 
the cleido-mastoideus. 

The rectus capitis ventralis minor is larger than in the horse. 

The rectus capitis lateralis and longus colli resemble those of the horse. 

The intertransversales are large. From the sixth cervical vertebra forward 
they form a muscular mass (M. intertransversarius longus) which is inserted into 
the wing of the atlas. 

B. LATERAL GROUP 

The splenius is thin. It arises directly from the first three or four thoracic 
spines, and ends by a thin tendon on the occipital bone, the wing of the atlas, 
and the transverse process of the axis, blending with the brachiocephalicus, longis- 
simus capitis, and omo-transversarius. The remaining muscles present no very 
marked differential features. 



348 



THE MUSCLES OF THE OX 




« I a 1 i 
g "3 'I T- <! 

S -J 1 ". a 



° a I s s 



f I 



MUSCLES OF THK THORAX — ABDOMINAL MUSCLES 349 



Muscles of the Thorax 

The levatores costarum mimber ten or eleven pairs. 

The external intercostal muscles are thick; they terminate at the costo- 
chondral junctions. The internal intercostals are specially thick in relation to the 
cartilages of the sternal ribs; here tlicre exist bundles (comparable to the levatores 
costarum) which are attached in front to the sternum, behind to a costal cartilage. 
The interosseous j^art thins toward the upper end of the spaces. 

The diaphragm presents several important differential features. Its slope is 
much steeper and its width is greater than in the horse. The upper limit of the 
costal attachment extends almost in a straight line from the last rib about a hand- 
lireadth above its middle to the junction of the eighth rib with its cartilage, and 
along the latter to the sternum. The midline slopes from the twelfth thoracic 
vertebra obliquely as far as the foramen veniE cavse, beyond which it is almost 
vertical. The right crus divides into two branches, which circumscribe the hiatus 
cesophageus, unite below, and then s]3read out in the tendinous center. The left 
crus is small. The hiatus cesophageus is situated about four to five inches (10 to 
12 cm.) below the eighth thoracic vertebra, a little to the left of the median plane. 
The foramen vense cavse is a little more ventral and almost in the median jilane.^ 

In the sheep the costal attachment differs from that of the ox. The ujiper 
limit of the attachment extends in a gentle curve (convex ventrally) from the 
last rib about the junction of its middle and ventral thirds to the ventral end of 
the ninth rib. 



Muscles of the Back and Loins 

The serratus dorsalis anterior is very thin. It is inserted on the fifth to the 
eighth ribs when fully (levelo])e(l, but it may be reduced to two or three digitations 
or may be aljsent. The serratus dorsalis posterior is inserteil on the last three or 
four ribs. 

The longissimus costarum has a distinct lumbar portion which is attached to 
the lumbar transverse processes and the tuber coxae. 

The longissimus dorsi resembles that of the horse, but it is more fleshy anter- 
iorly, and the spinalis dorsi is clearly distinguishable from the common mass. In 
the lumbar region the tendons meet across the summits of the spines. 

Intertransversales are present in the back, and interspinales in the back and 
loins. 

Muscles of the Tail 

These resemble in general those of the horse ; the coccygeus is, however, much 
more developed. 

Abdominal Muscles 

The obliquus abdominis extemus is somewhat thinner and has a less extensive 
origin, which begins at the lower part of the fifth intercostal space and ends on 
the last rib above its middle. The direction of the fibers in the flank is horizontal, 
and they do not reach to the tuber coxce, nor as high as the lumbar transverse proc- 
esses. (In this region the abdominal tunic has a strong attachment to the point 

' The sternal part is clearly separable from the costal part. The costal attachment is much 
higher posteriorly than in the horse, thus diminishing the capacity of the thorax in comparison 
with that animal. The last digitation is thus some seven or eight inches (ca. 18 to 20 cm.) above the 
corresponding digitation of the transversus abdominis. There are small intermediate digitations 
at the last two intercostal spaces. 



350 



THE MUSCLES OF THE OX 



of the hip and the lumbo-dorsal fascia.) The aponeurosis is intimately united with 
the abdominal tunic, and does not detach a femoral lamina. 

The obliquus abdominis intemus is more developed and has an additional 
origin from the lumbo-dorsal fascia. The aponeurosis blends with that of the 
external ol)lique near the linea alba, and detaches a layer which assists in the for- 
mation of the internal sheath of the rectus. 

The rectus abdominis arises on the lateral border of the sternum as far for- 
ward as the third costal cartilage. The two muscles are separated, except near 
the pelvis, by an interval varying from two to four inches (ca. 5 to 10 cm.), so that 
this part- of the abdominal wall is entirely fibrous. (The umbilicus is in a trans- 
verse plane through the third lumbar vertebra.) There are five tendinous inscrip- 
tions, at the third of which is a foramen for the passage of the subcutaneous ab- 
dominal vein. The prepubic tendon has, in addition to lateral branches inserted 




Fig. 304. — Deeper Muscles of Neck, Shoulder, and Thorax of Ox. 
c', Cleido-occipitalis muscle; d, sterno-cephalicus; /, /'. long and lateral heads of triceps; g, superficial pectoral 
muscle; h, h\ deep pectoral muscle; i, i', serratus ventralis; ^•, latissimus dorsi; /, obliquus abdominis externus; u', 
biceps brachii; w, spienius; z, rhomboideus; y, longissimus capitis et atlantis; z, supraspinatus; z' , infraspinatus; 
z", tendon of insertion of 2' ; i', cartilage of scapula; ;5, tuberosity of spine of scapula; S, acromion; 5, lateral tuberosity 
of humerus; ^, deltoid tuberosity; 5, olecranon; ;?t», transverse processes of cervical vertebrse; ;?7, posterior auricular 
muscles: X, wing of atlas. (After Ellenberger-Baum, Anat. fUr Kiinstler.) 



into the ilio-pectineal eminences, a strong attachment to the median common ten- 
don of the adductors of the thigh, so that the abdominal wall is strongly retracted 
and almost vertical at its junction with the pubis. 

The transversus abdominis presents no striking differential features. The 
transversalis fascia is strong and tlistinct except over the diaphragm. 



Muscles of the Thoracic Limb 
i. muscles of the shoulder girdle 

The trapezius is much thicker and broader than in the horse, and is undivided. 
It arises on the ligamentum nuchse and supraspinous ligament, from the atlas to 
the twelfth thoracic vertebra. 



MUSCLES OF THE SHOULDER — MUSCLES OF THE ARM 351 

The omo-transversarius arises on the wing of the atlas, and, inconstantly, 
the transverse process of the axis, anil is inserted into the scapular spine and fascia. 

The rhomboideus is clearly divided into cervical and thoracic parts, the latter 
extending further than in the horse. 

The latissimus dorsi has a broad tendon of origin, which blends with the 
lumbo-dorsal fascia; it is also attached to the eleventh and twelfth ribs and the 
fascia over the external intercostal and oblique abdominal muscles. The anterior 
fibers end on the tendon of the teres major, the middle part on an aponeurosis on 
the medial surface of the caput longum, and the posterior part on a tendon which is 
common to this muscle anfl the deep pectoral. 

The brachiocephalicus has two distinct parts. The dorsal division, the cleido- 
occipitalis, arises on the occipital bone and the ligamentum nuchiE. The ventral 
part, the cleido-mastoideus, is smaller and arises by a round tendon on the mastoid 
process and the rectus cajjitis ventralis major, and by a thin tendon on the mandible. 

The superficial pectoral nmscle is thinner than in the horse and its two parts 
are not so clearly separable. 

The deep pectoral muscle arises as far forward as the second rib and is un- 
divided. However, the scapular portion may be considered to be represented by a 
small branch which arises from the anterior part of the sternum and the first rib 
and passes upward to end on the deep face of the brachiocephalicus in front of the 
shoulder joint.' A tendon detached from the dorsal edge blends with the latissimus 
dorsi and coraco-brachialis. 

The serratus ventralis is clearly divided into cervical and thoracic parts. 
The former is large and extends from the third (or second) cervical vertebra to 
the fifth rill, being overlapped behind by the thoracic part. It is inserted on a 
large triangular area on the antero-superior part of the costal surface of the scapula. 
The thoracic part is relatively thin and is covered by a very strong aponeurosis; 
it is attached to the fourth to the ninth ribs by six digitations, and is inserted by a 
flat tendon which insinuates itself between the middle and posterior parts of the 
subscapularis to end on a rough line — equivalent to the posterior serratus area of 
the horse — and also on the cartilage of the scapula in continuity with this line. 



n. MUSCLES OF THE SHOULDER 

The deltoid is clearly divided into acromial and scapular parts. The former 
(Pars acromialis) arises on the acromion, the latter (Pars scapularis) on the posterior 
border of the scapula and the aponeurotic covering of the infraspinatus. The 
scapular part of the muscle is largelj- inserted into the fascia covering the triceps. 

The supraspinatus, infraspinatus, and teres minor do not differ materially 
from those of the horse. 

The subscapularis consists of three parts with a common tendon of insertion. 

The teres major and coraco-brachialis resemble those of the horse. 

The capsularis is absent. 

m. MUSCLES OF THE ARM 
The biceps is smaller and less tendinous, and is situated more medially than 
in the horse. The tendon of origin is flat, and is bound down in the intertuberal or 
bicipital groove by a fibrous band. The tendon to the extensor carpi radialis is 
less distinct than in the horse. (In the sheep the tendon of origin is round and is 
invested by the synovial membrane of the shoulder joint. The tendon of inser- 
tion bifurcates; one branch ends on the tuberosity of the radius, the other on the 
ulna.) 

' According to Meckel and Lesbre, this is the homologue of the subclavius of man. 



3o2 



THE MUSCLES OP" THE OX 



The medial head of the triceps is more developed than in the horse, and ex- 
tends up to the neck of the humerus. 

The tensor fasciae antibrachii is a slendei- muscle which lies along the posterior 

border of the triceps and is not 
connected with the latissimus 
dorsi. 




Fig. 30.5. — Muscles of Antibra- 
CHIU.\I AND Mands OF Ox; 
Lateral View. 
a, Extensor carpi radialia: 6, 
extensor digiti tertii; c, extensor 
digitalis communis; d, extensor 
digiti quarti; e, ulnaris lateralis; 
/. extensor carpi obliquus; /', ul- 
nar head of flexor carpi ulnaris; o, 
brachialis; h, interosseus medius 
or suspensory ligament; i, flexor 
tendons; i', branch of h, to super- 
ficial fiexor tendon; 8, olecranon; 
11, accessory carpal bone; 13', 
metacarpal tuberosity. (After 
Ellenberger-Baum, Anat. fiir 
Kiinstler.) 




Fig. 306. — Mu.scles of Anti- 

BRACHIUM AND MaNUS OF 

Ox; Medial View. 

a, Extensor carpi radialis; 
b, tendon of extensor digiti ter- 
tii; /, tendon of extensor carpi 
obliquus; p, brachialis; A, inter- 
osseus medius or suspensory 
ligament: i, flexor tendons; i', 
branch of /(,■ k, flexor carpi radi- 
alis; /, flexor carpi ulnaris; m, 
superficial digital flexor. (After 
Ellenberger-Baum, Anat. fiir 
Kiinstler.) 



The extensor carpi obliquus resembles that of 



IV. MUSCLES OF THE FOREARM 
AND MANUS 

A. Extensor Division 
The extensor carpi radialis 

is like that of the horse. There 
is sometimes a small muscle 
lying along its medial border, 
which may represent the exten-' 
sores pollicis. 

There are three digital ex- 
tensors: 1 . The common digital 
extensor (M. extensor digitalis 
communis) arises by two heads 
from the lateral epicondyle of 
the humerus and from the ulna. 
The heads fuse about the middle 
of the forearm, and terminate 
soon on a tendon which passes 
over the carpus and metacarpus, 
gradually inclining forward. At 
the fetlock joint it divides into 
two branches, each of which is 
inserted into the extensor pro- 
cess of the corresponding third 
phalanx. 2. The medial digital 
extensor (M. extensor digiti ter- 
tii proprius) arises on the lateral 
epicondyle, and is inserted by 
two branches into the second 
and third phalanges of the me- 
dial digit. The tendon receives 
two reinforcing slips from the 
suspensory ligament. 3. The 
lateral digital extensor (M. 
extensor digitalis lateralis s. 
digiti quarti proprius) is stronger 
than that of the horse; it arises 
from the lateral ligament of the 
elbow joint, the lateral tuber- 
osity of the radius, and the 
ulna. The tendon terminates 
like that of the preceding 
muscle. 1 
the horse. 



' It may be remarked that, in addition to the extension action, tlie common extensor approxi- 
mates the digits, while the others tend to abduct them. 



MUSCLES OF THE FOREARM AND MANUS 



353 



The extensor tendons are bound down at the carpus by an annular ligament, 
and are furnished with synovial sheaths (Figs. 307, 308). 

B. Flexor Division 

The three flexors of the carpus are like those of the horse, but the long tendon 
of the lateral flexor ends on the large metacarpal bone, not on the small one. The 
tendon of the medial flexor naturally ends on the medial part of the large meta- 
carpal bone. 

The superficial digital flexor is somewhat lilended at its origin with the miildle 
flexor of the carpus. It divides into two bellies, superficial and deep, terminating 





Fig. .107. — Right Cahpus of Ox with Bohs.e and 

Sy.vovial Sheaths Injected; Later.\l View. 

1, Extensor carpi radialis, with synovial sheath (/') anti bi 
sheath {2') and bursa {2") ; 3, extensor digiti tertii proprius; J, 
sheath of 3 and 4.' 5, extensor digiti quarti proprius, with synovial sheath (50 ; 6, 6', ulnaris lateralis, with bursa 
{6")\ 7, flexor carpi radialis, with synovial sheath; 8, deep digital flexor, with synovial sheath {8'); 9, flexor carpi 
ulnaris; 10, superficial digital flexor, with synovial sheath, 10'; a, radius; b, carpus; c, metacarpus; d, cut edge of 
annular ligament. (After Schmidtchen.) 



''iG. 30S. — Right Carpus of Ox with Burs.e and 

Synovial Sheaths Injected; Medial View. 
rsa(/"): .^.extensor carpi obliquus, with synovial 
extensor digitalis communis; 5', common synovial 



on tendons at the distal part of the forearm. The superficial tentlon passes over 
the posterior annular ligament (Lig. carpi transversum), perforates the metacarpal 
fascia, and joins the deep tendon about the middle of the metacarpus. The deep 
belly is connected with the deep flexor by a strong fibrous band. Its tendon passes 
under the annular ligament of the carpus in a groove on the deep flexor, from which 
it receives fibers. The conjoineil tendon soon bifurcates, each branch receiving a 
reinforcing band from the suspensory ligament, and forming near the fetlock a 
ring for the corresponding branch of the deep flexor tendon. Passing under two 
digital annular ligaments, they are inserted into the volar surfaces of the second 
phalanges by three slips. 
23 



354 THE MUSCLES OF THE OX 

The deep digital flexor has the same heads as in the horse, the humeral head, 
as before mentioned, being connected with the deep part of the superficial flexor. 
The tendon, which is not reinforced by a check ligament as in the horse, divides 
near the distal end of the metacarpus into two branches which are inserted into the 
volar surfaces of the third phalanges. 

The synovial sheaths at the carpus present the following special features: 
One is found in connection with the tendon of the superficial part of the superficial 
flexor of the digits. There is a common sheath for the tendons of the common ex- 
tensor and the medial extensor. 

Bursas may occur under the tendons of the proper extensors of the digits at the 
fetlock; they are constant only in old animals (Schmidtchen). The branches of 
the tendon of the common extensor are provided with synovial sheaths from their 
origin to the middle of the second phalanx. There are two digital synovial sheaths 
for the flexor tendons; they may communicate at their upper part, and they ex- 
tend from the distal third of the metacarpus nearly to the distal sesamoids. Bursae 
occur between the latter and the branches of the deep flexor tendon. 

A feeble pronator teres is present on the medial surface of the elbow along the 
medial collateral ligament. 

The fascia on the volar face of the metacarpus and digit is very thick. It is 
continuous above with the ligamentum carpi transversum, and is attached on either 
side to the metacarpal bone. At the fetlock it forms the fibrous basis for the small 
claws, and below this it detaches two strong bands which diverge to be inserted into 
the second and third phalanges, blending with the collateral ligaments. 

The liunbricales are absent, unless we regard as such the muscular bundles 
which arise on the deep flexor and are inserted into the superficial flexor tendon at 
the carpus. 

The interosseus medius, or suspensory ligament, is somewhat more muscular 
than in the horse; indeed, in the young subject it may be almost entirely fleshy. 
Its arrangement is somewhat complex. Single at its origin, it detaches about the 
middle of the metacarpus a band which joins the tendon of the superficial flexor 
and concurs near the fetlock in the formation of the ring for the deep flexor tendon.' 
A little lower down it divides into three and then into five branches. The abaxial 
branches (two pairs) are attached to the corresponding sesamoids and tendons of 
the proper extensors, while the middle branch passes through the sulcus at the distal 
end of the metacarpus and bifurcates, each division fusing with the tendon of the 
corresponding proper extensor. 



The Muscles of the Pelvic Limb 
i. the sublumbar muscles 

The psoas minor begins at the disc between the twelfth and thirteenth thoracic 
vertebrae. 

The psoas major has a fleshy origin on the posterior border of the last rib, and 
a thin tendon attached to the twelfth rib ; it is relatively narrower than in the horse 
and does not entirely cover the quadratus lumborum. 

The iliacus begins under the body of the sixth lumbar verteljra, anil is more 
closely united with the psoas major than in the horse. 

The quadratus limiborum extends as far forward as the body of the tenth or 
eleventh thoracic verteljra. It is wider than in the horse and extends beyond the 
lateral border of the psoas major. 

' Lesbre regards this band as the subcarpal check Hgament, which on this basis is blended 
with the suspensory ligament above. 



LATERAL MUSCLES OF THE HIP AND THIGH 



355 



n. LATERAL MUSCLES OF THE HIP AND THIGH (Figs. 303, 309) 

The tensor fasciae latae is large, and the flesliy part extends further down than 
in the horse. 

Tlie gluteus superficialis is not present as such; apparently its anterior part 
has fused with the tensor fascise latae and its posterior part with the biceps femoris. 

The gluteus medius is small, the lumbar part being insignificant and extend- 
ing forward only to the fourth lumbar vertebra. Its deep portion (gluteus ac- 
ccssorius) is easily separable, and its strong tendon is inserted into the femur below 
the trochanter major, under cover of the upper 
part of the vastus lateralis. 

The gluteus profundus is thin, but exten- 
sive, arising as far forward as the tuber coxae, 
and from the lower part of the sacro-sciatic liga- 
ment. The fibers converge on a broad, strong 
tendon which passes under the upper part of 
the vastus lateralis, and is inserted into a tu- 
bercle a short distance below the great tro- 
chanter. 

The biceps femoris is very wide at its 
upper part, having apparently absorbed the 
posterior part of the superficial gluteus. It 
arises from the sacral spines, sacro-sciatic liga- 
ment, and tuber ischii. It is divided by a 
fibro-elastic septum in the thigh into two por- 
tions, which end in front and below on a wide 
aponeurosis; the latter is attached to the patella 
and its lateral ligament and blends with the fas- 
cia cruris and fascia lata. There is no femora! 
attachment. A large bursa occurs between the 
muscle and the great trochanter in the adult. 
The part of the tendon which fuses with the 
lateral patellar ligament presents a fibro-cartil- 
aginous thickening, and an extensive bursa is 
interposed between it and the lateral condyle 
of the femur. 




A layer derived from the fascia lata is intimately 
adlierent to tiie deep face of tfie muscle, and cases occur 
in whicli tiiis fascia is ruptured Ijy the trochanter major, 
thus fixing the muscle behind the trochanter. 



Fig. 309. — GLtrxEAi., Femoral, and Crttral 
Regions of Ox, .\fter Removal of 
Superficial Muscles. 
p, Gluteus medius: r, semitendinosus; w, 
coccygeus: SS, vastus lateralis; 2S', rectus fe- 
moris; 29, semimembranosus; 30, gastrocnemi- 
us; 31, sacro-sciatic ligament; 16, tuber coxae; 
17, tuber ischii; 19, trochanter major; 20, patel- 
la; £1', lateral condyle of tibia. (After EUen- 
berger-Baum, Anat. fiir Kiinstler.) 



The semitendinosus and semimembrano- 
sus arise on the ischium only. The latter is very large and has a branch attached 
to the medial condyle of the tibia. 



m. ANTERIOR MUSCLES OF THE THIGH 

The quadriceps femoris resembles that of the horse; but the vasti (and es- 
pecially the medial one) are not so thick, and the vastus intermedins is more clearly 
separable, and consists of two parts. Bursse occur under the insertions of the 
medial and lateral vasti, and often under the end of the rectus in the adult. 

The articularis genu is a small muscle which lies under the distal part of the 
vastus intermedins, and is partlj' inserted on the suprapatellar cul-de-sac of the 
synovial membrane of the stifle joint. 

The capsularis is absent. 



356 THE MUSCLES OF THE OX 

IV. MEDIAL MUSCXES OF THE THIGH 

The sartorius arises by two heads, one from the tendon of the psoas minor 
and the ihac fascia, the other from the shaft of the ihum. The femoral vessels 
pass between them. 

The gracilis is more extensively united with its fellow at its origin than in the 
horse. 

The pectineus is large, and arises by a single head from the pubis and prepubic 
tendon. It divides into two branches, one of which is inserted as in the horse, 
while the other extends to the medial epicondyle of the femur. 

The adductor resembles that of the horse, but does not reach to the medial 
condyle of the femvu'. 

The quadratus femoris and obturator extemus resemble those of the horse. 

The obturator intemus has no iliac head, and its tendon passes through the 
obturator foramen. 

The gemellus is large; some of its fibers of origin join the oljturator internus- 
through the lesser sciatic foramen. 

V. MUSCLES OF THE LEG AND FOOT 

A. DORSO-LATERAL GrOUP 

There are four digital extensors, two of which are fused with each other and 
the peroneus tertius in the u]5por third of the leg. 

1. The long digital extensor (M. extensor digitalis longus) arises in common 
with the peroneus tertius and the medial extensor in the extensor fossa of the femur, 
and separates from the other muscles near the middle of the leg. At the distal 
end of the tibia it terminates on a tendon which passes down over the hock (bound 
down l^y two annular ligaments) and ends like that of the thoracic limb. 

2. The medial digital extensor (M. extensor digiti tertii proprius) arises in com- 
mon with the preceding muscle and the peroneus tertius, and is covered by them 
to the distal third of the tibia. Its tendon passes under the annular ligaments 
between those of its cogeners and ends on the second phalanx of the medial digit. 

3. The lateral digital extensor (M. extensor digitalis lateralis s. digiti quarti 
proprius)' arises on the lateral ligament of the stifle joint and the lateral condyle of 
the tibia. Its tendon passes over the lateral surface of the hock, and terminates 
on the dorsal surface of the second phalanx of the lateral digit. 

The reinforcing bands from the suspensory ligament are arranged as in the 
forelimb. 

4. The short digital extensor (M. extensor digitalis brevis) resembles that of 
the horse; it is inserted on the tendon of the long extensor. 

The peroneus longus (not present in the horse) is situated in front of the lateral 
extensor. It arises on the lateral condyle of the tibia and the fibrous band which 
represents the shaft of the fibula. Its tendon passes downward and backward 
over the lateral surface of the hock, crosses over that of the lateral extensor and 
under the lateral ligament, and ends on the first tarsal bone and the proximal end 
of the large metatarsal bone. It is enveloped by a synovial sheath. It would ap- 
parently' act as an inward rotator at the hock joint. 

The peroneus tertius is a well-developed muscle which arises on the common, 
tendon with the long and medial extensors. It has a large, fusiform belly, which 
is superficially situated on the front of the leg. Close to the tarsus it ends on a 
flat tendon, which is perforated by that of the tibialis anterior, and ends on the 
proximal end of the large metatarsal and second and third (fused) tarsal bones. 

1 Lesbre regards this muscle as the homologue of the peroneus brevis of man and other 
pentad actyls. 



MUSCLES OF THE LEG AND FOOT 



357 



The tibialis anterior is smaller, and arises by two heads. The larger head 
springs from the lateral surface of the tuberosity and crest of the tibia; the lateral, 
smaller one (M. extensor hallueis longus), arises from the upper part of the lateral 



iw'^i 




Fig. 310.— Muscles of Left Leg and Foot op Ox; 
Antehior View. 
a, Peroneus tertius; a', tibialis anterior; b, long 
digital extensor; 6', extensor digiti tertii; c, peroneus 
loHgiis; d, extensor digiti quarti; i, i, annular liga- 
ments; k, lateral ligament of hoclc joint; /, branch of 
suspensory ligament; 20, patella; 21', lateral condyle 
of tibia; S8, tuberosity of tibia. (After Ellenberger- 
Baum, Anat. fur Kiinstler.) 



Fig. 311. — Muscles of Left Leg and Foot of Ox; 
Lateral View. 
a, Peroneus tertius; a\ tibialis anterior; b, long 
digital extensor; b', tendon of b; c, peroneus longus; 
d, extensor digiti quarti; e, deep digital flexor; e', ten- 
don of e; e", branch of interosseus medius or suspen- 
sory ligament; /, gastrocnemius (the soleus lies just in 
front of /) ; /', tendon of superficial digital flexor; h, in- 
terosseus medius or suspensory ligament; i, i, annular 
ligaments; 30, patella; 21', lateral condyle of tibia; 
2S, tuberosity of tibia. (After Ellenberger-Baum, Anat. 
fiir Kiinstler.) 



border of the tibia and the fibrous band whieh replaces the shaft of the fibula. The 
tendon perforates that of the preceding muscle, passes to the medial face of the 
h©ck, and ends on the metatarsal and second and third tarsal l.)ones. 



358 



THE MUSCLES OF THE OX 




1 ^ 


Ti 








- -P 





















S 


1 i* 
3 T3 


J2 


Ch 






CC 








































1 - 




1 


g 




1 

3 


"o ^ 




THE MUSCLES OF THE PIG — MUSCLES OF THE FACE 359 

B. Plantar Group 

The gastrocnemius and soleus resemble those of the horse. 

The superficial flexor is more fleshy than in the horse. Its tendon termi- 
nates as in the forelimb. 

The deep flexor in general resembles that of the horse, but the tibialis poste- 
rior (superficial head) is distinct and is larger than in the horse. The flexor digitalis 
longus (medial head) is also larger, while the flexor hallucis longus (deep head) is 
smaller. The common tendon ends like that on the forelimb. 

The synovial sheaths and bursse of the muscles of the leg and foot are shown in 
Figs. 312-315. 



THE MUSCLES OF THE PIG 
Muscles of the Face 

The facial cutaneus is pale, thin, and tlifficult to separate from the skin. 

The orbicularis oris is little developed. 

The levator nasolabialis is thin and pale, and is undivided. 

The levator labii superioris proprius may well be termed the levator rostri. 
It has a large pennate bell^', which arises in the preorbital fossa. The tendon ends 
on the anterior part of the os rostri. A muscular slip connects it with the premaxilla. 

The zygomaticus arises on the fascia over the masseter and ends at the angle 
of the mouth. 

The depressor labii inferioris separates from the buccinator only near the 
angle of the mouth; it entls l)y a number of tendinous branches in the lower lip. 

The dilatator naris lateralis is well developed. It arises under the levator 
rostri and ends by a tendinous network around the nostril. 

The transversus nasi is represented oiily by a few fibers which cross over the 
OS rostri. 

The depressor rostri arises on the facial crest. It has a long strong tendon 
which passes below the nostril and turns dorso-medially to meet the tendon of the 
opposite side antl end in the skin of the snout. It depresses the snout and con- 
tracts the nostril. 

The malaris is absent, and the other palpeljral muscles present no special 
features. 

MANDIBULAR MUSCLES 

The masseter is thick. 

The pterygoideus medialis is wide at its insertion. 

The pterygoideus lateralis is large and distinct. 

The digastricus has only one belly and has no connection with the hyoid bone. 
It ends on the metlial and lower surface of the mandible, in front of the groove for 
the facial vessels. 

HYOID MUSCLES 

The mylo-hyoideus consists of two more or less distinct layers, the superficial 
one being the transversus mandibulie. 

The occipito-hyoideus and kerato-hyoideus are small. 

The hyoideus transversus is absent. 

The omo-hyoideus and stemo-hyoideus are referred to in connection with the 
muscles of the neck. 



360 



THE MUSCLES OF THE PIG 



Muscles of the Neck 

The cutaneus consists of two layers which cross each other oljliqiiely. The 
fibers of the superficial layer are directed nearly vertically, those of the deep layer 
toward the face, on which they are continued to form the facial portion. 

Tlie brachiocephalicus is described with the other muscles of the shoulder girdle. 

The stemo-cephalicus arises on the sternum and is inserted by a long round 
tendon on the mastoid process. 

The thyroid part of the stemo-thyro-hyoideus has a peculiar arrangement. 
It arises (separately from the opposite muscle) on the manubrium sterni. About 
the middle of the neck it has an oblique tendinous intersection, beyond which it 




Fig. 316. — Sttperficial Muscles of Pig, After Removal of M. Cutaneus. 
a. Levator nasolabialis; b, levator labii superioris proprius; 6', fleshy slip of b which comes from premaxilla: c, 
dilatator naris lateraUs; d, depressor rostri; e, orbicularis oris; /, depressor labii inferioris; p, zygomaticus; A, masseter; 
i i', i", brachiocephalicus (cleido-occipitahs, cleido-niastoideus, pars cla\'icularis deltoidei) ; k^ sterno-cephalicus; U 
sterno-hyoideus; m, omo-transversarius ; n, n\ trapezius: o, anterior deep pectoral; p, latissimus dorsi; q, lumbo- 
dorsal fascia; r, obliquus abdominis externus; r', aponeurosis of r; s, serratus dorsalis; /, serratus ventralis; w, posterior 
deep pectoral : r, supraspinatus; w, w', deltoideus; 3;, long head of triceps; y, lateral head of triceps; r, tensor fascite 
antibrachii; 1, brachialis; 2, extensor carpi radialis; 5, extensor digiti quarti; 4. extensor digiti quinti; 5, extensor 
carpi ulnaris; 6, ulnar head of deep flexor; 7, gluteus medius; 8, tensor fascise latae; 9, 10, 10', biceps femoris; 11, 
semitendinosus: 12, semimembranosus; 13, caudal muscles; I4, panniculus adiposus in section. (After Ellenberger, 
in Leisering's Atlas.) 



divides into two branches: one of these is inserted in the usual fashion, the other 
ends on the laryngeal prominence. The hyoid part is well developed. 

The omo-hyoideus is thin. It arises as in the horse, but has no connection 
with the brachiocephalicus nor with the opposite muscle. 

The omo-transversarius arises on the first or second cervical vertebra (under 
cover of the Ijrachiocephalicus), and is inserted into the lower part of the scapular 
spine. 

There are two scaleni. The scalenus ventralis (s. primsB costs) resembles 
that of the ox, is attached to the last four ci'r\-ical \'crtebr£e, and is perforated by 
the nerves of the brachial plexus. The scalenus dorsalis (s. supracostalis) arises 
on the transverse processes of the third to the sixth cervical vertebra, and ends 
on the third ril). 

Tlie ventral muscles of the head present no special features. 

The longus colli is si'inirated from the opposite muscle, so that part of the 
bodies of the cervical vertebrae is exposed as in man. 



MUSCLES OF THE THORAX — MUSCLES OF THE BACK AND LOINS 361 

The intertransversales resemble those of the ox. 

The splenius is tliick and extensive. It ends in three parts on the occipital, 
the temporal, antl the wing of the atlas (inconstant). 

The longissimus capitis et atlantis is small, antl its atlantal part is blended 
with the longissimus cervicis. 

The complexus is large, and is clearly divided into two parts: the dorsal part 
(Biventer cervicis) is marked by several tendinous intersections; the ventral part 
is the complexus jiropor. 

The obliquus capitis posterior is relatively thin. 

The recti capitis dorsales are thick and more or less fused. 

Muscles of the Thorax 

The levatores costarum and rectus thoracis present no special features. 

The external intercostal muscles arc absent under the serratus dorsalis and the 
digitations of the external oliliciue. 

The internal intercostals are thick between the cartilages of the sternal ribs. 

The retractor costae and the transversus thoracis resemble those of the horse; 
the latter extends back to the eighth cartilage antl fuses with the transversus ab- 
dominis. 

The diaphragm has seven costal digitations on each side, the posterior ones 
being attached to the ribs at some distance (ca. one-third to one-fourth of rib- 
length) from tlie costo-chondral junction.' The line of attachment reaches the 
latter at the tenth rib, and passes along the eighth cartilage to the xiphoid process. 
The tendinous center is more rounded than in the horse. The crura are well 
developed. The right crus is very large, and is perforated by the extensive slit- 
like hiatus CESophageus, which is median in position, and lies about two and one- 
half to three inches (ca. 6 to 8 cm.) below the twelfth thoracic vertebra. The hiatus 
aorticus is between the crura. 

Abdominal Muscles 

The abdominal tunic is little developed. 

The obliquus abdominis extemus has an extensive fleshy portion and a cor- 
respondingly narrow ajxjneurosis; the latter does not detach a femoral lamina, 
but is reflected in toto to form the inguinal ligament. 

The obliquus abdominis intemus resembles that of the ox; a small fusiform 
muscle, which crosses the inguinal canal obliquely and is attached on the abdominal 
surface of the inguinal ligament, is apparently a detached slip of the internal 
obliciue. 

The rectus abdominis is extensive and thick. It has seven to ten inscriptions. 
Its tension of insertion fuses largely with the common tendon of the graciles, and 
does not give off an accessory band to the head of the femur. 

The fleshy part of the transversus abdominis is well developed. It blends 
in front with the transversus thoracis. 

The cremaster extemus is present in the female as well as in the male. 

Muscles of the Back and Loins 

The serratus dorsalis anterior is inserted into the fifth to the eighth ribs 
inclusive, the serratus dorsalis posterior into the last four or five ribs. There are 
usually no digitations attacherl to the ninth and tenth ribs. 

' It is intere.sting to note that the diaplxragm has no attachment to the fifteenth rib, which is 
often present and well developed. 



362 THE MUSCLES OF THE PIG 

The longissimus costarum extends to the wing of the atlas. 

The spinalis et semispinalis can be separated without mucli difficulty from 
the longissimus dorsi, the division from the common mass of the loins beginning 
about the first luniljar vertebra. 

The multifidus resemliles that of the horse. 

Interspinales are present, as well as distinct intertransversales of the back 
and loins. 



Muscles of the Tail 

The dorsal and lateral sacro-coccygei arise as far forward as the last lumbar 
vertelira. Gurlt explains the twist of the tail as being due to the spiral arrangement 
of the insertions of the tendons. 



Muscles of the Thoracic Limb 
muscles of the shoulder girdle 

The trapezius is very wide, its line of origin extending from the occipital bone 
to the tenth thoracic vertebra. There is no clear division between its two parts, 
which are both inserted into the scapular spine. 

The omo-transversarius resembles that of the ox. 

The rhomboideus consists of three parts. The cervical part (Rhomboideus 
cervicalis) is greatly developed, its origin extending from the second cervical to the 
sixth thoracic vertebra. The cephalic part (Rhomboideus capitis) arises with the 
splenius on the occii^ital bone, and is inserted with the cervical part. The thoracic 
part (Rhomboideus thoracalis) extends as far back as the ninth or tenth thoracic 
vertebra. 

The latissunus dorsi is attached to the four ribs preceding the last. It is 
inserted into the meilial tuberosity of the humerus. 

The brachiocephaUcus divides into two parts, the cleido-mastoideus and 
cleido-occipitalis, which arise on the mastoid process and nuchal crest respectively, 
and unite at the fibrous vestige of the clavicle. 

The anterior superficial pectoral muscle is thin. The posterior superficial pec- 
toral muscle is divided into two parts, one of which ends on the humerus, the other 
on the fascia of the forearm. The anterior deep pectoral muscle resembles that of 
the horse, iDut its origin docs not extend behind the first two chondro-sternal joints. 
The posterior deep pectoral muscle is very long. 

The cervical part of the serratus ventralis is greatly developed, its origin ex- 
tending from the wing of the atlas to the upper part of the fifth rib, and passing 
under the thoracic part; the latter resembles that of the ox. 

MUSCLES OF THE SHOULDER 

The deltoid is undivided; it arises from the aponeurosis covering the infra- 
spinatus, and it ends largely on the deltoid ridge, but partly on the fascia of the arm. 

The supraspinatus is large; it has a small attachment to the medial tuberosity 
and ends chiefly on the lateral tuberosity of the humerus. There is a bursa between 
the tendon antl the anterior part of the lateral tuberosity. 

The infraspinatus is^\dde; it is inserted into a depression below the posterior 
division of the lateral tuberosity. There is a bursa between the tendon and the 
tuberosity. 

The teres minor is large and rounded; it ends on a tubercle between the 
lateral and deltoid tuberosities of the humerus. 



MUSCLES OF THE ARM — MUSCLES OF THE FOREARM AND MANUS 363 

The subscapularis is very broad at its upper part. It extends posteriorly up 
to the dorsal angle of the scapula, but anteriorly only about two-thirds of the way 
up to the vertebral border. 

The teres major presents nothing remarkal)le. 

The coraco-brachialis is short, wide, and untlivided. There is a Ijursa Ijetween 
its broad tendon of origin and the tendon of insertion of the subscapularis. 

The capsularis is variable; it may be half an inch wide or very small and 
is frequently absent. 

MUSCLES OF THE ARM 

The biceps brachii is fusiform and not greatly developed. Its tendon of origin 
is rounded and the underlying bursa communicates so freely with the shoulder joint 
as to be regarded as an evagiuation of the synovial membrane of the latter. A small 
band binds clo«ai the tendon in the bicipital groove. The tendon of insertion di- 
vides into two branches. One branch passes back across the medial surface of the 
neck of the radius to end on the proximal extremity of the ulna. The other is 
attached to the radius under cover of the brachialis tendon. 

The brachialis is large. Its tendon of insertion divides. The small branch is 
inserted into the medial border of the radius distal to the biceps tendon. The large 
branch crosses the medial border of the radius and ends on the medial surface of the 
ulna distal to the bicejjs tendon; there is a bursa under this tendon. 

The tensor fasciae antibrachii resembles that of the horse, but is very wide and 
bends around the posterior Ijorder of the triceps. 

The long head of the triceps is inserted into the summit of the olecranon by two 
tendons, between whicli there is a synovial bursa. The lateral head is inserted into 
a crest on the lateral surface of the olecranon by a thin tendon, under which there 
is a bursa. The medial head arises from the proximal third of the medial surface 
of the humerus; it is inserted into the medial surface of the olecranon by a short 
tendon, under which there is a small bursa. 

There are two anconei. 



MUSCLES OF THE FOREARM AND MANUS 

The extensor carpi radialis is a strong, fleshy muscle, the tendon of which is 
inserted into tlie proximal end of the third metacarpal bone. It may be divitled 
into two parts (M. extensor carpi radialis longus, brevis). 

The extensor carpi obUquus is well developed; it arises from the distal two-thirds 
of the lateral surface (jf tlie radius and ulna and ends on the second metacarpal bone. 

The common digital extensor (M. extensor digitalis communis) arises on the 
lateral epicondyle of the hmnerus and the lateral ligament of the elbow, and divides 
into three parts. The tentlon of the medial head ends chieflj^ on the third digit, 
but commonly sends a small branch to the second. The tendon of the middle head 
divides lower tlown into two branches for the third and fourth (chief) digits; above 
this bifurcation it detaches a small branch to the second digit, which usually unites 
with the tentlon of the extensor tligiti secundi. The tendon of the deep head di- 
vides into two branches, the medial one joining the tendon of the middle head, while 
the lateral one ends on the fifth fligit. 

The extensor of the second digit (M. extensor digiti secundi proprius) is covered 
by the preceding muscle, with which it is partially fused. It arises on the ulna. 
Its delicate tendon usually unites with the tendon of the middle head of the common 
extensor which goes to the second digit. 

The lateral digital extensor (M. extensor digitalis lateralis) consists of two dis- 
tinct parts: (1) The large dorsal muscle is the extensor digiti quarti proprius; it 
has a long tendon which ends on the fourth digit, and often sends a slip to the fifth 



364 



THE MUSCLES OF THE PIG 



digit. (2) The small volar muscle is the extensor digiti quinti proprius; it ends by 
a long tendon on the lateral aspect of the fifth digit. 

The supinator, when present, is a pale, thin muscular slip wliich arises on the 

lateral border of the radius just above the interosseous space, extends medially and 

downward across the dorsal surface of the bone to its medial 

border, where it l^lends with the ratlial head of the deep 

flexor. 

The pronator teres is a delicate, fusiform muscle which 
lies along the medial surface of the elbow and proximal part 
of the forearm. It arises from the medial epicondyle and 
collateral ligament of the elbow and is inserted by a thin 
tendon to the medial Ijorder of the radius about its middle. 
The flexor carpi radialis is well developed. It arises 
on the medial ei)icondylo of the humerus, and is inserted 
into the third metacarpal bone. 

The flexor carpi ulnaris is narrow and has no ulnar 
head. It runs oljliquely down the back of the forearm in 
the furrow between the superficial and deep flexors of the 
digit. It arises from the medial epicondyle of the humerus 
and ends on the accessory carpal bone. 

The ulnaris lateralis (M. extensor carpi ulnaris) is 
covered by a tendinous band, which is a thickened part 
of the fascia of the forearm and extends from the lateral 
epicondyle to the accessor}^ carpal bone and lateral aspect 
of the carpus. The belly of the muscle is round : its ten- 
don of insertion perforates this bantl in the distal part of 
the forearm and ends on the proximal end of the fifth 
metacarpal bone. 

The superficial digital flexor arises from the medial 
epicondyle of the humerus and consists of two parts. The 
tendon of the superficial head passes down behind the pos- 
terior annular ligament of the carpus (bound down by a 
special annular ligament), forms a ring at the fetlock for a 
tendon of the deep flexor, and ends by two branches on the 
second phalanx of the fourth digit. It receives a small 
band from the accessory carpal bone. The tendon of the 
deep head, after detaching a strong branch to the tendon 
of the deep flexor, passes down with the latter (for which 
it forms a ring), and ends on the third digit. 

The deep digital flexor has three heads — humeral, 
ulnar, and radial. The himieral head is very large and 
forms the greater part of the contour of the volar face of 
the forearm. It consists of two parts — a large superficial 
part, and a much smaller deep part which arises with the 
superficial flexor. Each ends at the distal part of the fore- 
arm on a short tendon. These unite and receive the ten- 
dons of the radial and ulnar heads and a branch from the 
superficial flexor tendon. The ulnar head has a short, 
thick, prismatic belly which arises from the medial surface of the proximal 
part of the ulna. Its long, thin tendon passes downi on the humeral head and 
joins the tendon of the latter at the level of the accessory carpal bone. The 
radial head is small. It arises from the upper part of the medial border of the 
radius and from the deep fascia, and its tendon joins that of the humeral head at 
the distal end of the forearm. The connnon tendon divides into four branches, 




. 317. — Muscles of Anti- 

BRACHIC.M AND MaNUS 

OF Pig; Dorso-lateral, 



a. 


«'. 


Extensor 


carpi 


radialis 


b. 


extensor 


carpi 


obliquu 


(s. 


abductor 


polUcis 


longus) 


c, d 


c, comm 


on dig- 


ital extensor; 


c', c", tendons of 


insertior 


of c. 


d', d", 


tendons 



of d; c', e", tendons of e; f, 
tendon of extensor digiti se- 
cundi; g, extensor digiti quarti; 
h, extensor digiti quinti; h', 
tendon of h; i, tendinous, and 
k, fleshy, part of ulnaris later- 
alis; k', tendon of k; I, ulnar 
head of deep digital flexor; m, 
superficial digital flexor; n , 
brachialis. (After EUenberger, 
in Leisering's Atlas.) 



MUSCLES OF THE HIP AND THIGH 3()5 

the larger central pair enrling on the third phalanges of the principal digits, the 
smaller abaxial pair on the accessory digits. The latter are bound down by a 
peculiar spiral bantl. There is no subcarpal check ligament. The carpal sheath 
envelops the tendon of the deep flexor and that of the deep part of the superficial 
flexor. It extends from the distal third of the forearm to the distal third of the 
metacarpus. At the proximal part of the metacarpus a small muscular band ex- 
tends from the deep flexor tendon to the tendon of the deep part of the superficial 
flexor. Another muscular bundle passes from the tleep flexor tendon to the second 
digit. 

The lumbricales are represented by bundles which extend from the deep flexor 
tendon to the tendon of the deep head of the superficial flexor. 

The third and fourth interossei are present. Each sends two slips to the cor- 
responding sesamoid bones and extensor tendon. 

There are flexors, adductors, and abductors of the second and fifth digits. 



Muscles of the Pelvic Limb 
sublumbar muscles 

The psoas minor is intimatel.y united with the psoas major in front, and has a 
long small tendon which ends on the psoas tubercle. It has no thoracic part. 

The psoas major is large and rounded. It begins at the last ril). 

The quadratus lumborum is well developed, and extends to the last three or 
four thoracic vertefirse. 

MUSCLES OF THE HIP AND THIGH 

The tensor fasciae latae is broad, and its fleshy part reaches almost to the patella. 

The gluteus superficialis has a sacral head only; it blends with the biceps 
femoris. 

The gluteus medius has a small lumbar part which does not extend so far 
forward as in the horse. The deep part (Ciluteus accessorius) is pretty clearly 
marked. 

The gluteus profundus is extensive, reaching nearly to the tuber coxae. 

The biceps femoris lias a narrow origin from the sacro-sciatic ligament and 
tuber ischii. It ends i)elow like that of the ox. 

Tlie semitendinosus has two heads like that of the horse. 

The semimembranosus arises from the tuber ischii and has two insertions as 
in the ox. 

The sartorius has two heads of origin, between which the external iliac vessels 
are situated. The medial one arises from the tendon of the psoas minor, the lat- 
eral one from the iliac fascia. 

The graciles are united at their origin even more than in the ox. 

The pectineus is well developed and is flattened from before liackward. 

The adductor shows no division and is partially fused with the gracilis. It 
ends on the femur just above the origin of the gastrocnemius. 

The quadratus femoris is large. 

The obturator extemus resembles that of the horse. 

The obturator intemus is extensive and strong; its tendon emerges through 
the obturator foramen. 

The gemellus is fused in part with the obturator internus. 

The quadriceps femoris is more clearly divided than in the horse, and its 
action is transmitted by a single patellar ligament. 

The capsularis is absent. 



366 



THE MUSCLES OF THE PIG 



MUSCLES OF THE LEG AND FOOT 

The peroneus tertius is a well-developed muscle which is in great part super- 
ficially situated on the front of the leg. It covers the long digital extensor, with 
which it is imitecl except in the distal third of the leg. It arises from the extensor 
fossa of the femur by a common tendon with that muscle, 
a synovial pouch from the femoro-tibial joint extending 
down under the origin. 

This sac is an inch and a half or more (ca. 3 to 4 cm.) in length 
in large subjects and extends around the lateral edge of the tendon 
to its superficial face, .so as to make a partial sheath and underlie 
the origin of the peroneus longus also. 

The muscle is continued at the distal end of the leg 
by a strong tendon which passes over the flexion surface of 
the hock, between the tendon of the long extensor (lateral) 
and that of the tibialis anterior (medial), all three being 
bound down by a strong annular ligament which extends 
across from one malleolus to the other. It ends by two 
or more branches on the first and second tarsal and third 
metatarsal bones. Not rarely there is a thin tendon in- 
serted into the fourth metatarsal bone. The tendon usu- 
ally receives a small branch from that of the tibialis an- 
terior at the annular ligament. 

The tibialis anterior is smaller than the preceding. It 
arises from the lateral surface of the tuberosity and lateral 
condyle of the tibia. At the distal end of the leg the ten- 
don passes under the amiular ligament mentioned above 
(where it detaches a small branch to the peroneus tertius), 
and ends on the second tarsal and the proximal end of the 
second metatarsal bone. The terminal part passes under a 
superficial layer of the medial ligament of the hock, and is 
provided with a bursa. 

The peroneus longus descends in front of the fibula and 
the lateral extensor. It arises chiefly from the lateral con- 
dyle of the tibia. The tendon of insertion descends through 
a groove on the lateral malleolus, crosses over the tendons 
of the lateral extensor, then under the lateral ligament to 
the plantar surface of the hock, to end on the first tarsal 
bone. There is a bursa under the tendon where it lies in 
the groove on the fourth tarsal. The muscle is a flexor of 
the hock. 

The long digital extensor arises in common with the 
peroneus tertius, by which it is largely covered and with 
which it is united to the distal third of the leg. Three ten- 
dons appear at the proximal annular ligament and extend 
downward and a little medially over the flexion surface of 
the hock. Here they are bound down by an annular liga- 
ment given off from the tendon of the peroneus tertius and attached laterall.y 
to the distal end of the fibular tarsal bone. The tendons gradually diverge as 
they descend the metatarsus. The central one divides at the distal end of the 
metatarsus into two branches which end on the third phalanges of the chief 
(third and fourth) digits. This tendon is joined before bifurcating by the tendon 
of the extensor digitalis brevis. The medial tendon ends on the second and third 
phalanges of the medial chief (third) digit. It receives a branch from the inter- 




FiQ. 318. — Muscles of Leg 
AND Foot of Pig; Dorso- 
lateral View. 
a, Tibialis anterior; a', 
tendon of preceding; b, pero- 
neus tertius; 6', tendon of b; 
c, long digital extensor; d, e, /, 
/', /". tendons of c; g, peroneus 
longus; g' , tendon of g; h, 
extensor digiti quart i; h' , 
tendon of h, which receives h" 
from the interosseus medius; 
i, extensor digiti quinti ; k, deep 
digital flexor; /, soleus: m, 
gastrocnemius; n, extensor dig- 
italis brevis. (After EUenber- 
ger, in Leisering's Atlas.) 



MUSCLES OF THE LEG AND FOOT 367 

osseus at the distal end of the first phalanx, and may detach a tendon to the second 
digit. The lateral tendon is smaller. Its branches end on the third phalanges of 
the accessory (second and fifth) digits and on the lateral chief (fourth digit) ; there 
may be a Ijranch to the third digit, and the branch for the fourth may go to the 
corresponding branch of the central tendon. Other variations occur. 

The sjTiovial sheath for the tendons of the extensor longus and peroneus tertius at the hock 
extends nearly half an inch (ca. 1 cm.) above the proximal annular ligament and an inch or more 
(ca. 2 to 3 cm.) below the distal annular ligament in a large adult. 

The lateral digital extensor lies on the lateral face of the leg, behind the per- 
oneus longus. It arises from the lateral surface of the fibula, the lateral femoro- 
tibial ligament, and the intermuscular septum between this muscle and the deep 
digital flexor. It consists of two parts. The larger anterior muscle (extensor 
digiti quarti) has a tendon which appears a little distal to the middle of the leg, de- 
scends on the grooved lateral surface of the fibula, inclines forward, crossing under 
the tendon of the peroneus longus, and ends on the extensor process of the third 
phalanx of the lateral chief (fourth) digit. It receives an interosseus tendon at 
the first phalanx. The tendon of the posterior muscle (extensor digiti quinti) 
accompanies that of the anterior one to the tarsus and descends to the lateral ac- 
cessory (fifth) digit. 

The two tendons are bound down at the lateral malleolus by an annular ligament. The 
anterior tendon may receive a branch of the long exteasor tendon and send a tendon to the fifth 
digit. The posterior tendon may send a reinforcing branch to the tendon of the long extensor for 
the fifth digit. There may be a third small head which arises from the middle of the fibula and 
sends a dehcate tendon to join that of the posterior head. 

The extensor hallucis longus is a small, fusiform muscle which is covered by the 
extensor longus and peroneus longus. It arises from the proximal end of the fibula 
and its delicate tendon descends at first under that of the peroneus tertius, inclines 
medially at the hock, and ends on the medial accessory (second) digit. 

The extensor digitalis brevis is a well-developed muscle which lies on the dor- 
sal face of the distal part of the tarsus and on the chief metatarsal bones. It arises 
from the neck of the tibial tarsal and the body of the fibular tarsal bone, and is 
partially divided into three parts. The tendon of the superficial part joins that of 
the long extensor for the chief digits. The deep part has two tendons which join 
those of the long extensor for the accessory digits. 

The gastrocnemius has short but wide and thick heads. The lateral one is 
the larger and is united with the superficial digital flexor to the distal third of the 
leg. The tendon forms a groove for the superficial flexor tendon above the hock 
and is inserted chiefly into the prominences on each side of the notch of the tuber 
calcis. 

The soleus is thick and wide and blends with the lateral head of the gastroc- 
nemius. It arises from the lateral epicondyle of the femur and the deep fascia 
at the stifle. Its tendon joins that of the gastrocnemius. 

The popUteus presents nothing remarkable. 

The superficial digital flexor has a belly of considerable size. It arises with the 
lateral head of the gastrocnemius, with which it is fused to the distal third of the 
leg. The tendon is almost entirelj' enclosed by the twist of the gastrocnemius in 
the lower part of the leg. At the tuber calcis it is thick and largely cartilaginous, 
and is molded on the groove and ridges of the bone. It is attached by a strong 
band to each side of the tuber calcis. A large bursa under the tendon extends up- 
ward in the groove formed by the gastrocnemius almost to the muscular part and 
downward to the middle of the fibular tarsal bone. The tendon divides distally 
into two branches which go to the chief digits. It also detaches from its plantar 
surface two bands which join the fascia of the accessory digits. 

The deep digital flexor presents three distinct heads: (1) The tibialis pos- 



368 THE MUSCLES OF THE DOG 

terior is the smallest. It has a fusiform belly in the proximal half of the leg and 
arises from the grooved plantar surface of the fibula. The tendon joins that of the 
flexor hallucis at the distal end of the leg. (2) The flexor digitalis longus is much 
larger and has a fusiform, pennate belly which extends o1)liciucly across the prox- 
imal two-thirds of the leg. It arises from the proximal end of the fil:)ula, the pop- 
liteal line, the middle third of the medial part of the plantar surface of the tibia, and 
the intermuscular septum between this muscle and the flexor hallucis. The ten- 
don (which has a synovial sheath) descends in a groove behind the medial malleolus, 
bound do\\ar by an annular ligament, inclines laterally on the joint capsule, and 
joins the tendon of the flexor hallucis. (3) Tlie flexor hallucis has a large fusiform 
belly which extends almost to the distal end of the leg. It arises from the greater 
part of the plantar surface of the tiloia, the medial surface and plantar border of 
the fibula, and the interosseous membrane. The tendon descends in the tarsal 
canal, receiving the tendons of the other heads, and ends like the corresponding 
one of the forelimb. The tarsal s\Tiovial sheath begins at the distal end of the 
muscular part and extends to the middle of the metatarsus. 

The lumbricales are aljsent, l)ut there are four interossei. Ruilimentary 
adductors of the second and fifth digits may be found. 



THE MUSCLES OF THE DOG 
Muscles of the Face 

The cutaneus of the face is well devehjped. JNIost of it is a continuation of the 
cervical cutaneus; the bundles extend forward over the lower part of the lateral 
surface of the face to the angle of the mouth and the upper lip. Other buntlles ex- 
tend upward; some of these spread out on the clicek and lateral nasal region, and 
a thin layer passes toward the lower eyelid, blending with the orbicularis oculi and 
constituting a malaris muscle. Another stratum is attached to the scutiform carti- 
lage and spreads out on the masseter. 

The orbicularis oris is poorly developed. In the upper lip it is divided cen- 
trally, and in the lower lijj it is tlistinct only near the angles of the mouth. 

The levator nasolabialis is wide and undivided. It has an extensive origin on 
the frontal and nasal liones. The fibers run downward and forward to the lateral 
wing of the nostril and the upjier lip. 

The levator labii superioris proprius arises l:)ehind the infraorbital foramen, 
runs forward under the preceding nuiscle, and ends in numerous small tendons 
which are in part inserted around the nostril, in part blend with those of the oppo- 
site side. 

The zygomaticus is narrow and very long; it arises on the scutiform cartilage, 
and ends at the angle of the mouth. 

The depressor labii inferioris is al)sent. 

There are no special nasal muscles. The homologue of the lateral dilator is 
triangular; it is .small at its origin just ventral to the levator labii superioris pro- 
jirius, and ends almost entirely in the upper lip. 

The buccinator is wde and very thin, and the two jjlanes of fibers cross each 
other. 

The palpebral muscles present no very noteworthy special characters. Two 
small muscles act on the upper eyelid. (3ne of these, the corrugator supercilii, 
arises from the fascia on the frontal bone and ends near the medial canthus. The 
other arises from the zygomatic arch and ends near the lateral canthus. 



MUSCLES OF THE FACE 



369 




Fig. 319. — Musci^s of Head of Dog. 
a, Scutularis; b, c, anterior auricular muscles; d, helicis; e, antitragicus; /, /, zygomaticus, out of which a portion 
is cut; Q, stump of cutaneus attached to scutiform cartilage; h, parotido-auricularis; i, masseter; k, malaris; /, 
levator nasolabialis; m, levator labii superioris proprius; n, dilatator naris ii^teralis; o, p, buccinator (buccalis, molaris) ; 
q, retractor anguU oris {from cutaneus); r, occipito-mandibularis; s. mylo-hyoideus; i. base of concha: 3, parotid 
gland; 2', parotid duct; 3, mandibular gland; 4, mandibular lymph glands; 5, buccal glands; 6, zygomatic arch; 
7, maxilla; S, dorsum nasi; 9. parotid lymph gland. (Ellenberger-Baum, Anat. d. Hundes.) 





Fig, 320. — Superficial Mcscles of Dog, After Removal of M. crT.txECS. 
1, Levator nasolabialis; 2. levator labii superioris proprius; 3, dilatator naris lateralis; 4. 4'. buccinator; -5, re- 
tractor anguli oris; ff, zygomaticus; 7, malaris; S, masseter; 9, occipito-mandibularis, 10, scutularis; 11. other auric- 
ular muscles; 12, parotido-auricularis; 13, mylo-hyoideus; 14, sterno-hyoideus; 13, sterno-thyroideus; 16, splenius; 
17, lumbo-dorsal fascia; 18, rectus abdominis; 19, obliquus abdominis externus; 19', aponeurosis of preceding; 30, 
intercostal muscle; 21. sacro-coccygeus accessorius: 22, sacro-coccygeus dorsalis; 23, sacro-coccygeus ventralis; 24' 
great trochanter; ^5, jugular vein; a, &, c, brachiocephalicus; d, clavicle; e, /, trapezius; ff, serratus cervicis; h, onxo- 
transversarius; i, latissimus dorsi; k, posterior deep pectoral; /, supraspinatus; m, m', deltoid; n, infraspinatus; o, 
triceps, long head; o', triceos, lateral head; p, brachiaUs; q, extensor carpi radiaUs; r, gluteus medius; s, gluteus 
superficiaUs; t, t\ tensor fascise latae; u, sartorius; r, biceps femoris; t', fascia lata; u\ semitendinosus; x, semimem- 
branosus; y, sartorius: z, gracilis; 26, pronator teres; 27, flexor carpi radialis; 2S, flexor carpi ulnaris; 29, tibialis 
anterior; 30, popliteus; 5/, 3/', deep digital flexor; 3^, superficial digital flexor; 33, gastrocnemius; 34, spine of scap- 
ula: a, parotid gland, with o', its duct; fi, mandibular gland; 5, mandibular Ijinph glands; jj, parotid lymph gland; 
f, inferior buccal glands. (After Ellenberger, in Leisering's Atlas.) 
24 



370 



THE MUSCLES OF THE DOG 



MUSCLES OF THE MANDIBLE 

The masseter is thick and its superficial face is strongly convex. It arises 
from the zygomatic arch, and extends beyond the branch of the jaw below and be- 
hind. Three partly separate strata may be recognized in its structure. 

The temporalis is very large and 
strong, and contains much tendinous, 
tissue. It arises from the temporal 
fossa and the orbital ligament and 
ends on the coronoid process of the 
mandible. It blends in part with 
the masseter. 

The pterygoideus lateralis is 
not distinct from the medialis. 

The digastricus is absent. 

The occipito-mandibularis is a 
strong, round, fleshy muscle, which 
arises on the paramastoid process 
and is inserted into the border and 
medial surface of the ramus of the 
mandible at the level of the last 
molar teeth; it sometimes has a 
tendinous intersection. 



HYOID MUSCLES 

The mylo-hyoideus is well de- 
veloped. 

The stylo-hyoideus is very slen- 
der, and is inserted into the body of 
the hyoid bone. 

The hyoideus transversus and 
omo-hj-oideus are absent. 

The stemo-thyro-hyoideus is 
large and arises chiefly on the first 
costal cartilage. It is clearly di- 
vided into stemo-thyroideus and 
stemo-hyoideus. 




Fig. 321. — Ventral Muscles of Head, Neck, and Thorax 
GF Dog. 
a, Mylo-hyoideua; b, occipito-mandibularis; c, stemo- 
hyoideus; c', stemo-thyroideus; d, sterno-cephalicus; e,brachio- 
cephalicus; /, subscapularis ; g, superficial pectoral; h, deep pec- 
toral; i, rectus abdominie; ^•, obliquus abdominis externus; I, 
long head of triceps; m, medial head of triceps; n, biceps 
brachii; o, brachialis; 1, 1', 1", mandibular lymph glands; 3, 
thyroid gland; 5, external jugular vein. (EUenberger-Baum, 
Anat. d. Hundes.) 



Muscles of the Thoracic Limb 



The trapezius is thin, and is 
divided into cervical and thoracic 
portions by a narrow aponeurotic 
part. Its line of origin extends from 
about the middle of the dorsal bor- 
der of the neck to the ninth or tenth thoracic spine, the right and left muscles 
meeting (except at their posterior part) on a median fibrous raphe. It is inserted 
into the entire length of the spine of the scapula. 

The omo-transversarius arises by a tendon on the lower part of the spine of 
the scapula (where it is often partially blended with the trapezius), and is inserted 
into the wing of the atlas. 



MUSCLES OF THE THORACIC LIMB 371 

The rhomboideus consists of three parts. The rhomboideus thoracalis is 
small ; it arises from the fourth to the sixth or seventh thoracic spine, and is inserted 
into the medial surface (chiefly) of the dorsal angle of the scapula. The rhom- 
boideus cervicalis arises from the ligamentum nuchse as far forward as the secontl 
or third cervical vertebra, and is inserted into the medial surface of the cervical 
angle of the scapula. The rhomboideus capitis is a narrow band which is given off 
laterally from the preceding; it is inserted into the nuchal crest. 

The latissLmus dorsi is extensive ; it has an attachment to the last two ribs and 
also to the u]ii)er part of the spine of the scapula in addition to the origin from the 
lumbo-dorsal fascia. Its lower edge blends near the shoulder with the cutaneus. 

The brachiocephalicus contains in front of the shoulder a tendinous intersec- 
tion and a fibrous mass in which the clavicle is embedded. Anterior to this it sepa- 
rates into two diverging parts. The dorsal part is the cleido-cervicalis, which 
widens above and is attached to the median raphe oftheneckandtothe occipital bone. 
The ventral part is the cleido-mastoideus ; it is narrow and is attached to the mas- 
toid process. The common mass posterior to the clavicle and the fibrous inter- 
section, which is attached to the humerus, is homologous with the clavicular part 
of the deltoid of man. 

The superficial pectoral muscle is small. It arises on the sternum from the 
manubrium as far liack as the third costal cartilage, and is inserted into the humerus 
at the border between the medial and anterior surfaces. A superficial slip detached 
from it is inserted into the fascia of the forearm. The deep pectoral has no scapular 
part. It arises on the sternum and costal cartilages from the second costal to the 
xiphoid cartilage, ^nd from the aponeurosis of the obliquus abdominis externus. 
It is inserted chiefly into the medial tuberosity of the humerus, but also b}' small 
slip.s into the lateral tuberosity and the fascia of the arm. 

The serratus ventralis shows no clear division into cervical and thoracic parts. 
It arises from the last five cervical vertebrae and the first eight ribs, and is inserted 
into the upper part of the costal surface of the scapula. 

The deltoid is clearly divided into scapular and acromial parts. The scapular 
part is triangular and arises from almost the entire length of the spine of the scapula; 
it is inserted largely into the fascia on the lateral surface of the arm. The acromial 
part is short, thick, and fusiform; it arises fi'om the lower edge of the acromion, 
and ends on tlio deltoid tuberosity. 

The supraspinatus is large; it ends chiefly on the lateral tuberosity of the hu- 
merus, but has a small attachment to the medial tuberosity also. 

The infraspinatus is bipemiate. The tendon of insertion passes in a groove on 
the lateral tuberosity of the humerus, to end on a well-defined mark on the same; a 
large bursa lies under the tendon. 

The teres minor is short and fusiform ; it arises on a tubercle on the posterior 
border of the scapula, just above the glenoid cavity, and is inserted into a tubercle 
on the upper part of the deltoid ridge. 

The subscapularis is wide and is multipennate in structure, being intersected 
by fibrous septa which are attached to the rough lines on the costal surface of the 
scapula. It is inserted into the medial tuberosity of the humerus. 

The teres major is thick. It arises on the upper part of the posterior border 
of the scapula and on the subscapularis, and is inserted into an eminence (tuber- 
ositas teres) on the proximal third of the medial surface of the humerus by a com- 
mon tendon with the latissimus dorsi. 

The coraco-brachialis has a short and undivided belly. It arises from a small 
depression on the medial surface of the tuber scapulae, and ends on the proximal 
third of the humerus, just medial to the brachialis. The tendon of origin has a syno- 
vial sheath. 

The capsularis is absent. 



372 



THE MUSCLES OF THE DOG 



The biceps brachii lies almost entirely on the medial surface of the humerus. 
It is long and fusiform. The tendon of origin is round, and is bound down in the 
intertuberal groove by an annular ligament. It is enveloped by an extension of 
the synovial membrane of the shoulder joint. The tendon of insertion is Ijifid; 



Teres major 




Subsca pularis 



-ij —Supraspinatus 



Lutissimus dorsi ' 

£^ 

Long head of triceps 

Tensor fasdm antibrachii 

Medial head of triceps- - 

/ 

Flexor carpi ulnaris 

Flexor carpi radialis - 

Superficial digital flexor- - — 

Deep digilal flexor 





Coraco-tirachialis 
Accessory head of triceps 

Biceps brachii 



Extensor carpi radialis 
-. Pronator teres 



Radial head of deep 
digital flexor 



Fig. 322. — Muscles of Thoracic Limb 



CEUenberger-Baum, Anat. dea Hundes.) 



one branch is attached to a rough mark on the lateral surface of the ulna, just below 
the semilunar notch; the other branch ends on a distinct mark on the postero- 
medial aspect of the proximal part of the shaft of the radius, one to two inches be- 
low the head. 



MUSCLES OF THE THOKACIC LIMB 



373 



The brachialis is very little curved. Its tendon of insertion passes over the 
meilial ligament of the elbow and under the ulnar tendon of the biceps and ends 
just proximal to the latter. The tendon of the biceps forms a partial sheath for 
that of the brachialis. 

The tensor fasciae antibrachii is thin and narrow. It arises on the tendon and 
lateral surface of the latissimus dorsi, and ends on the 
olecranon and the fascia of the forearm. 

The triceps has an additional deep head (Caput 
accessorium), which arises just below the head of the 
humerus. The medial head is very long; it arises from 
a mark on the proximal fourth of the medial surface of 
the humerus, just behind the insertion of the teres major 
and latissimus dorsi. A bursa lies on the olecranon in 
front of the common tendon of insertion. 

The brachioradialis is a long, narrow, delicate mus- 
cle, situated superficially on the dorsal surface of the 
forearm. It arises with the extensor carpi on the crest 
above the lateral epicondyle of the hmnerus, and is in- 
serted into the distal part of the medial border of the 
radius. It is often much reduced, and is sometimes ab- 
sent. It rotates the forearm antl paw outward. 

The extensor carpi radialis arises on the lateral con- 
dyloid crest and divides into two parts. The larger lat- 
eral part, the extensor carpi radialis brevis, ends on the 
proximal end of the third metacarpal bone. The medial 
and more superficial part, the extensor carpi radiaUs 
longus, ends on the secontl metacarpal bone. (A ten- 
don to the foiu'th metacar])al may occur.) 

The extensor carpi obliquus or abductor pollicis 
longus arises from the lateral border and dorsal surface 
of the ulna, the interosseous ligament, and the proximal 
part of the lateral border of the radius. It is inserted 
into the first metacarpal bone by a tendon which con- 
tains a small sesamoid bone. It abducts the first digit. 

There are three (or four) extensors of the digits. 

1. The common digital extensor (M. extensor digi- 
talis communis) arises on the lateral epicondyle of the 
humerus and the lateral ligament of the elbow joint. 
It has four bellies, each of which has a tendon of inser- 
tion. These end on the third phalanges of the second, 
third, fourth, and fifth tligits. 

2. The extensor of the first and second digits (M. 
extensor pollicis longus et extensor indicis proprius) is 
small, and is covered by the common and lateral ex- 
tensors. It arises on the proximal half of the ulna. Its 
tendon descentls vfith that of the common extensor and 
divides into two branches. The delicate medial branch 
ends on the first digit, while the larger lateral one ends 
with the tendon of the common extensor for the second 
digit. 

3. The lateral digital extensor (M. extensor digitalis lateralis) consists of two 
muscles which are not rarely fused. They arise on the lateral epicondyle of the 
humerus and the lateral ligament of the elbow joint. The larger superficial muscle 
is the extensor of the third and fourth digits (M. extensor digiti tertii et quarti); 




Fig. 323.— Muscles oi 

CHIUM AND MaNUS OF DOG; 

Lateral View. 

o, Triceps brachii; b, brachi- 
alis: c. extensor carpi radialis; d, 
common digital extensor; d\ d", 
d"\ d"" , tendons of preceding; e, 
lateral digital extensor; e' , /, ten- 
dons of preceding; g, ulnarid 
lateralis; h, ulnar head, h' , hu- 
meral head of flexor carpi ulnaris; 
r, extensor carpi obliquus (s. ab- 
ductor pollicis longus) ; k, inter- 
ossei; I, branches from preceding 
to extensor tendons; 7, olecranon; 
2, radius; 5, lateral epicondyle of 
humerus. (.\fter Ellenberger, in 
Leisering's Atlas.) 



374 



THE MUSCLES OF THE DOG 



its tendon divides at or near the carpus into two branches, which arc inserted into 
the third phalanges of the third and fourth chgits, blending with the corresponding 
tendons of the common extensor. The posterior muscle is the extensor of the fifth 
digit (M. extensor digiti quinti) ; its tendon fuses with that of the common extensor 
for the fifth digit. 

The ulnaris lateralis or extensor carpi ulnaris is a large flat muscle which lies 
on the lateral surface of the ulna. It arises on the lateral epicondyle of the humerus, 
and is inserted into the proximal end of the fifth metacarpal and the accessor^' carpal 
bone. It is chiefly an abductor of the paw. 

The flexor carpi ulnaris consists of two quite distinct heads. The larger 
humeral head arises on the medial epicondjde, while the smaller, 
superficial ulnar head arises on the posterior border of the ulna. 
The tendons of the two end on the accessory carpal bone and 
have a bursa lietween them. 

The flexor carpi radialis arises on the medial epicondyle of 
the humerus and is inserted by a bifid tendon into the second' 
and third metacarpal bones. 

The tendons of the foregoing eight muscles are provided 
with synovial sheaths at the carpus. 

The pronator teres is a fusiform muscle, which is situated 
superficially on the proximal part of the medial border of the 
radius. It arises on the medial epicondyle of the humerus, and 
is inserted into the dorsal surface and medial border of the radius 
almost half way to the carpus. It is related deeply to the radial 
vessels, the median nerve, and the tendon of the biceps. Its 
action is to flex the elbow and rotate the forearm inward (pro- 
nation) . 

The superficial digital flexor is situated superficially on 
the medio-volar surface of the forearm. It arises on the medial 
epicondyle of the humerus and terminates near the carpus on a 
tendon which passes downward outside of the carpal canal and 
receives below the carpus two reinforcing bantls, one from the 
accessory carpal, the other from the sesamoid bone at the medial 
side of the carpus. It divides distall.y into four branches, which 
are inserted into the second phalanges of the second, third, 
fourth, and fifth digits. 

The deep digital flexor has hiuneral, ulnar, and radial 

heads; the radial head arises from the medial border of the 

radius. They unite on a common tendon which passes down 

through the carpal canal, gives ofT a branch to the first digit, 

and divides into four branches. These perforate the tendons 

of the superficial flexor and are inserted into the third phalanges 

of the second to the fifth digits. The tendons are provided with 

sj'novial sheaths from the middle of the metacarpus downward, 

and are held in place by three digital annular ligaments. 

The palmaris longus' is a small muscle which arises from the deep digital 

flexor below the middle of the forearm, and ends bj' two tendons which unite with 

those of the superficial flexor for the third and fourth digits. 

The supinator is a short, flat, fusiform muscle which arises from the front of 
the lateral eiDicondyle of the humerus with the lateral ligament, and from the lateral 
prominence of the head of the radius, and is inserted into the proximal fourth of the 

' The homology here i.s doubtful. Sussdorf regards the ulnar head of the deep digital flexor 
as the homologue of the palmaris longus of man, while Alexais considers tliat the latter is repre- 
sented by the superficial digital flexor. 




Fig. 324. — Volar Mus- 
cles OF Left Fore- 
Paw OF Dog. 
a. Abductor pol- 
licis brevis et opponcns 
poIUcis; 6, flexor polli- 
cis brevis; c, adductor 
pollicis; d, adductor 
digiti secundi; e, ad- 
ductor digiti quinti; /, 
flexor digiti quinti 
brevis; g, abductor 
digiti quinti; h, in- 
terossei ; 1 , accessory 
carpal bone; 2, first 
digit; 3~G, sesamoids 
of metacarpo-phalan- 
geal joints. (Ellen- 
berger-Baum, Anat. d. 
Hundes.) 



MUSCLES OF THE THORACIC LIMB 375 

dorsal surface and the medial border of the radius. (A pouch of the capsule of the 
elbow joint lies under the tendon of origin.) Its action is to rotate the forearm 
outward (supination). 

The pronator quadratus consists of a thin layer of fibers which cross the volar 
surface of the radius and the interosseous ligament of the forearm, except at the two 
extremities of the latter. The fibers extend from the medial border of the radius 
backward and outward to the interosseous border of the ulna. It rotates the fore- 
arm inward (pronation). 

The palmaris brevis (?) is a very small muscle, which arises on the tendon of 
the superficial digital flexor at the carpus, and is inserted at the fifth metacarpo- 
phalangeal joint into the sheath and annular ligament of the deep flexor. 

The lumbricales are three very delicate muscles, which arise on the volar sur- 
face of the tendons of the deep flexor, and are inserted into the first phalanges of the 
third, fourth, and fifth digits. 

The abductor pollicis brevis et opponens pollicis, a very small pale muscle, 
arises on the fibrous band which connects the superficial flexor tendon with the 
medial carpal sesamoid, and emls on the distal end of the first metacarpal bonie and 
the first phalanx of the first digit. It abducts the first digit.' 

The flexor pollicis brevis arises on the volar carpal ligament over the second 
metacarpal bone, and ends on the volar sesamoid of the first digit. 

The adductor pollicis, situated lateral to the preceding, is the largest of the 
thumb muscles. It arises between the preceding and the second interosseous 
muscle, and is inserted into the first phalanx of the first digit. 

The adductor digiti secvmdi is situated between the second interosseous 
muscle and the adductor digiti quinti. It arises on the volar carpal ligament, and 
ends on the first phalanx of the second digit. 

The adductor digiti quinti arises close to the preceding muscle, and passes 
outward to end on the first phalanx of the fifth digit. 

The flexor digiti quinti arises on the ligament connecting the accessory carpal 
to the third and fourth metacarpal bones, crosses the corresponding interosseous 
muscle, and ends on the fifth digit with the next muscle. 

The abductor digiti quinti is larger than the two preceding muscles; it arises 
on the accessory carpal l^one, and ends on the lateral sesamoid of the fifth digit and 
on the lateral ligament. 

There are four interossei which lie on the volar surface of the metacarpus. 
They are well developed and fleshy. They arise on the distal row of the carpus 
and on the proximal ends of the metacarpals. Each divides distally into two 
branches, which are inserted by small tendons on the corresponding sesamoid 
bones, and detach slips to the extensor^tendons. 

The cliief facts with regard to the synovial membranes in connection mth the muscles of the 
forearm and manus are as follows: The tendons of the extensor carpi radialis frequently have a 
synovial sheath at the distal part of the forearm, and there may be one or two bursae at the carpus. 
The tendons of the extensor digitaUs communis have a synovial sheath which extends from the distal 
part of the forearm to the carpus or to the proximal part of the metacarpus. The tendons of the 
extensor digitalis lateralis have in about half of the cases a syno\ial sheath at the distal part of the 
forearm and at the carpus. The tendon of insertion of the extensor carpi obUquus has a synovial 
sheath. The tendon of insertion of the ulnaris lateralis sometimes has a bursa between it and the 
styloid process of the ulna. The tendon of insertion of the flexor carpi radialis has a synovial 
sheath. There is a bursa between the two tendons of the flexor carpi ulnaris at their insertion; 
it usually communicates with a subfascial bursa which lies on the accessory carpal bone. The 
superficial digital flexor has a bursa imder its origin; this communicates T\-ith another bursa wliich 
lies between the deep digital flexor and the flexor carpi ulnaris. The tendons of the digital flexors 
for the second to the fifth digits have a common sheath for each digit which begins at the distal 
part of the metacarpus. ^ The tendon of the deep flexor for the first digit has a synovial sheath. 

' Movements of individual digits are specified with regard to the axis of the manus (paw), 
and not to the median plane of the body. 



376 THE MUSCLES OF THE DOG 



Muscles of the Neck 

The cervical cutaneus consists of two strata. One of these is composed of thin 
bundles which curve across the ventral region of the neck and fade out laterally. 
The other layer is thicker and rnore extensive. Its bundles begin at the dorsal 
margin of the neck, are directed obliquelj^ over the sides, and are for the most part 
continued by the facial part as previously described. 

The stemo-cephalicus is well developed. It arises on the manubrium sterni, 
diverges from its fellow, and ends on the mastoid process, blending with the cleido- 
cervicalis. It may be termed the sterno-mastoideus. It is crossed superficially 
by the external jugular vein. 

The scalenus ventralis (s. primse costae) arises on the last four cervical trans- 
verse processes, and is inserted into the first rib. 

The scalenus dorsalis (s. supracostalis) is large. It blends with the preceding 
muscle in front, and divides into two parts posteriorly. The dorsal part is inserted 
on the third antl fourth ribs, the ventral part by a long, thin tendon on the seventh 
or eighth rib. 

The longus colli resembles that of the horse. 

The rectus capitis ventralis major arises on the transverse processes of the 
second to the sixth cervical vertebrae anil ends as in the horse. The rectus capitis 
ventralis minor and rectus capitis lateralis resemble those of the horse. 

The intertransversales resemlile those of the ox. 

The splenius is strong and extensive. It arises on the first four or five thoracic 
spines and the median raphe of the neck, and is inserted into the nuchal crest and 
mastoid process. 

The complexus is composed of dorsal and ventral parts — the biventer cervicis 
and the complexus major. The biventer cervicis arises from the transverse proc- 
esses of the fifth and sixth, and the sj^ines of the second to the fifth (or sixth) 
thoracic vertelirue, from the ligamentum nuclue, and the median rai^he. It has 
four oblique tenilinous intersections. The complexus major arises on the trans- 
verse processes of the first three or four thoracic vertebrae and the articular 
processes of the last five cervical. Both end on a strong common tendon which is 
inserted into the nuchal crest and the depression below it. 

The longissimus capitis et atlantis consists of two unequal parts. The large 
dorsal part, the longissimus capitis, arises from the transverse processes of the first 
four thoracic and the articular process of the last three or four cervical vertebrae, 
and ends with the splenius on the mastoid process of the temporal bone. The 
small ventral part, the longissimus atlantis, arises from the articular processes of 
the third, fourth, and fifth cervical vertebrae, and ends on the wing of the atlas. 

The other muscles present no striking differential features, but it may be noted 
that distinct interspinales are present. There are also small muscular bundles 
which lie beneath the multifidus in the back. These extend from the transverse 
process of one vertebra to the spine of the preceding one, and are appropriately 
termed the submultifidus. 



Muscles of the Thorax 

There are twelve pairs of levatores costarum. 

The external intercostal muscles do not occu]5y the spaces between the costal 
cartilages. 

The diaphragm is very strongly curved, and has a small tendinous center. 
The hiatus oesophageus is between the crura and is ventral to the twelfth thoracic 
vertebra. The costal part is attached to the lower (horizontal) part of the ninth 



MUSCLES OF THE ABDOMEN 



377 



costal cartilage, to the tenth and eleventh cartilages a little (ca. 1 to 2 cm.) below 
the junction with the rib, to the twelfth rib at its ventral end and to the last rib 
below its middle. The cupola is very unsymmetrical ; on the left side it is opposite 
the sixth rib, while on the right it is an intercostal space further back. 



Muscles of the Back and Loins 

The serratus dorsalis anterior arises from the median raphe of the neck and the 
first six or seven thoracic spines, and is inserted into the second to the ninth ribs. 
It is well developed. The serratus dorsalis posterior — much weaker — arises from 
the lumbo-dorsal fascia, and is inserted into the last three or four ribs. Thus one 
or two ribs intervene between the two. 

The longissimus costarum is well developed, and extends from the ilium to the 
sixth, fifth, or fourth cervical vertebra. 

The longissimus dorsi resembles that of the other animals, but the spinalis et 
semispinalis separates clearly from the longissimus proper at the sixth or seventh 
thoracic vertebra. It is inserted into the articular and spinous processes of the 
last six cervical vertebrte. 

It has no depression in the ■-,.,^ jj 

lumbar region for the glu- „^^^~-^ S h 

teus medius. 

The intertransversales 
are flcshj', as in the ox. 

The interspinales are 
distinct and are most devel- 
oped in the lumbar region. 




Muscles of the Tail 

These present the 
same general arrangement 
as in the horse. The sacro- 
coccygei, however, arise on 
the lumbar vertebrae also, 
and the coccygeus on the 
ischiatic spine. There is a 
sacro-coccygeus accessor- 
ius, which arises on the 
medial border of the ilium, 
the edge of the sacrum, and 
the transverse processes of 
the first coccygeal vertebrae, and is inserted between the dorsal and lateral sacro- 
coccygei. It is homologous with the intertransversales. 



Fig. 325. — Muscles of Tail. Anus, and Genital Groans of Dog. 
/. Ilium; 2, femur; 3, tuber ischii; 4. sacro-aciatic ligameat; 5, sacral 
region; 6, tait; 7, peais; 5, anus; 9, rectum; a, aacro-coccygeus dorsalis: 
ft, sacro-coccygeua accessorius; c.Jcoccygeus; rf, sacro-coccygeus ventralis; e, 
retractor ani; /, /'. sphincter ani externus; g, retractor penis; h, bulbo- 
cavernosus; i. tranaversus perinei (?); fc, m, iachio-urethrales; I, ischio- 
cavernosus: n, tendon of obturator internus; o, [gemellus, p, urethral 
muscle, (.\fter Ellenberger, in Leiaering's Atlas.) 



Muscles of the Abdomen 

The abdominal tunic is practically absent. 

The obliquus abdominis externus has an extensive fleshy part. It arises from 
the last eight or nine ribs and tlie lumbo-dorsal fascia. 

The obliquus abdominis internus arises from the tuber coxae and the lumbo- 
dorsal fascia. The fibers have an almost vertical direction, and there is a fleshy at- 



378 THE MUSCLES OF THE DOG 

tachment to the last rib. The anterior part of the aponeurosis divides into two 
layers, which concur in the formation of the internal and external sheaths of the rec- 
tus. 

The rectus abdominis is attached by a long tendon on the first five or six costal 
cartilages, and by fleshy fibers on the xiphoid cartilage. It usually has five ten- 
dinous inscriptions. The two recti diverge very gradually in front, so that they are 
about half an inch (ca. 1 cm.) apart in the xiphoid region. 

The transversus abdominis presents no special features except that the poste- 
rior part of its aponeurosis splits into two layers which include the rectus between 
them. 



Muscles of the Pelvic Limb 

The psoas minor arises from the bodies of the last three or four thoracic and 
first three or fom' lumbar vertebrae, and is inserted into the iliopectineal line. Its 
anterior part blends with the quadratus lumborum. 

The psoas major is relativelj^ small and short; it arises from the last three or 
four lumbar vertebrae. 

The lateral head of the iliacus is small, while the medial head is large and fuses 
with the psoas major to constitute an ilio-psoas. 

The quadratus lumborum is well developed, and extends laterally beyond the 
edge of the ilio-psoas. It arises from the last three or four thoracic vertebrae in 
common ■with the psoas minor, and from the last rib and the lumbar transverse 
processes, and ends on the pelvic surface of the wing of the ilium. 

The tensor fasciae latse arises from the lateral border of the ilium and the 
gluteus medius; it consists of two parts. The anterior part is long and rounded; 
the posterior is shorter and fan-like. 

The gluteus superficialis is small. It arises from the gluteal fascia, the lateral 
part of the sacrum, first coccygeal vertebra, and sacro-sciatic ligament. It is in- 
serted below and behind the trochanter major of the femur, on the lateral branch of 
the linea aspera. In some cases there is a bursa between the tendon and the tro- 
chanter major. 

The gluteus medius has no lumbar portion. It is inserted into the trochanter 
major by a strong tendon. There is a bursa under the tendon of insertion which 
also extends under the gluteus profundus. 

The gluteus profundus is broad and fan-shaped. It arises on the superior 
ischiatic spine and on the ilium as far forward as the gluteal line, and is inserted 
into the trochanter major below the medius.' 

The piriformis is not blended with the gluteus medius. It arises from the 
border and ventral surface of the sacrum and from the sacro-sciatic ligament, and 
ends on the trochanter major with or close to the gluteus medius. 

The obturators, gemellus, and quadratus femoris resemble in arrangement 
those of the horse, and present no notalile special features. There is a large bursa 
under the tendon of the obturator internus. 

The biceps femoris has two heads of origin which soon fuse. The larger head 
arises from the sacro-sciatic ligament and tuber ischii, the .smaller one from the tuber 
ischii. The aponeurosis of insertion ends on the patella, the patellar ligament, 
the fascia lata, and the tibial crest. There is also a tendinous band, which comes 
from the deep face of the muscle and terminates at the tarsus, as in the horse. 
There is usually a bursa between the muscle and the trochanter major. 

The abductor cruris posterior may be regarded as an accessory head of the 
biceps femoris. It is a thin nmscular band which arises from the sacro-sciatic 

• Lesbre maintains that this is the scansorius, and that the gluteus profundus is so intimately 
united with the medius as to have been regarded by anatomists as part of the latter. 



MUSCLES OF THE PELVIC LIMB 



379 



ligament, passes downward between the biceps and semimembranosus, and ends by 
blending with the former. 

The semitendinosus arises from the tuber ischii only. It ends on the crest and 
medial surface of the tibia. 

The semimembranosus is large and arises from the ischium only. It divides 
into two parts: the anterior part ends on the tendon of the pectineus, on the femur 
above the medial condyle, and on the medial sesamoid bone; the posterior part 



I K 326. — Muscles of Pelvic Limb of Dog; Medial View. 
a Ilio-psoas; 6, tendon of psoas minor; c, aacro-coccy- 
^ us ventralis lateralis: d, coccygeus; e, piriformis; /, obtur- 
tjrinternus; fl, origin of retractor ani; A, A', sartorius; i, ree- 
ls femoris; k, vastus medialis; I, pectineus; m, adductor; 
sracili^ 0, semitendinosus; p, semimembranosus; q, gas- 
I rnemius, medial head; q' , tendon of gastrocnemius; r, 
ijii rficial digital flexor; r', tendon of r; s, tarsal tendon 
1 biceps femoris; t, popliteus; u. flexor hallucis longus; u\ 
1 iig digital flexor; u", common tendon of u and u'; v, tendon 
of tibialis posterior; w, tibialis anterior; x, tendon of long 
digital extensor; }, pelvic surface of ilium; 2, section of sym- 
ph\sis pelvis; S, tuber ischii; 4. medial condyle of femur; 
o Iigamentum patellffi; 6, 7. medial surface of tibia; S, tarsus; 
^' fabular tarsal bone; d, metatarsus. (EUenberger-Baum, 
Vnat d. Hundes.) 




ends on the medial condyle of the tibia, the tendon passing under the medial liga- 
ment of the stifle joint. 

It is not possible clearly to separate the quadriceps femoris into four heads. 
The vastus lateralis is so much larger than the vastus medialis as to indicate that 
the vastus intermedius is incorporated with the former. The rectus femoris has 
only one tendon of origin. There is a bursa under the iimscle at the distal third 
of the femur. The single patellar ligament acts as the tendon of insertion of the 
quadriceps. 



380 THE MUSCLES OF THE DOG 

The capsularis is usually present, but is small and pale. 

The sartorius consists of two parts. The anterior part arises from the tuber 
coxse and its flat tendon ends on the patella. The posterior part arises from the 
lateral border of the ilium and ends on the medial surface of the tibia, its tendon 
blending with that of the gracilis. The anterior part is superficial in front of the 
tensor fasciae latse and forms here the anterior contour of the thigh. 

The graciles are not so much fused at their origin as in the other animals. 
Its anterior part is thin. Its broad tendon is inserted into the tibial crest, and 
blends with those of the sartorius and semitendinosus. 

The pectineus is long and slender. It arises from the ilio-pectineal eminence 
and ends on the medial branch of the linea aspera above the distal end of the femur. 

The adductor femoris is a large muscle which arises on the ventral surface of 
the pubis and ischium; it ends on the linea aspera of the femur and the medial 
surface of the stifle. It is commonly separable into two parts. 

The peroneus tertius is represented by a tendinous band which arises on the 
medial surface of the tibia below the crest. It passes on the medial surface of the 
tibialis anterior, blends with the annular ligament above the tarsus, and is attached 
to the joint capsule and the proximal end of the third metatarsal bOne. 

Arloing and Lesbre say: "The third peroneus is a proper extensor of the fifth digit; it 
is a very feeble, fleshy band, situated behind the peroneus bre\as, which it partially covers. It 
is attached to the upper part of the filiula, and is continued by a long, deUcate tendon which 
passes In the same malleolar groove with the muscle mentioned; it then crosses behind the tendon 
of the peroneus longus and extends to the plialanges of the outer digit, where it joins one of the 
branches of the common extensor." 

The tibialis anterior is large and superficial. It arises on the lateral condyle 
and crest of the tibia, and is inserted into the first metatarsal bone, or into the 
first tarsal and second metatarsal. 

There are four extensors of the digits. 

1. The long digital extensor (M. extensor digitalis longus) is fusiform, and lies 
largely mider the preceding muscle. It arises from the extensor fossa of the femur. 
The tendon is bound do\vn by two annular ligaments: the proximal one, at the 
distal end of the tibia, encloses also the tendon of the tibialis anterior; the distal 
one is at the lower part of the tarsus. The tendon divides at the tarsus into 
four branches, which end on the distal phalanges of the digits (second to fifth). 

2. The lateral digital extensor (M. extensor digitalis pedis lateralis s. digiti 
quinti) has a small, unipennate belly which is covered by the peroneus longus 
and the deep digital flexor. It arises on the fibula below the head. The tendon 
descends behind that of the peroneus longus, inclines forward under the lateral 
ligament of the tarsus and the peroneus tendon, and joins the branch of the 
tendon of the long extensor for the fifth digit. 

3. The extensor hallucis longus is a very thin muscle which arises from the 
fibula under the long extensor. Its delicate tendon accompanies that of the tibialis 
anterior to the first metatarsal bone, or becomes lost in the fascia. 

4. The extensor digitalis brevis has three divisions. It arises on the fibular 
tarsal bone and the adjacent ligaments. The three tendons are inserted into 
the second, third, and fourth digits, blending with the interossei. (Sometimes 
there is a tendon for the rudimentary first digit, which may represent the extensor 
hallucis brevis. There may be a fourth belly for the tendon to the second digit.) 

The peroneus longus arises on the lateral condyle of the tibia, the head of 
the fibula, and the lateral ligament. The belly does not extend to the middle of 
the leg, and the long tendon passes down the leg parallel to the fibula. It is bound 
down in the groove of the lateral malleolus by an annular ligament, crosses the 
plantar surface of the tarsus transversely, and ends on the first metatarsal bone. 

The peroneus brevis is unipennate and arises from the distal half or more 



MUSCLES OF THE PELVIC LIMB 



381 



of the lateral face of the tibia and the fibula. Its tendon accompanies that of 
the lateral extensor over the lateral malleolus, and ends on the proximal end of the 
fifth metatarsal bone. 

The soleus is absent. (It is present and large in the cat.) 

The gastrocnemius arises from the rough lines above the condyles of the 
femur. The origin of each head contains a sesamoid 
bone about the size of a pea (Os sesamoideum m. gas- 
trocnemii), which articulates with the corresponding 
condyle of the femur. The tendon comports itself as 
in the horse. 

The superficial digital flexor has a large round 
belly. It arises in common with the lateral head of 
the gastrocnemius from the lateral rough line and sesa- 
moid bone, and from the aponeurosis of the vastus 
lateralis. The tendon winds around that of the gas- 
trocnemius, passes over the tuber calcis (where it is 
arranged as in the horse) , and divides below the tarsus 
into two branches. Each of these divides into two 
branches which end as in the forelimb. The lateral 
and medial branches detach slips to the suspensory 
ligaments of the large digital pad. Muscle-fibers 
often occur in the tendon in the metatarsal region. 

The deep digital flexor has two heads. The large 
lateral head, the flexor hallucis longus, arises from the 
posterior surface of tlie tibia and fibula, filling the in- 
terosseous space. The small medial head, flexor digi- 
talis pedis longus, also arises from the tibia and fibula; 
its tendon passes through the groove on the medial 
malleolus, inclines backward in its descent over the 
tarsus, and joins that of the large head below the 
tarsus. The common tendon detaches a branch to 
the large digital jiad and terminates as in the forelimb. 

The tibialis posterior is a very small ])ut distinct 
muscle, which arises on the proximal part of the fibula. 
The delicate tendon accompanies that of the flexor 
longus and ends on the medial ligament of the tarsus. 

The tendon of origin of the popliteus contains a 
.small sesamoid bone. 

The adductors of the second and fifth digits, the 
lumbricales, and the interossei are arrangetl as in the 
thoracic limb. 

The quadratus plantae arises on the lateral surface 
of the distal end of the fibular tarsal bone and on the 
lateral tarsal ligament, passes downward and inward, 
and terminates on a thin tendon which fuses with that 
of the deep flexor. 

The abductor digiti quinti is a very small muscle 
which consists of two parts. One of these is a tendin- 
ous slip which extends from the plantar surface of the 
proximal part of the fibular tarsal bone to the head of 
the fifth metatarsal bone ; the other part arises from 
the medial surface of the fibular tarsal bone (or from the tendinous part) and ends 
on the first phalanx of the fifth digit. 

In case the skeleton of the first digit is well developed, there are three muscles 




Fig. 327.— Mc 

Foot of Dog; Lateral 
a. Quadriceps femoris; 6, gas- 
trocnemius, lateral head; c, super- 
ficial digital flexor; d, deep digital 
flexor; e, peroneus longus; /, ten- 
don of lateral extensor; g, peroneus 
brevis; h, long digital extensor; h\ 
h'\ h"\ tendons of preceding; i, 
tibialis anterior; i-, extensor brevis; 
I, slips from interossei (m); 1, lateral 
condyle of femur; 2, patella; 3, 
tibia; 4, tuber calcis; 5, 6, annular 
ligaments. (,\fter Ellenberger, in 
Leisering's .4tlas.) 



382 THE MUSCLES OF THE DOG 

which are homologous wdth those of the same digit in the forelimb. These are 
the abductor hallucis, adductor hallucis, and flexor hallucis brevis. 

The principal bursae and synovial sheaths of the muscles of the leg and foot are as follows: 
The tibialis anterior has a bursa under its tendon at the tarsus. A pouch of the syno\'ial membrane 
of the stifle joint underlies the tendon of origin of the extensor digitalis longus, and is partially 
reflected upon the superficial face of the tendon; the tendons of insertion are provided with a 
synovial sheath which begins at the end of the muscular part and extends to the proximal part of 
the metatarsus. The tendons of the lateral digital extensor and peroneus breads have a common 
synovial sheath at the distal end of the leg and proximal part of the tarsus. The tendon of the 
peroneus longus has a syno^^al sheath which begins an inch or more above the lateral malleolus 
(in a good-sized dog) and extends about to the middle of the tarsus; another sheath ^envelops the 
tendon to the point where it bends round to the plantar surface of the hock; a bursa lies between 
the tendon and the joint capsule and fourth tarsal bone, and communicates with the joint ca\'ity. 
A bursa underUes the terminal part of the tendon of the peroneus brevis. There is a bursa in 
front of the distal part of the tendon of the gastrocnemius; it extends an inch or more (in large 
dogs) above the tuber calcis. A bursa underlies the superficial flexor tendon at the tarsus; in large 
dogs it extends about an inch above and below the tuber calcis. The tendon of the tibialis posterior 
has a synovial sheath at the cUstal end of the leg. The tendon of the flexor digitalis longus has a 
synovial sheath which begins a httlc above the medial malleolus and extends to the junction with 
the tendon of the flexor hallucis. The tarsal sheath of the flexor hallucis begins (in large dogs) 
about an inch and a half above the level of the medial malleolus and extends to the distal end of 
the tarsus; it communicates with the tibio-tarsal joint cavity. The synovial apparatus in the 
distal part of the hmb resembles that of the foreUmb. 



SPLANCHNOLOGY 

This branch deals with the viscera of the digestive, respiratory, and uro- 
genital systems.' Eacli of these systems consists fundamentally of a tube or tract 
which is lined with mucous membrane (Tunica mucosa) and communicates with 
the exterior at one end or both. Thus the epithelium of the mucous membranes 
is continuous with the epidermis at the various natural openings. In addition to 
this fundamental part there are to be considered aggregations of secreting cells 
known as glands, muscular tissue, fibrous membranes, serous membranes, vessels 
anil nerves. 

Mucous Membranes. — These vary, much in thickness, color, and other char- 
acters. In many places they form folds (Plicae mucosae) which may be temporary 
or permanent. In other places they form ridges (Rugee). With certain excep- 
tions they are moistened by a viscid secretion, termed mucus, which is derived 
from glands or gotilet cells of the epithelium. The membrane consists of two dis- 
tinct parts : the epithelium, which forms the free surface and is protective and secre- 
tory; and the lamina propria, a layer of connective tissue which contains and sup- 
ports the peripheral ramifications of the vessels and nerves. The mucous mem- 
brane is connected with surrounding structures by areolar submucous tissue 
(Tela submucosa). In many places there is a layer of unstriped muscle, the mus- 
cularis mucosae, in the deepest part of the mucous membrane. In many situa- 
tions the tunica j^ropria presents numerous elevations, known as papillae. When 
small (microscopic) , the papillae do not modify the surface of the mucous membrane, 
since the epithelium levels up the depressions between them, but when large (ma- 
croscopic) , they are conspicuous surface features, and are named according to their 
shape as conical, foliate, etc. 

Glands. — The term gland (Glandula) is usually understood to mean an aggre- 
gation of epithelial cells, the secretion of which is extruded on the free surface of the 
membrane, or is conveyed away in the blood or lymph stream.^ Glands are divided 
according to their form into two chief classes, tubular and alveolar, each of which 
may be simple or compound; many, however, combine the characters of both types 
and are termed tubulo-alveolar or alveolo-tubular. A simple tubular gland is a cylin- 
drical depression lined l>y epithelium which is continuous with that of the surround- 
ing mucous membrane, from which it develo]5ed originally as an outgroA\d:h. The 
deeper part of such a gland is termed the fundus, and here the epithelium is differ- 
entiated and has taken on secretory function. The more superficial part which 
conveys the secretion to the surface is called the duct; in it the epithelium resembles 
more or less closely that of the surrounding surface. Many glands are microscopic, 
while others are large organs. The larger ones are composed of subdivisions known 
as lobules (Lobuli), which are held together by areolar interlobular tissue; each 
loI)ule has its duct and by the union of these ducts there is formed an excretory 
duct (Ductus excretorius), through which the secretion is conveyed. Some glanils 

' The term viscus is applied in general to the organs which are contained in the body cavities. 
It is usual to exclude the heart, except when considering the thoracic organs topograpliically. 
Certain other organs which do not belong to these systems are usually considered with them as a 
matter of convenience. 

- But unicellular glands are recognized in lower forms, and in higher forms the goblet-cells 
of many mucous membranes have the same function. Other organs which are not epithelial in 
structure are commonly classed as glands; such, for example, are the lymph glands and nodules, 
the thymus, and the spleen. They are usually termed ductless or vascular glands, and are des- 
cribed with the organs with which they are associated anatomically. 

383 



384 SPLANCHNOLOGY 

consist of divisions of a larger order which are known as lobes (Lobi) ; these may be 
separated by layers of connective tissue (Septa interlobares) or by fissures (In- 
cisure interlobares) . 

There is no correspondence between the size of a gland and the number of its excretory ducts. 
Thus the largest gland in the body, the liver, has a single excretory duct, while some small glands 
have many. 

Muscular Tissue. — Most of the hollow organs are provided with a muscular 
coat (Tunica muscularis) outside of the mucous membrane. This is in great part 
composed of strata of unstriped muscle, but in certain places — and especially in the 
vicinity of the natural apertures — it consists of striped muscle. Some of the solid 
organs contain muscular tissue in their capsule or stroma. 

Fibrous Membranes. — Many viscera are enclosed by a fibrous coat (Tunica 
filiro.sa). In the case of glands such an enveloping membrane is usually called the 
capsule. Other membranes of a like character are knowii as a tunica albuginea 
or tunica adventitia; the former consist mainly of dense white fibrous tissue, while 
the latter usually contain many elastic fibers and are loo.ser in texture. 

Serous Membranes. — These are thin membranes which line the body-cavities 
and cover more or less the external surface of the viscera contained therein.^ They 
include the peritoneum in the abdomen, and the pleura and the deep layer of the 
pericardium in the thorax. Their free surface is formed by a mesothelium of 
flat cells; it is smooth and glistening and is moistened by a film of serum, thus re- 
ducing friction to a minimum. The external surface is in most places connected 
with the structure covered by areolar subserous tissue (Tela subserosa) which 
often contains fat. The part which lines the wall of a cavity is termed the parietal 
layer (Lamina parietalis), while the visceral layer (Lamina visceralis) is that which 
forms the serous coat (Tunica serosa) of the viscera. Doulile layers which connect 
viscera with the wall or with each other are in general called serous folds (Plicse 
serosse) or serous ligaments (Ligamenta serosa), but many special terms are in use 
and will be referred to later. 

' The serous membranes form closed sacs, except in the female, in which case the uterine 
tubes open into the peritoneal cavity and also communicate indirectly with tlie exterior. 



THE DIGESTIVE SYSTEM 

This apparatus (Apparatus digestorius) consists of the organs directly con- 
cerned in the reception and digestion of the food, its passage through the l)ody, 
and the expulsion of the unabsorbed portion. These organs are conveniently 
grouped under two heads, viz. : (1) the alimentary canal ; (2) the accessory organs. 

The aUmentary canal (Tractus alimentarius) is a tul)e which extends from the 
lips to the anus. It has a complete lining of mucous membrane, external to which 
is an almost continuous muscular coat. The abdominal portion of the tube is 
largely covered with a serous membrane — the visceral peritoneum. The canal 
consists of the following consecutive segments: (1) The mouth; (2) the pharynx; 
(3) the oesophagus; (4) the stomach; (5) the small intestine; (6) the large intestine. 

The accessory organs are the teeth, tongue, salivary glands, liver, and pancreas. 



DIGESTIVE SYSTEM OF THE HORSE 
THE MOUTH 

The mouth' (Cavum oris) is the first part of the alimentary canal. It is 
bounded laterally by the cheeks; dorsally, by the palate; ventrally, by the body of 
the mandible and the mylo-hyoid muscles; behind, by the soft palate. In the 
horse it is a long, cylindrical cavity, and when closed, it is almost entirely filled up 
by the contained structures; a small space remains between the root of the tongue, 
the soft palate, and the epiglottis; this may be termed the glosso-epiglottic space. 
The entrance to the mouth (Rima oris) is closed by the lips. 

The cavity of the mouth is subdivided into two parts by the teeth and alveolar 
processes. The space external to these and inclosed by the lips and cheeks is 
termed the vestibule of the mouth (Vestibulum oris). In the resting state of the 
parts the walls of this cavity are in contact, and the .space is practically obliterated. 
Its existence becomes very evident in facial paralysis, when the food tends to collect 
in it laterally, pouching out the cheeks. The space within the teeth and alveolar 
processes is termed the mouth cavity proper (Cavum oris proprium). When the 
teeth are in contact, it communicates with the vestibule only by the interdental 
spaces and the intervals behind the last molar teeth. Posteriorly it communicates 
with the pharynx through the isthjnus faucium. 

The mucous membrane of the mouth (Tunica mucosa oris) is continuous at 
the margin of the lips with the common integument, and behind with the mucous 
lining of the pharjTLX. During life it is chiefly of a pink color, but may be more 
or less pigmented. 

The lips (Labia oris) are two musculo-membranous folds which surround the 
orifice of the mouth. Their angles of union (Anguli oris s. coramissiu'se labiorum) 
are situated near the first cheek tooth and are rounded. Each lip presents two 
surfaces and two borders. The external surface is covered by the skin, which pre- 
sents long tactile hairs in addition to the ordinary fine hair. The upper lip has 
a shallow median furrow (Philtrum), the lower a rounded prominence, the chin 

'The term "mouth" is commonly used to signify either the cavity (Cavtim oris) or the 
entrance to it (Rima oris). 

25 385 



386 



DIGESTIVE SYSTEM OF THE HORSE 




THE MOUTH 387 

(Mentum). The internal surface is covered with mucous membrane which is com- 
monly more or less pigmented. The small papillae on the surface show on their 
summits the openings of the ducts of the labial glands. Small folds of mucous 
membrane which pass from the lip to the gum form the fraenula labii (superioris, 
inferioris). The free border of the lip is dense and bears short, very stiff hairs. 
The attached border is continuous with the surrounding structures. 

Structiire. — The lips are covered externally by the skin, and are lined by 
mucous membrane; between these are muscular tissue, glands, vessels, and nerves. 
The skin lies directly on the muscles, many fibers of which are inserted into it. The 
muscles have been described (p. 255). The labial glands (Glandulae labiales) 
form a compact mass at the commissures; they are numerous in the upper lip, 
fewer in the lower. The mucous membrane is often pigmented, and is reflected 
upon the lioncs of the jaws to form the gums. 

Vessels and Nerves. — The arteries are derived from the superior and inferior 
labial and palato-labial arteries. The veins go chiefly to the external maxillary 
vein. The lymph vessels go to the mandibular lymph glands. The sensory 
nerves come from the trigeminus, and the motor nerves from the facial nerve. 

The cheeks (Buccae) form the sides of the mouth, and are continuous in front 
with the lips. They are attached to the alveolar borders of the bones of the jaws. 

Structure. — This comprises: (1) The skin; (2) the muscular and glandular 
layer; (.3) the mucous membrane. The skin offers nothing in particular to notice. 
The muscular tissue is formed mainly by the buccinator, but also by parts of the 
cutaneus, zygomaticus, dilatator naris lateralis, levator nasolabialis, and depressor 
labii inferioris. The buccal glands (Glandulae buccales) are arranged in two rows. 
The superior buccal glands lie on the outer surface of the buccinator muscle, near 
its upper border. The anterior part of the row consists of scattered lobules; the 
posterior part, which lies under cover of the masseter muscle, is more developed and 
compact. The inferior buccal glands, less voluminous than the upper, are situated 
in the submucous tissue at the lower border of the buccinator muscle. The mucous 
membrane is reflected above and below upon the gums, and is continuous behind 
with that of the soft palate. It is reddish in color and frequently shows pigmented 
areas. The parotid duct opens opposite the third upper cheek tooth on a papilla 
(Papilla salivalis). Linear series of small papillae above and below indicate the 
orifices of the small ducts of the buccal glands. 

Vessels and Nerves. — The blood-supply is derived from the facial and bucci- 
nator arteries, and the blood is carried away by veins of the same name. The lymph 
vessels go to the mandibular lymph glands. The sensory nerves come from the 
trigeminus and the motor nerves from the facial nerve. 

The gums (Gingivae) are composed of a dense fibrous tissue which is intimately 
united with the periosteum of the alveolar processes, and blends at the edges of 
the alveoli with the alveolar periosteum ; the latter fixes the teeth in their cavities. 
They are covered by a smooth mucous membrane, destitute of glands, and of a 
low degree of sensibility. 

The hard palate (Palatum durum) is bounded in front and on the sides by 
the alveolar arches, and is continuous with the soft palate behind. Its osseous 
basis is formed by the premaxilla, maxilla, and palatine bones. The mucous mem- 
brane is smooth, and is attached to the bones by a submucosa which contains in 
its anterior part an exceedingly rich venous plexus, constituting an erectile tissue. 
A central raphe (Raphe palati) divides the surface into two equal portions. Each 
of these presents about eighteen transverse curved ridges (Rugae palatini) which 
have their concavity and their free edges directed backward. They are further 
apart and more prominent anteriorly. The central prominence just behind the 
first pair of incisors is the papilla incisiva; it is margined by a fissure on each side. 
There are no glands in the submucosa. The ductus incisivus (s. ductus nasopa- 



388 



DIGESTIVE SYSTEM OF THE HORSE 



latinus) is a small tube of mucous membrane which extends very obliquely through 
the palatine fissure. Its ventral or palatine end is blind and lies in the submucous 
tissue of the palate. The dorsal or nasal end communicates with the nasal cavity 
(in common with the vomero-nasal organ) by a slit-like opening in the anterior 
part of the ventral nasal meatus. 

Vessels and Nerves. — The blood-supply is derived chiefly from the palatine 

arteries and the veins go to the vena re- 
flexa. The nerves come from the tri- 
geminus. 

The soft palate (Palatum molle) 
is a musculo-membranous curtain 
which separates the cavity of the 
mouth from that of the pharynx, except 
during swallowing. It slopes down- 
ward and backward from its junction 
with the hard palate. The oral surface 
faces ventrally and somewhat forward, 
and is covered with a mucous mem- 
brane continuous with that of the hard 
palate. It presents a rounded, median 
ridge, flaioked usually by a sagittal fold 
on either side. Numerous small ducts 
of the palatine glands open on this sur- 
face. On each side a short, thick fold 
passes to the lateral border of the 
tongue; this is the anterior pillar of 
the soft palate (Areus glossopalatinus). 
The pharyngeal surface faces dorsally 
and a little backward and is covered by 
a mucous membrane continuous with 
that of the nasal cavity. The free bor- 
der (Arcus palatinus) is concave and 
thin ; it is in contact (except during deg- 
lutition) with the epiglottis. It is con- 
tinued by a fold of the mucous mem- 
brane, which passes on each side along 
the lower part of the lateral wall of the 
pharynx and unites with the opposite 
fold over the Ijeginning of the oesopha- 
gus; this fold is termed the posterior 
pillar of the soft palate (Arcus pharyn- 
gopalatinus). The space between the 
diverging anterior and posterior pillars 
(Sinus tonsillaris) is occupied by the 
tonsil (Tonsilla palatina) . In the horse, 
however, there is not a compact tonsil, 
as in man, dog, etc., but a series of 
masses of lymphoid tissue and mucous 
glands which extend liackward from 
the root of the tongue on either side a distance of about four inches (ca. 10 cm.). 
These cause elevations of the surface, on which there are depressions (crypts) in 
which the gland ducts open. The soft palate is greatly developed in equids, its 
average length, measured medially, being about six inches (15 cm.). Its length and 
contact with the epiglottis may account for the fact that in these animals mouth- 




SOFT 



LI 



Fig. 329. — Hard Palate a.vd Ad.iacent Part 
Palate of Horse, 
1, Raph^of palate; 2, ridges of palate; 3, soft palate; 
7. 1, I. 2, first and second incisor; Di. 3, deciduous third 
P. l~4t premolars; M. IS, molars. 



THE MOUTH 



389 



breathing does not occur under normal conditions, and that in vomiting the ejected 
matter escapes usually through the nasal cavity.' 

Structure. — The soft palate consists of: (1) The oral mucous membrane, 
continuous with that of the hard palate, which it resembles; it covers also a narrow 
marginal area of the pharyngeal surface along the free border; (2) the palatine 
glands (Glandulae palatinae), which form a layer about half an inch in thickness; 
(3) the aponeurotic and muscular layer; (4) the pharjTigeal mucous membrane, 
continuous with that of the nasal cavity, which it resembles. 



Septum nasi Dormil iiicatun 



N aso-lacrimal duct 



Infraorbital nerve 
and vessels 

Levator labii superi- 
oris proprius 



Dorsal turbinate 
Common meatus 



Idle meatus 
Ventral turbinate 



Superior bueeiil 
nerve 
Facial artirij 

Superior 1,urr„l 



Labial veins 
Inferior labial artery 
M ylo-hyoidcus 




Bueeitiator nerve 
Bra/ielies of lingual nerve 



Mandibular duet 
Sulilintjual gland 



Digastricus Suhliugual artery 



Fig. 330. — Cnoas-SECTioN op Head of Horse at Anterior End of Facial Crest. 

t. Cavity of dorsal turbinate: 3, cavity of ventral turbinate: 3, cavum oris: 4, 4. genio-glossi : -5, -5, genio-hyoidei; 6, 

hyo-glossus; 7, upper, 7', lower, fourth cheek tooth. Line to facial artery crosses zygomaticus. 



The muscles proper to the soft palate are the palatinus, the levator palati, 
and the tensor palati. 

The palatinus (M. palatinus) consists of two small muscular Ijundles which 
lie together at the median line. It is attached through the medium of tlie palatine 
aponeurosis to the palatine bones, and terminates near the free edge of the soft 
palate. Usually a bundle from it is continued a short distance into the posterior 
pillar. Its action is to shorten the soft palate. 

The levator palati (M. levator veli palatini) arises from the muscular process 

' The epiglottis may be either in front of or behind the soft palate; most often it is in front 
(prevelar), as shown in fig. 349. 



390 DIGESTIVE SYSTEM OF THE HORSE 

of the petrous temporal bone and from the lateral lamina of the Eustachian tube, 
and passes at first forward, lateral to the latter; it then inclines ventrally across 
the deep face of the anterior pharyngeal muscles and turns medially into the soft 
palate, in which it spreads out above the glandular layer. It raises the soft palate, 
thus closing the posterior nares during deglutition. 

The tensor palati (M. tensor veli palatini) is larger than the levator, and is 
fusiform and flattened. It arises from the muscular process of the petrous tem- 
poral bone, the pterygoid bone, and the lateral lamina of the Eustachian tube, 
and passes forward, lateral to the levator, across the medial surface of the origin of 
the pterygoideus medialis. Its tendon is then reflected around the hamulus of the 
pterygoid bone, where it is held in position by a fibrous band and lubricated by a 
bursa, turns inward and expands in the aponeurosis of the soft palate. It tenses 
the soft palate. 

Vessels and Nerves. — The blood-supply of the soft palate is derived from the 
internal and external maxillary arteries and the blood is carried away by the corres- 
ponding veins. The lymph vessels go to the pharyngeal lymph glands. The nerves 
come from the trigeminus, vagus, and glosso-pharyngeal nerves. 

The floor of the mouth in its anterior part is free and is formed by the body of 
the mandible, covered by mucous membrane. The remainder is occupied by the 
attached portion of the tongue in the undisturbed state of the parts. The follow- 
ing features are exposed by raising the tongue and drawing it to one side. About 
opposite the canine tooth on each side is a papilla, the caruncula sublingualis, 
through which the duct of the mandibular gland opens. Just behind these papillae 
is a median fold of mucous membrane which passes to the ventral surface of the 
tongue, constituting the frenum linguae. On either side is the sublingual fold 
(Plica sublingualis) which extends from the frenum to the level of the fourth cheek 
tooth. The fold indicates the position of the underlying sublingual gland, and 
presents numerous small papillae, through which the ducts open. Behind the last 
tooth a vertical fold of the mucous membrane passes from upper to lower jaw. This 
is termed the plica pterygomandibularis ; it contains a ligament of like name. 

The isthmus faucium is the orifice of communication between the mouth and 
the pharynx. It is bounded above by the soft palate, below by the root of the 
tongue, and laterally by the anterior pillars of the soft palate. It is relatively 
small and not very dilatable in the horse, and is closed by the soft palate under 
normal conditions, except during deglutition. 



THE TONGUE 

The tongue (Lingua) is situated on the floor of the mouth, between the rami of 
the mandible, and is supported mainly in a sort of sling formed by the mylo-hyoid 
muscles. Its posterior part, the root (Radix linguae), is attached to the hyoid bone, 
soft palate, and pharynx. Only the upper surface of this part is free, and slopes 
downward and backward. The middle part, the body (Corpus linguae), has three 
free surfaces. The dorsal surface is slightly rounded. The lateral surfaces are 
nearly flat for the most part, but anteriorly become rounded and narrower. The 
ventral surface is attached to the mandible. The apex or tip (Apex linguae) is 
free, spatula-shaped, and jiresents upper and lower surfaces and a rounded border. 
The term dorsum linguae is applied to the dorsal surface; it is free throughout, 
and in the resting state of the parts is in contact with the palate except at the glosso- 
epiglottic space. 

Structure. — The tongue consists of: (1) The mucous membrane; (2) the 
glands; (3) the muscles; (4) vessels and nerves. 

The mucous membrane (Tunica mucosa linguae) adheres intimately to the 
subjacent tissue, except on the lower part of the lateral surfaces of the body and 



THE TONGUE 



391 



Thyroid 



the ventral surface of the tip. It varies considerably in thickness. On the dorsum 
it is very thick and dense; underneath this part there is a dense fibrous cord, which 
extends medially a distance of five or six inches forward from the vallate papillae. 
On the sides and ventral surface of the tongue the membrane is much thinner and 
smooth, and can more readily be dissected off the muscular tissue.^ From the 
lower surface of the free part of the tongue a fold of the mucous membrane passes 
to the floor of the mouth, forming the frenum linguae. Posteriorly a fold passes 
on each side from the edge of the dor- 
sum to join the soft palate, forming the 
anterior pillars of the latter. A thick 
central glosso-epiglottic fold (Plica 
glossoepiglotticaj passes from the root 
to the base of the epiglottis; this en- 
closes the hyoepiglottic muscle. The 
mucous membrane presents numerous 
papillae, which are of four kinds — fili- 
form, fungiform, vallate, and foliate. 
The filiform papillae (Papillae filiformes) 
are fine, thread-like projections which 
stud the dorsum and the sides of the 
tip; they are absent on the root. On 
the anterior part they are so small as 
to be scarcely visible, but on the pos- 
terior part they are much larger and 
give the surface a distinct pile. The 
fungiform papillae (Papillae fungiformes) 
are larger and easily seen; they are 
rounded at the free end, which is sup- 
ported by a neck. They occur princi- 
pally on the lateral part of the tongue, 
but are also found scattered over the 
dorsum. The vallate papillae (Papillae 
vallatae) are usually two or three in 
number. The two constant ones are a 
quarter of an inch or more (ca. 6 to 7 
nun.) in diameter, and are found on 
the posterior part of the dorsum, one 
on each side of the median plane, about 
an inch (ca. 3 cm.) apart. The third, 
when present, is behind these, is cen- 
trally situated, and is always smaller. 
Rarely a fourth may be found. They 
are rounded, broader at their exposed 
than at their attached surfaces, and are 
sunk in a depression which is bounded 
by an annular wall. Their free surface 

is tuberculate, i. e., bears small, round secondary papillae. The foliate papillae 
(Papillae foliatae) are situated just in front of the anterior pillars of the soft palate, 
where they form a rounded eminence about an inch (ca. 2 to 3 cm.) in length, 
marked by transverse fissures. The last three varieties are covered with micro- 
scopic secondary papillae and are furnished with taste-buds. The mucous mem- 
brane of the root of the tongue presents numerous folds and rounded elevations. 

' The mucous membrane is thick and closely adherent where food naturally comes in contact 
with the tongue. 




Trachea 

Crico-arytenoid- 
eus dorsalis 
muscle 
Arytenoideus 

muscle 
Arytenoid carti- 
lages 

Vocal cord 

Aditus laryngis 
Epiglottis 



Radix linguae 

Anterior ■pillar oj 
soft palate (cut) 



Dorsum linguee 



Apex lingum 



OF Trachea of 



392 



DIGESTIVE SYSTEM OF THE HORSE 



The latter are marked by cryi:)ts and consist essentially of a mass of lymphoid 
tissue; they are known as lingual follicles (Folliculi linguales), and taken together 
form what is sometimes called the lingual tonsil. The lingual glands (Glandulse 
linguales) constitute a thick layer in the loose submucous tissue and also lie between 
the muscle bundles. Mucous glands are found also in part of the dorsum and sides 
of the tongue. 

The lingual muscles (Mm. linguse) may be divided into intrinsic and extrinsic. 
The intrinsic musculature consists, not of distinct muscles, but rather of systems 
of fibers which run longitudinally, vertically, and transversely, blending with the 
extrinsic muscles, which are now to be described. '^ 




Fig. 332.— Muscles of Tongue, Hvoid Bone, Pharyn.y, etc., of Horse. 
T. p., Tensor palati; L. p., levator palati; Pt. p., pterygo-pharyngeus: P. p., palato-pharyngeus; ^S. p., stylo- 
pharyngeus; Th. p., th.vro-pharyngeus; C p., crico-pharyngeus: Th. h., thyro-hyoideus; Hyo. gl., hyo-glos.sus: G. p., 
guttural pouch; F. p., foliate papilla; A. v., facial arter.v and vein. Most of the left ramus of the mandible is removed. 
The concealed parts of the hyoid bone are indicated by dotted lines. 



1. Stylo-glossus. — This is a long, thin muscle, which lies along the lateral part 
of the tongue.. It arises by a thin tendon from the lateral surface of the great 
cornu of the hyoid bone, near the articulation with the small cornu. It terminates 
near the tip of the tongue by blending with its fellow of the opposite side and with 
the intrinsic musculature. The action is to retract the tongue. Unilateral con- 
traction would also draw the tongue toward the side of the muscle acting. 

\ .small muscular band sometimes arises on the thyroid cornu of the hyoid bone and ends 
on the tendon of origin of the sty!o-glossu3. In some cases a similar band arises higher uj), with 
and on the hyo-glossus. 

2. Hyo-glossus. — This is a wide, flat muscle, somewhat thicker than the pre- 

' This distinction is more or less conventional. It is evident that much of what may appear 
on cross-sections of the tongue to be intrinsic muscle is in reality a part of the extrinsic musculature. 
The arrangement is further complicated by the existence of bundles running in various directions, 
intercrossing of bundles, and the Iireaking up of the systems by masses of fat. 



THE TONGUE 



393 



ceding. It lies in the lateral part of the root and body of the tongue, partly under 
cover of the preceding muscle. Its deep face is related to the genio-glossus. It 




Forniiwn for anterior 
hiryngeal nerve 



Depressor Inhii inferioris (slump) 



Fig. 333. — Muscles of Tongue, Pharvn.x, Larvnx, etc.; Deep Dissection, 
T. p.. Tensor palati; L. p., levator palati, concealed part indicated by dotted line; PI. 
P. p.. palato-pharyngeus; .S(. p., stylo-phary ngeus ; C. o., erico-arytenoideus dorsalis; C. Ih.. 
thyroid cartilage (lamina) ; T/i. A., thyro-hyoideus; A'. A., Iccrato-hyoideus: jT/i. r,, thyroid ( 
L. p.. lingual process; F. p., foliate papilla; Fu. p., fungiform papillae. Part of great cornu 
by dotted lines. 



>., pterygo-pharyngeus; 
rico-thyroideus; Th. c._ 
■nu; S. c, small cornu; 
removed and indicated 



arises from the lateral a.spect of the hyoid lione, from the lingual process to the oral 
extremity of the great cornu, and from the thjroid cornu. The fibers pass oliliquely 



394 DIGESTIVE SYSTEM OF THE HORSE 

forward and upward, and for the most part turn toward the median plane of the 
dorsum of the tongue. Its action is to retract and depress the tongue.' 

3. Genio-glossus. — This is a fan-shaped muscle, which lies parallel to the me- 
dian plane of the tongue. It is separated from the muscle of the opposite side by a 
layer of fat and areolar tissue. It arises from the medial surface of the ramus 
of the mandible just behind the symphysis. From the tendon the fibers pass in 
a radiating manner, some curving forward to the tip, others pass toward the dorsum, 
and others toward the root of the tongue; some fibers pass from the posterior end 
of the tendon to the body and small cornu of the hyoid bone. The muscle as a 
whole is a depressor of the tongue, and especially of its middle portion; when both 
muscles act, a median groove is formed on the dorsum. The posterior fibers pro- 
trude the tongue, the middle fibers depress the tongue, and the anterior fibers 
retract the tip of the tongue. 

In some cases there is a small anomalous muscle wliich arises by a delicate tendon with the 
genio-glossus and is attached behind with the genio-hyoideus. 

Vessels and Nerves. — The arteries of the tongue are the lingual and sub- 
lingual branches of the external maxillary artery. The veins go to the internal 
ami external maxillary veins. The lymph vessels go chiefly to the pharyngeal 
lymph glands. The sensory nerves are the lingual and glosso-pharyngeal, and the 
muscles are innervated by the hypoglossal nerve. 



THE TEETH IN GENERAL 

The teeth are hard white or yellowish-white structures implanted in the alveoli 
of the bones of the jaws. Morphologically they are large calcified papillae. Func- 
tionally they are organs of prehension and mastication, and may serve as weapons. 
The domesticated mammals have two sets of teeth. The teeth of the first set 
appear during early life and are known as deciduous or temporary teeth (Dentes 
decidui),- since they are replaced during the jieriod of growth liy tlie permanent 
teeth (Dentes permanentes) . They are classified according to form and jjosition 
as follows: 

1. The incisor teeth (Dentes incisivi) are situated in front and are implanted 
in the premaxilla and mandible. 

2. The canine teeth (Dentes canini) are situated a little further back, and 
interrupt the interalveolar space. 

3. The premolar aiid molar teeth (Dentes prsemolares et molares) form the 
sides of the dental arch. The premolars form the anterior part of the series; they 
appear in both sets. The molars appear only in the ]>ermanent dentition. The 
term cheek teeth is used to include both premolars and molars. 

The interval between the incisors and premolars is the interalveolar or inter- 
dental space. 

As the teeth of the two sides of the jaw are alike in number and character 
(in normal cases), the complete dentition may be briefly indicated by a dental 
formula such as the following: 



/ 2 1 2 :s\ 
2 I I - C - P - M - ) = 32. 
V 2 1 2 3/ 



In this formula the letters indicate the kinds- of teeth, and the figures above and 
below the lines give the number of teeth of one side in the upper and lower jaw 
respectively in man. 

' It may be possible to recognize in this muscle three parts, which would correspond to 
the baseo-, kerato-, and chondro-glossus of man. 

* They are also popularly spoken of as "milk" teeth. 



THE TEETH IN GENERAL 395 

The individual teeth of each group are designated numerically, the starting- 
point being the middle line ; thus the incisor on either side of the middle line is the 
first incisor, and may be conveniently indicated by the notation P. The deciduous 
teeth may be designated in a similar manner, prefixing D (for deciduous) to the 
letter indicating the kind of tooth. In addition to the above systematic method of 
notation other terms have received the sanction of popular usage. Thus the first 
incisors are commonly called middle incisors, "pinchers," or "nippers"; the second, 
intermediate; and the third, corner teeth. The canines, when highly developed, 
may be termed tusks or fangs. The vestigial and inconstant first premolar of the 
horse is popularly termed the "wolf tooth." 

Each tooth presents for description a part coated with enamel, termed the 
crown (Corona dentis), and a part covered with cement, termed the root (Radix 
dentis). The line of union of these parts is the neck (CoUum dentis).' In many 
teeth the neck is distinct and is embraced by the gum, e. g., the teeth of the dog 
and the temporary incisors of the horse. In other teeth no constriction is present, 
e. g., the permanent incisors of the horse. Between these extremes are the molars 
of the horse, in which the neck is seen only in advanced age. 

The surface of a tooth directed toward the lips is termed labial; that toward 
the cheek, buccal; and that toward the tongue, lingual (Facies labialis, buccalis, 
lingualis). The surface opposed to a neighboring tooth of the same dental arch 
is termed the contact surface (Facies contactus). The masticatory surface (Facies 
masticatoria) is that which comes in contact with a tooth or teeth of the opposite 
jaw.= 

Structure. — Teeth are composed of four tissues, which are considered here 
from within outward. The pulp of the tooth (Pulpa dentis) is a soft, gelatinous 
tissue, which occupies a space in the central part of the tooth termed the pulp 
cavity (Cavum dentis). The pulp is well supplied with blood-vessels and nerves. 
It occupies a relatively large space in young growing teeth, but later the dentine 
deposited on its surface gradually encroaches on it until, in advanced age, the cavity 
is much reduced or obliterated. The dentine (Substantia eburnea) forms the bulk 
of most teeth, covering the surface of the pulp. It is hard, and is yellowish-white 
in color. The enamel (Substantia adamantina) , the hardest tissue of the body, 
constitutes a layer of varying thickness covering the dentine of the crown of the 
tooth. It is easily distinguished by its clear, bluish-white appearance and its ex- 
treme density. The cement (Substantia ossea) is the outermost tooth substance. 
In simple teeth it forms usually a thin layer on the surface of the root only, but 
in complex teeth it exists in considerable quantity, tending to fill in the spaces 
between the enamel folds of the crowoi also. Its structure is practically the same 
as that of bone without Haversian canals, and even these occur where the cement 
forms a thick layer. The embedded part of the tooth is attached to the alveolus 
by a vascular layer of connective tissue, the alveolar periosteum (Periosteum 
alveolare) ; this is the periosteum of the alveolus and performs a like function 
with regard to the embedded part of the tooth. The name pericementum has also 
been applied to it. 

' It will be noted that this definition of crown and root does not agree exactly with the 
popular view that the crown is the free part and the root the embedded part. The objection to 
the latter statement lies in the fact that it is not capable of general application. Thus the mor- 
phological crown of the permanent molars in the horse is extremely long, and is, for the most 
part, embedded in the bone in the young animal. The root proper begins to form at four or five 
years of age, and continues its growth for about eight years. As the exposed part of the crown 
wears down, the embedded part erupts, thus preventing deficiency of length. On the old basis 
we should have to say that successive portions of the root become crown, while in point of fact it 
is only in very extreme age that the true root comes into wear. This difficulty does not arise in 
cases in which the eruption of the teeth is completed rapidlj', c. g., man, dog. In such brachydont 
forms the short crown is clearly marked off from the root or roots by a neck, which is embraced 
by the gum. The opposite extreme is seen in the incisors of typical rodents, which grow con- 
tinuously and have no roots. 

^ This is popularly termed the grinding surface or "table" of the tooth. 



396 



DIGESTIVE SYSTEM OF THE HORSE 



The blood-supply to the pulp is derived from the alveolar branches of the in- 
ternal maxillary artery; the nerve-supply comes from branches of the trigeminus. 



The Teeth of the Horsed 

The Permanent Teeth 
The formula of the permanent teeth of the horse is: 



(3 1 3 or 4 3 \ 
I - C - P M - I 
3 13 3/ 




?,0i^ 



Fig. 334. — Upper Teeth of Horse, About Four and _One-hAlf Fig. 335 — Lower Teeth of Horse, 

Years Old. Four Years of Age. 

/',/-. /\ Incisors: C. canine; P'. P^, /*>, PS premolars; .1/'..)^. /', I'-, First and second permanent 

.l/», molars. The eruption of the third incisor is not complete and incisors; Di's, third deciduous incisor. The 

the tooth is unworn. cheek teeth are numbered according to 

popular usage 

^ Other figures illustrating the teeth are to be found in the description of the skull. 



THE PERMANENT TEETH 



397 



In the mare the canines usually are very small and do not erupt, reducing the num- 
ber to 36 or 38.' 

Incisor Teeth. — These are twelve in num])er. The six in each jaw are placeil 
close together, so that their labial edges form almost a semicircle in the young 
horse. They have the peculiarity (not found in existing mammals other than the 
equidte) of presenting, instead of the simple cap of enamel on the crown, a deep 
invagination, the infundibulum, which becomes partly filled up with cement. 
Hence as the tooth wears, the masticatory surface (or "table") has a central ring 
of enamel surrounding this cavity in addition to the peripheral enamel. The 
cavity becomes darkened by deposits from the food, and is commonly termed 
the "cup" or "mark." Each tooth is curved so that the labial surface is convex 





Fig. .33G.— Urn.u 
The labial surface 



.\i l-'-ai Ti:i:tii of HohsE. 
i of the teeth have been exposed by i 



Fig. 337. — Lower Incisor Teeth of Horse. 
3val of the bone. Subject was five years old. 



and the embedded parts converge. The average total length of an incisor at five 
or six years of age is about two and a half to three inches (ca. 7 cm.). Thfy taper 
regularly from exposed crown to apex, without any constriction, and in such a 
mamier that in young horses the masticatory surface is broad transversely ; toward 
the middle the two diameters of a cross-section are about equal; near the apex 
the antero-posterior diameter is considerably greater than the transverse. 

This fact is of value in the determination of age by the teeth, since the mas- 
ticatory surfaces at different ages represent a series of cross-sections. As the ex- 
posed crown wears down, the embedded part (.reserve crown) emerges from the 

' Ellenberger found, as the result of extensive observations (8000 subjects), that about 
2 to 3 per cent, of mares have ervipted canines in both jaws; that 6 to 7 per cent, have them in 
the upper jaw; while 20 to 30 per cent, have them in the lower jaw. The numerical variation in 
the above formula results from the fact that the first premolar ("wolf-tooth") is often absent and 
further that it is doubtful to what set it belongs when present. It is commonly not included in 
the enumeration. 



398 



DIGESTIVE SYSTEM OF THE HOESE 



Infundibuluin 

Central enamel 
Dentine 
Peripheral 
enamel 

Cement 



alveolus, so that the masticatory surfaces of the first and second lower incisors 
are at first oval, with the long diameter transverse; 
later — at about fourteen years usually for the first 
lower incisors — they are triangular, with the base 
at the labial edge. At the same time the infundib- 
ulum or "cup" becomes smaller, approaches the 
lingual border, and finally disappears; it remains 
longer on the upper incisors, as it is deeper in 
them. Another marked feature in old age is the 
progressive approach to a horizontal direction as 
seen in profile; at the same time the exposed 
crowns of the teeth become parallel and finally 
convergent. 

Canine Teeth. — These are four in number intlae 
male; in the mare they are usually absent or rudi- 
mentary.^ They interrupt the interdental space, 
dividing it into unequal parts. The upper canine 




/ ( 'cment 



Fig. 338. — Longitudinal Section of 

Lower Incisor Tooth of Horse. 

C Pulp cavity. Cement is shown in the 

infundibulum, but is not marked. 



Peripheral 
Dentine 
Central enamel 
Cement 



Fig. 339. — Cross-section of Lower Incisor Tooth 
/. Infundibulum. 




is situated at the junction of the premaxilla and the maxilla; the lower canine is 
nearer the corner incisor. The canines are simple teeth, smaller than the incisors. 





Fig. 340. — Lower Incisor and Canine Teeth i 
Horse, Five Years Old. 
The lingual border of the third upper 



341. — Upper Incisor and Canine Teeth of 
Horse, Five Years Old. 



and are curved with the concavity directed backward. The exposed crown in the 

1 It is interesting to notice that vestigial canines are not at all uncommon in mares, espe- 
cially in the lower jaw. They are very small, and do not usually erupt; their presence is indi- 
cated in the latter case by a prominence of the gum. This is in conformity with the fact that 
they were present in both sexes in Eocene and Miocene ancestors of existing equidse. 



THE PERMANENT TEETH 



399 



young subject is compressed, convex and smooth laterally, concave with a median 
ridge medially; its edge is sharp in the unworn tooth. The embedded part (usu- 
ally called the root) is round and the pulp cavity is large, persisting to advanced 




age. In old subjects, when the compressed part of the crown has worn away, the 

exposed ]3art is rounded and blunt. 

Cheek Teeth (Premolars and Molars). '— The constant number of these is 
1 It is common in veterinary works to apply the term "molar" to all the cheek teeth since, 

in the horse particularly, the premolars are molariform, i. e., do not differ materially fron the true 

molars in size or form. The term cheek teeth convemently includes the premolars and molars. 



400 



DIGESTIVE SYSTEM OF THE HORSE 



twenty-four — twelve in each jaw. Quite commonly, however, the number is in- 
creased by the presence in the upper jaw of the so-called "wolf-tooth." This 
tooth, the first premolar, is usually situated just in front of the first well-developed 
tooth; it is a much-reduced vestige, not often more than one-half or three-fourths 
of an inch (ca. 1 to 2 cm.) in length. (It is interesting as being the remnant of a 
tooth which was well developed in the Eocene ancestors of the horse.) It may 
erupt during the first six months, and is often shed about the same time as the 
milk-tooth behind it, but may remain indefinitely. The occurrence of a similar 
tooth in the lower jaw — which rarely erupts — increases the dental formula to 44, 
which is considered the typical number for mammals.' The cheek teeth are very 
large, prismatic in form, and quadrilateral in cross-section, except the first and 

last of the series, which are three-sided. The 
Dentine Cement cro\vn is remarkably long, most of it being em- 

bedded in the bone or projecting into the max- 
illary sinus in the young horse. As the exposed 
part wears away the embedded part erupts to 
replace it, so that a functional crown of about 
four-fifths of an inch (ca. 2 cm.) is maintained. - 
The root begins to grow at about five years 
of age, and is complete at twelve to fourteen, 
although the deposition of cement may con- 
tinue indefinitely. 

The maxillary or upper cheek teeth are 
embeckled in the alveolar processes of the niax- 



Ccment 



Cement 




Root canal 




-Frontal Section oj 
EEK Tooth of Horse 



Fig. 343.- 
Ch 

C. C, Pulp cavities. Infundibulu 
witli cement. 



G. 344. — Cross-section of Upper Cheek Tooth of Horse. 
cal (lateral) surface to left. /, Anterior, I ', posterior infundib- 
uluni, both almost filled up with cement. 



ilia. The exposed parts of the crowns are normally in close contact, forming a 
continuous row which is slightly curved, with the convexity toward the cheek. 
The embedded parts diverge in the manner shown in the annexed figures (Figs. 342, 
347). Thus the long axis of the first is directed upward and a little forward, that 
of the second is almost vertical, while in the remainder it is curved backward in 
an increasing degree; the last tooth in particular is strongly curved in the adult. 
The average length at six years of age is a little more than three inches (ca. 8 cm.). 
The buccal surface presents a central ridge running lengthwise, and separating two 
grooves; the first tooth has, in addition, adess prominent ridge in front of the 
primary one. The lingual surface is marked by a wide, rounded ridge, the acces- 
sory pillar or column, which separates two very shallow grooves. The masticatory 

' The question to which set these teeth belong is an open one. 

2 For teeth of this kind it is convenient to employ the terms functional crown and reserve 



THE PERMANENT TEETH 



401 



surface presents two infundibula, anterior and posterior. It slopes obliquely down- 
waril and outward, so that the buccal etlge is prominent and sharjj. Its average 
width, except at each end of the series, is about an inch (ca. 2.5 cm.). The first 
and last teeth have three roots, the remainder four or three. 

As may be seen in Fig. 342, the individual teeth of the serie.s vary in length. In the speci- 
men from which the photograph was taken the lengths of the upper teeth in centimeters enumer- 
ated from before backward were: 6. .3, 7.7, 8.5, S.O, S.8, 8.2. The distance between the two rows 
was 6.6 cm. at the anterior end and 8.6 cm. at the posterior end. 

The position of the embedded crowns and roots of the last four varies at 

tlifferent ages and in different subjects. Two factors in this variation may be 

noted. All of these teeth are develo])ed in the posterior part of the body of the 

maxilla. As growth jDroceeds the teeth move forward, so that commonly only the 

last three, but sometimes also the third, project into 

the maxillary sinus. The second cause of variation 

is the fact that the anterior limit of the maxillary 

sinus may be at the extremity of the facial crest, or 

about an inch beyond it. In the latter case the third 

tooth projects into the sinus.' 

The mandibular or lower cheek teeth are im- 
planted in the rami of the mandiljle, forming two 
straight rows which diverge behind. The space be- 
tween the rows is considerably less than that separat- 
ing the upper teeth, especially in the middle of the 
series. The length of the lower teeth is about the 
same as that of the upper set. Their direction is 



Deidine Ccmcnl 



Cement 




Fig. 345. — Froxt.^l Sectio.x of 

Lower Cheek Tooth or Horse. 

C, Pulp cavity. Infundibulum filled 

with cement. 




Fig 346. — Cross-sectiox of Lowe 
Buccal surfac 



Cheek Tooth of Horse. 



also similar, but the embedded portions diverge even more, with the exception 
of the first and second. The long axis of the first is vertical; the remainder 
jiroject downward and backward in a gradually increasing obliquity. The buc- 
cal surface has a longitudinal furrow; the last molar has a secondary shal- 
lower furrow in addition. The lingual surface is uneven, but the grooves are 
not regular; there are usually three on the first and last tooth. The mastic- 
atory surface is oblique, sloping upward and inward in correspondence with the 
opi:)osing tooth; thus the lingual edge is prominent. Its average width (except 
at each end of the series) is somewhat less than three-fourths of an inch (ca. 1.8 cm.). 

' The student is advised to amplify these very general statements by the examination of 
heads of subjects of varying ages. It may also be noted that the position of the septum between 
the two divisions of the sinus varies much. 
26 



402 



DIGESTIVE SYSTEM OF THE HORSE 



The first five have two roots, while the sixth commonly has three. The width of the 
lower molars is a little more than half that of the upper. 

The structure is quite complex. Two infundibula rma vertically through the 







I; 1^ -^ '^ 



nn 



i ■ * 

S S^ o 



entire length of the crown; these become filled with cement. In the upper teeth 
there are five main divisions of the pulp-cavity and five enamel folds, four of which 
are arranged symmetrically, while the fifth is an outgrowth from the antero-medial 
fold.' In the lower teeth the infundibula are open along the lingual surface imtil 



THE DECIDUOUS TEETH — ERUPTION OF THE TEETH 403 

closed by deposit of cement. The pulp-cavity has two main divisions (anterior 
and posterior) and three or four secondary diverticula. The enamel folds corres- 
pond, forming a pattern even more complicated than on the upper teeth. On 
the exposed crown of the unworn tooth the enamel folds form rounded ridges 
covered with a thin layer of cement. After the tooth comes into wear the enamel 
on the masticatory surface stands out in the form of sharjj, prominent ridges. "^ 
Progressive cementation of the periphery of the tooth takes place, thus leveling up 
the irregularities of surface to a considerable extent. 

The lengths of the lower teeth shown in Fig. 342 were in centimeters: .5.7, 7.9, 9.0, 8. .5, 8.3 
7.6. The distance between the two rows was 4.7 cm. at the anterior end and 7 cm. at the posterior 
end. 

The Deciduous Teeth 
The deciduous teeth are smaller and fewer than those of the permanent set. 
The formula is: 



/ 3 3\ 
2 I Di - Dc - Dp - ) 

V 3 3/ 



24 



The deciduous incisors are much smaller than the permanent ones. They 
have a distinct neck at the junction of the crown and root. Tlic crown is short, 
white in color, and its labial surface is smooth. The infundibulum is shallow. 
The root is flattened; it undergoes absorption as the permanent tooth develops 
l.iehind it. 

The deciduous canines are quite vestigial. They occur in both sexes as slender 
spiculse about a ((ua.rter of an inch in length, but do not erupt. The lower one 
develops close to the corner incisor. They are not usually included in the formula, 
as they are never functional. 

The deciduous premolars differ from the permanent set chiefiy in that they 
have much shorter crowns than the latter. The roots form early, so that a distinct 
neck occurs. 

Vessels and Nerves. — The blood supj^ly of the teeth is derived from the 
infraorbital and ah-eolar branches of the internal maxillary artery. The lymph 
vessels go to the mandibular and pharyngeal lymph glands. The nerves come 
from the trigeminus. 

Eruption of the Teeth 
The subjoined table indicates the average periods of the eruption of the teeth: 

Teeth Eruption 

A. Deciduous: 

1st incisor (Di 1) Birth or first week. 

2nd " (Di 2) 4-6 weeks. 

3rd " . (Di 3) 6-9 months. 

Canine (Dc ) 

m premolar...... (Dp 2,| 

3rd " (Dp 4) J two weeks. 

B. Permanent: 

1st inci.sor (I 1) 2 Ja years. 

2nd " (I 2) 3)^ years. 

3rd ■' (I 3) iVi years. 

Canine '. (C ) 4—5 years. 

1st premolar (or wolf-tooth) (P 1) 5-6 months. 

2nd " (P 2) 2} ., years. 

3rd " (P 3) 3 years. 

4th " (P 4) 4 years. 

1st molar (M 1) 10-12 months. 

2nd " (M 2) 2 years. 

3rd " (M 3) 3}^-4 years. 

(The periods given for P 3 and 4 refer to the upper teeth; the lower ones may erupt 
about six months earlier.) 

' It is estimated that the enamel ridges of an upper cheek tooth of a young adult horse, if 
straightened out, would form a hne more than a foot long. The extent diminishes with age. 



404 DIGESTIVE SYSTEM OF THE HORSE 



THE SALIVARY GLANDS 

This term is usually restricted to the three pairs of large glands situated on the 
sides of the face and the adjacent part of the neck — the parotid, mandibular, and 
sublingual. Their ducts open into the mouth. 

The parotid gland (Glamlula ])arotis) (Fig. 560) — so named from its proximity 
to the ear — is the largest of the salivary glands in the horse. It is situated chiefly 
in the space between the ramus of the mandible and the wing of the atlas. It is 
somewhat triangular in shape, the apex partially embracing the base of the external 
ear, Its length is about eight to ten inches (ca. 20 to 25 cm.), and its average thick- 
ness nearly an inch (ca. 2 cm.). Its average weight is about seven ounces (ca. 
200 to 225 g.). It presents for description two surfaces, two borders, a base, and 
an apex. The lateral (or superficial) surface is covered by the parotid fascia and 
the cutaneus and parotido-auricularis muscles. It is crossed obliquely by the j ugular 
vein, which is largely embedtled in the gland. It is also related to the great auricular 
vein, the cervical branch of the facial nerve, and branches of the second cervical 
nerve. The medial (or deep) surface is very uneven, and has numerous important 
relations. Some of these are: the guttural pouch and the great cornu of the 
hyoid bone ; the masseter, occipito-mandibularis, digastricus, and occipito-hyoideus 
muscles; the tendons of the brachio-cephalicus and sterno-cephalicus (which 
separate the parotid from the underlying mandibular gland) ; the external carotid 
artery and some of its branches; the facial nerve; the pharyngeal lymph glands. 
The anterior or facial border is closely attached to the ramus of the mandiljle and 
the masseter muscle; it overlaps the latter to a varying extent.^ The posterior 
or cervical border is concave, and is loosely attached to the underlying muscles. 
The base or ventral border is related to the external maxillary vein. The apex 
is attached to the base of the external ear, which it partially embraces. The gland 
has a yellowish-gray color and is distinctly lobulated. It is inclosed in a capsule 
formed by the fascia. The parotid duct (Ductus parotideus)^ is formed at the 
ventral part of the gland, near the facial edge, by the union of three or four radicles. 
It leaves the gland about an inch (ca. 2 to 3 cm.) above the external maxillary 
vein, crosses the tendon of the sterno-cephalicus, and gains the medial face of the 
pterygoideus medialis. It then runs forward in the mandibular space below the 
external maxillary vein and winds around the ventral border of the mandible be- 
hind the vein, passes upward between the vein and the masseter muscle for about 
two inches (ca. 5 cm.), turns forward underneath the facial vessels, and perforates 
the cheek obliquely opposite the third upper cheek tootli. Before piercing the 
cheek it is somewhat dilated, but its termination is small, and is surrounded by a 
circular mucous fold (Papilla salivalis). The gland belongs to the compountl 
alveolar glands of the serous type. 

Blood-supply. — Branches of the carotid and maxillary arteries. 

Nerve-supply. — Trigeminal, facial, and sympathetic nerves. 

The mandibular or submaxillary gland (Glandula mandibularis s. submax- 
illaris)^ is much smaller than the parotid. It is long, narrow, and curved, the 
dorsal edge being concave. It extends from the fossa atlantis to the body of the 
hyoid bone, so that it is covered partly by the parotid gland, partly by the lower 
jaw (Fig. 646). Its length is eight to ten inches (ca. 20 to 25 cm.), its width an inch 
to an inch and a half (ca. 2.5 to 3 cm.), and its thickness about half an inch (ca. 
1 cm.). It weighs about one and a half to two ounces (ca. 45 to 60 g.). It is often 

* In some cases there is a well-marked triangular facial process, which covers the temporo- 
mandibular joint, the facial nerve, and the transverse facial vessels. 
' Formerly known as Stenson's or Steno's duct. 
' The term "submaxillary, " although firmly established by usage, is a misnomer. 



THE PHARYNX 405 

cliATisible into two parts. It presents for description two surfaces, two borders, and 
two extremities. The lateral surface is covered by the parotid gland, the occipito- 
mandibularis, digastricus, and pterygoideus mediahs muscles. The tendon of the 
sterno-cephalicus crosses this surface, and, together with the aponeurosis connect- 
ing it with that of the brachiocephalicus, is a useful guide in separating the parotid 
gland from it. The medial surface is related to the rectus capitis ventralis major, 
the guttural poucli, the larynx, the division of the carotid artery, and the tenth, 
eleventh, and sympathetic nerves. The dorsal border is concave and thin. It 
is related to the guttural pouch and the duct of the gland. The ventral border 
is convex and thicker. It is related to the external maxillary vein and often to 
the thyroitl gland. Tlic posterior extremity is loosely attached in the fossa atlantis. 
The anterior extremity lies at the side of the root of the tongue, and is crossed 
laterally by the external maxillary artery. The mandibular or submaxillary duct 
(Ductus mandiljularis s. submaxillaris) ^ is formed Ity the union of small radicles 
which emerge along the concave edge. It runs forward along this border, and, after 
leaving the anterior extremity, crosses the intermediate tendon of the digastricus, 
passes between the hyo-glossus and mylo-hyoideus, and gains the medial surface 
of the sublingual gland. Its terminal part lies on the body of the mandible, under 
the mucous membrane, which it pierces opposite the canine tooth. The orifice is 
at the end of a flattened papilla, the canmcula sublingualis. The gland differs 
in finer structure from the parotid in possessing serous, mucous, and mixed 
alveoli. 

Blood-supply. — Occipital, external carotid, and external maxillary arteries. 

Nei"ve-supply. — Chorda tympani and sympathetic nerves. 

The sublingual gland (Glandula sublingualis) (Figs. 330, 561) is situated be- 
neath the mucous membrane of the mouth, between the body of the tongue and the 
ramus of the mandible. It extends from the symphysis to the third or fourth 
lower cheek tooth. Its length is about five or six inches (ca. 12 to 15 cm.) and its 
weight aliout half an ounce (ca. 15 to 16 g.). It is flattened laterally, and has a 
thin dorsal border which underlies the sublingual fold of the mucous membrane 
of the floor of the mouth. The lateral surface is related to the mylo-hyoideus 
muscle, and the medial surface to the genio-glossus and stylo-glossus, the mandib- 
ular duct, and branches of the lingual nerve. The ventral border is related to 
the geniohyoid muscle. The sublingual ducts (Ductus sut)Iiuguales), about thirty 
in number, are small, short, and twisted; they open on small papillae on the sub- 
lingual fold. The gland has mixed alveoli. 

Blood-supply. — Sublingual artery. 

Nerve-supply. — Trigeminal and sympathetic nerves. 



THE PHARYNX 

The pharynx is a musculo-membranous sac which belongs to the digestive and 
respiratory tracts in common. It is somewhat funnel-shaped, the large anterior 
part joining the mouth and nasal cavity, while the small end is continued by the 
oesophagus. Its long axis is directed obliquely downward and backward, and has 
a leng-th of about six inches (ca. 15 cm.). The pharynx is attached by its muscles 
to the palatine, pterygoid, and hyoid bones, and to the cricoid and thyroid cartilages 
of the larynx. 

Its principal relations are : dorsally, the base of the cranium and the guttural 
pouches; ventrally, the larynx; laterally, the medial pteryoid muscle, the great 
cornu of the hyoid bone, the external carotid and external maxillary arteries, the 

' Formerly known as Wharton's duct. 



406 



DIGESTIVE SYSTEM OF THE HORSE 



glosso-pharyngeal, anterior laryngeal, and hypoglossal nerves, the mandibular 
salivary gland, and the parapharjiigeal Ijinph glands. 

The cavity of the pharynx (Cavum pharyngis) presents seven openings. 
Through the posterior nares or choanae it communicates dorsally with the nasal 
cavity. The pharjmgeal orifices of the two Eustachian tubes (Ostia pharyngea 



Nerms III, 
IV, VI, and 
ophthalmic 
IriUriial max- 
illary artery 
Transverse 
facial nerve 
Buccinator- 
nerve 
Inferior al- 
veolar nerve 

Inferior al- 
veolar artery 

Great cornu of. 
hyoid bo7ie 

lAngual branch. 

of IX nerve 
External max- 
illary artery 
Hypoglossa 
nerve 

Masseteric. 



Thyroid cornv. 
of hyoid bone 




Temporal muscle 



Parotid duct 



Lymph gland 



('monoid process 



Transverse fa- 
cial vessels 
Transverse fa- 
cial nerve 
Lateral ptery- 
goid muscle 

Internal maxil- 
lary vein 

Medial pteryoid 
muscle 

Ramus of man- 
dible 

Hyo-phnryngeus 
muscle 

Isthmus faucium 

■Tonsil 

igastricus (in- 
termed, tendon) 

Anterior end of 
mandibidar gland 

Sublingual vein 

External maxil- 
lary vein 



Fig. 348. — Cross-section of Head of Horse. 
The section passes through the anterior part of the temporo-mandibular articulation, but is slightly oblique, passing 
a few millimeters further forward on left side than on right. 1, Corpus callosum; 2, lateral ventricle of brain; 5, 
caudate nucleus; .J, internal capsule; 5, lenticular nucleus; 6. optic chiasma; 7, middle cerebral artery; 5, sphenoidal 
sinuses; 9, cavernous sinus; 10, Eustachian tube, medial lamina; It, 11, guttural pouches; 13, soft palate; 13, epi- 
glottis; ^4, byo-epiglottic muscle; ^5, thyro-hyoid muscle. The tensor palati (not marked) lies medial to the ptery- 
goideus lateralis, and medial to the tensor is the levator palati, which blends above with the outer lamina of the Eustach- 
ian tube. 



tubiB auditivffi) are situated on the lateral wall behind the posterior nares and below 
the level of the ventral nasal meatus. They are slit-like openings, directed ob- 
liquely downward and backward, and are a little more than an inch (ca. 3 cm.) 
in length. They are bounded medially by a fold which encloses the expanded 
extremity of the cartilaginous Eustachian tube. The isthmus faucium is the oral 
open"ng; it is closed by the soft palate except during swallowing. The aditus 



THE PHARYNX 407 

laryngis occupies the greater part of the ventral wall or floor of the pharynx; it 
is open except during deglutition. Behind this is the aditus oesophagi, the entrance 
to the CESophagus. 

The wall of the pharynx comprises, from without inward, the muscles, the 
pharyngeal aponeurosis, and the mucous membrane. 

The muscles of the pharyixx (Mm. pharyngis) (Figs. 332, 333) are covered 
by the pharyngeal fascia, which is attached to the base of the skull, the great cornu 
of the hyoid bouc, and the thyroid cartilage of the larynx. They are as follows: 

1. The stylo-pharyngeus arises from the medial surface of the dorsal third 
of the great cornu of the hyoitl bone, passes ventro-medially, and enters the wall of 
the pharynx by passing between the pterygo-pharyngeus and palato-pharyngeus. 
Its fibers radiate, many bundles passing forward, others inward or backward be- 
neath the hyo-pharyngeus. It raises and dilates the pharynx to receive the bolus 
in swallowing. 

2. The palato-pharyngeus arises chiefly by means of the aponeurosis of the 
soft palate from the jxilatine and pterygoid bones; some fibers are attached to the 
anterior wide part of the Eustachian tube. Its fibers pass backward on the lateral 
wall of the pharynx, and are inserted in part into the upper edge of the thyroid 
cartilage, in part turn inward to end at the median fibrous raphe. Its action is to 
shorten the pharynx, and to draw the larynx and oesophagus toward the root of the 
tongue in swallowing.^ 

3. The pterygo-pharyngeus is flat and triangular. It lies on the anterior part 
of the lateral wall of the jiharynx. It arises from the pterygoid bone above the 
preceding muscle, — from which it is not distinctly separated, — crosses the levator 
palati, antl is inserted into the m<^clian raphe. Its action is similar to the preceding. 

4. The hyo-pharyngeus may consist of two parts: 

(a) The kerato-pharyngeus is a small and inconstant muscle which arises 
from the medial surface of the great cornu of the hyoid bone near its ventral end. 
It passes ujjward and backward on the lateral face of the palato-pharyngeus, 
turns toward the rajihe, and spreads out under the next muscle. 

(6) The chondro-pharyngeus, broad and fleshy, arises from the thyroid cornu 
of the hyoid bone and by a thin fasciculus from the lamina of the thyroid cartilage. 
The bundles spread out and end at the median raphe. The posterior part dips 
under the thyro-pharyngeus, while the anterior part overlies the pterygo- and 
palato-pharyngeus. 

5. The thyro-pharyngeus arises from the lateral surface of the lamina of the 
thyroid cartilage on and behind its oblique line. Its fibers pass forward and 
medially to the median i-aphe. 

6. The crico-pharyngeus arises from the lateral part of the arch of the cricoid 
cartilage and entls at the raphe. The fibers are directed upward, forward, and 
inward ; they blend behind with the longitudinal fibers of the oesophagus. 

The last three muscles are constrictors of the pharynx. 

The pharjmgeal aponeurosis is attached to the base of the cranium. It is 
well developed on the medial face of the palato-pharyngeus muscle and forms a 
median raphe pharyngis dorsally, which is wide in its posterior part. 

The mucous membrane of the pharynx is continuous with that of the several 
cavities which open into it. It is thin and closely adherent to the base of the skull 
in the vicinity of the posterior nares, where the muscular wall is absent. Behind 
the Eustachian openings there is a median cul-de-sac, the phar3mgeal recess (Re- 
cessus pharyngeus). The recess is somewhat variable, l3ut is usually al)out an inch 
in depth and will admit the end of the finger. In the ass and mule it is much deeper. 
Here also the muscular wall is absent and the mucous membrane lies against the 

1 Vermeulen states that the pharyngeal orifice of the Eu.stachian tube is opened by the 
contraction of that part of the muscle which is attached to the tube. 



408 



DIGESTIVE SYSTEM OF THE HORSE 



guttural pouches. From the Eustachian opening a fold of the mucous membrane 
(Plica salpingo-pharyngea) passes toward but does not reach the aditus laryngis. 
A horizontal fold, the posterior pillar of the soft palate (Arcus pharyngo-palatinus), 
passes along the ventral part of the lateral wall and iniites with its fellow over the 
entrance to the oesophagus. The dorsal part of the cavity (Pars respiratoria) 
is lined with a ciliated epithelium, while the ventral jjart (Pars digestoria) has a 
stratified squamous epithelium. The communication between the two is oval 




Fig. 349. — Posterior Part of a Sagittal Section of Head and Part of Neck of Hohse, Cut about 1 cm. to the 
Left of the Median Plane. 
1, Posterior nares; 2, pharyngeal orifice of Eustachian tube; S, aditus laryngis; 4, aditus oesophagi; 5, posterior 
pillar of soft palate; 6\ junction of 6 with its fellow over entrance to oesophagus; 6, epiglottis; 7, body of thyroid 
cartilage; S, arytenoid cartilage; 9, 9, cricoid cartilage; 10, true vocal cord; 11, false vocal cord; 12, lateral ventricle 
of larynx; 13, crico-arytenoideus dorsalis; 14, cesophagus; lo, external carotid artery; 16, hypoglossal nerve; 17, 
glosso-pharyngeal nerve; iS, great cornu of hyoid bone; i9, Eustachian tube; 20, body of hyoid bone; 2i, hyoideus 
transversus; 2S, ridges of hard palate; 2«', soft palate; gS, septum between frontal sinuses; 24, olfactory mucous 
membrane; £S, sphenoidal sinus; Be, basilar part of occipital bone; 28', supra-occipital; 27, body of sphenoid bone; 
2S, pituitary body; 29, chiasma opticum; SO, corpora quadrigemina; 32, thalamus; S2, arachnoid; SS, odontoid 
ligament; 34, posterior auricular muscles. 



and is bounded by the free edge of the soft palate and its posterior pillars; it is 
termed the pharyngeal isthmus. On either side of the aditus laryngis is a narrow 
deep depression, the piriform recess (Recessus piriformis). 

The submucous tissue contains numerous mucous glands (OlandulEe pharyn- 
gese). In the young subject the lymph follicles are numerous and form a collection 
dorsally and between the Eustachian openings, known as the pharyngeal tonsil 
(Tonsilla pharyngea). 



THE (ESOPHAGUS 409 

Vessels and Nerves. — The arteries are derived from the common carotid, 
external carotid, and external maxillary arteries. The lymph vessels pass to the 
pharyngeal and anterior cervical lymph glands. The nerves are derived from the 
trigeminus, glosso-pharyngeus, and vagus. 



THE (ESOPHAGUS 

The oesophagus is a musculo-membranous tube, about 50 to 60 inches (ca. 
125 to 150 cm.) in length, which extends from the pharynx to the stomach. In 
its course it shows several changes of direction. It begins in the median plane above 
the anterior border of the cricoid cartilage of the larynx. At the fourth cervical 
vertebra it has passed to the left side of the trachea, and continues this relation 
as far as the third thoracic vertebra. Here it again gains the dorsal surface of the 
trachea, and, passing backward, crosses the aortic arch, by which it is pushed over 
to the right of the median plane. It continues in the mediastinum between the 
lungs, backward and a little dorsally, inclining gradually to the left, and reaches 
the hiatu.s cesophageus of the diaphragm. Passing through this it terminates at 
once at the cardiac orifice of the stomach,. a little to the left of the median plane, 
and about four or five inches (ca. 10 to 12 cm.) ventral to the vertebral end of the 
fourteenth rib.^ 

Viewed with reference to the horizontal plane, its course is downward and 
backward till it enters the thorax and passes upward to gain the dorsal face of 
the trachea. Then for a short distance (i. e., to the root of the lung) its direction is 
almost horizontal; behind this it passes somewhat upward to its termination. 
The cervical part (Pars cervicalis) of the tube is about four to six inches (10 to 15 
cm.) longer than the thoracic part (Pars thoracalis), while the so-called abdominal 
part (Pars abdominalis) is aljout an inch (2 to .3 cm.) long.- 

The principal relations of the oesophagus at its origin are: to the cricoid 
cartilage and dorsal crico-arytenoid muscles ventrally; to the guttural pouches 
and the ventral straight muscles dorsally; and to the carotid arteries laterally. 
In the middle of the neck the relations are: to the left longus colli muscle dorsally; 
to the trachea medially; to the left carotid artery, vagus, sympathetic, and recurrent 
nerves laterally. Near the thoracic inlet the oesophagus is usually in contact 
with the left jugular vein for a short distance. At its entrance into the thorax 
it has the trachea on its medial side; the first rib, the roots of the Ijrachial plexus 
of nerves, and the left posterior cervical ganglion laterally. After gaining the 
dorsal surface of the trachea, it has the aorta on its left and the vena azygos and 
right vagus nerve on its right side. In its course through the posterior medias- 
tinum the oesophageal trunks of the vagus nerves lie above and below it, and the 
oesophageal artery is dorsal to it. 

Structure. — The wall is composed of four coats: (1) A fibrous sheath tenned 
the tunica adventitia; (2) the muscular coat; (3) a submucous layer; (4) the 
mucous membrane. The muscular coat is of the striped variety as far as the base 
of the heart, where it rapidly changes to the unstriped type. In addition to this 
change, the muscular coat becomes much thicker and firmer, while the lumen is 
diminished. Except at each end of the tube the muscular coat consists chiefly of 

' The distance between the terminal part of the cesophagus and the vertebra varies. In 
formalin-hardened subjects it is most commonly as given above, but in soft specimens or in those 
which have been frozen without previous fixation it is usually nearer the spine. 

' Careful observations (especially on frozen subjects and those in which the organs have been 
hardened in situ) show that there is no abdominal part of the oesophagus in the strict sense of the 
term. The stomach here lies directly on the diaphragm, so that the last inch or so of the oesopha- 
gus is placed obliquely in the hiatus cesophageus, and is coveretl on the right and ventrally by the 
pleura, but not by peritoneum. In soft subjects the weight of the stomach, or traction on it, draws 
part of the oesophagus into the abdomen, inclosed in a collar of peritoneum. 



410 DIGESTIVE SYSTEM OF THE HORSE 

two layers of fibers arranged spirally or elliptically, which interbross dorsally and 
ventrally. At the origin two bundles nearly an inch (ca. 2 cm.) wide arise from 
the wide posterior part of the pharyngeal raphe and from a tendon common to 
the crico-pharyngeus and thyro-pharyngeus. These bundles, which blend and 
decussate at their origin, diverge and pass to each side of the oesophagus. In the 
angle between them a deeper laj'er of circular fibers is visible. Two small ventral 
bundles emerge from the depression between the lamina of the cricoid cartilage 
and the arytenoid cartilages. These curve around to the side of the cesophagus 
and blend with the dorsal bundles before described. In the terminal part there 
is an external longitudinal layer and an internal circular layer, the latter being 
extremely thick. The mucous membrane is pale, and is covered with squamous 
stratified epithelium. It is loosely attached to the muscular coat by an abundant 
submucosa, and lies in longitudinal folds which obliterate the lumen except during 
deglutition.' 

Blood-supply. — Carotid, broncho-cesophageal, and gastric arteries. 

Nerve-supply. — Vagus, glosso-pharyngeal, and sympathetic nerves. 



THE ABDOMINAL CAVITY 

The abdominal cavity (Cavum abdominis) is the largest of the Ijody cavities. 
It is separated from the thoracic cavity by the diaphragm and is continuous behind 
with the pelvic cavity. The line of demarcation between the abdominal and 
pelvic cavities is known as the terminal line, or brim of the pelvis; it is formed Ijy 
the base of the sacrum dorsally, the ilco-jjectineal lines laterally, and the anterior 
borders of the pubic bones ventrally. 

The cavity is ovoid in form, l^ut is somewhat compressed laterally. Its long 
axis extends obliquely from the center of the pelvic inlet to the sternal part of the 
diaphragm. Its dorso-ventral diameter is greatest at the first lumbar vertebra, 
while its greatest transverse diameter is a little nearer the pelvis. 

The dorsal wall or roof is formed by the lumbar vertebrae, the lumbar muscles, 
and the lumbar part of the diaphragm. 

The lateral walls arc formed by the oblique and transverse abdominal muscles, 
the abdominal tunic, the anterior parts of the ilia with the iliacus muscles, the 
cartilages of the asternal ribs, and the parts of the posterior ribs which are below 
the attachment of the diaphragm. 

The ventral wall or floor consists of the two recti, the aponeuroses of the oblique 
and transverse muscles, the abdominal tunic, and the xiphoid cartilage. 

The anterior wall is formed by the diaphragTn, which is deeply concave, thus 
greatly increasing the size of the abdomen at the expense of the thorax. 

It should be noted that the diaphragm also concurs practically in the formation of a con- 
siderable part of the lateral walls, since its costal part even during ordinary inspiration lies directly 
on the ribs over a width of four or five inches (ca. 10 to 12 cm.); in expiration this area of contact 
includes about all of the costal part. This fact is of clinical importance, with reference to auscul- 
tation and percussion and penetrating wounds. The cupola of the diaphragm extends as far 
forward as a plane through the sixth rib to the right of the heart. 

The muscular walls are lined by a layer of fascia, distinguished in different 
parts as: (1) The diaphragmatic fascia; (2) the transversalis fascia; (3) the iliac 
fascia; (4) the deep layer of the lumbo-dorsal fascia. 

The subserous tissue (Tela subseros^) vmites the fascia and peritoneum. 

' The potential lumen is difficult to determine at all accurately. When distended, its average 
diameter (according to Rubeli) is a little more than 6 cm. The thickness of the wall varies (in- 
versely as the lumen) from 0.4 to 1.2 cm. or more. The change in type of the muscular tissue is 
gradual, and begins in the deep part; bimdles of striped muscle are present even after the apparent 
change to unstriped muscle, and may extend to the stomach. In the posterior part of the tube 
many bundles intercross in an irregular plexiform manner. 



THE PERITONEUM 411 

It is areolar tissue, and is more or less loaded with fat according to the condition 
of the subject, except over the diaphragm. It sends laminae into the various 
peritoneal folds. 

The peritonemn, the serous membrane which lines the cavity, wU be described 
later. 

The abdominal walls are pierced in the adult by five apertures. These are 
the three foramina of the diaphragm and the inguinal canals, which have been 
described. In tlie foetus there is the umbilical opening also. This transmits the 
urachus, a tube which connects the bladder with the allantois; the two umbilical 
arteries, which carry blood from the foetus to the placenta; and the umbilical 
vein, which returns blood from the placenta to the liver of the foetus. After birth 
the orifice is closed by fibrous tissue, leaving a scar, the umbilicus, which is more 
or less distinctly visible in the median ventral line in a transverse plane about 
tangent to the ventral end of the last ril). 

The cavity contains the greater part of the digestive and urinary organs, part 
of the internal genital organs, numerous nerves, blood vessels, Ijnnpli vessels and 
glands, ductless glands (spleen and adrenal bodies), and certain foetal remains. 

For topographic purposes the abdomen is divided into nine regions by imagi- 
nary planes.' Two of these planes are sagittal and two are transverse. The 
sagittal planes cut the middles of the inguinal ligaments; the transverse planes 
pass through the last thoracic and fifth lumbar vertebrae, or the ventral end of the 
fifteenth rib and the tuber coxae respectively. The transverse planes divide the 
abdomen into three zones, one behind the other, viz., epigastric, mesogastric, 
and hypogastric: these are subdivided by the sagittal planes as indicated in the 
subjoined table: 

Left parachondriac Xiphoid Right parachondriac 

Left lumbar Umbilical Right lumbar 

Left iliac Prepubic Right iliac 

Other useful regional terms are: sublumbar, diaphragmatic, inguinal. The 
first two reciuire no explanation. The inguinal regions (right and left) lie in front 
of the inguinal ligament. The flank is that part of the lateral wall which is formed 
only of soft structures. The triangular depression on its upper part is termed 
the paralumbar fossa; this is bounded dorsally by the lateral border of the lon- 
gissimus, ventrally by the upper border of the oblicjuus abdominis internus, and 
in front by the last rib. 

THE PERITONEUM = 

The peritoneum is the thin serous membrane which lines the abdominal cavity 
and the pelvic cavity (in part), and covers to a greater or less extent the viscera 
contained therein. In the male it is a completely closed sac, but in the female 
there are two small openings in it ; these are the abdominal orifices of the uterine 
or Fallopian tubes, which at their other ends communicate with the uterus, and so 
indirectly with the exterior. The peritoneal cavity (Cavum peritonaei) is oi^ly a 
.potential one, since its opposing walls are normally separated only by the thin 
film of serous fluid (secreted by the membrane) which acts as a lubricant.^ 

The free surface of the membrane has a glistening appearance and is very 
smooth. This is due to the fact that this surface is formed by a layer of flat mes- 

1 This method of division, although long in use, is practically valueless for accurate descrip- 
tion. It is mentioned here chiefly because agreement on a more useful topographic method has 
not been arrived at. 

- Only a general account of the arrangement of the peritoneum is given in this section, since 
a detailed description cannot be understood without a knowledge of the viscera concerned. 

' It is necessary' not to confuse the peritoneal ca^^ty with the abdominal ca\'ity. The 
organs are all extraperitoneal and the peritoneal cavity contains only the serous fluid. 



412 



DIGESTIVE SYSTEM OF THE HORSE 



othelial cells, and is moistened by the peritoneal fluid. Friction is thus reduced 
to a minimum during the movements of the viscera. The outer surface of the peri- 
toneum is related to the subserous tissue, which attaches it to the abdominal wall 
or the viscera. 

In order to understand the general disposition of the peritoneum, we may 
imagine the abdominal cavity to be empty and lined by a simple layer of perito- 
neum, termed the parietal layer (Lamina parietalis). We may further imagine 
the organs as beginning to develop in the subserous tissue, enlarging, and migrat- 
ing into the abdominal cavity to a varying extent. In doing so they carry the per- 
itoneum before them, producing introversion of the simple sac, and forming folds 
which connect them with the wall or Math each other. The viscera thus receive 
a complete or partial covering of peritoneum, termed the visceral layer (Lamina 
visceralis). The connecting folds are termed omenta, mesenteries, ligaments, 
etc. They contain a varying quantity of coimective tissue, fat, and lymph glands, 

and furnish a path for the vessels and nerves of 
the viscera. Some contain unstriped muscular 
tissue. An omentum is a fold which passes from 
the stomach to other viscera. There are three of 
these, namely: (1) Thelesser omentum (Omentum 
minus), ^ which passes from the lesser curvature of 
the stomach to the liver; (2) the gastro-splenic 
omentum (Ligamentum gastrolienale), which ex- 
tends from the greater curvature of the stomach 
to the spleen; (3) the greater omentum (Omen- 
tum majus),^ which passes from the greater curva- 
ture of the stomach and from the spleen to the 
terminal part of the great colon and the origin of 
the small colon. It does not pass directly from 
one organ to the other, but forms an extensive 
loose sac (ligs. 377, 378). A mesentery (Mesen- 
terium) is a fold which attaches the intestine to 
the dorsal wall of the abdomen. There are two 
mesenteries, namely: (1) The great mesentery, 
which connects the greater part of the small in- 
testine with the dorsal abdominal wall; (2) the 
colic mesentery, which attaches the small colon 
to the dorsal al xlominal wall. Ligaments are folds 
which pass between viscera other than parts of the 
digestive tube, or connect them with the abdom- 
inal wall. The term is also applied to folds which attach parts of the digestive tract 
to the abdominal wall, but do not contain their blood-vessels and nerves. Some (e. g., 
the lateral and coronary ligaments of the liver) are strengthened by fibrous tissue ; 
others (e. g., the broad ligaments of the uterus) contain also unstriped muscular 
tissue. 




Fig. 350. — Diagrammatic Cross-section 

OF Abdomex. 

To show arrangement of peritoneum 

when reduced to its simplest form. The 

external black line indicates the body-wall. 

1, Organ (e. g„ kidney) in contact with wall; 

2, organ (e. g., small intestine) at a dis- 
tance from wall; 3, parietal peritoneum; 4, 
4, visceral peritoneum; 5, mesentery; C, 
peritoneal cavity. 



THE PELVIC CAVITY 

The pelvis is the posterior part of the trunk. It incloses the pelvic cavity 
(Cavum pelvis), which conmiunicates in front with the abdominal cavity, the line 
of demarcation being the terminal line or pelvic brim. 

The dorsal wall or roof is formed by the sacrum and first three coccygeal 
vertebrae. The lateral walls are formed by the parts of the ilia behind the ilio- 

' Also known as the gastro-hepatic omentum. 
^ Also known as the gastro-colic omentum. 



THE PELVIC CAVITY 



413 



pectineal lines and the sacro-sciatic ligaments. The ventral wall or floor is formed 
by the pubic and ischial bones. The boundary of the outlet is formeil l^y the third 
coccygeal vertebra dorsally, the ischial arch ventrally, and the posterior edges 
of the sacro-sciatic ligaments and the semi- 
membranosus muscles laterally. The out- 
let is closed by the perineal fascia ; this con- 
sists of superficial and deep layers which 
are attached around the margin of the outlet 
and centrally to the organs at the outlet — 
the anus and its muscles, the vulva (in the 
female), and the root of the penis (in the 
male) . 

The cavity contains the rectum, parts 
of the internal genital and urinary organs, 
some foetal remnants, muscles, vessels, and 
nerves. It is lined by the fascia pelvis, and 
in part by the peritoneum. 

The pelvic peritoneum is continuous in 
front with that of the abdomen. It lines the 
cavity for a variable distance backward, and 
is then reflected on to the viscera, and from 
one organ to another. We may therefore distinguish an anterior, peritoneal, and a 
]30sterior, retroperitoneal, part of the cavity. Along the middorsal line it forms 
a continuation of the colic mesentery, the mesorectum, which attaches the first or 
peritoneal part of the rectum to the roof. In animals in fair condition a consider- 




FlG, 



OF Sagittal Section" 
TO SHOW Disposition 



Male Pelvis to 

Peritoneu-m. 

o, Sacro-rectal pouch, continuous laterally with 
b, recto-genital pouch; c, vesico-genital pouch; rf, 
vesico-pubic pouch. The lateral line of reflection 
of the peritoneum is dotted. 





Fig. 352. — Schematic Cross-section to Seow Ar- Fig. 353. — Schematic Cross-section to Show Ar- 

rangement OF Pelvic Peritoneum in the Male. rangement of Pelvic Peritoneum in the Female. 

o. b. Recto-genital pouch; c, c, vesico-genital pouch; d, d, vesico-pubic pouch; 1, mesorectum; 2. 2, genital folds 
in male, broad ligaments of uterus in female; 3, 3, lateral ligaments of bladder; 4, middle ligament of bladder; v,d., 
ductus deferentes; u.m., uteru^j masculinus. 



able quantity of subserous and retroperitoneal fat is found on the walls and in the 
various interstices. 

In the male the general disposition of the peritoneum here is as follows. If 
traced along the dorsal wall, it is reflected from the sacrum on to the rectum, 



414 DIGESTIVE SYSTEM OF THE HORSE 

forming the visceral peritoneum for the first part of that tube.' Laterally it is 
reflected in a similar fashion. If the rectum be raised, it will be seen that the 
peritoneum passes from its ventral surface and forms a transverse fold which lies 
on the dorsal surface of the bladder (Fig. 370). This is the genital fold (Plica 
genitalis). Its concave free part passes on either side into the inguinal canal. 
The ventral layer of this fold is reflected on to the dorsal surface of the bladder. 
Thus there is formed a pouch between the rectum and bladder — the recto-vesical 
pouch (Excavatio recto-vesicalis), which is partially subdivided by the genital 
fold into recto-genital and vesico-genital cavities. The fold contains the ductus 
deferentes, part of the vesiculse seminales, and the uterus masculinus (a foetal 
remnant). If the bladder is now raised, it is seen that the peritoneum passes 



Left exlremity 




Ayttriiiii pi/loricuin 



Fig. 354. — Stomach of Horse; Parietal Surface. 

The organ was fixed in situ when well filled. The lesser curvature has been opened up slightly and the peritoneum, 

etc., in this vicinity removed. The larger branches of the anterior gastric artery and vein are visible. 

from its ventral surface on to the pelvic floor, forming centrally the median um- 
bilical fold or middle ligament of the bladder (Plica umbilicaUs mctlia). It also 
passes from each side of the blatlder to the lateral pelvic wall and forms thus 
the lateral umbilical fold or ligament of the blackler (Plica umbihcalis lateralis); 
this contains in its edge the so-calleil roimd ligament of the bladder (Ligamentum 
teres vesicae) — the partially occluded umbilical artery, which is a large vessel 
in the foetus.^ 

In the female the arrangement is modified by the presence of the uterus; 

' The point at which the reflection takes place is quite variable, and apparently depends 
chiefly on the amount of feces in the rectum. When the bowel is very full the reflection may be 
little behind the promontory; when it is empty, the reflection may be at the posterior end of the 
sacrum. 

^ In the foetus and new-born foal these three folds extend to the umbilicus in conformity with 
the abdominal position of the Ijladdcr. When the latter becomes a pelvic organ, the lateral folds 
conform to the change and end at the verte.x of the bladder. The median fold may still be trace- 
able to the umbilicus. 



THE STOMACH 



415 



the genital fold is enlargi 
It forms two extensive 
uteri), which attach th, 
part of the abdominal 
completely into dorsal 
cavatio recto-uterinal) 
Further details will 



:ed, so as to inclose the uterus and a small part of the vagina, 
folds, the broad ligaments of the uterus (Ligamenta lata 
at organ to the sides of the pelvic cavity and the lumbar 
wall (Big. 530). It thus divides the recto-vesical pouch 
and ventral compartments — the recto-genital pouch (Ex- 
and the vesico-genital pouch (Excavatio vesico-uterina). 
be given in the description of the pelvic viscera. 



THE STOMACH 
The stomach (Ventriculus) is the large dilatation of the alimentary canal 
behind the diaphragm ; it intervenes between the oesophagus and the small intestine. 
It is a sharply curved, U-shaped sac, the right part being, however, much shorter 



Area of attachment to dia- 
phragm (non-peritoneal) 




Fig. 355. — Stomach of Horse; Visceral Sdkface, with Fihst Part of Ddodenum. 
Fixed in silu when full but not distended. The posterior gastric artery and its larger branches with two satellite i 

are shown. 



than the left one. The convexity is directed ventrally. When moderately dis- 
tended, there may be a slight constriction which indicates the division into right 
and left sacs. It is relatively small, and is situated in the dorsal part of the ab- 
dominal cavity, behind the diaphragm and hver, mainly to the left of the median 
plane. 

It presents for description two surfaces, two curvatures, and two extremities. 
The parietal surface (Fades parietalis) is convex and is directed forward, upward, 
and toward the left ; it lies against the diaphragm and liver. The visceral surface 
(Facies visceralis), also convex, faces in the opposite direction; it is related to the 
terminal part of the large colon, the pancreas, the small colon, the small intes- 



416 



DIGESTIVE SYSTEM OF THE HORSE 



tine, and the greater omentum. The liorders between these surfaces are 
termed the curvatures. The lesser curvature (Curvatura ventricuH minor) 
is very short, extending from the termination of the a?sophagus to the junc- 
tion with the small intestine. When the stomach is in situ, its walls are here in 
contact, and the cardia and pylorus close together.^ The greater curvature (Cur- 
vatura ventriculi major) is very extensive. From the cardia it is first directed 
dorsally and curves over the left extremity; it then descends, passes to the right, 
crosses the median plane, and curves upward to end at the pylorus. Its left part 
is related to the spleen, while its ventral portion rests on the left parts 
of the great colon. The left extremity (Extremitas sinistra) has the form of a 
rounded cul-de-sac termed the saccus csecus ; it lies ventral to the left crus of the 
diaphragm, and so beneath the dorsal ])art of the sixteenth and seventeenth ribs. 
It is related to the pancreas and the termination of the great colon Ijehind and the 
base of the spleen laterally. The right or pyloric extremity (Extremitas dextra) 

is much smaller and is continuous with 
the duodenum, the junction being in- 
dicated by a marked constriction. It 
lies just to the right of the median 
]ilane, and about two inches (ca. 5 cm.) 
lower than the cardia; it is in contact 
with the visceral surface of the liver. 
Aljout two or three inches (ca. 5 to 8 
vm.) from the pylorus there is a con- 
striction which marks off the antnun 
pyloricum from the rest of the right 
sac. The oesophageal orifice is termed 
the cardia; it is situated at the left 
end of the lesser curvature, but about 
eight to ten inches (ca. 20 to 25 cm.) 
from the left extremity." The cesopha- 
gus joins the stomach very obliquely. 
The oj^ening is closed by the sphincter 
cardiae and numerous folds of mucous 
membrane. The pylorus is the open- 
ing into the intestine. Its position is 
indicated externally by a distinct con- 
striction. Internally it presents a cir- 
cular ridge caused by a ring of mus- 
cular tissue — the sphincter pylori. 

The stomach is hekl in ]50sition 
mainly by the pressure of the sur- 
The following peritoneal folds connect 




Fig. 356. — Everted Stomach of Horse from which 
THE Mucous Membrane has been Removed. 
O, OEsophagus; D, duodenum; 6, circular layer; 
c', internal oblique fibers; c", loop around cardia; (•'", 
transition of internal to external oblique fibers; d, fibers 
connecting the two branches of the cardiac loop; p, 
antral sphincter; p', pyloric sphincter. (EUenberger- 
Baum, Anat. d. Haustiere.) 



rounding viscera and liy the cesoijhagus. 
it with the adjacent parts: 

.1. The gastro-phrenic ligament (Lig. gastrophrenicum) connects the greater 
curvature, from the cardia to the left extremity, with the crura of the diaphragm. 
This leaves a narrow area uncovered with peritoneum, and here the stomach is 
attached to the diaphragm by areolar tissue. 

' The more expressive term "incisiira angulari.s" has been suggested and is worthy of adop- 
tion. 

- The position of the cardia varies of course with the excursion of the diaphragm. It is 
usually an inch or more (ca. 3 cm.) to the left of the median plane and ventral to the vertebral end 
of the fourteenth rib. When the diaphragm is contracted the cardia may be six inches (ca. 15 cm.) 
below the level of the spine; when the diaphragm is relaxed, the in ter\'al may be reduced to about 
two inches (ca. 5 cm.). 



THE STOMACH 417 

The use of the term ligament in regard to the arrangement here is somewhat misleading, 
since the stomach is attached to the crus of the diaphragm by areolar tissue; the peritoneum 
passes from the diaphragm to the stomach on each side of the area of atlliesion. In soft material 
there is the appearance of a ligament composed of two layers of peritoneum, but tliis is an artefact. 

2. The lesser omentum (Omentum minus) connects the lesser curvature and 
the first part of the duodenum with the liver below the oesophageal notch and the 
portal fissure. 

The part of the omentum which extends from the liver to the stomach is designated the lig. 
hepato-gastricum, and the remainder wliich goes to the duodemmi as the lig. hepato-duodenale. 

3. The gastro-splenic omentimi (Lig. gastrolienale) passes from the left part 
of the greater curvature to the hilus of the spleen; it is continuous ventrally with 
the greater omentum. 

4. The greater omentimi (Omentum majus) connects tlie ventral part of the 
greater curvature and the first curve of the duodenum with the terminal part of the 
great colon and the initial part of the small colon. It does not pass directly between 
these parts but forms a large sac, which will be described later. 

5. The gastro-pancreatic fold (Plica gastropancreatica) extends from the left 
sac above the cardia to tlie duodenum. It is attached dorsally to the liver and 
vena cava, ventrally to the pancreas. 

The stomach of the equidse is relatively small, its capacity varying from two 
to four gallons (ca. 8 to 15 liters). 

The size, form, and position of the stomach are subject to considerable variation. When 
the stomach is nearly empty, the saccus caecus contains only gas and is strongly contracted; the 
middle part (physiological fundus) contains the ingesta and preserves its rounded character, 
while the pyloric part is contracted. In tliis state coils of small intestine usually lie ventral to the 
stomach and may separate it entirely from the colon. In exceptional cases, when the organ is 
empty and contracted, even the pyloric end is to the left of the median plane. When distended, 
the middle part settles down some four or five inches, pushing back coils of the small intestine 
which may lie between the greater curvature and the large colon, and also pushing to one side the left 
dorsal part of the great colon ; the spleen, small colon, and small intestine are pushed back by the 
distention of the left sac. When the stomach is moderately full, its most ventral part Ues oppo.site 
to the ninth intercostal space and tenth rib, about a handbreadth above the level of the left costal 
arch. 

Structure. — The wall is composed of four coats — serous, muscular, submucous, 
and mucous. The serous coat (Tunica serosa) covers the greater part of the organ 
and is closely adherent to the muscular coat except at the curvatures. It partially 
bridges over the lesser curvature, and covers here elastic tissue which assists in 
retaining the bent form of the stomach. The peritoneal folds have been described. 
The muscular coat (Tunica muscularis) consists of three incomplete layers, aij 
external of longitudinal, a middle of circular, and an internal of oblique fibers. The 
laj'er of longitudinal fibers (Stratum longitudinale) is very thin and exists only 
along the curvatures and at the antrmn. It is not present on the saccus csecus, 
and about the middle of the greater curvature it is almost entirely replaced by 
elastic fibers to the antrum pylori. At the lesser curvature it is continuous wth the 
longitudinal fibers of the oesophagus. On the antrum pylori it forms a well-de- 
veloped complete layer which is separate from that of the curvatures. The layer 
of circular fibers (Stratum circulare) exists only on the glandular part. At the 
pyloric orifice it forms a thick ring — the pyloric sphincter (Sphincter pylori). 
Anotiier ring, the antral sphincter, is fotmd at the left end of the antrum pylori. 
The oblique fibers (Fibrie oliliquse) are arranged in coarse bundles in two layers. 
The external stratum covers the left sac and is largely a continuation of the longi- 
tudinal fibers of the oesophagus. The internal stratmn is found also on the left 
sac; it is continuous with the circular fibers of the oesophagus and stomach and 
exchanges fibers with the external oblique layer. It forms a remarkal)le loop 
around the cardiac orifice, constituting a powerful cardiac sphincter (Sphincter 
cardiee). The submucous coat (Tela submucosa) is a layer of loose connective 
27 



418 



DIGESTIVE SYSTEM OF THE HORSE 



Saccus ccecus 
{left extremity) 




Fundus 
gland 
region 



-Frontal Section of 
C, Cardiac orifice. 



Diverticulum duodeni 
Pylorus 

Pyloric gland region 



Stomach and First Part of Duodenum of Horse. 
Photograpli of specimen lixed in situ. 



tissue which connects the muscular and mucous coats; in it the vessels and nerves 
ramify before entering the mucosa. Tlie mucous coat (Tunica mucosa) is clearly 

divided into two parts. That which 
lines the greater part of the left sac re- 
sembles the oesophageal mucous mem- 
brane, and is termed the oesophageal 
part (Pars oesophagea). It is white in 
color, destitute of glands, and covered 
with a thick, squamous, stratified epi- 
thelium. At the cardiac orifice it pre- 
sents numerous folds which occlude the 
opening.' It terminates abruptly, form- 
ing an irregular, sinuous, raised edge, 
termed the margo plicatus (or cuticular 
ridge). Below and to the right of this 
line the mucous membrane has a totally 
different character, being soft and vel- 
vety to the touch, and covered by a mu- 
coid secretion. It contains the gastric 
glands (Glandulse gastricse), and is there- 
fore termed the glandular part (Pars glandularis). It is subdivided into three zones 
according to the tyjjes of glands which it contains, but no distinct lines of demar- 

' This occlusion is usually so complete that, distention of the stomach by air or fluid forced 
in through the pylorus may be carried far enough to rupture the stomach without Ugating the 
oesophagus. 




-Diagram of Zones of Mucous Membrane 
OF Stomach of Horse. 



THE SMALL INTESTINE 419 

cation exist. A narrow zone next to the margo plicatus has a yellowish-gray color, 
and contains short tubular cardiac glands (cardiac gland region). Next to this is a 
large area which has a mottled, reddish-brown color, and contains fundus glands 
(fundus gland region) ; these glands have two distinct types of cells. This part of 
the mucous membrane is thick and very vascular, and corresponds to the fundus 
of the stomach in man and the dog. The remainder of the mucous membrane is 
thinner, has a reddish-gray or yellowsh-gray color, and contains pyloric glands, 
which have a single type of cells corresponding to the chief cells of the fimdus glands 
(pyloric gland region) ; it corresponds to the pyloric portion of man and the dog. 
The folding of the stomach wall at the lesser curvature produces a prominent 
ridge which projects into the cavity of the stomach. The circular fold which 
covers the pyloric sphincter is termed the pyloric valve (Valvula pylori). 

The cesophageal part constitutes one third to two-fifths of the mucous membrane. The 
cardiac gland region is extremely narrow(ca. 0..5 to 1 mm. ) at the greater curvature, but becomes about 
an inch wade toward the pyloric part. Since the majority of the glands here are not typical 
cardiac glands, like those of the pig and other animals, but are intermediate in type between these 
and pj'loric glands, the term intermediate zone might well be used. 

Vessels and Nerves. — The stomach receives blood from all the branches of 
the cceliac artery. The gastric veins drain into the portal vein. The lymph 
vessels go chiefly to the gastric lymph glands, thence to the cisterna chyli. The 
nerves are derived from the vagus and sj-mpathetic nerves. 



THE SMALL INTESTINE 

The small intestine (Intestiuum tenuc) is the tube which connects the stomach 
with the large intestine. It begins at the pylorus and terminates at the lesser 
curvature of the cfficum. Its average length is about seventy feet (ca. 22 meters), 
and when distended its diameter varies from three to four inches (7.5 to 10 cm.). 
Its capacity is about twelve gallons (40 to 50 liters). 

It is clearly divisible into a fixed and a mesenteric part. The fixed part is 
termed the duodenum, while the mesenteric part (Intestinum tenue mesenteriale) 
is arbitrarily divided into parts termed the jejunum and ileum.' 

The duodenum is about three to four feet (ca. 1 m.) long. Its shape is 
somewhat like a horseshoe, the convexity being directed toward the right. The 
first part (Pars prima duodeni) is directed to the right and forms an co-shaped 
curve. The convexity of the first part of the curve is dorsal, of the second, ventral. 
It is in contact with the middle and right lobes of the liver, and presents two am- 
pullse with a constriction between them. The duodenal angle (or head) of the 
pancreas is attached to the concavity of the second curve, and here, five to six 
inches (ca. 12 to 15 cm.) from the pylorus, the pancreatic duct and the bile duct 
pierce the bowel wall. The second part (Pars secunda duodeni) passes upward 
and backward on the right dorsal part of the colon and ventral to the right lobe of 
the liver, and, on reaching the right kidney and the base of the caecum, it curves 
toward the median plane, opposite the last rib. The third part (Pars tertia duo- 
deni) passes from right to left behind the attachment of the base of the caecum, 
crosses the median plane behind the root of the great mesentery, and turns forward 
to become continuous with the mesenteric part under the left kidney.- The sac- 
culations of the first part have a diameter of three to four inches (ca. 7.5 to 10 cm.). 
It is attached by a short peritoneal fold termed the mesoduodenum. This fixes 

' No natural line of demarcation exists, but there is a marked increa.se of the thickness of 
the wall toward the terminal part. Other differences will be noted in the further description. 

- The duodenum commonly curves around the periphery of the right kidney, from which it 
is separated by the base of the caecum, but in some cases it is in contact with the ventral surface 
of the kidney. It may cross the median plane ventral to the second lumbar vertebra or further 
back, depending apparently on the fulness of the caecum. 



420 



DIGESTIVE SYSTEM OF THE HORSE 



the first part of the duodenum closely to the liver and the right dorsal part of the 
colon; the remainder is somewhat less closely attached by it to the base of the 
caecum and right kidney, the sublumbar muscles, and (more closely) to the terminal 
part of the great colon and the first part of the small colon.' 

The mesenteric part, or jejuno-ileum, has been conventionally subdivided into 
the jejunum and ileum, but no distinct point exists at which to make the demarca- 
tion. With the exception of the origin and the last two or three feet, the mesen- 
teric part of the intestine varies so much in position that only a general statement 
can be made. It lies in numerous coils, mingled with those of the small colon, 
chiefly in the dorsal part of the left half of the abdomen, from the visceral surface 
of the stomach to the pelvis. It may insinuate itself between the left parts of the 
colon and the abdominal w"all; also between the ventral parts of the colon, reaching 




Fig. 359. — Topography of Viscer.4 of Mare; Left View. 
I.R., First thoracic vertebra; I.L., first lumbar vertebra; 2.K., second sacral spine; S., scapula; .4., humerus; 
St., sternum; B., ilium; O., femur; L., lung in complete expiration: /., dotted Una indicating contour of lung in in- 
spiration; //..pericardium; 2., costal part of diaphragm; Z'., tendinous center of diaphragm; i.A^., left kidney; l.v.C, 
left ventral colon; v.Q., sternal flexure of colon; d.Q., diaphragmatic flexure of colon; /)., small intestine; M., small 
colon; A/'., rectum; a, coccygeus muscle: 6, retractor ani ; c, c, sphincter ani externus; d. constrictor vulvae; e, sacto- 
coccygeus ventralis; /, anterior gluteal artery; g, internal pudic artery; h, abdominal wall in section. (After EUen- 
berger, in Leisering's Atlas, reduced.) 



the floor of the abdomen. In some cases coils of .it lie against the right flank when 
the caecum contains little material. The terminal part of the intestine (ileum) 
passes to the medial (left) surface of the caecum and joins the lesser curvature of 
its base. The average diameter of the jejuno-ileum is about two and a half to three 
inches (ca. 6 to 7 cm.). In the cadaver one often finds much of the tube presenting 
irregular constricted and dilated parts which are not to be regarded as permanent 
conditions. The last three or four feet (ca. 1 m.) are usually tightly contracted, 
resembling somewhat the terminal part of the oesophagus. This part may be termed 
the ileum. 

The mesenteric part is connected with the dorsal abdominal wall by the great 
mesentery. This is a wide, fan-shaped fold, consisting of two layers of peritoneum, 

• It will be noticed that the mesoduodenum is not continuous with the great mesentery, but 
ends by a free edge. The mesentery begins on the opposite surface of the end of the duodenum, 
so that the bowel is attached by two peritoneal folds at this point. 



THE SMALL INTESTINE 



421 



between which the vessels and nerves reach the bowel; it also contains the mesen- 
teric lymph glands and some fat. The visceral border of the mesentery contains 
the intestine, while the parietal border or root of the mesentery (Radix mesenterii) 
is attached to a small area around the great mesenteric trunk under the first and 
second lumbar vertelsrae. The root is thick, as it contains a large number of vessels 
and nerves placed close together. The mesentery is short at first, but soon reaches 
a length of one and a half to two feet (ca. 50 cm.) — sufficient to allow coils of the 
intestine to reach the abdominal floor, the pelvic cavity, or even to descend into 
the scrotum through the inguinal canal. Near its termination the intestine leaves 
the border of the mesentery, so that the latter has a free edge which passes to the 
ciEcum. Thus there is formed the ileo-caecal fold (Plica ileocsecalis), which at- 
taches the ileum to the lesser curvature of the caecum. 

Structure. — The wall consists of four coats — serous, muscular, sulimucous, and 
mucous. The serous coat is complete except at the mesenteric edge, where the 
vessels and nerves reach the bowel. The muscular coat consists of an external 
longitudinal and an internal circular layer, the latter being the thicker. In the 
last few feet of the intestine the muscular coat is very thick, and being usually 
firmly contracted in the dead subject, gives the impression that this part of the bowel 
is of smaller caliber ; such, however, is 
not the case during life. The sub- 
mucous coat is a layer of areolar tissue 
in which the vessels and nerves ram- 
ify. It contains also the duodenal 
glands and the bases of the solitary 
antl aggregatetl lunjjh nodules. The 
mucous membrane is soft and vel- 
vety. It has a grayish or yellowish- 
red color and is very vascular. About 
five or six inches from the pjdorus it 
forms a pouch, the diverticulum duo- 
deni, in which the pancreatic and he- 
patic ducts open. On a small papilla 
nearly opposite this is the termina- 
tion of the accessory pancreatic duct. 
At the ileo-csecal opening the mucous 
membrane projects slightly into the 
cavity of the caecum, forming the ileo-caecal valve. The free surface is thickly 
beset with villi, small i:)rojections of the mucous membrane which can be seen well 
by placing a piece of the membrane in water. Thej' are relatively short and thick 
in the horse. Each contains a central Ijanph- vessel (lacteal), and around this a 
plexus of capillaries, lymphoid tissue, and unstriiaed muscle-fibers. They are im- 
portant agents in absorption from the contents of the intestine. The epithelium 
is columnar, with many goblet cells. Underneath the basement membrane is a 
layer of unstriped muscle-fibers, the muscularis mucosae. The glands of the small 
intestine are of two kinds; their secretion is termed the succus entericus. 

1. The intestinal glands (Glandulae intestinales) are present throughout. They 
are simple tul)ular glands which open between the villi. 

2. The duodenal glands (Glandulae duodenales)' are present in the first 
twenty feet or more (ca. 6 to 7 m.) of the bowel. They are branched tubulo- 
alveolar glands, and are situated in the submucosa, so that their ducts perforate 
the muscularis mucosae and the mucous membrane. 

' These were formerly known as Brunner's glands, but in the B. N. A. are termed glandute 
duodenales. On account of their extension beyond the duodenvmi and tlieir submucous position, 
EUenberger has suggested the name glandules submucosa;. 




Diverticulum 
duodeni 



FlQ. 360.— Dl 



Solid line indicates 



SCTION OF 

OF Horse. 

membrane ; 

are not showr 



422 



DIGESTIVE SYSTEM OF THE HORSE 



Lymphoid tissue occurs in the form of distinct nodules (NoduH IjTnphatici), 
which are either scattered or in groups. In tlie former case they are termed solitary 
nodules (Nochdi lymphatici solitarii), in the latter aggregated nodules or Peyer's 
patches (Noduli l\Tnphatici aggregati). The solitary nodules are ahout the size of 
a millet-seed or a small sago grain. The patches are situated chiefly along the 
surface opposite to the mesenteric attachment and begin about three or four feet 
from the pylorus. They nuinber one to two hundred, and are usually one to two 
inches (2 to 5 cm.) long and a cjuarter of an inch to one-half inch (ca. 2 to 14 mm.) 
wide. Larger ones occur in the terminal part, where one patch may have a length 
of seven to fifteen inches (ca. 17 to 38 cm.) and a width of half an inch to one inch 
(ca. 5 to 25 mm.) in young horses (Ellenberger). They vary much in number, 
size, and distriliution in different individuals, and undergo atrophy in old subjects. 

Vessels and Nerves. — The arteries of the small intestine come from the 
cceliac and anterior mesenteric arteries. The veins go to the portal vein. The 
lymph-vessels are numerous and go to the mesenteric lymph glands, thence to the 





Fig. 3fil. — Larue , 



cisterna chyli. The nerves are derived from the vagus anil sympathetic through 
the cceliac j)lexus. 

THE LARGE INTESTINE 
The large intestine (Intcstinum crassum) extends from the termination of the 
ileum to the anus. It is about twenty-five feet (ca. 7.5 to 8 m.) in length. It 
differs from the small intestine in its greater size, in lieing sacculated for the most 
part, possessing longitudinal bands, and having a more fixed position. It is divided 
into csecum, great colon, small colon, and rectum. 

The Cecum 

The caecum (Intestinum csecum) is a great cul-de-sac intercalated between the 

small intestine antl the colon. It has a remarkable size, shape, and position in the 

horse. Its average length is about four feet (ca. 1.25 m.), and its capacity about 

seven to eight gallons (ca. 25 to 30 liters).^ It is conical in form, and is curved 

^ The length given here is measured from end to end along the side and midway between the 
curvatures. 



THE C^CUM 423 

somewhat like a comma. It is situated chiefly to the right of the median plane, 
extending from the right iliac and subhimbar regions to the abdominal floor behind 
the xiphoid cartilage. Both extremities are blind, and the two orifices are placed 
close together on the concave curvature. It presents for description a base, a body, 
and an apex. The base (Basis cseci s. Saccus caucus) extends forward on the right 
side as far as the fourteenth or fifteenth rib, about a handbreadth below its middle, 
and backward to the tuber coxae.' It is strongly curved, the greater curvature 
being dorsal, the lesser ventral; connected with the latter are the termination of 
the ileum and the origin of the colon. The rounded blind end is directed ventrally. 
The body (Corpus cseci) extends downward and forward from the base and rests 
largely on the ventral wall of the abdomen. Its lesser curvature is about parallel 




f... 



Fl^. ■MJ. -C.L,LLM UF UuKSE; LkJT ViEW. 

B. c, Base; C. c, body; .4. c, apex; 7, ileum; 1, 2, longitudinal bands; 3, ileo-csBcal fold. The cseca! vessels and 
lymph glands have been removed to expose the medial band (1). 

with the costal arch and some five to six inches (10 to 1-5 cm.) ventral to it. The 
apex (Apex caeci) lies on the abdominal floor, usually to the right of the median 
plane, and about a hand's length behind the xiphoid cartilage. 

The right or parietal surface of the caecum is related chiefly to the right ab- 
dominal wall, the diaphragm, duodenum, and liver. The left or visceral surface lies 
against the left and terminal parts of the colon, the root of the great mesentery, 
and the small intestine. 

The base is attached dorsally by connective tissue and peritoneum on the 
ventral surface of the pancreas and right kidney, and a small area of the abdominal 
wall behind these; it is attached medially to the terminal part of the great colon, 
and ventrally to the origin of the great colon. The body is attached dorso-laterally 

1 The forward extent of the base of the CEBCum is subject to some variation. It may be 
noted that the blind end is not the most anterior part. 



424 



DIGESTIVE SYSTEM OF THE HORSE 



to the first part of the colon by the caeco-colic fold. The apex is free, and conse- 
quently may vary in position. 

The cfficum has four longitudinal bands (Ta;nise cseci), situated on the dorsal, 
ventral, right, and left surfaces; these cause four rows of sacculations (Haustra). 

The ventral band is almost entirely exposed or free (Taenia libera); it begins on the highest 
part of the base, extends along the medial side of the greater curvature, and joins the medial band 
near the apex. It is concealed only at its origin where the bowel is attached to the wall. The 
dorsal band extends along the lesser curvature from the termination of the ileum to the apex. 
Till' medial band extends along the medial part of the lesser curvature of the base, inclines 
venf rally further forward, and ends by joining the ventral band. It is covered at its origin by the 
adhesion to the right dorsal part of the great colon and beyond this by the CEecal vessels and l\-mph 
glands. Medial to the termination of the ileum it projects from the wall of the bowel as a falcifdrm 
band which can be felt distinctly although covered by vessels and fat. The lateral band is 
continuous with that of the right ventral part of the colon. It is covered by vessels, lymph glands 
and fat, but can be felt in its posterior part, where it forms a concave projecting edge. It inclines 
ventrally in front and may extend to the apex or fade out without reacMng it. 




363. — Orifices of Cecum of Ho 
orifice; 2, CEeeo-coIic orifice; 3, intervening fold. 



The ileo-caecal orifice (Ostium ileoca?cale) is situated in the lesser curvature of 
the base, about two or three inches (ca. 5 to 7.5 cm.) to the right of the median 
plane, antl in a transverse plane through the first or second lumbar vertebra. The 
end of the ileum is partially telescoped into the csecum, so that the orifice is sur- 
rounded by a fold of mucous membrane which encloses a thick circular muscular 
layer, the sphincter ilei. 

The caeco-colic orifice (Ostium csecocolicum) is lateral to the preceding one; 
the interval between them is only about two inches (ca. 5 cm.), and they are separ- 
ated by a large fold which projects into the interior of the csecum. The orifice is 
small in relation to the size of the ctecum and colon. It is slit-like, or has a narrow 
oval outline, and is about two inches (ca. 5 cm.) long. It has a thick valvular fold 
(Valvula CEBCocolica) at its ventral margin and is encircled by a muscular ring, the 
sphincter caeci.^ Large crescentic or semilunar folds (Plicae cseci) project into the 
cavity of the bowel, and between these are large jjouches (Cellulae cseci). 

' The anatomical arrangement gives no support to the view which is sometimes expressed 
that ingesta may pass directly from the ileum to the colon. 



THE GREAT COLON 



425 



It is somewhat difficult to get a correct idea of the csecal orifices. The caecum is sharply 
curved here and a large fold projects into its interior, somewhat like a shelf, and separates the two 
orifices. The ileo-cEecal orifice faces chiefly dorsally, wliile the caeoo-cohc orifice faces forward 
into the ctecum. 

The Great Colon 
The great colon (Colon cras.sum) begins at the caeco-colic orifice, and terminates 
by joining the small colon behind the saccus caecus of the stomach. It is ten to 
twelve feet (ca. 3 to 3.7 m.) long, and its average diameter (exclusive of its narrowest 
part) is about eight to ten inches (ca. 20 to 25 cm.). Its capacity is more than 
double that of the csecum. When removed from the abdomen, it consists of two, 
parallel parts, which are connected by peritoneum and partially by areolar and 
muscular tissue also. In situ it is folded so that it consists of four parts, which are 
designated according to their position or numerically. The three bent connecting- 
parts are termed the flexures. The first part, the right ventral colon (Colon ventrale 
dextrum), begins at the lesser curvature of the base of the csecum, al)0ut opposite 
the ventral part of the last rib or intercostal space.' It forms an initial curve, the 



Origin of smnll colon 



Ileum 
Fig. 364. — Diagram op C-ecum and Large Colon op Horse. 



Diaphragmalic 
flexure 




convexity of which is directed upward and backward; this part is in contact with 
the upper part of the right flank. It then passes downward and forward along the 
right costal arch and then along the floor of the abdomen.' Over the xiphoid 
cartilage it bends sharply to the left and backward, forming the sternal flexure 
(Flexura sternalis s. diaphragmatica ventralis). The second part, the left ventral 
colon (Colon ventrale sinistrum), passes backward on the al)dominal floor, to the left 
of the first part and the csecum and, on reaching the pelvic inlet, bends sharply 
dorsally and fonvard, forming the pelvic flexure (Flexura pelvina) . This is continued 
by the third part, the left dorsal colon (Colon dorsale sinistrum), which passes 
forward dorsal or lateral to the left ventral part, and on reaching the stomach, 
(liai)liragm, and left lobe of the liver, turns to the right, forming the diaphragmatic 
flexure (Flexura diaphragmatica dorsalis). The fourth part, the right dorsal colon 
(Colon dorsale dextrum), passes backward dorsal to the first part, and on reaching 

' The position of the origin of the great colon is variable, and one may easily get a wrong 
impression on account of the pecuUar arrangement of the bowel here. The colon usually presents 
a saccular dilatation at the lesser curvature of the base of the CEecum, which may be mistaken for 
its origin. The real origin is a constricted part or neck anterior to the sacculation. Thus the 
colon passes at first backward and then curves sharply downward and forward. Schmaltz ha.s 
proposed the name "vestibulum coli" for this sacculation. 



426 



DIGESTIVE SYSTEM OF THE HORSE 




Fig. 365. — Topography cf Viscera, of Horse; Right View. 
IR., First thoracic vertebra; IL., first lumbar vertebra; 2K., second sacral spine; S., scapula; A., hu 
St., sternum; B., ilium; O., femur; L., right lung; H., pericardium; Z., diaphragm (pars costalis) ; r.v.C, right ven- 
tral colon; V.Q., sternal flexure of colon; (f.Q., diaphragmatic flexure of colon; T., body, C, base, C"., apex, of cEecum; 
D., small intestine; F., pelvic flexure of colon; M., rectum; a., abdominal wall in section; b. duodenum; c, coccygeus 
muscle; d, retractor ani; e, e, sphincter ani externus; /, anterior gluteal artery; g, internal pudic artery; h, xiphoid 
cartilage. The origin of the colon would be above the blind end of the base of the caecum marked C (After EUeu- 
berger, in Leisering's Atlas.) 




Fig. 366. — Topography of Viscera of Horse; Right Side, Deeper View. 
I.R., First thoracic vertebra; I.L., first lumbar vertebra; £.K., second sacral spine; S.. scapula; A., humerus; 

B, ilium; 0., femur; Sc/i., pubis; St., ischium; S(., sternum; L., right lobe of liver; r.iV., right kidney; C, body, 

C, base, C"„ apex of caecum; r.u.C, right ventral colon; v.Q., sternal flexure of colon; d.Q., diaphragmatic flexure of 
colon; r.d.C, right dorsal colon; F., pelvic flexure of colon; Z>., small intestine; H., urinary- bladder; M., rectum; 
a, left ventricle; a', right ventricle; 6, 6', right coronary artery; c, left atrium; c', right atrium; (/, left coronary artery, 
circumflex branch; e, vena azygos; /, anterior vena cava; g, posterior vena cava; h, sinus venosus; i, right phrenic 
nerve; A:, right vagus, with its dorsal (A') and ventral (fc") divisions; ^ aorta; m, oesophagus; n, trachea; o, diaphragm 
(median section); p, right lateral Ugament of liver; g, duodenum; r, dotted line indicating position in median section 
of diaphragm in inspiratory phase; s, recto-coccygeus muscle; ^ suspensory ligament of rectum; w, sphincter ani; v, 
vesicula seminalis; u;, prostate; x, bulbo-urethral gland; ?/, urethra; z, abdominal wall; 2^, xiphoid cartilage. (After 
EUenberger, in Leisering's Atlas, reduced.) 



THE GREAT COLON 



427 



the medial surface of the base of the caecum it turns dorsally and to the left behind 
the left sac of the stomach; here it becomes constricted, and joins the small colon 
lielow the left kidney. 

The sternal flexure extends forward to a point opposite to the ventral part of the seventh rib, 
and the diaphragmatic flexure as far as the sixth intercostal space on the right of the median plane. 

The caliber of the great colon varies greatly at different jjoints. At its origin 




Fig. 367. — .AlBdominal Viscera of Horse; ^'E^•TRAL View. 
The ventral wall and part of the lateral walls of the abdomen are removed. C, Caecum; r.v.C, right ventral 
part of colon; v.Q., sternal flexure of colon; [Lv. C, left ventral part of colon; d.Q., diaphragmatic flexure of colon; 
D., small intestine: M,, small colon; a. ventral free band of caecum: b, medial band of CEBCum; c, lateral band of ventral 
part of colon d, ventral band of ventral part of colon; e, point of elbow; /, anterior end of sternal region; g, xiphoid 
cartilage; h, teats. (After Ellenberger-Baum, Top. Anat. d. Pferdes.) 



it is only about two to three inches (ca. 5 to 7.5 cm.) in diameter.' This soon 
increases to about eight to ten inches (ca. 20 to 25 cm.) for the ventral parts. 
Beyond the pelvic flexure the diameter is reduced to about three or four inches 
(ca. 8 to 9 cm.). Near the diaphragmatic flexure the caliber rapidly increases, and 
reaches its maximum in the last part, where it forms a large sacculation, which may 

1 Usually there is a sacculation of considerable size wliich succeeds the constricted origin. 



428 



DIGESTIVE SYSTEM OF THE HORSE 



have a diameter of about twenty inches (50 cm.). This is succeeded by a funnel- 
shaped terminal contraction. 

The right ventral part of the great colon is attached to the lesser curvature of 
the ctecum by two layers of peritoneum which form the caeco-colic fold (Plica 
csecocolica). The right parts are united by peritoneum on either side and also by 
areolar tissue and muscular fibers, the surface of contact being about four or five 
inches (ca. 10 to 12 cm.) wide; the left parts are attached to each other in a similar 
fashion near the anterior flexures, but further back the connection is by a peritoneal 
fold which gradually becomes wide enough to allow them to be dra\vn apart about 

six inches (ca. 15 cm.) near the pelvic 
flexure. The terminal part of the colon 
is attached by peritoneum and areolar 
tissue to the ventral surface of the pan- 
creas dorsally and to the base of the 
caecum laterally. It is connected in- 
directly with the diaphragm and liver 
^^ ^^^ by means of a fold derived from the 

W ^B^ ' ''^^1 right lateral ligament of the liver, 

r^ i^E^ !^^l The relations are complex, but the 

more important facts are as follows: 
The ventral parts have extensive con- 
tact with the abdominal wall ventrally 
and laterally. On the right side the 
colon is almost entirely excluded from 
contact \vith the flank by the csecum; 
on the left side it has no contact with 
the upper part of the flank, being ex- 
cluded here by coils of the small colon 
and small intestine. Dorsally the chief 
relations are to the stomach, duodenum, 
liver, pancreas, small colon, small intes- 
tine, aorta, posterior vena cava, and 
portal vein. Since there are no trans- 
verse attachments of the right and left 
parts, and the latter have no attach- 
ment to the wall, they are subject to 
considerable displacement.^ The pel- 
vic flexure is variable in position, but 
usually it is directed against the poster- 
ior part of the right flank or lies in the 
right inguinal region. - 

The longitudinal bands (Taeniae 

coli) vary in number on the different 

parts. The ventral parts have four bands. The pelvic flexure has a band along 

its lesser curvature. The left dorsal colon has at first only one band, which is 

a continuation of the preceding one; further forward two other bands appear, and 

' Abnormal displacement, e. g., torsion of the left parts, is not rare, and is liable to produce 
death if not promptly reduced. 

- The length of the left parts varies and this appears partly to account for the differences to 
be found in the arrangement of their posterior parts and the pelvic flexure. In subjects in which 
these parts of the colon are relatively long, their posterior ends are usually bent to the right across 
the pelvic inlet so that the pelvic flexm-e lies to the right of the inlet. In few cases the left parts 
of the colon seem relatively short and the pelvic flexure lies at the pelvic inlet. Other dispositions 
are encountered. 




1, Left dorsal part 



Posterior Portion of Left 
OF Horse; Dorsal View 
left ventral part; 



THE SMALL COLON THE RECTUM 429 

the three are continued on the right dorsal part. The ventral parts have alternate 
constrictions and sacculations (Haustra coli). 

On the right ventral colon two bands are dorsal, and extend along the medial and lateral 
sides of the attachment to the right dorsal colon. The medial one is covered by the colic vessels, 
etc., and the lateral one is concealed entirely or almost entirely by the attachment to the right 
dorsal part. A lateral band comes from the lesser cur\'ature of the CKCum and becomes ventral 
at the sternal flexure; it is free. The ventral band is also free. On the left ventral colon also two 
bands are dorsal. Of these, the medial one is covered by the vessels and lymph glands and in the 
anterior part also by the adhesion to the left dorsal part. At the pelvic flexure it is continued 
along the concave face of the bowel to the left dorsal part; it is important clinically as being the 
only distinct band on the flexure and may be felt per rectum. The dorso-lateral band is largely 
free, but is covered in front by the attachment to the left dorsal part. It fades out at the pelvic 
flexure. The ventro-medial and ventro-lateral bands are free and fade out at the pelvic flexure. 
The left dorsal colon has at first only one band, which is the continuation of the one along the lesser 
curvature of the pelvic flexure; it extends along the ventral surface and is continued on the right 
dorsal colon. Toward the middle of the left dorsal colon two dorsal bands begin, diverge very 
gradually, and are continued on the right dorsal colon; both are free and broaden at the diaphrag- 
matic flexure. On the right dorsal colon the ventral band is concealed by the attachment to the 
right ventral colon and by the vessels and lymph glands. The two dorsal bands are free except 
at the parietal attachment of the bowel; the lateral one is very wide and somewhat indistinct; 
the medial one is narrower and more distinct, and is continued along the mesenteric border of the 
small colon. 

The Small Colon 

The small colon (Colon tenue) begins at the termination of the great colon, 
behind the saccus csecus of the stomach and ventral to the left kidney, and is con- 
tinued by the rectum at the pelvic inlet. ^ Its length is about ten to twelve feet 
(ca. 3.5 m.), and its diameter three to four inches (ca. 7.5 to 10 cm.). 

Its coils lie chiefly in the space between the stomach and the pelvic inlet, 
dorsal to the left parts of the great colon. They are mingled with those of the 
small intestine, from which thej' are easily distinguished by the tsenise and saccula- 
tion. 

It is attached to the sublumbar region by the colic mesentery, and to the 
termination of the duodenum liy the narrow duodeno-colic fold of peritoneuni 
(Lig. duodeno-colicum) . The greater omentum is also attached to the initial 
part of the bowel. The colic mesentery is narrow at its origin, but soon reaches 
a width of about three feet (ca. 80 to 90 cm.). Its parietal border is attached along 
a line extending from the ventral surface of the left kidney to the sacral promontory ; 
it is continuous in front with the root of the great mesenterj-, and behind with the 
mesorectum. 

There are two longitudinal bands and two rows of sacculations. One of the 
bands is free, the other is concealed by the mesentery. When the bowel is hardened 
in situ its lumen between the pouches is reduced to a narrow sHt. 

The Rectum 

The rectum (Intestinum rectum) is the terminal part of the bowel; it extends 
from the pelvic inlet to the anus.- Its length is about one foot (ca. 30 cm.). Its 
direction may be straight or oblique. The first or peritoneal part of the rectum is 
like the small colon, and is attached by a continuation of the colic mesentery termed 
the mesorectum. The second or retroperitoneal part forms a flask-shaped dilata- 
tion termed the ampulla recti ; it is attached to the surrounding structures by con- 
nective tissue and muscular bands. 

The first part of the rectum commonly lies along the left wall of the pelvic 
cavity, but may be about median or (more rarely) deflected to the right. It is 
related to coils of the small colon and (inconstantly) to the left parts or pelvic 

• The position of the funnel-shaped termination of the great colon and the origin of the small 
colon is fixed, and this fact is of clinical importance in regard to impaction, which is not rare here. 
In horses of medium size this part of the bowel can be palpated per rectum when distended. 

'There is no natural line of demarcation between the small colon and rectum: the plane 
of the pelvic inlet is selected as the division for convenience of description. 



430 



DIGESTIVE SYSTEM OF THE HORSE 



flexure of the great colon; ventrally to the bladder (when full) or to the uterus. 
The second part of the rectum is related dorsally and laterally to the pelvic wall, 
^^entrally the relations difTer in the two sexes. In the male they are the bladder, 
the terminal parts of the ductus deferentes, the vesiculse seminales, the prostate, 
the bulbo-urethral glands and the urethra. In the female they are the uterus, 
vagina, and vulva.' 

Structure of the Large Intestine 
The serous coat covers the difTerent parts in varying degree. It does not 
cover (a) the opposed surfaces of the caecum and colon which are between the layers 




) ^. 



Fig. 369. — Topography of Viscera of Mare; Left Deep View. 
IR., First thoracic vertebra; IL., first lumbar vertebra; 2K., second sacral spine; S., scapula; .4., humerus; 
B., ilium; F., femur; Sch., pubis; Su, ischium; L., liver (left lobe); Ma., stomach, the posterior contour of which is 
indicated by dotted line x; Mi., spleen; ^A^., left kidney, concealed part indicated by dotted line; iV/., small colon; D., 
small intestine, parts of which have been removed: l.d.C, left dorsal colon; l.v.C, left ventral colon; v.Q., sternal 
flexure; d.Q., diaphragmatic flexure; O., left ovary; L'. , horn of uterus ; L.i., broad ligament of uterus; M'., rectum; T'., 
vagina; H., bladder; a, left ventricle; a', right ventricle; b, left coronary artery with descending (6') and circumflex 
(6") branches; c, left auricle; rf, pulmonary artery (cut) ; e, aorta; /, ligamentum arteriosum; ff, brachiocephalic trunk 
(anterior aorta); A, trachea; i, oesophagus; i', left phrenic nerve; ?, diaphragm in median section; m. uterine tube; 
7i, bursa ovarica; o, urethra; p, cut edge of broad ligament; 5, line of reflection of pelvic peritoneum; r, recto-coccygeus; 
s, suspensory ligament of rectum; ^ sphincter ani internus; u, sacro-eoccygeus ventralis; v, abdominal wall in section; 
w, xiphoid cartilage. (After Ellenberger, in Leisering's Atlas.) 



of the cseco-colic fold and mesocolon; (6) the areas of parietal attacament of the 
csecum and colon ; (c) the retroperitoneal part of the rectum. 

The muscular coat consists of longitudinal and circular fibers. The bulk of 
the former is in the bands of the caecum and colon. It is to be noted, however, 
that the bands of the caecum and the ventral parts of the great colon are largely 
composed of elastic tissue. The liands of the dorsal parts of the colon are largely 
muscular, and those of the small colon are almost entirely muscular. Some of the 
circular fibers pass from one part of the colon to another, where they are attached 
to each other, forming the fibrae transversae coli. The muscular coat of the ampulla 
of the rectum presents special features. The longitudinal layer of fibers is very 

' The anterior part of the rectum is variable in position and relations. The amount covered 
by peritoneum dorsally and laterally is very variable, and appears to be in inverse proportion to 
the fulness of the bowel. 



STRUCTURE OF THE LARGE INTESTINE 



431 



thick and consists of large bundles which are rather loosely united. A large band, 
the recto-coccygeus, is detached from it on either side, and passes upward and 
backward to be inserted into the fourth and fifth coccygeal vertebrae. 

The submucous tissue is abundant in the wall of the rectum, so that the mucous 
membrane is loosely attached to the muscular coat, and forms numerous folds 
when the bowel is empty. 

The mucous membrane of the large intestine is thicker and tlarker in color 
than that of the small intestine. It forms large crescentic or semilunar folds 




Fig. 370. — Pelvic Inlet and Posterior Part of Abdominal Wall of Horse, Viewed from the Front. 
The left inguinal canal is partially opened. The peritoneum is retained except over a part of the left cremaster 
muscle. The sublumbar region is greatly foreshortened in this view, a, a' , Kidneys; a", adrenal; b., ureter; c, renal 
artery; d, aorta; e, stump of cceliac artery; /, stump of anterior mesenteric artery; g, posterior mesenteric 
artery; h, circumflex iliac artery; i, external iliac artery; k, internal iliac artery; I, spermatic artery in peritoneal 
fold (plica vasculosa), m; n, ductus deferens, enclosed in genital fold, o; p, urinary bladder: g, round ligament of blad- 
der; r, middle ligament of bladder; s, rectum; t, margin of vaginal ring; u, posterior abdominal artery; v, external 
pudic artery; w, rectus abdominis muscle; x, transversus and obliquus internus abdominis; y, y', cremaster externus; 
2, posterior vena cava (cut). (After EUenberger-Baum, Top. Anat. d. Pferdes.) 



(PlicEe semilunares) , corresponiling to the external constrictions. It has no villi 
nor duodenal glands. The intestinal glands are large and numerous. Solitary 
nodules are numerous, and there are aggregated lymph nodules at the apex of the 
caecum and in the pelvic flexure and the adjacent portion of the left dorsal part of 
the colon. 

Vessels and Nerves. — The arteries come from the anterior and posterior 
mesenteric and internal pudic arteries. The veins go to the portal and internal 
pudic veins. The lymph vessels of the caecum and colon go to the csecal and colic 
lymph glands, thence to the cisterna chyli. Those of the rectum go to the internal 



432 DIGESTIVE SYSTEM OF THE HORSE 

iliac and lumbar glands. The nerves are derived from the mesenteric and pelvic 
plexuses of the sympathetic. 

The Anus 

The anus is the terminal part of the alimentary canal. It is situated below the 
root of the tail, where it forms a round projection, with a central depression when 
contracted. It is covered externally by an integument which is thin, hairless, and 
provided with numerous sebaceous and sweat glands. Its lumen, the anal canal 
(Pars analis recti), is about two inches (ca. 5 cm.) long; except during defecation 
it is closed by the contraction of the sphincter muscles and folds of the mucous 
lining. The mucous membrane is pale, glandless, and covered with a thick, squa- 
mous, stratified epithelium. 

There are three muscles of the anus. 

1. The sphincter ani intemus is the terminal thickening of the circular coat 
of the bowel. 

2. The sphincter ani extemus is a broad ring of striped muscle-fibers outside 
the internal sphincter. Some fibers are attached to the coccygeal fascia above, 
others to the perineal fascia below. Its action is to close the anus. 

3. The retractor ani is a flat muscle which lies between the rectum and the 
sacro-sciatic ligament; its fibers are directed backward and somewhat upward. 
It arises from the superior ischiatic spine and the sacro-sciatic ligament, and ends 
under the sphincter ani externus. Its action is to reduce the partial prolapse which 
the anus undergoes during defecation. 

The suspensory ligament of the anus (Lig. suspensorium ani) is a band of 
unstriped muscle which arises from the first coccygeal vertebra, passes downward 
under cover of the retractor ani, and unites with its fellow below the anus. In the 
male it is largely continued by the retractor penis muscle; in the female it blends 
with the constrictor vulvae. It may act as an accessory sphincter of the anus. 

Vessels and Nerves. — The blood-supply comes from the internal pudic arteries, 
and the veins go to the internal pudic vein. The lymph vessels go to the anal 
lymph glands. The nerves come from the pudic nerve. 



THE PANCREAS 

The pancreas is situated transversely on the dorsal wall of the abdomen, the 
greater part being to the right of the median plane. Its central part lies under the 
sixteenth and seventeenth thoracic vertebrae. When fresh, it has a reddish cream 
color, but if left in the unpreserved cadaver, it rapidly decomposes and becomes 
dark. It resembles the salivary glands in appearance, but is softer, and its lobules 
are more loosely united. Its average weight is about twelve ounces (ca. 350 g.). 
When hardened in situ its shape is very irregular. It is triangular in outline, and 
presents for description two surfaces, three borders, and three angles.' 

The dorsal surface (Facies dorsalis) faces dorsally and forward. It is partially 
covered l)y peritoneum. It is related chiefly to the ventral surface of the right 
kidney and adrenal, the posterior vena cava, the portal vein, the coeliac artery and 
its divisions, the gastro-phrenic ligament, and the saccus CEecus of the stomach, the 
right and caudate lobes of the liver, and the gastro-pancreatic fold. There are 
grooves for the divisions of the coeliac artery and a large one for the splenic vein. 

The ventral surface (Facies ventralis) faces ventrally and backward; it is in 
general concave. It presents two impressions, separated by an oblique ridge. The 
smaller of these (Impressio caecalis) lies to the right, and is caused by the pressure 
of the base of the csecum; the larger one (Impressio colica) indicates the area of 

' A descriptive method based on that in use in human anatomy cannot be applied with 
clearness to the organ in the horse. 



THE PANCREAS 



433 



contact with the terminal part of the great colon and its junction with the small 
colon. It has usually no peritoneal covering except over a small area at the anterior 
angle. 

The right border is nearly straight ; it is related to the second part of the duo- 
denum. 

The left border is slightly concave, and is related to the first part of the duode- 
num, the left sac of the stomach, and the splenic vessels. 

The posterior border presents a deep notch (Incisura pancreatis) where the 
root of the great m(>sentery is in contact with the glantl. To the right the portal 
vein lies in the notch, and passes through the gland very obliciuely; there is a thin 




Fig. 371. — Pancreas of Horse with Chief Relations; Ventral View. 
The pancreatic duct and its two chief radicles are indicated by dotted lines, since they are in the substance of the gland. 



bridge of gland tissue dorsal to the vein, thus forming the portal ring (Annulus 
portae). 

The anterior or duodenal angle (Angulus cranialis)' is the most ventral part 
of the gland ; it is attached to the concavity of the second curve of the duodenum 
and the adjacent part of the right lobe of the liver. The ducts leave at this ex- 
tremity. 

The left or splenic angle (Angulus sinister)- fits into the space between the 
saccus ceecus of the stomach in front, the left kidney behind, the base of the spleen 
dorsally, and the termination of the great colon ventrally. 

The right angle (Angulus dexter) is rounded, and lies on the ventral surface of 
the right kidney and adrenal body. 

' This corresponds to the head of the pancreas of man. 
^ This corresponds to the tail of the pancreas of man. 
28 



434 DIGESTIVE SYSTEM OF THE HORSE 

The pancreas is attached dorsally by connective tissue to the kidneys and 
adrenal bodies, the gastro-phrenic ligament, the suspensory ligament of the spleen, 
the posterior vena cava, the portal fissure, and the gastro-pancreatic fold. The 
ventral surface is mainly attached by areolar tissue to the base of the csecum and 
the terminal part of the great colon. 

There are almost invariably two ducts. The large one is termed the pan- 
creatic duct (Ductus pancreaticus).' It is formed by the union of two radicles 
which come from the right and left extremities, and passes through the duodenal 
angle to end at the duodenal diverticulum alongside of the bile-duct. The duct 
is nearly half an inch (ca. 1 cm.) wide, and is very thin walled. It is situated in the 
substance of the gland near its dorsal surface; none of it is free. The accessory 
pancreatic duct (Ductus pancreaticus accessorius)^ arises either from the chief 
duct or its left radicle, and ends on a papilla in the duodenum opposite the chief 
duct. 

Structiire. — The pancreas belongs to the class of tubulo-alveolar glands, the 
alveoli Ijeing long, like those of the duodenal glands; in other respects it resembles 
the serous salivary glands very closely. It has no proper capsule and the lobules 
are rather loosely united. 

Vessels and Nerves. — The arteries of the pancreas come from the branches of 
the cceliac and anterior mesenteric arteries. The veins go to the portal vein. The 
nerves are derived from the cceliac and mesenteric plexuses of the sympathetic. 

THE LIVER 

The liver (Hepar) is the largest glaml in the bodj'. It is situated oblirjuely 
on the abdominal surface of the diaphragm. Its highest point is at the level of 
the right kidney, its lowest on the left side, usually about three or four inches 
(ca. 8 to 10 cm.) from the abdominal floor, opposite the ventral end of the seventh 
or eighth rib. The greater part of it lies to the right of the median plane. 

It is red-brown in color and is rather friable. Its average weight is about ten 
to twelve pounds (ca. okg.),but inalargedraft horse it weighs about twenty pounds. 
When in the body, or if hardened in situ, it is stronglj^ curved and accurately adapted 
to the abdominal surface of the diaphragm. When removed in the soft state, it 
flattens out into a cake-like form quite different from its natural configurati($n. 
It presents for description two surfaces, and a circumference which may be divided 
into four borders. 

The parietal surface (Facies diaphragmatica) is strongly convex, and lies 
against the diaphragm. It faces chiefly dorsally and for^vard. Its most anterior 
part is opposite the ventral third of the sixth intercostal space or seventh rib. It 
presents, just to the right of the median plane, a sagittal groove for the posterior 
vena cava (Fossa vense cavse), which is partially embedded in the substance of the 
gland. 

The visceral surface (Facies visceralis) faces in general A-entrally and backward; 
it is concave ami irregular, being molded on the organs which lie against it'. It 
presents the foUowng features: (1) The portal fissure (Porta hepatis) is a depres- 
sion above the middle of the surface and a little to the right of the median plane; 
through it the portal vein, hepatic artery, and hepatic plexus of nerves enter, and 
the hepatic duct and lymph vessels leave the liver. The hepatic lymph glands are 
also found here. The pancreas is attached at and to the right of the fissure, and 
the lesser omentum around it. Above the fissure is the caudate lobe (Lobus cau- 
datus), which is continued to the right by the pointed caudate process (Processus 
caudatus). (2) The gastric impression (Impressio gastrica) is an extensive con- 

' Formerly termed the canal of Wirsung. 

' Formerly called the ductus pancreaticus minor or duct of Santorini. 



THE LIVER 



435 



cave area which is the surface of contact with the stomach. (3) Leading from this 
to the right of the portal fissure and dorsally is the duodenal impression (Impressio 
duodenahs). (4) The colic impression (Impressio coHca) is situated ventrally and 
to the right of the gastric antl duodenal impressions, from which it is separated by 
a ridge; it corresponds to the extensive contact of the diaphragmatic flexure and 
right dorsal part of the colon. (5) A caecal impression (Impressio C£ecalis) may 
be found dorsal to the preceding; it corresponds to the anterior part of the base of 
the caecum.' Coils of the small intestine may also lie on this surface, and the apex 
of the s])leen may reach to it when the stomach is empty. 

The dorsal border (Margo dorsalis s. obtusus) is thick for the most part. It 
presents from right to left : (1) The attachment of the right lateral ligament ; (2) 
a depression for the right kidney (Impressio renalis); (3) a notch, which is the 



Right lateral ligament 
\ . 



Posterior vena cava 



QSxoTphageal 

jiotch ■^'/' lateral Uganienl 




lobe 



Falciform ligament 



Fig. 372. — Liver of Vou-vg Horse, Hardened in situ; Parietal Surface. 



dorsal end of the fossa vense cavse ; (4) the deep oesophageal notch ( Impressio oesoph- 
agea), which is occupied partly by the end of the oesophagus, but mainly by the 
thick margin of the hiatus oesophageus; (5) the attachment of the left lateral liga- 
ment. 

The ventral border (]\Iargo ventralis) is thin, and is marked by two deep 
interlobar fissures or incisures (Incisurse interlobares) , which partially divide the 
organ into three ])rincipal lobes — right, middle, and left. The right lobe is the 
largest, except in old subjects, in which it is frequently much atrophied. The 
middle lobe is the smallest. It is marked by several small fissures and by the 
umbilical fissure (Incisura umbilicalis) ; the latter contains the umbiHcal vein in 
the ftt'tus, which is transformed into the round ligament after birth. 

' These impression.s are not evident on the soft organ. In hardened material they are 
clearly mapped out, although, of course, variable in size, in conformity with the degree of fulness 
of the various hollow viscera. The caecal impression may not be evident if, as often happens in 
old horses, the right lobe of the liver is much atrophied. 



436 



DIGESTIVE SYSTEM OF THE HORSE 



The right border (Margo dexter) is thin and long; it extends backward usually 
to the sixteenth rib, a little below its middle.' 

The left border (Margo sinister) is thin and convex. It begins at the left side 
of the oesophageal notch, about a handhreadth ventral to the fourteenth thoracic 
vertebra. It curves downward, outward, and somewhat forward to a point opposite 



Renal impression 



Caudate process 



Posterior vena cava 

Attachment of yastro-pancreatic fold 
Portal vein 
Portal fissure 
Hepatic artery 



Attachment of lesser omentum 
Hepatic duel 
(Esophageal notch 



Left lateral 
ligament 




Umbilical fissure 



Fig. 373. — Liveb of Horse; Visceral Surface. 
from middle-aged subject, hardened in situ. The fissure between the left and middle lobes i 



the ventral end of the ninth rib, and then runs forward aljout parallel with the 
costal arch as far as the ventral end of the seventh rib. The ventral and lateral 
borders together constitute the margo acutus. 

The liver is held in position largely by the pressure of the other viscera and 
by its close application and attachment to the diaphragm. It has six ligaments. 

' The right border varies much in subjects in the dissecting room, since in old subjects the 
right lobe is often greatly atrophied. Atrophy of the left lobe is extremely rare. 



THE LIVER 437 

1. The coronary ligament (Lig. coronarium hepatis) attaches it closely to the 
diaphragm. It consists of two strong laminae. The right one is attached to the 
right of the fossa vense caviB; the left one l^egins to the left of the vena cava and 
passes dorsally and laterally, becoming continuous with the left lateral ligament at 
the left margin of the oesophageal notch; it detaches a middle fold which extends 
to the oesophageal notch and is continuous with the lesser omentum. The two 
laminse unite below the vena cava to form the next ligament. 

2. The falciform ligament (Lig. falciforme hepatis) is a crescentic fold which 
attaches the middle lol)e to the sternal part of the diaphragm and to the abdominal 
floor for a variatil(> distance. 

3. The round ligament (Lig. teres hepatis) is a fibrous cord in the concave 



Renal impression 



Posterior vena cava 

Portal vein 
Hepatic artery 
Hepatic duct 
(Esophageal notch 




Umhilical vein 



Fig. 374. — Liver of New-born Foal, Hardened in situ; Visceral SiniF.icE. 
The differences, when compared with the organ in the adult, are very striking. 

edge of the falciform ligament which extends from the umliilical fissure to the 
umbilicus; it is the vestige of the umbilical vein, which in the foetus carries the 
blood from the placenta to the liver.' 

4. The right lateral ligament (Lig. triangulare dextrum) attaches the dorsal 
border of the right lolie closely to the costal part of the diaphragm. 

5. The left lateral ligament (Lig. triangulare sinistrimi) is a triangular fold 
which attaches the dorsal edge of the left lobe to the tendinous center of the dia- 
phragm. 

6. The hepato-renal or caudate ligament (Lig. hepatorenale) attaches the 
caudate process to the right kidney and the base of the caecum. 

The lesser omentum and the first part of the mesoduodenum are formed by the 

' It is to be noted that a remnant of the lumen of the vein is usually present, but has no 
endothelial lining. 



438 DIGESTIVE SYSTEM OF THE HORSE 

peritoneum leaving the visceral surface at the portal fissure and along a curved 
line which extends from the fissure to the oesophageal notch. They pass to the 
lesser curvature of the stomach and the first part of the duodenum. 

As stated above, the liver is divided by fissures into three principal lobes — 
right, middle, and left. The right lobe (Lobus dexter) is the largest in the young 
subject and is irregularly quadrilateral in form. On its dorsal part is the caudate 
lobe (Lobus caudatus), which ends in a pointed caudate process directed outwartl 
and assists in forming the cavity for the right kidney. The central or middle lobe 
(Lobus centralis) is normally much the smallest. The left lobe (Lobus sinister) is 
oval in outline and thickest centrally. In old or middle-aged subjects it commonly 
exceeds the right one in size, and in many cases constitutes the bulk of the gland. 
In some cases the atrophy of the right lobe is so extreme that the middle lobe may 
exceed it in size.' 

The hepatic duct (Ductus heiiaticus) is formed at the ventral part of the portal 
fissure by the union of right and left chief lobar ducts. It is about two inches 
(ca. 5 cm.) long and about half an inch (ca. 1 to 1.5 cm.) wide. It passes be- 
tween the two layers of the mesoduodenum, and pierces the wall of the duodenum 
five or six inches (ca. 12 to 15 cm.) from the pylorus, alongside of the pancreatic 
duct. The ducts pass obliquely through the wall of the duodenum for about 
half an inch (ca. 1 cm.) before opening into the diverticulum duodeni. The arrange- 
ment forms a valve, which prevents regurgitation from the intestine. There is no 
gall-bladder. 

In the new-born foal the liver presents striking differences when compared with the gland of 
the adult. It is relatively large and weighs 2'-2 to 3 pounds (ca. 1.25 kg.). It is thick and is strongly 
curved, and a considerable part of the parietal surface is in contact with the floor of the abdomen. 
The umbilical fissure is large and contains the umbilical vein. The latter is a very large vessel 
which carries blood from the placenta and joins the portal vein in the substance of the Uver; it is 
in the edge of the falciform ligament, which at this time extends to the umbilicus. The visceral 
surface is deeply concave and is in contact chiefly with the stomach and duodenum. 

Structure. — The liver is covered by an external serous, and an internal fibrous, 
coat. The serous coat (Tunica serosa) covers the gland except at the attachment 
of the pancreas and at the portal fissure ; it is reflected from it to form the ligaments 
and the lesser omentum. The fibrous capsule (Capsula fibrosa) is in general thin; 
it sends laminae into the ligaments, and also trabeculse into the gland. At the portal 
fissure it is abundant and siuTounds the vessels and ducts, which it accompanies 
in the portal canals of the gland substance. 

The gland substance is composed of the parenchyma and the interstitial 
tissue. The parenchyma is made up of polygonal lobules (Lobuli hepatis) , about 
1 .5 mm. in diameter, which are held together by a small amoimt of interlobular 
connective tissue. On account of the very small amount of the latter, the 
lobulation of the horse's liver is not usually at all distinct; for the same reason the 
organ is also quite friable. The lobules are composed of the polyhedral liver cells, 
a delicate reticulum, the bile capillaries, a plexus of blood capillaries, and a central 
vein. 

Vessels and Nerves. — The portal vein enters at the portal fissure. It conveys 
blood from the digestive tract and the spleen, which contains various products of 
digestion and numerous white blood-cells. The hepatic artery also enters at the 
portal fissure; it may be termed the nutrient vessel. All the blood is returned from 
the liver to the posterior vena cava by the hepatic veins. The portal vein and the 
hepatic artery both divide into interlobular branches, which run together in the 

' Flower and Ruge describe the mammalian liver as being primarily di\'ided by the umbilical 
fissure into two parts, the right and left lobes. Secondary fissures on either side maj' subdivide 
each of these primary lobes. On this basis we may recognize in the liver of the horse right lateral, 
right central, left central, and left lateral lobes. In the young foal these four lobes are distinctly 
recognizable. The two central lobes would correspond to the central or middle lobe of the foregoing 
description, and the right central lobe would be the equivalent of the quadrate lobe of man. 



THE SPLEEN 



4139 



portal canals of the interlol)ular tissue. The branches of the portal vein (Vente 
interlobulares) give off intraloliular branches which form plexuses of capillaries in 
the lobules and give rise to a central vein (Vena centralis). The interlol)ular 
branches of the hepatic artery (Rami arteriosi interlobulares) are of relatively 
small size. They supply mainly (if not exclusively) the interlobular tissue, the 
capsule, and the walls of the vessels and ducts. The hepatic veins' (Vente hepaticse) 
empty into the posterior vena cava as it lies in the fossa of the gland. Their 
ultimate radicles are the central lobular veins (Venae centrales) , which emerge from 
the bases of the lobules and join 
the sublobular veins (Vena? sub- 
lobulares) ; the latter unite to form 
the hepatic veins. The largest 
hepatic veins, three or four in 
number, join the posterior vena 
cava just before it leaves the liver 
to pass through the diaphragm. 

The nerves come from the 
hepatic plexus, which is composed 
of branches from the vagus and 
sympathetic nerves. 



THE SPLEEN 
The spleen (Lien) is the 
largest of the heterogeneous group 
of organs which are usually desig- 
nated ductless glands.^ It is situ- 
ated chiefly in the left parachon- 
di'iac region, in close relation to the 
left part of the great curvature of 
the stomach, to which its long axis 
corresponds. Its size and weight 
vary greatly in different subjects, 
and also in the same subject under 
different conditions, depending 
chiefly on the great variability of 
the amount of blood contained in 
it. The average weight is about 35 
to 40 ounces (ca. 1 kg.), its length 
about 20 inches (ca. 50 cm.), and 
its greatest width about 8 to 10 
inches (ca. 20 to 25 cm.). It is 
usually bluish-red or somewhat purple in color 
yielding, but not friable. 

The weight, which is extremely variable, appears to range ordinarily from about one to eight 
pounds, although the latter figure even may be e.xceeded ■n'ithout any apparent evidence of disease. 

' The hepatic veins may be recognized on section from the fact that they remain open, 
being connected closely with the parenchyma. 

- The ductless glands are organs which elaborate substances that pass directly into the 
veins or lymphatics, instead of being conveyed away by ducts. Tliis process is termed internal 
secretion. The ductless glands include the lymph glands, which are described with the organs 
of circulation; the thyroid and thymus bodies, described usually with the respiratory organs; 
the adrenal or suprarenal bodies, described with the urinary organs; the pineal and pituitary 
liodies, described with the brain; and the spleen, described with the digestive system as a matter 
of convenience. The spleen is not, strictly speaking, a gland at all: it is not epithelial in origin 
or structure, but is mesenchymatous. 




angk's; 



Fig. 375. — Spleen of Horse: Pari 
Dorsal extremity < 
: (I, anterior borde 
of last three 



Surface. 
se; h, c, anterior and posterior basal 
ventral extremity or apex; 1, 2, 3, 



In the natural state it is soft and 



440 



DIGESTIVE SYSTEM OF THE HORSE 



The author recently'observed in a horse, which weighed about 1200 pounds, a spleen which weighed 
10 J4 pounds, and measured 26 inches in length and 11 inches in width at the base. The ventral 
1 end was situated opposite the lower part of the seventh intercostal space. In the new-born foal 
the weight is about 10 to 12 ounces (ca. 300 gm.). There does not seem to be any constant relation 
to the body-weight. For example, the spleen of a colt of medium size about ten months old 
weighed three and a half pounds, while it often weighs less than two pounds in horses weighing 
1000 to 1200 pounds. The chief variation in outline consists of increase of width, especially of the 
dorsal part. 

It extends obliquely in a curved direction, corresponding to the left part of the 
greater curvature of the stomach, from the left crus of the diaphragm to the ventral 

third of the tenth or eleventh rib. It 
^ presents for description two surfaces, 

two borders, and two extremities. 

The parietal or lateral surface (Fa- 
cies parictalis) is convex, and lies chiefly 
against the diaphragm, but is in contact 
with the upper parts of the last two ribs 
and usually to a small extent with the 
flank at the lumbo-costal angle. 

The visceral or medial surface (Fa- 
cies visceralis) is in general concave. It 
is divided into two unequal parts by a 
longitudinal ridge; on this is a groove, 
the hilus, in which the vessels and nerves 
are situated. The area in front of the 
ridge (Facies gastrica) is molded on the 
greater curvature of the stomach; it 
is about two inches (ca. 5 cm.) wide. 
The area behind the ridge (Facies intes- 
tinalis) is much more extensive; it is 
related to the small colon, the left parts 
of the great colon, the small intestine, 
and the great omentum. It may be 
marked by one or two fissures. 

The anterior border (Margo crani- 
alis) is concave and thin, being wedged 
in between the diaphragm and the 
greater curvature of the stomach. 

The posterior border (Margo cau- 
dahs) is convex and thin. 

The dorsal extremity or base (Ex- 
tremitas dorsalis) is beveled, and fits into 
the interval between the left crus of 
the diaphragm and sublumbar muscles 
above, and the saccus csbcus of the stomach and the left kidney below. When 
hardened in situ, it shows an impression (Facies renalis) where it lies against the 
kidney. The left extremity of the pancreas touches it also. The anterior basal 
angle fits in between the saccus csecus of the stomach and the left kidney opposite 
to the last thoracic vertebra; the posterior basal angle usually lies against the 
upper part of the left flank, just behind the last rib.^ 

The ventral extremity or apex (Extremitas ventralis) is small and varies in 
position. It is commonly foimd opposite the tenth or eleventh rib, a handbreadth 
or more above the costal arch, but may be further forward and higher. 




Fig. 376. — Spleen of Horse, Hardened 
CERAL Surface. 
a, Dorsal extremity or base; b, c, anterior and poste- 
rior basal angles; d, anterior border; e, cut edge of sus- 
pensory ligament: /, y, splenic artery and vein in hilus. 
The area marked intestinal impression is related to the 
first coil of the small colon. The area enclosed by the 
suspensory ligament ia non-peritoneal. 



• It is uncommon to find the spleen extending more than two or three inches behind the last 
rib; on the other hand, the posterior basal angle may lie just at the last rib. 



THE PERITONEUM 441 

The position of the ventral part depends largely upon two factors — the degree of fulness of 
the stomach and the size of the spleen. When the stomach is empty or nearly so and the spleen 
small (contracted), the latter is strongly curved, and its ventral end may be between the left lobe 
of the liver and the left dorsal part of the great colon. When the stomach is full, it pushes the 
spleen backward, affecting most the ventral part of the latter. Of course the spleen is affected 
by the respiratory movements, as may be readily observed by examination per rectum of the 
living subject. 

The spleen is attached by two peritoneal folds, the suspensory ligament and 
the gastro-splenic omentum. The suspensory ligament of the spleen (Lig. sus- 
pensorium lienis) attaches the dorsal end to the left crus of the diaphragm and the 
left kidney; it contains a quantity of elastic tissue. The dorsal layer of the liga- 
ment, which passes to the diaphragm, is the ligamentum phrenico-lienale, and blends 
with the gastro-phrenic ligament; the ventral part, which goes to the kidney, is 
termed the ligamentum renolienale. The gastro-splenic omentum (Lig. gastro- 
lienale) passes from the hilus to the left part of the greater curvature of the stomach. 
It is narrow dorsally, where it joins the suspensory ligament; ventrally it becomes 
much wider and is continuous with the great omentum. 

Small globular or lenticular masses of splenic tissue may be found in the gastro-splenic 
omentum. They are termed accessory spleens (Lienes accessorii). 

Structiure. — The spleen has an almost complete serous coat (Tunica serosa). 
Subjacent to this and intimately united with it is a capsule of fibrous tissue (Tunica 
albuginea), which contains many elastic fibers and some unstriped muscular tissue. 
Numerous trabeculse (Traljeculse lienis) are given off from the deep face of the 
capsule and ramify in the substance of the organ to form a supporting network. 
In the interstices of this framework is the spleen pulp (Pulpa lienis), a dark red, soft, 
grumous material. This is supported bj' a delicate reticulum, and contains numer- 
ous leukocjd;es, the large splenic cells, red blood-corpuscles, and pigment. The 
pulp is richly supplied with lilood. The branches of the splenic artery enter at 
the hilus and pass along the trabecule. The arteries which enter the pulp have a 
sheath of Ijanphoid tissue, which collects on the vessel wall at certain points, form- 
ing small splenic l3rmph nodules (Noduli lymphatici lienales).i These are visible 
to the naked eye as white spots, about as large as the head of a pin. The blood 
passes into cavernous spaces lined by endotheliimi which is continuous with the 
cells of the reticulum of the pulp. From these the veins arise. The splenic vein 
runs in the hilus in company with the artery and nerves, and joins the posterior 
gastric vein to form a large radicle of the portal vein. 

Vessels and Nerves. — The arteries are derived from the splenic artery, which 
is the largest Ijranch of the coeliac artery. The splenic vein lies behind the artery 
in the hilus; it goes to the portal vein. The l5rmph vessels go to the splenic lymph 
glands. The nerves, derived from the coeliac plexus of the sympathetic, accom- 
pany the vessels. 

THE PERITONEUM 

The general disposition of the peritoneum has been described, and other facts 
in regard to it were mentioned incidentally in the description of the viscera. It is 
now desirable to study it as a continuous whole- (Figs. 351, 352, 353, 377, 378). 

We may consider the peritoneum as consisting of two sacs — a greater and a 
lesser. The greater sac lines the greater part of the abdoininal cavity, and covers 
most of the viscera which have a peritoneal investment. The lesser sac is an 
introversion or invagination of the greater sac, formed during the development of 
the viscera. The two sacs communicate by a relatively narrow passage, termed 

* These are also known as Malpighian corpuscles. 

- The student is strongly recommended to study the peritoneum of a foal or other small 
subject when the opportunity occurs, as in these the viscera are easily handled, and the course 
of the peritoneum can be followed without difficulty. 



442 



DIGESTIVE SYSTEM OF THE HORSE 



the epiploic foramen (Foramen epiploicum).' This opening is situated on the 
visceral surface of the liver dorsal to the portal fissure. It can be entered by passing 
the finger along the caudate lobe of the liver toward its root. Its dorsal wall is 
formed by the caudate lobe and the posterior vena cava. Its ventral wall consists 
of the pancreas, the gastro-pancreatic fold, and the portal vein. The walls are 
normally in contact, and the passage merel.v a potential one. It is usually about 
four inches (ca. 10 cm.) in length. It is narrowest at the lateral extremity, where 
it is about an inch (ca. 2.5 to .3 cm.) wide.- If the finger is passed into the foramen 
from right to left, it enters the cavity of the lesser sac' If now an opening is made 
in the great omentum and the other hand introduced through it, the fingers of the 
two hands can touch each other over the lesser curvature of the stomach. The 
formation and boundaries of the lesser sac should now be examined by spreading 
out the great omentum. It will be found that the latter now encloses a considerable 
cavity behind the stomach; this is termed the omental cavity (Bursa omentalis). 
Passing forward over the lesser curvature of the stomach, we enter another space, 
the vestibule of the omental cavity (Vestibulum bursse omentalis). This sijace is 




Fig. 377. — Diagram of General Arrangement op Peritoneum (of Mare) in Sagittal Tracing. 
Sacro-rectal pouch, continuous with 6, recto-genital pouch; c, vesico-genital pouch: d, pubo-vesical pouch; /, lesser 
omentum; Int., small intestine. The arrow points to the epiploic foramen. 



closed on the left by the gastro-phrenic ligament, ventrally and on the right by 
the lesser omentum, and dorsally by the gastro-pancreatic fold, which is attached 
to the dorsal border of the liver and to the posterior vena cava. Above the oeso- 
phageal notch there is a recess, into which the fingers can be passed around the 
border of the liver and the vena cava till the coronary ligament is encountered. 
Thus the vestibule is closed except — (1) on the right, where it communicates with 
the cavity of the greater sac by the epiploic foramen; and (2) behind, where it 
communicates with the cavity of the omentum. 

The general arrangement of the greatej: omentum has already been indicated. 
We may now trace its line of attachment, which would correspond to the mouth of 
the sac. Beginning at the ventral part of the greater curvature of the stomach, it 
passes to the ventral face of the pylorus, then crosses obliquely the first part of 
the duodenum to the point where the pancreas is adherent to it. Here it passes 
to the anterior face of the terminal part of the great colon, runs along this trans- 
versely (from right to left), and continues for some ten or twelve inches (ca. 25 

' Also known as the foramen of Winslow. 

' The passage is subject to a good deal of variation in caliber and is sometimes occluded. 



THE PERITONEUM 



443 



to 30 cm.) on the small colon. It then form.s an acute angle, passes medially and 
forward along the small colon to the dorsal part of the hilus of the spleen, where it 
blends with the suspensory ligament of the latter, and forms a recess (Recessus 
lienalis) behind the saccus caucus of the stomach. It now passes along the hilus 
of the spleen, and is continued to the greater curvature of the stomach by the 
gastro-splenic omentum. It is convenient to regard the spleen as being interca- 
lated in the left part of the greater omentum; on this basis the gastro-splenic 
omentum would be that part of the greater omentum which connects the hilus of 
the spleen with the greater curvature of the stomach. The greater omentum is 
relatively small in the horse, and is 

usually not visible when the abdo- ^ Diaphragm 

men is opened. It is generally folded 
up in the space between the visceral 
surface of the stomach and the in- 
testine.^ 

The lesser sac furnishes the perito- 
neal covering for: (1) the \-isceral surface 
of the stomach and a small area of the first 
curve of the duodenum; (2) a large part of 
the dorsal surface of the pancreas and por- 
tal vein; (3) a small part of the visceral sur- 
face of the liver above the attachment of 
the lesser omentum and the portal fissure; 
(4) the posterior vena cava, from the level 
of the epi]>loic foramen to its passage 
through the diaphragm (in so far as it is 
not embedded ) ; (5) the part of the parie- 
tal surface of the Uver between the right 
and middle divisions of the coronary liga- 
ment; (6) the corresponding part of the 
diaphragm, and the right part of the right 
crus of the same; (7) part of the anterior 
surface of the terminal part of the great 
colon, and the origin of the .small colon; 
(8) the left extremity of the pancreas (in- 
constant); (9) the spleen. 

We may now trace the perito- 
neum in a longitudinal direction, be- 
ginning in front. It is reflected from 
the ventral abdominal wall and the 
diaphragm upon the liver, forming 
the ligaments and serous coat of the 
gland. It leaves the visceral surface 
of the liver as lesser omenttmi, and 
the crura of the diaphragm as the 

gastrophrenic' ligament, reaches the saccus ciecus and lesser curvature of the stomach 
and the first curve of the duodenum, covers these organs, and is continued by the 
greater omentum. 

On the left it passes from the left crus of the diaphragm and the left kidney to 
form the suspensory ligament of the spleen, clothes that organ, a^d leaves it to be 
continued by the greater and gastro-splenic omenta. 

On the right it passes from the right crus of the diaphragm and the dorsal 
border of the liver to the concave border of the duodenum, forming the gastro- 
pancreatic fold (second part of the mesoduodenum), and covering part of the dorsal 
surface of the pancreas. From the margin of the pancreas, the right kidney, and 
a small area of the sublumbar region behind the latter, it passes on to the base of 

' In dissecting-room subjects (which are usually aged) the omentum often exhibits patho- 
logical changes, such as adhesions, rents, tumors, formation of twisted strands, etc. 




Fig. 378. — Diagram of Abdominal Peritoneum in Front.\l 
(OR Horizontal) Tracing. 
D, Duodenum; 1. falciform ligament: 2, leaser omentum; 
3, gastro-splenic omentum; 4, greater omentum; 5, cavity of 
omentum; 6, mesoduodenum; 7, general peritoneal cavity. 
Arrow indicates epiploic foramen. By an oversight the pan- 
creas, in front of the colon, is not marked. 



M4 



DIGESTIVE SYSTEM OF THE OX 



the caecum and the terminal part of the great colon. From these it passes on the 
right to the duodenum, forming the third part of the mesoduodenum. On the left 
it covers part of the ventral surface and the lateral border of the left kidney, from 
which it passes to the base of the spleen, forming the ventral layer of the suspen- 
sory ligament of the latter. Behind the terminal part of the great colon it is reflected 
from the abdominal wall around the great mesenteric artery to form the great 
mesentery. Behind this it is reflected almost transversely from the roof of the 
cavity and from the origin of the small colon on to the duodenum, forming the 
terminal part of the mesoduodenum. The line of origin of the colic mesentery 
begins on the medial part of the ventral surface of the left kidney, and extends to 
the sacral promontory, where the mesorectum begins. At the termination of the 
latter the peritoneum is refiected from the rectum on to the dorsal and lateral walls 
of the pelvic cavity. Below the rectum it forms the genital fold, and passes on to 
the dorsal surface of the bladder, covers its anterior part, and is reflected on to the 
body-wall laterally and ventrally, forming the lateral and middle ligaments of the 
bladder. In the female the broad ligaments of the uterus replace the genital fold, 
with which they are homologous. 

In the new-born foal certain folds are specially large. The falciform ligament 
of the liver extends to the umbilical opening, and contains in its free edge the large 
umbilical vein. The bladder — at this time an abdominal organ — has a ventral 
median fold (Plica umbilicalis media), which connects it and the urachus with the 
abdominal floor. This is flanked on either side by a fold (Plica umbilicalis lateralis), 
which also extends to the umbilicus, and contains the large umbilical artery. 



DIGESTIVE SYSTEM OF THE OX 
THE MOUTH 

The cavity of the mouth is shorter and wider than that of the horse, and the 
vestibule is more capacious (Figs. 381, 386). 

The lips are thick, wide, and comparatively immobile. The middle part of 
the upper lip and the surface between the nos- 
trils is bare, and is termed the muzzle (Planum 
nasolabiale) . It is smooth, and (in health) is 
kept cool and moist by a clear fluid secreted 
by the naso-labial glands (Glandulse nasolalii- 
ales) ; they form a subcutaneous layer about 
half an inch (ca. 1.5 cm.) thick. It shows ir- 
regular lines, mapping out small polygonal areas 
on which the orifices of the gland ducts are visi- 
ble. There is also a narrow bare strip along 
the edge of the lower lip. The remainder of 
the integument is provided with ordinary and 
tactile hairs. The free edge and the adjacent 
part of the lining membrane bear short, blunt, 
horny papillae ; toward the angles the papillce 
become longer and sharp-pointed. The labial 
glands occur only near the angles, where thej- 
form compact masses (Fig. 385) . 

The cheeks are more capacious than in 
the horse. The mucous membrane presents 




Fig. 379. — Lips and Muzzle of Ox. 

1, Muzzle; 2, nostril; 3, 4, wings of nos- 
tril; 5, 6, commissures of nostril; 7, 8, upper 
and lower lip. 



THE MOUTH 



445 



large pointed conical papillae (Papillae conicae), which are directed toward the 
isthmus faucium and are covered with a horny epithelium. The largest of these 
have a length of about half an inch (ca. 1 to 1.5 cm.) and are situated around 
the angle of the mouth and parallel with the cheek teeth. The orifice of the parotid 
duct is opposite the fifth upper cheek tooth. The buccal glands (Fig. 385) are very 
well developed, and are arranged 
in three parts. The dorsal part 
extends from the angle of the 
mouth to the maxillary tubero.s- 
ity ; its lobules are of a light yel- 
low color. The ventral part con- 
sists of a compact brownish mass 
which reaches from the angle 
of the mouth a short distance 
under the masseter midscle. The 
middle part consists of loosely 
arranged yellow lobules. The 
small ducts of these glands open 
between the papillae of the cheek. 

A linear series of large pa- 
pillae exists on the floor of the 
mouth on each side of the frenum 
linguae. Near these are found 
the openings of the small ducts 
of the sublingual gland. The 
caruncula sublingualis, the pa- 
pilla on which the sub-maxil- 
lary duct opens, is wide, hard, 
and has a serrated edge (Fig. 
383). 

The hard palate is wide, and 
is usually more or less pigmented. 
The body of the premaxilla is 
covered with a thick layer of 
dense connective tissue, which 
has a thick, horny epithelial cov- 
ering — forming the so-called den- 
tal plate or pad. The palatine 
ridges extend from this liack- 
ward about two-thirds of the 
length of the hard palate; they 
number 15 to 19. They are 
nearly straight, and, with the 
exception of a few at the poste- 
rior end of the series, are serrated on the free edge. A median raphe extends 
between the ridges. The posterior third of the palate is smooth. Between 
the dental plate and the first ridge is the triangular papilla incisiva; on either 
side of this is a deep furrow, in which is the oral opening of the ductus incisivus.' 
The duct is two inches or more (ca. 5 to 6 cm.) in length and opens on the floor 
of the nasal cavity; it also communicates by a slit-like opening with the vomero- 
nasal organ. 




1. Dental pad or plate; 2, placed ou papilla incisiva with lines 
to orifices of ductus incisivi; 3, ridge of palate; 4, raph^ of palate; 
5, smooth part of palate showing orifices of palatine glands; 6, 
upper lip; 7, conical papillse of cheek. 



' This is also known as the naso-palatine canal. 



446 



DIGESTIVE SYSTEM OF THE OX 



The soft palate is somewhat shorter than that of the horse, but is long enough 
to close the isthmus faucium. The posterior pillars do not extend to the origin of 
the oesophagus. The palatinus muscle is much better developed than in the horse. 
The fibrous aponeurosis is for the most part replaced by muscular tissue. 



Dorsal Dorsal 

turbinate meatus 



Cavity 
Septum of dorsal 
nasi turbinate 



Frontal 



Middle meatus- 



Ventral 
turbinate 



Xaso-lacrimnl 
duct 



Infraorbital 
nerve 



Masseter 




11 y I'.oglossal nerve 



Ventral buccal 
gltmds 



Sublingual gland 
igaslricus 



Mandibular duet Lingual nerve 
Fio. 381. — Cross-section of Head of Ox. 



The section passes through the medial canthi. L. a.. Lingual arteries. The ; 
tween the maxillary and palatine i 



indicates the communication be- 



The isthmus faucium is wide and dilatable. On either side, behind the an- 
terior pillar of the soft palate, there is a deep depression, the tonsillar sinus (Sinus 
tonsillaris) ; lateral to this is the compact, bean-shaped tonsil, which is about one 
to one and a half inches (ca. 3 to 4 cm.) in length. The tonsil does not project into 
the isthmus faucium, but outward instead: hence it does not occupy the tonsillar 
sinus, and is not visible internally, as is the case in most animals. 



THE TONGUE 



447 



THE TONGUE 

The tongue of the ox is often varialjly pigmented. The root and body are 
wider than that of the horse, but the free part is more pointed. The posterior part 
of the dorsum forms a remarkable elhptical prominence, which is sharply defined 
in front liy a transverse depression. "In front of this prominence there are large 
and horny conical papillae (Papillse coniese), with sharp points directed backward; 




Fig. 3S2. — Tongue and Fauces of Ox; Dorsal View. 
The pharynx and soft palate are cut dorsally and reflected, a, Vallate papilla; fa, prominence of dorsum with 
broad, flattened papillse; c, fungiform papillse; d, conical papillfe of tip; 1, glosso-epiglottic space; 2, tonsillar sinus; 3, 
cut surface of soft palate; 4, pharynx; 5, posterior pillar of soft palate; 6. epiglottis; 7, aditus laryngis. 



they impart to the tongue its rasp-like roughness. The papillse on the prominence 
tire large, broad, and horny ; some have a blunt, conical form, others are rounded or 
flattened and are termed lenticular papillse (Pajsillse lenticulares). Behind the 
prominence, the papillse are long and soft, ('. e., not horny. The fungiform jjapillae 
are numerous and distinct; they are scattered over the dorsum and edges of the 
free part. The vallate pajjillae number 8 to 17 on each side; they are smaller than 
those of the horse, and form a long, narrow group on either side of the posterior 
part of the prominence of the dorsum. The foliate papillae and the lingual fibrous 
cord are absent. There are lingual follicles in the posterior part of the root and on 



448 DIGESTIVE SYSTEM OF THE OX 



each side of the glosso-epiglottic fold. The muscles are well developed, and re- 
semble in general those of the horse; the hyo-glossus arises by additional portions 
from the great and middle cornua of the hyoid bone. The tongue is highly pro- 
tractile and is the chief organ of prehesion. 

THE TEETH 1 
The formula of the permanent teeth of the ox is: 



/ 3 3\ 

2 ( I - C - P - M - ) = 

V 4 3 3/ 



The incisors are absent from the upper jaw. There are eight incisors in the 
lower jaw, arranged in a somewhat fan-like manner. They are simple teeth, 
without infundibulum. The cro\\^I is white, short, and shovel-shaped. The root 
is rounded, and is embedded in the jaw in such a manner as to allow a small amount 
of movement. There is a distinct neck. In addition to the simple numerical 
designation, the following terms are commonly applied to the individual teeth: 




Fig. 383. — Incisor Teeth of Ox; Lingual Aspect. 
C. 5., Caruncula sublingualis. 

central, first intermediate, second in,termediate, and corner incisors. It is probable 
that the latter are much modified canines. The incisors of the adult ox do not 
undergo continued eruption, as is the case in the horse; in old age, however, the 
gum retracts so that the roots are partly exposed and may come into wear.^ The 
deciduous incisors differ from the permanent set chieflj' in being much smaller. 
The cro^\nis are narrower and diverge more. 

The canines are absent (unless the fourth incisors be considered to represent 
them in the lower jaw).' 

The cheek teeth (Figs. 134, 384) resemble those of the horse in number and 
general arrangement. They are, however,' smaller, and also differ in the fact that 
they progressively increase in size from before backward. This feature is so marked 
that the first tooth is quite small, and the space occupied by the first three {i. e., 
the premolars) is only about one-half of that required for the posterior three (i. e., 
the molars). The enamel folds stand out even more prominently in relief on the 
masticatory surface than in the horse. The occurrence of wolf-teeth is rare. 

' Other figures which show the teeth are to be found in the description of the skull. 

2 The reader will note here the difference between the structure and behavior of the bracny- 
dont (short-crowned) incisors of the ox and the hypsodont (long-crowned) type of the horse. 

' According to A. Hoffman, the anlagen of the upper canines are present in the foetus, but 
soon disappear. 



THE TEETH 



449 




450 DIGESTIVE SYSTEM OF THE OX 

The formula of the deciduous teeth is : 

20 



/no 3\ 

( Di - Dc - Dp - ) = 
V 4 3/ 



TABLE OF AVERAGE PERIODS OF ERUPTION OF THE TEETH IN THE OX 

Teeth " Eruption 

A. Temporary: 

First incisor (Di 1) 1 

Second incisor (Di 2) tj- ^i ^ o ^ 

Third incisor (Di 3) f ^'"'^ *° ^ weeks. 

Fourth incisor ( Di 4 ) J 

First cheek tooth (Dp 1) Birth to 3 weeks. 

Second cheek tooth ( Dp 2) \ n- i\. ^ r j 

Third cheek tooth (Dp 3) / ^"■*'^ '° f''^' ^ays. 

B. Permanent: 

First incisor (ID IJ^ to 2 years. 

Second incisor (12) 2 to 2J^ years. 

Third incisor (13) 3 years. 

Fourth incisor (I 4) 3J^ to 4 years. ' 

First cheek tooth (PI) 2 to 2)^ years. 

Second cheek tooth (P 2) IJ/^ to '2p2 years. 

Third cheek tooth(P 3) 2}^ to 3 years. 

Fourth cheek tooth (Ml) 5 to 6 months. 

Fifth cheek tooth (M 2) 1 to 1 J^ years. 

Sixth cheek tooth (M 3) 2 to 2}i years. 

The eruption of the permanent teeth is subject to great variation. The above 
figures are the average of observations of improved breeds under favorable condi- 
tions. 




Fig. 385. — Salivary Glands of Ox. 
a. Parotid gland; b, mandibular gland; e, ventral, d, middle, and e, dorsal buccal glands; /, labial glands; 
buccinator nerve; h, buccinator vein; 1, masseter (cut); S, ramus of mandible; 3, zygomaticus muscle; 4, coni 
papilla of lip ; 5, buccinator muscle. (After EUenberger, in Leisering's Atlas.) 



THE SALIVARY GLANDS THE CESOPHAGUS 451 



THE SALIVARY GLANDS 

The parotid gland is smaller and denser in texture than that of the horse, and 
is light red-brown in color; its average weight is about four ounces (ca. 115 g.). 
It has somewhat the form of a very narrow long triangle, and lies chiefly on the 
posterior part of the masseter muscle. The dorsal part is wide and thick; its 
anterior border partly covers a large parotid lymph gland. The small ventral end 
is bent forward and fits into the angle of union of the jugular and external maxillary 
veins; it lies on the mandibular gland. The parotid duct leaves the ventral part 
of the deep face; in its course it resembles that of the horse, but it pierces the cheek 
opposite the fifth upper cheek tooth. 

- The mandibular gland is larger than the parotid, and is pale yellow in color; 
its average weight is about five ounces (ca. 140 g.). It is covered to a small extent 
by the parotid. Its general form resembles that of the horse, but its ventral end 
is large and rounded, and is separated by a small interval only from the gland of 
the other side (Fig. 302). This part can be distinctly felt in the living animal, and 
is related laterally to a large lymph gland. The duct leaves the middle of the 
concave border of the gland, crosses the stylohyoideus and the intermediate ten- 
don of the digastricus, and is then disposed as in the horse. 

The sublingual gland consists of two parts. The dorsal part (Glandula sub- 
lingualis parvicanalaris) is long, thin, and pale yellow in color. It extends from the 
anterior pillar of the soft palate about to the symphysis of the mandible. It has 
numerous small tortuous ducts (Ductus sublinguales minores) , which open between 
the papillfe under the side of the tongue. The ventral part (Glandula sublingualis 
grandicanalaris) is shorter and thicker, and lies ventral to the anterior portion of 
the dorsal part; it is salmon pink in color. It has a single duct (Ductus sublin- 
gualis major), which either opens alongside of or joins the mandibular duct. 



THE PHARYNX (Figs. 386, 476, 478) 
The pharjTix is short and wide. The vault (Fornix pharyngis) is divided into 
two culs-de-sac by a median fold of mucous membrane (Septum nasi membrana- 
ceum), which is a continuation of that of the septum nasi; on the lateral wall of 
each is the relatively small opening of the Eustachian tube, which is covered by a 
simple fold of mucous membrane. The posterior nares are small. The entrance 
to the oesophagus is large. 

On the dorsal wall of the pharynx there are two large suprapharyngeal lymph glands, which, 
when enlarged, cause difficulty in swallowing and breatliing (Fig. 386). 



THE (ESOPHAGUS 

This is much shorter, wider, and more dilatable than that of the horse. Its 
average diameter (when moderately inflated) is about two inches (ca. 5 cm.), and 
its length in an animal of medium size is about three to three and a half feet (ca. 
90 to 105 cm.). The wall is relatively thin, and the muscular tissue is striped 
throughout. The latter consists, in the greater part of the tube, of two strata of 
spiral fibers, except near the stomach, where they are longitudinal and circular. 
Fibers are continued into the wall of the stomach for some distance. The mucous 
membrane forms a prominence at the ventral side of the pharyngeal end of the 
tube which contains glands; elsewhere it is non-glandular. There is no terminal 
dilatation, and no part in the abdominal cavity. 

A very large mediastinal lymph gland lies above the posterior part of the oesophagus and 
may, if enlarged, obstruct it (Fig. 389) . 



452 



DIGESTIVE SYSTEM OF THE OX 



THE ABDOMINAL CAVITY 

The abdominal cavity of the ox is very capacious, both absolutely and rela- 
tively, as compared with that of the horse. This is due to several factors. The 
lumbar part of the spine is about one-fourth longer than that of the horse. The 
transverse diameter between the last ribs is greater. The costal attachment of the 
diaphragm is almost vertical in direction from the ventral part of the ninth rib to 



Frontal sinus 



Cavity of great ethmoturbinal 




Cavity of superior turbinal 



Cavities of inferior turbinal 



Fig. 386. — Sagittal Section of Head of Cow, Cut a Little to the Right of the Median Plane. 

J, Cerebral hemisphere: 2, corpus striatum; 3, hippocampus; 4, olfactory bulb; o, corpora quadrigemina; 6, 
optic nerve; 7, pons; .S, medulla oblongata; i^, spinal cord; 70, pituitary body; i/, sphenoidal sinus; i^, lateral mass 
of ethmoid; 13, ventral straight muscles; 14, suprapharyngeal lymph gland; lo, longus colU; 16, soft palate; /T, 
vallate papillse; IS, tonsillar sinus; 19, conical papillae of cheek; iSO, hyo-epiglotticus muscle; 21, epiglottis; 22, hyo- 
glossus muscle; CI, C2, atlas, axis. Subject was hardened with-mouth open. 



the dorsal end of the thirteenth. Thus the abdomen is increased at the expense 
of the thorax, and the last three or four ribs enter more largely into the formation 
of the abdominal wall than in the horse. The flank is also much more extensive. 
The ilia, on the other hand, do not extend forward beyond a transverse plane 
through the middle of the last lumbar vertebra. The epigastric and mesogastric 
regions would be separated by a plane through the ventral end of the tenth pair of 



THE PELVIC CAVITY THE STOMACH 453 

ribs, or through the last thoracic vertebra. The chief differential features in the 
arrangement of the peritoneum will be described with the viscera. The sub- 
peritoneal tissue is more abundant than in the horse, and in general contains a 
much larger amount of fat. 

THE PELVIC CAVITY 

The pelvic cavity is relatively long and narrow. The inlet is more oblique 
than that of the horse; it is elliptical in outline, and the transverse diameter is 
smaller than that of the horse. The pubic part of the floor is about horizontal, 
but the ischiatic part slopes dorsally to a marked degree; this part is also deeply 
concave transversely. The roof is concave in both directions. The peritoneum 
extends backward as far as the first coccygeal vertebra, so that the retroperitoneal 
part of the cavity is short. 

THE STOMACH 

General Arrangement. — The stomach of the ox is very large, and occupies 
nearly three-fourths of the abdominal cavity. It fills the left half of the cavity 
(with the exception of the small space occupied by the spleen) and extends con- 
siderably over the median plane into the right half. 

It is compound, and consists of four divisions, viz., rumen, reticulum, omasum, 
and abomasum.' The division is clearly indicated externally l)y Furrows or con- 
strictions. The first three divisions are often regarded as proventriculi or oeso- 
phageal sacculations, the fourth being the stomach proper (in the narrower sense 
of the term). The oesophagus opens into the stomach on a sort of dome, the 
atriimi ventriculi, and is continued through the reticulum by the oesophageal 
groove. From the ventral end of the latter a groove traverses the ventral wall of 
the omasum, thus giving a direct path from the reticulum to the abomasum for 
finely divided food or fluid. The abomasum joins the small intestine. 

Capacity. — The capacity of the stomach varies greatly, depending on the age 
and size of the animal. In cattle of medium size it holds 30 to 40 gallons, in large 
animals 40 to 60, in small, 25 to 35. The relative sizes of the four parts vary with 
age, in correlation with the nature of the food. In the new-born calf the rumen and 
reticulum together are about half as large as the abomasum; in ten or twelve weeks 
this ratio is reversed. During this period the omasum appears to be contracted 
and functionless. At four months the rumen and reticulum together are about 
four times as large as the omasum and abomasum together. At about one and one- 
half years the omasum equals or approaches closely the abomasum in capacity. 
The four divisions have now reached their definitive relative capacities, the rumen 
constituting about 80 per cent., the reticulum 5 per cent., the omasum 7 or 8 per 
cent., and the abomasum 8 or 7 per cent, of the total amount. 

Exterior and Relations 
The rumen occupies almost all of the left half of the abdominal cavity, and 
extends considerably over the median plane ventrally and in its middle. It is 
somewhat compressed from side to side and may be described as having two sur- 
faces, two curvatures or borders, and two extremities. The parietal (or left) 
surface (Facies parietalis ) is convex and is related to the diaphragm, left wall of 
the abdomen, and spleen. It extends from the ventral part of the seventh inter- 
costal space almost to the pelvis. The visceral (or right) surface (Facies visceralis) 
is somewhat irregular, and is related chiefly to the omasum and abomasmn, the 

' In popular language these are regarded as so many stomachs, and are often designated 
numerically. Other names are in common use, e. g., paunch, honeycomb, manifold or manyplies, 
and rennet or true stomach. 



454 



DIGESTIVE SYSTEM OF THE OX 



intestine, the liver, pancreas, kidneys, the uterus in the female, and the posterior 
aorta and vena cava. The dorsal curvatxire (Curvatura dorsalis) is convex, fol- 
lowing the curve formed by the diaphragm and sublumbar muscles. It is firmly 
attached to the left portion of the crura of the diaphragm and the sul)lumbar 
muscles by peritoneum and connective tissue. The ventral curvature (Curvatura 
ventralis) is also convex and lies on the floor of the abdomen. The surfaces are 
marked by the right and left longitudinal grooves (Sulcus longitudinalis dexter, 
sinister), which indicate externally the division of the rumen into dorsal and ventral 
sacs.^ The reticular (or anterior) extremity (Extremitas reticularis) is divided 
ventrally by a transverse anterior groove (Sulcus ruminis cranialis) into two sacs. 
The dorsal sac is the longer of the two, and curves ventrally over the round, blind 



Dorh'6' iuiVJUy/f,^^ 




Fig. 387. — Stomach and Spleen of Ox; Left View. 
1, Left longitudinal groove of rumen; 2, rumino-reticular groove (not so distinct dorsally as shown here): 3, an- 
teridt groove of rumen; 4, posterior groove of rumen; 5, 6, coronary grooves; 7, S, anterior, 9, 10, posterior, blind 



end of the ventral sac. The former is continuous with the reticulum, the external 
line of demarcation being the rumino-reticular groove (Sulcus rumino-reticularis) . 
The groove is deep ventrally and is tlistinct on jxirt of the lateral surface, but dorsallj' 
no natural separation exists, tlie rumen and reticulum together forming a dome- 
like vestibule (Atrium ventriculi) on which the oesojjhagus terminates. The pelvic 
(or posterior) extremity (Extremitas pelvina), extends nearly to the pubis; it is 
related to the intestine and iiladder, and to the uterus in the cow. It is divided 
into dorsal and ventral blind sacs (Saccus csecus caudalis dorsalis, ventralis) by a 
deep transverse posterior groove (Sulcus ruminis caudalis), which connects the 
longitudinal grooves. The blind sacs are marked off from the remainder of the 

' It has been customary to term the sacs left and right respectively, but these do not repre- 
sent the relations as they exist in situ and as they are presented on frozen .sections. When the 
stomach is removed in the soft state, it loses its shape and the dorsal and ventral sacs of the rumen 
become left and right. 



EXTERIOR AND RELATIONS 



455 



rumen by the dorsal and ventral coronary grooves (Sulcus coronarius dorsalis, 
ventralis). 

The left longitudinal groove tSulcus longitudinalis sinister) begins at the anterior transverse 
groove, passes somewhat dorsally and backward and divides into two grooves. The ventral 
one is the chief groove, and passes backward to terminate in the angle of union of the posterior 
blind sacs. The dorsal (accessory) groove curves dorsally and then backward to terminate in 
the dorsal coronary sulcus. On the right surface there are two longitudinal grooves. The dorsal 
one is the chief sulcus (Sulcus longitudinalis dexter). It extends in a curved direction (the con- 
vexity being dorsal), and is continuous with the left longitudinal groove by means of the grooves 
between the dorsal and ventral blind sacs at each end. The ventral groove (Sulcus accessorius) 
curves somewhat ventrally and backward and joins the chief sulcus between the posterior blind 
sacs. 

The reticulum is the most anterior and the smallest of the four divisions; it 
is opposite to the ribs from the sixth to the seventh or eighth. It lies against the 




Fig. 3.S8.— Stom.v 

1, right longitudinal groove of rumei 

posterior blind sa 



OF Ox; Right View. 
2, posterior groove of 
of rumen; 7, pylorus. 



diaphragm and liver in sueh a position that the median plane divides it into two 
nearly equal portions. It is somewhat piriform, but compressed from before 
backward. The parietal or diaphragmatic surface (Facies diaphragmatica) faces 
forward; it is convex and lies against the diaphragm and liver. ^ The visceral or 
ruminal surface (Facies ruminalis) faces backward; it is flattened by the press- 
ure of the other three compartments; it ends dorsally by joining the wall of 
the rumen, the concave line of junction corresponding to a ridge in the interior 
of the stomach wliich forms the lower margin of the large rumino-reticular orifice. 
The lesser curvature faces to the right and dorsally, and is connected with the 

' It is important to notice that the reticulum is separated from the pericardium by an in- 
terval of about 1 to 1^2 inches (ca. 2 to 4 cm.) only, since foreign bodies which are often swal- 
lowed by cattle lodge in the reticulum, and not rarely (if sharp) perforate the reticulum and dia- 
pliragm. When the reticulum is full, its visceral surface is opposite to the eighth rib. 



456 DIGESTIVE SYSTEM OF THE OX 

omasum. The greater curvature faces to the left and ventrally; it lies against the 
diaphragm, opposite the sixth and seventh ribs. The ventral extremity forms a 
rounded cul-de-sac, which is in contact with the sternal part of the diaphragm, the 
liver, omasum, and abomasum; it may be termed the fxmdus reticuli. 

The omasum is ellipsoidal in form and somewhat compressed laterally. It is 
very clearly marked off from the other divisions. It is situated almost entirely 
to the right of the median plane, opposite the seventh to the eleventh ribs. The 
parietal (right) surface (Fades dexter) lies against the diaphragm, liver, and lateral 
wall of the abdomen. The contact with the latter extends over a small area only 
(ventral part of eighth, ninth, and tenth ribs usually). The visceral (left) surface 
(Facies sinistra) is in contact with the rumen and reticulum. The greater curvature 
is directed dorsally and somewhat backward; it is convex, and is related to the 
diaphragm, liver, and intestine. The ventral (lesser) curvature is concave, and 
faces ventrally and somewhat forward ; it is in contact -with the abomasum chiefly, 
the junction with the latter appearing as a constriction near the middle of the 
curvature; at its anterior part there is a neck (CoUum omasi) which is the con- 
nection with the reticulum. '^ 

The abomasum is an elongated, piriform sac, which lies for the most part on 
the abdominal floor, to the right of the reticulum and the ventral sac of the 
rumen. Its narrow posterior part is strongly curved, the concavity being dorsal. 
The parietal (right) surface lies against the abdominal wall from a point opposite to 
the seventh or eighth ril:) as far back as the eleventh or twelfth costal cartilage. The 
visceral (left) surface is related chiefly to the ventral sac of the rumen. The lesser 
curvature is dorsal, and is in contact with the omasum; the junction of the two sacs 
is indicated by a constriction about four or five inches (ca. 10 to 12 cm.) from the 
anterior extremity of the abomasum. The greater curvature is ventral, and rests 
on the abdominal wall from the xiphoid cartilage to the ventral part of the last 
(right) intercostal space; its direction is approximately parallel to the right costal 
arch." The fimdus or anterior extremity forms a rounded blind sac which lies 
against the reticulum. The pyloric or posterior extremity is much smaller and bends 
upward and forward to join the duodenum. The intermediate part is sometimes 
termed the body. About six to eight inches (ca. 15 to 20 cm.) from the pylorus there 
is a constriction which marks off the pyloric part from the Ijody and fundus. 

The rumen is attached by peritoneum and connective tissue to the crura of 
the diaphragm and left psoas muscles, from the hiatus oesophagus backward to 
the fourth or fifth lumbar vertebra. 

A small area of the anterior part of the right face of the rumen is adherent to 
the adjacent surface of the abomasum. The greater part of the ventral curvature 
of the omasum is attached by connective tissue to the dorsal face of the abomasum.* 

The lesser omentum attaches the right face of the omasum and the pyloric 
part of the al)omasuin to the visceral surface of the liver. 

Interior 

The cavity of the rumen is partially divided into dorsal and ventral sacs by 
the pillars (PilEe ruminis) ; these are folds of the wall, strengthened by additional 
muscular fibers, and correspond with the grooves on the outside. The two ex- 

1 The relative size of the omasum is subject to considerable variation. It may extend back 
to a point opposite the ventral fourth of the twelfth rib. The ventral curvature is usually opposite 
to the ninth, tenth, and eleventh costal cartilages, but in some subjects it faces chiefly forward and 
is opposite to the ventral third of the eighth or ninth rib. 

2 The greater curvature may be in contact in part with the costal arch, but is chiefly medial 
and ventral to it. It usually bends dorsally near the last costal cartilage and runs upward and 
forward to the eleventh intercostal space. 

' Adhesion of the reticulum to the diaphragm is frequently present, but is pathological; the 
same is true in regard to adhesion to the liver. 



INTERIOR 



457 



tensive chief pillars project like shelves into the anterior and posterior ends of the 
cavity, forming the blind sacs at either extremity. The anterior pillar ( Pila cranialis) 
projects obliciucly backward and upward from the ventral wall, and has a thick, 
concave free edge which is opposite to the tenth and eleventh ribs. Its width from 
the middle of the free edge to its attached border is about eight to ten inches (ca. 20 
to 25 cm.). It is continued on either side by the relatively narrow longitudinal 
pillars (Pila dexter, sinister), which connect it with the posterior pillar. The 
posterior pillar (Pila caudalis) is more nearly horizontal than the anterior one, and 
separates the large dorsal and ventral posterior blind sacs. Its concave free border 
is about a hand's breadth in front of a transverse plane through the tuber coxae. 
From it are detached three accessory pillars on either side ; of these, two pass around 
the blind sacs to meet the corresponding pillars of the opposite side. They thus 




Fig. 3S9. — Thoracic and Anteriok Abdominal Viscera of Ox ; Deep Dissection. 
Most of the rumen has been removed and the left wall of the reticulum cut away. A., Left pulmonary artery; 
B., left bronchus: V, V. I*., pulmonary veins: b. 5., bronchial lymph glands; L. g,, posterior mediastinal lymph gland; 
D., termination of duodenum; F, rumino-reticular fold. 



mark off the posterior blind sacs from the general cavity, and are termed the 
coronary pillars (Pila coronaria dorsalis, ventralis). It will be noticed that the 
ventral coronary pillar is complete, while the dorsal one is not. The other accessory 
pillars join the right and left longitudinal pillars. The right longitudinal pillar is 
in jDart double; its ventral division fades out about the middle of the surface, vt-hile 
the dorsal one joins the posterior pillar. The distance between the middles of the 
anterior and posterior pillars is only about sixteen to eighteen inches (ca. 40 to 45 
cm.) in a cow of medium size. In this space the dorsal and ventral sacs communi- 
cate freely. 

The anterior end of the dorsal sac of the rumen is separated ventrally from the 
reticulum by an almost vertical fold formed by the apposition of the walls of the 
two com]3artments. This rumino-reticular fold (Pila rumino-reticularis) is oppo- 
site to the seventh or eighth rib.' Its free dorsal edge is concave and forms the 

' The po.sition of this fold naturally varies with the degree of fulness of the reticulum. When 
the latter is full, it may extend back in part to the eighth intercostal space. 



458 



DIGESTIVE SYSTEM OF THE OX 



ventral and lateral margin of the large, oval rumino-reticular orifice (Ostium 
rumino-reticulare) . The medial margin of the fold, if continued, would end aliout 
at the cardia, but there is in this region no demarcation between rumen and reticu- 
lum; hence it is termed the atrium ventriculi. 

The lateral border of the rumino-reticular fold ends above the level of and behind the plane 
of the cardia, the medial one just behind the a'sophageal groove and about four to five inches 
lower down. Undoubtedly food or water swallowed with even a small degree of force passes first 
into the rumen. Foreign bodies (which are commonly swallowed by cattle) are, however, found 
in the reticulum. 

The cardia is opposite the seventh intercostal space or eighth rib, a little to the 
left of the median plane, and about a handbreadth (ca. 10-12 cm.) ventral to the 
vertebral column; it is not funnel-shaped. 

The mucous membrane of the rumen is bro\\Ti in color, except on the margins 







Fig. 390. — Reticull'-m of Ox. fboji Photogr.\ph. 
The specimen was cut along the greater curvature and laid open by reflecting the anterior wall. C is the cardia. 
The arrow pointa to the reticulo-omasal orifice. The spiral twist of the cesophageal groove was of necessity partly 
undone by reflecting the wall; its hps are drawn apart, showing some of the pecuhar birdclaw-like papillae in the 
ventral part. 



of the pillars, where it is pale. It is for the most part thickly studded with large 
papilliB, many of which are nearly half an inch (ca. 1 cm.) long. The edges of the 
chief pillars and a large part of the wall of the middle of the dorsal sac are, however, 
not papillated. The papillary arrangement is most developed in the blind sacs. 
The papillae vary much in size and form; the largest are foliate, many are narrow 
or filiform, and others are conical or club-shaped. The mucous meml^rane on the 
medial wall of the atrium is finely wrinkled and non-papillated, while dorsally and 
laterally it is papillated. The jiaiiillary arrangement also extends over the edge 
of the rumino-reticular fold an inch or two (ca. 2 to 5 em.). 

The oesophageal groove (Sulcus oesophagus) begins at the cardia and passes 



INTERIOR 459 

ventrally on the right wall of the atrium and reticulum to end at the reticulo- 
omasal orifice.' It is about seven or eight inches (ca. 18-20 cm.) in length. Its 
axial direction is chiefly dorso-vcntral, but it inclines forward to a variable extent 
and somewhat medially in its ventral part ; the ventral end, which is at the reticulo- 
omasal orifice, is about an inch (ca. 2.5 cm.) in front of the plane of the cardia and 
to the right of the median plane. The groove is twisted in a spiral fashion, so that 
its thickened edges or lips project first backward, then to the left, and finallj' for- 
ward. The twist involves chiefly the left lip, and the relative position of the lips 
is reversed at the ventral end. The mucous membrane on the lips of the cesoph- 
ageal groove is brown and wrinkletl, like that of the atrium; in the bottom of the 




1, 2, 3, 4, LaminEB of va 



Fig. 391. — Omasum of Ox, Sagittal Section-; Rig] 
IS orders; 5, muscular pillar; 6, neck connecting 



r View. 
■ith relic 



7, connection 



groove it is pale, like that of the ccsophagus, marked by longitudinal folds, and pre- 
sents pointed, horny ijajjillae on its ventral part. 

In the reticulum the mucous membrane is raised into folds about half an inch 
high, which enclose four-, five-, or six-sided spaces or cells (CelluliB reticuli) ; this 
peculiar arrangement suggested the scientific name and also the popular term 
■'honey-comb." These cells are subdivided by smaller folds, and the bottoms are 
studded with pointed, horny papillig. The cells grow smaller and gradually dis- 
appear near the oesophageal groove and the edge of the rumino-reticular fold; an 
inch or two from the latter the mucous membrane has the papillary arrangement 
of the rumen. At the reticulo-omasal orifice there are peculiar homy papillES, 
which are curved and resemble the claws of a small Ijird; hence they are termed 
unguliform (Papilloe unguliformes) . The reticulo-omasal orifice (Ostium reticulo- 
' It might better be termed the sulcus reticuli. 



460 



DIGESTIVE SYSTEM OF THE OX 



omasicum) is situated in tlie medial wall of the reticulum, about five or six inches 
above the bottom of the latter. It is rounded, and is limited below and laterally 
by the junction of the lips of the oesophageal groove. 

The cavity of the omasum is occupied to a considerable extent by about a 
hundred longitudinal folds, the laminae omasi, which spring from the dorsal wall 
and the sides. The largest of these — a dozen or more in numljer — have a convex 
attached edge, and a ventral, concave free edge, which reaches to within a short 
distance of the ventral Avail of the sac. If these are draAvn apart or a cross- 
section is made (Fig. 392), it will be seen that there is a second order of shorter 
laminse, and a third or fourth still shorter; finally there is a series of very low folds 
or lines. The food is pressed into thin layers in the narrow spaces between the 
lamince (Recessus interlaminares), and reduced to a fine state of division by being 
ground clown by the numerous rounded, horny papillse which stud the surfaces of 
the folds. The ventral wall of the omasum forms a groove, the sulcus omasi, 

which connects the reticulo- 
omasal opening with the 
omaso-abomasal opening; it is 
about three inches (ca. 7-8 
cm.) long, and is directed back- 
ward and downward. It is 
free from laminae, but presents 
usually slight folds and small 
papilte; it may function as a 
direct path from the reticulum 
to the abomasum for fluid and 
finely divided food. In the 
neck of the omasum there are 
thick folds, and a number of 
the peculiar papilla; already 
mentioned as occurring in the 
lower part of the oesophageal 
groove. The omaso-abomasal 
orifice (Ostium omaso-abo- 
masicum) is oval, and is about 
four inches (ca. 10 cm.) long. 
It is bounded in front by a 
thick muscular pillar, the fibers 
of which spread out above in 
the sides of the omasum. The 
mucous membrane forms an 
extensive fold on each side of the opening; these folds may act as valves (Valvulse 
terminal es), which probably prevent regurgitation of the contents of the abomasum. 
The cavity of the abomasum is divided by a constriction into two areas. The 
first of these (fundus gland region) is lined with a soft glandular mucous membrane, 
which forms a dozen or more extensive spiral folds (Plicse spirales). The second 
part (pyloric region) is much narrower and resembles in appearance the corre- 
sponding region of the horse's stomach. A small cardiac gland zone surrounds the 
omaso-abomasal orifice. The pyloric orifice is small and round. 

Structure. — The serous coat invests all of the free surface of the stomach. 
The surface of the rumon wliich is attached to the dorsal abdominal wall is, of 
course, uncovered, as well as the adjacent area to which the spleen is attached. 
The furrows are bridged over by the peritoneum and superficial muscle-fibers, 
and contain fat and (in most cases) branches of the gastric arteries. 

The lesser omentum passes from the visceral surface of the liver to the right 




Fig. 392. — Cross- 



OF Um.^sum of Ox. 
eck connecting with reticuln 



INTERIOR 461 

(parietal) face of the omasum and the pjdoric part of the abomasum and the first 
part of the duodenum. What might be regarded as a connection between the 
omenta is a fold between the ventral curvature of the omasum and the dorsal 
curvature of the abomasum. 

The greater omentum conceals the greater part of the intestine on the right 
side, with the exception of the duodenum, and covers the ventral sac of the rumen 
almost entirely. It is not lace-lilce, as in the horse, and contains a large amount 
of fat in animals in good condition. It may be described as consisting of two 
parts, each of which is composed of two layers of peritoneum; the two serous layers 
enclose a variable amount of fat. The superficial part extends from the left 
groove of the rumen vent rally around the ventral sac and ascends on the right 
side, covering the deep part. It ends along the retrograde part of the duodenum 
and the greater curvature of the abomasum. The deep part is attached along the 
visceral (right) surface of the rumen ventral to the right groove, and curves around 
the intestinal mass to the right side, where it is covered by the superficial part. It 




F, Fundus gland l 



Fig. 393.— Interior 
nth large spiral folds; P, pylor 



F .\bomasitm of O? 
region; D, duoden 



1. pylo 



torus pylo 



ends chiefly by blending with the medial layer of the mesotluodenum, but anter- 
iorly is attached on the first bend of the colon and the visceral surface of the liver 
along the ventral border of the pancreas. The two j^arts are continuous at the 
posterior groove of the rumen. They also join at the iliac flexure of the duodenum 
and at the origin of the colon. The epiploic foramen is almost sagittal in direc- 
tion. 

The muscular coat of the rumen consists of two layers. The fibers of the 
external layer are in general longitudinal; those of the thicker internal layer are 
largely circular in direction. The latter forms the bulk of the chief pillars, where 
it is about one-half to one inch (ca. 1 to 2 cm.) thick. Scattered bundles of striped 
muscle-fibers radiate from the cardia in the wall of the atrium and extend also along 
the oesophageal groove. 

The arrangement is in fact by no means so simple as might be inferred from the above brief 
statement, and much variation from the typical disposition is present. Along the furrows the 
fibers of the external layer are disposed more or less obUquely or even vertically in part; a super- 
ficial part of the layer bridges over the furrows (with the fat and vessels contained therein), wliile 
the deeper fibers extend into the pillars. The fibers of the inner layer on approaching the furrows 
change to an oblique or even horizontal direction. On entering the chief pillars this layer becomes 



462 



DIGESTIVE SYSTEM OF THE OX 



much thicker and its fibers have the same direction as the pillars. Thus the muscular tissue of 
the pillars is seen on cross-section to consist of two thick layers of longitudinal fibers, which are 
separated (except at the free margin of the pillar) by a thin axial layer of fibers disposed at right 
angles to the preceding. 

The muscular coat of the reticulum consists of two chief layers which begin 
and end at the oesophageal groove; they pass in a circular or oblique fashion around 
the sac, the fibers of the two layers crossing each other at varying angles. The 
walls of the cells contain a central muscular layer. The lips of the a:'Sophageal 
groove consist chiefly of a thick layer of longitudinal fibers, which are largely con- 
tinuous at, or cross each other below, the reticulo-omasal orifice. The bottom of 
the groove has two layers of oblique, unstriped muscle-fibers, 
with a variable outer layer of striped muscle continuous with 
that of the oesophagus. 

The external muscular layer of the oesophagus is in part continued 
down along the oesophageal groove (i. e., along the lesser curvature of 
the reticulum), but in greater part spreads out on the wall of the rumen 
and reticulum. The internal muscular layer of the oesophagus forms a 
loop over the cardia and is largely continued in the lips of the oesopha- 
geal groove; part of it is continuous with the muscular layer of the 
bottom of the groove. 

The muscular coat of the omasum consists of a thin ex- 
ternal longitudinal layer and a thick internal circular layer. 
At the omasal groove there is an incomplete inner layer of 
oblique fibers. The larger laminae contain three muscular 
strata. The fillers of the central layer extend from the at- 
Fia. 394. — .M L sc u LA- tached edge toward the free edge, but do not reach the latter; 

TXJRE OF (Esophageal 
Groove and Adjacent 
Part of Stomach of 

Ox, SEEN FROM WITHIN 
AFTER RemOV.\L OF 

Mucous Membr.\ne. 

a, CEsophagus; 6, in- 
ner muscular layer of atri- 
um; (/, reticulo-omasal ori- 
fice; e, e', muscle of lips of 
groove; g, lower end of 
muscle of larger lip, which 
curves around the reticulo- 
omasal orifice in part and 
spreads out in the inner 
muscular layer of the retic- 
ulum in part; A, lower 
end of muscle of smaller 
Up, which in part curves 
around the reticulo-omasal 
orifice and is in part con- 
tinuous with the inner mus- 
cular layer of the omasal 
groove and the omasum; 
i, inner muscular layer of 

reticulum. (Ellenberger- Fig. 395.-Stomach of New-born Calf; Right Vi 

Baum, Anat. d. Haustiere.) The rumen is raised. 





here there is a marginal band of longitudinal fibers. The central layer is contin- 
uous with the inner circular layer of the wall. On either side there is a layer of 
longitudinal fibers, which are continuous at the attached border with the muscu- 
laris mucosae. 

The muscular coat of the abomasimi consists of longitudinal and circular 
layers; the latter forms a well-developed jiyloric sphincter. 

The mucous membrane of the first three divisions is destitute of glands, and 
is covered with a thick, stratified, squamous epithelium; the superficial part of 



THE INTESTINE 



463 



the latter is homy, and is shed in large patches in the rumen and omasum. The 
tunica propria is papillated. The mucous membrane of the abomasum is glandular, 
and corresponds to that of the right sac of the stomach of the horse. The fundus 
glands (which are relatively short) occur in that part which presents the large folds, 
while the long pyloric glands are found in the remainder, except about the omaso- 
abomasal orifice, where cardiac glands occur. The mucosa of the fundus gland 
region is very thin as comi^ared with that of the 
horse; toward the pylorus there is an increase in 
thickness. There is a round prominence (Torus 
pyloricus) on the u]ii)er part of the pyloric valve. 
Vessels and Nerves. — The blood supply is 
derived from the coeliac artery, and the veins 
go to the portal vein. The nerves come from 
the vagus and sjonpathetic. Numerous ganglia 
are present in the submucous and intermuscular 
tissue, especially in the reticulum and oeso- 
phageal groove. S?fe «^.^1S) • . .- j 




THE INTESTINE 

The intestine of the ox is about twenty 
times the length of the body. It lies almost 
entirely to the right of the median plane, chiefl\' 
in contact with the right face of the rumen. It 
is attached to the sublumbar region by a com- 
mon mesentery. 

The small intestine has an average length 
of about 130 feet (ca. 40 m.) and a diameter of 
about two inches (ca. 5 to 6 cm.). The duo- 
denum is about three or four feet (ca. 1 m.) in 
length. Beginning at the pylorus (usually at the 
ventral end of the eleventh rib or intercostal 
space), it passes dorsally and forward to the 
visceral surface of the liver; here it forms, ven- 
tral to the right kidney, an S-shaped curve (Ansa 
sigmoidea). Thence it runs backward almost to 
the tuber coxae, where it turns on itself, passes 
forward alongside of the terminal part of the 
colon, and joins the mesenteric part (jejunum) 
under the right kidney. It is attached to the 
liver by the lesser omentum; the remainder of 
the mesoduodenum is a narrow fold which is 
largely derived from the right layer of the com- 
mon mesentery, but at the iliac flexure it comes 
directly from the sublumbar region. The bile 
duct opens in the ventral part of the S-shaped curv 
about a foot (ca. 30 cm.) further back. 

The remainder of the small intestine is arranged in mmierous very close coils, 
which form a sort of festoon at the edge of the mesentery. It lies chiefly in the 
space bounded medially by the right face of the ventral sac of the rumen, laterally 
and ventrally by the abdominal wall, dorsally by the large intestine, and anteriorly 
by the omasum and abomasum. It is not subject to much variation in position, 
but a few coils may find their way behind the blind sacs of the rumen to the left 
side. The terminal part leaves the edge of the mesentery and runs forward be- 




FiG. 390.—] 

FOLLICL 



E AND .Small Aggregated 
OR Peyer's Patches of 
STINE OF Ox (about }4 nat- 



The pancreatic duct opens 



464 



DIGESTIVE SYSTEM OF THE OX 



tween the caecum and colon, to both of which it is adherent. The orifices of the 
pancreatic duct and the l)ile duct are on papillae or thick folds, no diverticulum 
being present. There are permanent transverse folds of the mucous membrane 
(Plicae circulares). Duodenal glands occur in the first twelve to fifteen feet (4 to 4.5 




Fig. 397, — Projection of Viscera of Bull on Body-wall; Right Side. 
P., Pylorus; G.6., gall-bladder; R.K., right kidney; L.K., left kidney; P. (above duodenum), pancreas; Bl., 
bladder; V.s., vesicula seminalis; E.g., bulbo-urethral (Cowper's) gland. Costal attachment and median 
line of diaphragm are indicated by dotted lines. 




•JECTION OF Viscera of ^Cow on Body-wall; Left Side. 
Oes., CEsophagus: Ret., reticulum; b. s., anterior blind sac; h. s"., posterior blind sacs of rumc 
left kidney, concealed by the dorsal sac of the rumen, is indicated by dotted line. The median lii 
is dotted. 



; 0, ovarj-. The 
^ of the diaphragm 



m.), intestinal glands throughout. The aggregated follicles or Peyer's patches are 
larger and more prominent and distinct than in the horse, and vary greatly in size 
and number ; in adult cattle there are eighteen to forty ; in calves twenty to fifty- 
eight have been counted. They usually have the form of narrow bands. There 
is a patch close to the ileo-csecal valve. 



THE LIVER . 465 

The large intestine is much smaller in caliber than that of the horse, has no 
bands, and is not sacculated. Most of it is situated between the layers of the 
common mesentery in the right dorsal part of the abdominal cavity. It is related 
on the right to the lateral abdominal wall, from which, however, it is almost com- 
pletely separated by the greater omentum. On the left it is chiefly related to the 
rumen. The average length of the caecum is about thirty inches (ca. 75 cm.), and 
the diameter is about five inches (ca. 12 cm.). It is directly continuous in front 
with the colon, the conventional demarcation being the junction of the ileum with 
the large intestine.^ From this junction, which is on the medial side and usually 
near the ventral end of the last rib, the caecum extends backward and upward 
along the right flank (from which it is separated by the greater omentum), and its 
rounded blind end commonly lies at the right side of the pelvic inlet. The caecum 
is attached along its medial side to the mesentery, except the posterior third, which 
is free and variable in position. The terminal part of the ileum runs fonvard along 
the medial surface of the caecum and is attached to the latter. The dorsal surface 
is attached by areolar tissue and peritoneum to the colon. The colon is about 
thirty-five feet (ca. 10 m.) in average length. Its diameter is at first the same as 
that of the caecum, but diminishes to about two inches (ca. 5 cm.). The greater 
])art of it is arranged in double elliptical coils between the layers of the mesentery; 
the coils are attached to each other by areolar tissue. It begins as the direct 
continuation of the caecum, runs forward a short distance, and turns dorsally and 
backward opposite to the ventral part of the last two ribs. It continues backward, 
in relation to the right flank laterally and the caecum ventrally, to the posterior 
part of the sublumbar region. Here it turns forward and runs parallel with the 
retrograde part as far forward as the second lumbar vertebra, turns backward, and 
is continued by the spiral part (Ansa spiralis). The coils of this are alternately 
centripetal and centrifugal (Gyri centripetales et centrifugales) ; they are best 
seen frona the left side. The bowel gradually diminishes in caliber, and the ter- 
minal part (Ansa distalis) leaves the spiral mass, passes forward to the great mesen- 
teric artery, and runs backward dorsal to the terminal part of the duodenum. It 
inclines to the right in relation to the ventral surface of the right kidney, forms an 
S-shaped curve near the pelvic inlet, and joins the rectum; this part is attached to 
the sublumbar region by a narrow mesentery, and is also attached to the recurrent 
part of the duodenum. 

The rectum is somewhat shorter than that of the horse, and is usually covered 
with peritoneum as far back as the first coccygeal vertebra. The retroperitoneal 
part is surrounded by a quantity of fat. The anus is not prominent. 

The serous coat is of course al^sent on the adherent surfaces of the spiral i3art 
of the colon. There is a large amount of fat in the mesentery. The longitudinal 
fibers of the muscular coat are evenly distributed, consequently there is no saccula- 
tion of the bowel. There is a valvular mucous fold at the ileo-caecal orifice. A 
Peyer's patch occurs in the beginning of the caecum and one in the first part of the 
colon. 

THE LIVER 

The liver lies almost entirely to the right of the median plane. Its long axis 
is directed olsliquely downward and forwarcl, about parallel with the median plane, 
and corresponds to the curvature of the right portion of the diaphragm. It is less 
extensive, but thicker than that of the horse. Its average weight is about 10 to 
12 pounds (ca. 4.5 to 5.5 kg.). 

' In formalin-hardened material there is sometimes a constriction in front of the termination 
of the ileum. This might l>e regarded as the demarcation between the caecum and colon. The 
opening of the ileum is directly forward, so that material from it enters the origin of the colon. 
The posterior free part of the csecum is naturally variable in position; it may be bent ventrally. 
so that the blind end faces forward. 
30 



466 DIGESTIVE SYSTEM OF THE OX 

In small subjects the weight (according to Schmaltz) varies from 6J^ to 10 pounds (ca. 
3 to 4.5 kg.), in large subjects from 11 to 13 pounds (ca. 5 to 6 kg.). According to Schneider, the 
average weight is about 13 pounds (ca. 6 kg.) — a little over 1 per cent, of the live weight and 
about 2 per cent, of the dressed carcass. 

When hardened in situ, it is seen to be adapted accurately to the structures 
witli which it is in contact. 

The parietal surface is convex and is for the most part applied to the right 
part of the diaphragm, but a small part of it is in direct contact with the last two 
or three ribs and with the flank at the lumbo-costal angle. It faces dorsally, for- 
ward, and to the right. 

The curvature of the parietal surface is not quite regular. It is marked, except in its ventral 
part, by a blunt oblique ridge which divides the surface into two areas. Of these, the lateral one 



Caudate lobe 



Falcifomligaineiit (cul) 




: Coronary ligament (cut) 

Gall-bladder ^^^^^^^^^^ _^^^^^^_.^_ 

Posterior vena cava 

Hepatic veins 
(Esophageal notch 



FiQ. 399. — Liver of Ox, Pabietal Surface; Hardened in situ. 

is directed outward, is only sUghtly convex, and often shows impressions of the last three ribs; it is 
in contact in part directly witli the right abdominal wall, in part with the costal part of the dia- 
phragm which is in contact ordinarily with the lateral wall. The metlial area presents a depression 
produced by the right crus of the diaphragm, and otherwise is regularly convex and adapted to 
the tendinous center and sternal part of the diaphragm. The falciform hgament is attached to 
the surface from the oesophageal notch to the umbilical fissure. There is a triangular area of 
considerable size on the dorso-medial part of the surface which is without a peritoneal covering, 
since it is adherent to the diaphragm. 

The visceral surface is concave and very irregular; it presents impressions of 
the chief organs which are in contact with it — the omasum and reticulum. It is 
also related to the pancreas and duodenum. 

The following markings are quite distinct on the visceral surface of well-hardened speci- 
mens: (1) The omasal impression (Impressio omasica) is a deep central cavity below the portal 



THE LIVER 



467 



fissure. (2) The reticular impression (Impressio reticularis) is a smaller marginal depression below 
the oesophageal notch and the medial part of the preceding, from which it is separated by a rounded 
ridge. (.3) The abomasal impression (Impressio abomasica), present only in the young subject 



Renal impression 



Hepatic artery 
Portal vein 
Bile-duct 



Lesser omentum (cut) 
(Esophageal notch 




Fig. 400. — Liver of Heifer, Visceral Surface; Hardened in situ. 
The abomasal impression is shown to the right of the reticular impression, but by an oversight is not marked. 



Area of attachment to 
diaphragm {>wn-pcritoncal) 



Caudate lobe 




Coronary ligamenl 
Posterior vena cava 



Hepatic veins 



(Esophageal notch 
Fig. 401. — Liver of Ox, Left Marginal Vi: 



usually, corresponds to the fundus of the abomasum. It Ues along the ventral part of the surface 
and is separated by ridges from the preceding impressions. It usually disappears as the omasum 
and reticulum increase in size and displace the abomasum from contact with the liver. (4) Shallow 



d:68 DIGESTIVE SYSTEM OF THE OX 

grooves for the S-shaped portion of the duodenum (Impressio duodenahs) may be found dorsal 
and lateral to the portal fissure. (5) The fossa of the gall-bladder (Fossa vesicae fellea;) is distinct 
when that organ is full. In the calf the omasal impression is small, and the abomasal one large in 
correspondence with the relative sizes of these two sacs. 

The portal fissure is a well-defined rounded depression, situated dorsal to the 
omasal impression. It contains, [resides the vessels and duct, several large hepatic 
lymph glands. Dorsal and lateral to it a part of the pancreas is attached. 

The dorsal border is short and thick; it usually extends backward a short 
distance beyoiul the upper part of the last rib. It presents the large, thick, quad- 
rilateral caudate lobe, and a deep depression for the right kidney and adrenal. 

The ventral border is short and thin and has no interlobar incisures. 

The right (or lateral) border is marked by the umbilical fissure, in which the 
ligamentum teres is attached in the young subject. 

The left border presents the oesophageal notch below its middle; the notch is 
much shallower than in the horse. Above this it is practically median in position, 
and lodges the posterior vena cava, which is partially embedded in the gland. Be- 
low the notch the border extends an inch or two (ca. 2.5 to 5 cm.) to the left of the 
median plane, opposite the ventral third of the sixth rib or intercostal space. 

The right lateral ligament attaches the dorsal border to the anterior part of 
the sublumbar region. The ligament of the caudate lobe passes to the ventral 
surface of the right kidney. There is no left lateral ligament. The falciform liga- 
ment is generally i^resent, but the ligamentum teres is usually found only in young 
subjects. The lesser omentum leaves the liver along a line extending from the 
oesophageal notch to the portal fissure. The only distinct lobes in the adult are 
the caudate and papillary. The latter is best seen in the soft specunen; it is a 
tongue-like mass which partly overlaps the portal vein and fissure.^ 

A gall-bladder (Vesica fellea) is present. This is a pear-shaped sac, four to 
six inches (ca. 10 to 15 cm.) long, which lies partly in contact with the visceral 
surface of the liver (to which it is attached) , but largely against the abdominal wall 
at the ventral part of the tenth or eleventh intercostal space. It may be regarded 
as a diverticulum of the bile-duct, enlarged to form a reservoir for the bile. Its 
neck is continued by the cystic duct (Ductus cysticus), which joins the hepatic 
duct at an acute angle just outside of the portal fissure, to form with it the bile- 
duct (Ductus choledochus). The latter is short and enters the second bend of the 
S-shaped curve of the duodenum, {. e., about two feet (ca. 60 cm.) from the pylorus. 
The opening of the duct is at the end of a papilla or ridge-like fold. Several small 
ducts (Ductus hepatocystici) open directly into the gall-bladder. 

The wall of the gall-bladder consists of serous, muscular, and mucous coats. The muscular 
tissue consists of unstriped fibers which run in various directions; externally many are longitudinal, 
wliile internally (and especially at the neck) they are chiefly circular. The mucous membrane is 
covered by a cylindrical epithehum and contains numerous groups of branched tubular glands. 
The cystic and bile ducts have a similar structure. 

In the new-born calf the Uver is relatively much larger than in the adult. The visceral 
surface presents, below the portal fissure, a rounded eminence, which is caused by the pres- 
ence in the underlying gland substance of a large venous sinus into which the umbilical and portal 
veins empty. A large vessel, the ductus venosus, leafls from this sinus directly to the posterior 
vena cava. The umbihcal fissure is deep and partially divides the gland into two chief lobes. 



THE PANCREAS 

The pancreas of the ox is irregularly ([uadrilateral in form, and lies almost 

entirely to the right of the median plane. Its weight is about the same as that of 

the horse. Its dorsal surface is related to the liver, right kidney, crura of the 

diaphragm, posterior vena cava, and coeliac and anterior mesenteric arteries; it is 

1 The liver of the ox might be regarded as consisting of dorsal, ventral, caudate, and papillary 
lobes. Pathological adhesions of the ventral part of the liver to the cUaphragm and reticulum 
are often present in dissecting-room subjects. 



THE PANCREAS 



469 



covered to a large extent by peritoneum. It is attached to the liver at and lateral 
to the portal fissure, and to the crura of the diaphragm. Between the.se adhesions 
it is free and forms the ventral wall of the epiploic foramen. On the right side it 
extends backward beyond the caudate lobe of the liver between the layers of the 
mesoduodenum ; here it is in contact with the upper part of the flank at the lumbo- 
costal angle, and is related dorsally to the right kidney and by its ventro-lateral 




Gnll-bladder 
Round ligament 
of liver 



Fig. 402. — Pancreas and Related Structures of Ox. 
1, Left extremity of pancreas: 2, posterior vena cava; 3, portal vein; 4, gastro-spienic vein; 5, probe in epiploic 
foramen; 6, bile duct; 7, cystic duct; S, pancreatico-intestinal lymph gland; 9, cut edge of lesser omentum; 10, 
omasa! impression of liver. Intraglanduiar part of pancreatic duct and its cliief radicles are shown by dotted lines. 
Concealed parts of bile duct, cystic duct, and neck of gall-bladder are similarly indicated. 



border to the retrograde part of the duodenum. The ventral or gastro-intestinal 
surface is in contact with the dorsal curvature of the rumen and the intestine. 
There is a deep notch (Incisura pancreatis) for the portal vein and hepatic artery, 
and several lymph glands are present here. The left extremity is small and quad- 
rilateral; it is related dorsally to the crus of the diaphragm, left adrenal, and the 
coeliac and anterior mesenteric arteries, and is adherent ventrally to the rumen. 



470 



DIGESTIVE SYSTEM OF THE SHEEP 



The right or posterior part is wide and thin and is often divided into two branches. 
The duct leaves the posterior part of the ventro-lateral (or right) border and enters 
the duodenum about twelve inches (ca. 30 cm.) further back than the bile-duct. 



THE SPLEEN 

The spleen has an elongated, elliptical outline, both extremities being thin, 

rounded, and similar in size. 

Its average weight is about two pounds (ca. 900 gm.), or about /6 per cent, of 

the body-weight. Its average length is about 20 inches (ca. 50 cm.), its width 

about 6 inches (ca. 15 cm.), and in the 
Dorsal extremity middle its thickness is about an inch (ca. 

2 to 3 cm.). 

The dorsal extremity lies under the 
dorsal ends of the last two ribs, and may 
extend back as far as the first lumbar 
transverse process. The ventral extrem- 
ity is usually opposite the eighth or ninth 
rib, about a handbreaclth above its junc- 
tion with the cartilage. The parietal sur- 
face is convex, and is related to the dia- 
phragm. The visceral surface is concave, 
and is related chiefly to the left face of the 
rumen, but also usually to a narrow ad- 
jacent area of the reticulum. The dorsal 
part is attached to the left crus of the dia- 
phragm and the left surface of the rumen 
by peritoneum and connective tissue ; the 
ventral part is free. The hilus is situated 
on the dorsal third of the visceral surface, 
near the anterior border. 

About one-half of the \'isceral surface of the 
spleen is attached directly to the stomach and is 
therefore not covered by peritoneum ; the line of re- 
flection of the latter crosses the surface obliquely, 
from the upper part of the posterior border to 
the anterior border below its middle. Similarly 
there is a narrow uncovered area on the upper 
part of the parietal surface along the anterior 
border. The hilus is not a groove, but a simple 
depression. When hardened in situ, the organ is 
seen to be somewhat twisted, so that the upper 
part of the parietal surface faces dorsally and 
forward, while below it is directed laterally. In 
some cases the spleen is considerably longer than 
IS stated above, and may extend to the ventral end of the eighth rib. Not uncommonly there are 
pathological adhesions of the ventral part of the spleen to adjacent structures. 




Ventral extremity 



Fig. 403. — Spleen of Ox; Viscer.il Subface. 
Area of attachment to rumen (non-peritoneal) ; 
posterior border; S, line of peritoneal reflection. 



DIGESTIVE SYSTEM OF THE SHEEP 

The lips are thin and mobile; the upper one is marked by a very distinct 
philtrum, and otherwise is not bare. 

The anterior part of the hard palate is prominent and smooth, forming the 
so-called dental pad or plate. On the posterior part of this area there are two 



DIGESTIVE SYSTEM OF THE SHEEP 



471 



narrow depressions in tlie form of a V and separated by the central papilla incisiva, 

at the deep anterior ends of which the incisive or naso-palatine ducts open. The 

ridges of the palate, some fourteen in number, are irregular and their edges are 

smooth; most of them alternate with those of the 

opposite side, from which they are separated by the 

median raphe palati. The posterior third or rather 

more is not ridged and presents numerous orifices of 

ducts of the palatine glands. The mucous membrane 

is often more or less pigmented. The soft palate 

resembles that of the ox. 

The mucous membrane of the cheeks is covered 
with large papillse, many of which are long and sharp- 
pointed, while others are short and blunt. There is 
also a series of conical papillse on the floor of the 
mouth, under the lateral part of the tongue. 

The tongue resembles that of the ox in form, but 
the tip is comparatively smooth; the papillse here are 
very numerous, but short and blunt. This difference 
is in conformity with the dissimilarity in 'the mode of 
jirehension of the two species. The prominence of 
the dorsum is commonly not so pronounced nor so 
sharply marked off in front as in the ox. The root 
is smooth. The mucous membrane of the dorsiun is 
often pigmented in spots. 

The dental formula is the same as that' of the 
ox.' The incisor teeth form a narrow and strongly 
curved arch. The crowns are long and narrow; their 
labial surfaces are strongly convex and end at a sharp 
edge which is used in cropping the grass. The roots 
are more firmly embedded than in the ox. The cheek p^^ j^^ . 

teeth resemble those of the ox, but have a thinner ^^ Dental pad; 2, papilla in- 

layer of cement, which is often blackened by deposits cisiva; 3, 3, openinEs of incisive 
from the food. The average periods of eruption of canals; 1, rapM paiati; 5 phii- 

. . , , . . . , , trum; 6, conical papillsB of cheek; 

the teeth are mdicated m tlie subjoined table: 7, tonsils; s, palatine arch. 




: OF Sh 



Ii At birth or first week 1 to IJ^ years 

I2 First or second week 1 J-^ to 2 years 

I3 Second or third week 2J/^ to 3 years 

It Third or fourth -week 3J^ to 4 years 

Pa f 2 to 6 weeks 1 J^ to 2 years 

P3J 

Ml 3 months (lower), 5 months (upper) 

Mo 9 to 12 months 

Ms 13^ to 2 years 

The salivary glands resemble those of the ox in general. The parotid gland 
is darker in color and more compact in texture than the mandibular. It is rounded 
in outline, but has a pointed cervical angle at which the external jugular vein 
emerges. The duct leaves the lower part of the anterior Ijorder of the gland and 
runs forward over the masseter muscle, about an inch and a half (ca. 3.4 cm.) 
above the ventral border of the ramus; it opens opposite the third or fourth 
cheek tooth. 

The tonsil is bean-shaped and about half an inch (ca. 12 mm.) in length. It 
' A lateral view of the teeth is given in the description of the skull. 



472 



DIGESTIVE SYSTEM OF THE SHEEP 



does not project into the isthmus faucium. The mucous membrane of the latter 
presents two deep and very narrow tonsillar sinuses on either side. 

The fornix of the pharynx presents a median plicated fold which is a continua- 
tion of the septum nasi. The pharyngeal orifice of the Eustachian tube has the 
form of a crescentic slit, placed about on a level with the ventral nasal meatus. 
There are two large lymph glands and a number of hsemolymph glands above the 
pharynx. 

The oesophagus has a lumen of about an inch (ca. 2.5 cm.) when moderately 
distended ; otherwise it resembles that of the ox. 

The stomach is like that of the ox in its general arrangement. Its average 
capacity is about four gallons (ca. 15 liters). The cardia is opposite the eighth 
intercostal space; it is just to the left of the median plane, and about two inches 



Dorsal curvature of 
rumen 








^^'^' 







Fig. 405. — Stomach of Sheep; Left View. 
From photograph of specimen hardened in situ. The reticulum is 



hat contracted. 



(ca. 5 cm.) below the vertebral column. The dorsal sac of the rumen is a little longer 
than the ventral sac and extends considerably (ca. 7.8 cm.) further forward than 
the latter. The ventral sac is relatively larger and extends further to the right of 
the median plane than in the ox; its posterior blind sac extends further (ca. 6-8 cm.) 
back than that of the dorsal sac. The parietal attachment of the dorsal sac 
extends back to the second lumbar vertebra. The left longitudinal groove ex- 
tends upward and backward for a short distance only, and therefore does not 
connect with the posterior groove. There are two longitudinal grooves on the 
right side which join at each end, thus enclosing a long, narrow prominent area; 
the dorsal one contains the right ruminal artery, and the ventral one corresponds to 



DIGESTIVE SYSTEM OF THE SHEEP 



473 



the pillar. The left coronary grooves do not extend to the curvatures. There is 
no dorsal coronary groove on the right side, but the ventral one is very distinct and 
extends to the curvature. The arrangement of the pillars corresponds to these 
external features. The papilliE of the rumen are relatively large and somewhat 
tongue-like; the largest are about a fourth of an inch (ca. 6 mm.) in length. The 
dorsal part is papillated, not glabrous, as in the ox. The lateral part of the rumino- 
reticular fold ends half an inch or more (ca. 1.5 cm.) behind the cardia. The 
reticulum is relatively larger than in the ox. Its ventral part curves more back- 
ward and less to the right than in the ox. The parietal surface extends forward as 




Pylorns 



Fia. 406. — Stomach of Sheep; Right View. 
From photograph of specimen hardened in situ. Dotted Une indicates position of spleen. 

far as the sixth rib or intercostal space, and is related to the diaphragm and liver. 
The fundus lies on the sternal part of the diaphragm and is in contact behind with 
the abomasum. The oesophageal groove is disposed in general like that of the ox, 
and is about four to five inches (ca. 8 to 10 cm.) long. 

There are, however, several marked differences in the arrangement of the groove. Its ven- 
tral part curves backward, so that the reticulo-omasal orifice is directed dorsally and lies in a trans- 
verse plane about an inch (ca. 2-3 cm.) behind one passing through the cardia. These differ- 
ences are correlated with the small size of the omasum and the large size of the reticulum. 
Tubulo-alveolar glands have been found by Thanhofer and others; they occiu' chiefly in the 
submucous tissue at the angle of junction of the lips and bottom of the groove. 



The folds surrounding the cells of the reticulum are only 2-3 mm. in height, 



474 DIGESTIVE SYSTEM OF THE SHEEP 

and have serrated edges. The dorsal part of this sac has, in the vicinity of the 
rumino-reticular orifice, a papillated mucous membrane just like that of the 
rumen. The omasum is much smaller than the reticulum, its capacity being 
only about one pint. It is oval and compressed laterally. It is situated almost 
entirely to the right of the median plane, opposite to the ninth and tenth ribs. 




Fig. 407. — Cross-section of Sheep, THRonoH Ninth Thoracic Vertebra; Anterior View. 
1, Cardial 2, oesophageal groove; S, rumino-reticular orifice; 4, rumino-reticular fold; S, dorsal sac of rumen; 
6, body of ninth thoracic vertebra; T, vena hemiazygos; S, aorta; 9, posterior mediastinal lymph gland; 10, 10, crura 
of diaphragm; i/, posterior vena cava; i^, portal vein; K.i., right lung; !,.(., left lung; S, spleen; L, liver; B, reticu- 
lum (posterior wall) . Arrow points to reticulo-omasal orifice. The spleen is cut so obliquely as to appear much thicker 
than it really is. ' 

higher than in the ox, and has no contact with the alxlominal wall. It is related 
on the right to the liver and gall-bladder, on the left to the rumen, and ventrally 
to the abomasura. The lamina are less numerous than in the ox; in the neck 
which connects the omasum with the reticulum they ha\-e the form of low, thick 
ridges, and bear long, pointed, horny papilte. The abomasum is relatively 



DIGESTIVE SYSTEM OF THE SHEEP 



475 



larger and longer than in the ox. Its capacity is about twice that of the 
reticulum and averages about two quarts (ca. 1.75 to 2 liters). The blind 
anterior end lies almost centrally in the xiphoid region, in relation to the liver and 
reticulum. Its body extends backward a little ventral to and almost parallel 
with the right costal arch. The pylorus is usually opposite the ventral end 
of the eleventh or twelfth intercostal space. At the reticulo-omasal open- 
ing and on the adjacent part of the laminae of the omasum are large, pointed, 
horny papilliE. 

The general arrangement of the intestine is like that of the ox. The small 




Fig. 408. — Abdomin-al ^'ISCERA of Sheep; Superficial Ventral Vie 



intestine is about 80 feet (ca. 24 to 25 m.) long; its average diameter is about an 
inch ( ca. 2 to 3 cm.) , the caliber increasing in its terminal part, where a very extensive 
Peyer's patch is found. Duodenal glands occur for a distance of two feet or more 
(ca. 60-70 cm.) beyond the pylorus. The caecum is about 10 inches (ca. 25 cm.) 
long, 2 inches (ca. 5 cm.) wide, and has a capacity of aljout a ciuart- (ca. 1 liter) ; 
only al)out two inches (ca. 5 cm.) of it is free. The colon is about 15 feet (ca. 4 to 
5 m.) long. Its caliber is at fir.st about the same as that of the caecum, but dimin- 
ishes to aljout the width of the small intestine. 

The liver weighs about 20 to 25 ounces (ca. 550 to 700 gm.). It lies entirely 



476 



DIGESTIVE SYSTEM OF THE SHEEP 



to the right of the median plane. The parietal surface is related almost exclusively 
to the right part of the diaphragm. The visceral surface presents extensive reticular 
and abomasal impressions, and a small omasal impression medial to the portal 
fissure. The umbilical fissure is deep and partially divides the gland into two 
chief lobes, dorsal and ventral. The caudate lobe is prismatic and blunt-pointed. 
The oesophageal notch is represented by a slight impression. The gall-bladder is 
long and narrow. The bile-duct joins the pancreatic duct to form a common bile- 
duct (Ductus choledochus communis), which opens into the duodenum about one 
foot (ca. 30 cm.) from the pylorus. 

The pancreas is arranged as in the ox. Its duct unites with the bile- 
duct. 

The spleen (Fig. 405) is approximately triangular, with the angles rounded off; 



Posterior vena 
cava 



Portal vein 



Hepatic artery 



Omasal impres- 
sion 



Lesser omentu 



Reticular impres- 
sion 



Renal impression 



Caudate lobe 



Bile-duct 



Cystic duct 




Fig. 409 — Live 



Sheep, Visceral Surface; Harde 



the wider end or base is dorsal. It weighs about three or four ounces (ca. 100 grams) . 
Its length is about five to six inches (ca. 12 to 15 cm.), and its greatest width three 
to four inches (ca. 7.5-10 cm.). The long axis is oblique, and corresponds to a line 
drawn from the verteliral end of the last rib to about the middle of the tenth inter- 
costal space. The parietal surface is convex and is related to the diaphragm, to 
which rather more than the anterior third is adherent; when hardened in situ, it 
often shows impressions of the upper parts of the last three ribs. The visceral 
surface is concave, and its anterior half is attached to the dorsal curvature of the 
rumen. The borders are thin, the posterior one often being crenated. The dorsal 
end or base is attached to the left crus of the diaphragm under the last two ribs; 



DIGESTIVE SYSTEM OF THE PIG THE MOUTH 



477 




Fig. 410.- 
1, Posterior vei 



-Liver of Sheep, Parietal Surface; Hardened in situ. 

i cava; 2, falciform ligament; 3, gall-bladder; 4< umbilical fissure. 



it usually extends about an inch (ca. 3 cm.) behind the last rib. The hilus is on the 
visceral surface, close to the anterior basal angle; it is a round depression, not a 
groove. The ventral end is narrower and thinner than the base; it is usually 
situated opposite the tenth intercostal space or eleventh rib, a little above its middle. 



DIGESTIVE SYSTEM OF THE PIG 
THE MOUTH 

The rima oris is extensive, the angles of the mouth being situated far back. 
The upper lip is thick and short, and is blended with the snout; the lower lip is 
small and pointed. The labial glands are few and small. 

The mucous membrane of the cheeks is smooth. The buccal glands are 
compactly arranged in two rows opposite the cheek teeth. The parotid duct 
opens opposite the fourth or fifth cheek tooth. 

The hard palate is long and narrow ; it is marked by a median furrow, on each 
side of which are twenty or more ridges. On its anterior part there is a long narrow 
prominence, the incisive papilla, at the posterior part of which the incisive or naso- 
palatine ducts open. There is a round prominence in front of the first pair of 
incisors. 

The soft palate is very thick; its length in an animal of medium size is about 
two and a half inches (ca. 5 cm.). Its direction almost continues that of the hard 



478 



DIGESTIVE SYSTEM OF THE PIG 



palate, i. e., it is nearly horizontal. It extends to the middle of the oral surface 
of the epiglottis. It has in many cases a small median prolongation termed the 
uvula. The oral surface presents a median furrow, on either side of which is an 
oval raised area, marked by numerous crypts; these elevations are the tonsils. 
Tonsillar tissue also occurs in the lateral walls of the isthmus faucium and the root 
of the tongue. 

The tongue is long and narrow and the apex is thin. Two or three vallate 




^^^^' 



a 




Fig. 411. — Hard Palate or Young Pig. 

1, Papilla incisiva; 2, openings of ductus in- 
cisivi; 3, raph^ of palate; a, incisor teeth; 6, canine 
tooth; c, premolar teeth; d, molar teeth. 



Fig. 412. — Tongue of Pig. 
1, Apex; 3, dorsum: 3, root; a, orifices of ducts of 
lingual glands; b, papillae of root; c, vallate papilla (not 
really so distinct as in figure); d, foliate papilla; c, fungi- 
form papillae; /, epiglottis (pulled back); g, median glosso- 
epiglottic fold. (Ellenberger-Baum, Anat. d. Haustiere.) 



papillffi are present. The fungiform papillae are small and are most numerous 
laterally. The filiform papilla; are soft and very small. On the root there are 
soft, long, pointed papilla, directed backward. Foliate papillse are also present. 

There is a well-marked median glosso-epiglottic fold, on either side of which is 
a depression (Vallecula epiglottica). The frenum lingute is double. 

The dental f ormula^ of the pig is : 



/ 3 1 4 3\ 

!( I-C-P-M- ) 

\ 3 1 4 3/ 



2fI-C-P-M-| = 44 

• Several figures in the osteology also illustrate the teeth. 



THE MOUTH 



479 



The formula for the temporary teeth is: 



/ 3 1 4\ 

2 ( Di-Dc-Dp- I 

V 3 1 4/ 



The upper incisors are small; they are separated from each other by spaces, 
and from the canines by a larger interval. The first incisors are the largest; they 
are flattened and strongly curved, and the crowns are convergent; they have no 




Fig. 41.3. — Skull of Pig about a Year an 
lis, Incisora; C, canines; Pl-4, preniola 



t A Half Old, Sculptured to Show the Embedded Parts of the Teeth. 
3; Ml— 3, molars. The third molar has not erupted and its roots are not 
yet formed. 



Cement Enamel Dentine 



distinct neck. The convex labial surface has an extensive covering of enamel, but 
the latter covers only a small marginal area on the lingual surface. The second are 
much shorter and are only slightly curved; they have a short flattened cro'svn and 
a rounded root. The third incisors are much smaller, are 
flattened laterally, and have three small eminences on the 
crown. The lower incisors are almost horizontal and are 
convergent and close together. The first and second are 
about ecjual in size, are rod-like, very slightly curved, and 
deeply implanted in the jaw. The labial surface is slightly 
convex, the lingual concave and marked near its extremity 
by a ridge. The third incisor is much shorter and is some- 
what flattened ; it has a short narrow crown and a distinct 
neck. 

The canine teeth or tusks of the male are greatly de- 
veloped and project out of the mouth. The upper canine of the boar may be three 
or four inches (ca. 8 to 10 cm.) long. The crown is conical and is curved some- 
what backward and outward; the embedded part is curved and has a large pulp 




Fig. 414." 

Lower Conine Tooth 
OF Pig. 

c, Pulp cavity. 



480 



DIGESTIVE SYSTEM OF THE PIG 



cavity. The lower canine may reach a length of eight inches or more (ca. 20 cm.) ; 
the crown is prismatic and is curved backward and outward in front of the upper 
one, so that the friction between the two keeps a sharp edge on the lower tooth. 
In the sow they are much smaller.' 

The cheek teeth increase in size from before backward. They have (with 
certain exceptions noted below) complex tuberculate crowns; the term bunodont 
is applied to this condition, as distinguished from the lophodont and selenodont 
structure in horses and cattle, in which there are prominent ridges of enamel. 




Fig. 415. — Superficial Glands of Head of Pig. 
a, Parotid gland; a', a", cervical and mandibular angles of a; b, c, ventral and dorsal buccal glands; d, labial 
glands; e, masseter muscle; /, /', lymph glands; g, dotted line indicating outline of mandibular gland, which is con- 
cealed. (EUenberger-Baum, Anat. d. Haustiere.) 



They are short-crowned teeth with a distinct neck and round, pointed roots. The 
first tooth in each jaw is small, simple, and appears only once; in the lower jaw it is 
near the canine; in the upper, near the second cheek tooth.^ The next two teeth 
are larger, laterally compressed, and sectorial. The fourth tooth below is larger, 
but otherwise like the preceding ones, white the upper one is much wider and is 
tuberculate. The first premolar has two roots, the others three or four. The 
molars have four roots, but the anterior pair may be largely fused. 

1 The canines of the pig are "permanent pulp" teeth and therefore capable of continued 
growth, and are without roots in the strict sense. The convex surface is covered with enamel, the 
concave with cement. 

^ It is often absent in the lower jaw. 



THE MOUTH 



481 




Fig. 416. — Dissection of Mouth axd I'haeyxge.\l J{egiox of Pig. 
J, Hard palate; 2, tongue showing distinctly fungiform papiUse; 3, foliate papilla: 4. lymph nodules of soft palate; 
5, stylo-glossus muscle, out of which a portion has been cut; 6', hyo-glossus; 7, genio-glossus; 8, genio-hyoideus; 9, 
mylo-hyoideus (reflected): iO, stylo-hyoideus; 11, great cornu of hyoid bone; 12, tensor palati; 13, levator palati; 
J.i, pterygo- et palato-pharyngeus; iJ, stylo-pharyngeus; Jff, cervico-hyoideus; i7, sterno- et omo-hyoideus; 18,s\x- 
prapharyngeal lymph glands; a, bulla ossea; b, paramastoid process. (Ellenberger-Baum, Anat. d. Haustiere.) 



The average periods of eruption of tlie teetli are given in the suljjoined talile: 

Tooth Eruption Change 

Ii .... 2 to 4 weeks 12 months 

12 . . . . / upper 2 to 3 month.? 

\ lower 1 1^ to 2 months 16 to 20 months 

13 .... Before birth 8 to 10 months 

C .... Before birth 9 to 10 months 

Pi .... 5 months 

P2 .... 5 to 7 weeks l 

p (■ upper 4 to S days 

' ■ ' ' ■ 1 lower 2 to 4 week.s I 12 to 15 months 

p / upper 4 to S days | 

■* ■ ■ ■ ■ \ lower 2 to 4 weeks J 

Ml. .. .4 to 6 months 

M, 8 to 12 months 

Ma 18 to 20 months 

31 



482 DIGESTIVE SYSTEM OF THE PIG 

The parotid gland is large and distinctly triangular. It extends very little on 
to the masseter muscle, and its upper angle does not quite reach the base of the ear. 
It is pale in color, and is embetlded in fat in animals in good condition. On its deep 
face are several large subparotid lymph glands, some of which are only partially 
covered by the parotid. The parotid duct arises on the deep face, has a course 
similar to that of the ox, and perforates the cheek opposite the fourth or fifth upper 
cheek tooth. Small accessory parotid glands (Glandulse parotidese accessorise) may 
be found along the course of the duct. 

The mandibular or submaxillary gland is small, recklish in color, and oval in 
outline; it is covered by the parotid. Its superficial face is convex, and is marked by 
rounded ]5rominences. From its deep face a narrow process extends forward about 
two or three inches (ca. 5 to 7.5 cm.) beneath the mylo-hyoideus muscle along with 
the duct. The latter opens near the frenum linguae, but there is no papilla. 

The sublingual gland has an arrangement similar to that of the ox. The pos- 
terior part (Glandula sublingualis grandicanalaris) is reddish-yellow in color, and 
is about two inches (ca. 5 cm.) long and half an inch wide; its posterior end is in 
relation to the mandil^ular gland and its duct. The anterior part (Gl. sublingu- 
alis parvicanalaris) is much larger, being two or three inches (ca. 5 to 7 cm.) long 
and about twice the width and thickness of the posterior part. All or most of the 
ducts from the posterior part unite to form the ductus sublingualis major, which 
opens near the ductus mandibularis. Eight or ten ductus sublinguales minores 
convey the secretion from the anterior part through the floor of the mouth. 




Fig. 417. — S.\gittal Section of Pharyngeal Region of Pig, Partly Schematic. 
/, Palatine bone; .2, sphenoid bone; .2', sptienoidal sinus; 5", occipital bone; 5, epiglottis; .^, arytenoid cartilage; 
J, thyroid cartilage; G, root of tongue; 7, mouth cavity; 8, isthmus faucium; 9, hard palate; 10, septum nasi; 11, 
ventral muscles of head; a, soft palate; a', free edge of a; b, dorsal wall of pharynx; c, fornix of pharynx; d, cavity of 
larynx; e, ff, naso-pharynx; /, oro-phar.vnx; /t, posterior pillar of soft palate; i, dotted line indicating lateral boundary 
between nasal cavity and pharynx ; A-, aditus laryngis; /, aditus oesophagi; m, Eustachian orifice; n, pharyngeal recess; 
o, posterior naris. (.\fter Ellenberger, in Leisering's .\tlas.) 



THE PHARYNX 
The pharynx [presents in its posterior part a median cul-de-sac about an inch 
and a half (ca. 3 to 4 cm.) long, which is situated between the ventral straight 
muscles of the head and the origin of the oesophagus ; this is termed the diverticu- 
lum pharyngeum. Its ventral margin is formed by the junction of the posterior 
pillars of the soft palate, which contain muscular tissue derived from the palatinus 
and palato-pharyngeus. The fornix of the pharynx is divided by a median fold of 
mucous memljrane which is a direct continuation of the septum nasi. On either 
side of this is an infundil)ulum in which the Eustachian tube opens. 



THE (ESOPHAGUS THE STOMACH 



483 



THE (ESOPHAGUS 
The oesophagus is short and nearly straight. It has (according to Rubeh) a 
potential calil>er in the adult of nearly 3 inches (ca. 7 cm.) at either end, and about 
IjTj- inches (ca. 4.2 cm.) in its middle part.' The muscular coat is striated, except 
near the cardia, where the deep part is unstriped. There are numerous tubulo- 
alveolar glands in the anterior half of the tube ; further back they occur in decreas- 
ing numbers. Many lymph nodules and nmch lymphoid tissue are present. 



THE STOMACH 
The stomach is large; its average capacity is about IJ^ to 2 gallons (ca. 
5.7 to 8 liters). When full, its long axis is transverse and its greater curvature 
extends backward on the floor of the abdomen a little further than a point midway 



Difcrli- 
culuin 



Pylorus 



(Esophagus 




Fig. 418. — Stomach of Pig: Parietal Surface. 

The organ contained a rather small amount of ingesta 

and hence is somewhat contracted. 



Fig. 419.— Stoma 
Organ was fixed in 



: OF Pig; Visceral Surface. 
tu and is somewhat contracted. 



between the xiphoid cartilage and the umbilicus. The left part is large and rounded, 
while the right part (Pars pylorica) is small, and bends sharply upward to join the 
small intestine. The parietal surface faces chiefly forward, and is related to the 
liver and diaphragm. The visceral surface faces chiefly backward, and is related 
to the intestine, greater omentum, mesentery, and pancreas. The greater cur- 
vature is related to the diaphragm, spleen, liver, and abdominal floor. The 
pyloric end lies against the right lateral lobe of the liver, about opposite to the middle 
of the next to the last intercostal space. The left extremity is opposite to the last 
intercostal space or preceding rib, and is related to the dorsal end of the spleen and 
the left extremity of the pancreas; it presents a flattened conical blind pouch, the 
diverticulum ventricuU, the apex of which projects backward. The oesophagus 
joins the stomach very obliquely, almost in the median plane, and about three or 
four inches (ca. 8 to 10 cm.) ventral to the twelfth thoracic vertebra. The cardiac 

' It is usually stated that the cardiac end is funnel-shaped, but it is not so in formalin-hardened 
cadavers nor in frozen sections. The hiatus oesophagus is a long slit in the right crus of the dia- 
phragm, and the terminal part of the oesophagus, which lies in it, is flattened transversely. 



484 



DIGESTIVE SYSTEM OF THE PIG 



opening is slit-like and is bounded aVjove and to the left by a fold which contains a 
■thickening of the internal oblique layer of the muscular coat. The opening into 
the diverticulum is situated above and a little to the left of the cardia ; it is trans- 




SuRFACE OF Stomach of Pig, 
THE Serous Coat has been Re- 



-EvERTED StoAIACH < 

L-ous Me 



\HICH THE 



O, CEsophagus; D, duodenum; Di, diverticuk 
oblique fibers; c', internal oblique fibers; c", cardie 
entrance to diverticulum; p,, pyloric sphincter; p 



m; a, a', a", a"' , longitudinal fibers; b, circular fibers; t-, external 
3 loop; d, fibers which connect branches of cardiac loop; /, fold at 
, pyloric prominence. (Ellenberger-Baum, Anat. d. Haustiere.) 



versely oval, and is bounded (except laterally) by a thick fold which contains 
spirally arranged muscular fibers. The mucous membrane may be dividetl into 
four regions (Fig. 422). Over a quadrilateral area around the cardia (about one 



Fig. 422. — Diagram 




Membrane of .Stomach of Pig. 



inch on the right and two or three inches on the left side of the orifice) it is cesopha- 
geal in character, and presents a number of folds. A sharp line of demarcation 
separates this from the rest of the mucous membrane, which is soft and glandular. 
The cardiac gland region is pale gray in color and thin (ca. 0.5 to 1 mm.) ; it extends 



THE STOMACH 



485 



about to the middle of the stomach. The fundus gland region is readily distin- 
guished by its thickness (ca. 3 mm.) and its b^o^vnish-red, mottled appearance.' 
The fourth or pyloric region is pale, thinner than the preceding, and presents a 
numl>er of irregular folds.- At the pylorus a remarkable prominence (Torus pylo- 
ricus) projects from the wall of the lesser curvature antl diminishes considerably 
the size of the orifice. It is about an inch and a half (ca. 3 to 4 cm.) long antl 




The greater omentum ha 



Fig. 423.— Ai 
been removed, 
dicate course o 



Viscera of Pig; Ventr.\l View. 
urinar.v bhadder; G, gall-bladder; X, xiphoid cartilage. Arrows 
ils of colon. The spleen was contracted. 



nearly half an inch (ca. 1 cm.) high. Sometimes it is a grooved ridge; in other 
cases it has the form of a rounded eminence attached by a pedicle to the wall. It 
consists largely of fat, but fibers from the circular muscular coat extend into it. 
The arrangement of the muscular coat is showai in Figs. 420, 421. 

' It will be noted that the fundus gland region does not extend up to the lesser curvature; 
here the cardiac gland region joins the pyloric. 

' Microscopic examination shows that these regions are not sharply marked off from each 
other; instead, there are intermediate zones in which glands of both the adjacent regions are 
present, and also glands of intermediate histological character. 



486 



DIGESTIVE SYSTEM OF THE PIG 

THE INTESTINE 



The intestine is about fifteen times the length of the body. 
The small intestine is 50 to 65 feet (ca. 15 to 20 m.) long. The mesentery of 
about the first two feet (ca. 60 cm.) is two to two and a half inches (ca. 5 to 6 cm.) 




Fig. 424. — Diagram of Cecum and Colon of Pig. 
Coils of colon have been pulled apart. 



long; this part may be termed duodenum. The duodenum turns sharply medially 
on the visceral surface of the liver to the right of the portal fissure. It then passes 
backward, in relation to the medial part of the right kidney dorsally and the colon 
ventrally, and about the middle of the sublumbar region turns across the median 





Fig. 425. — Ileo-cecal Opening of Pig. 
1, lleo-c£eeal opening; 2, 2, frenulum ilei. 



_FiQ. 426. — Solitary Nodules of Large Intestine 
OF Pig. (EUenberger-Baum, Anat. d. Hauetiere.) 



plane and runs forward to be continued by the mesenteric part. The right end of 
the pancreas is attached to the first part, and here the pancreatic duct opens into 
the bowel. The remainder of the bowel (Jejuno-ileum) has a mesentery about six 
to eight inches (ca. 15 to 20 cm.) long, which is thick and contains a quantity of fat, 



THE INTESTINE 



487 



and numerous large lymph glands at its root; the root is attached in the sublumbar 
region behind the stomach and blends here with the mesentery of the large intestine. 
The mesenteric part is arranged in close coils and lies mainly above the colon and 
Cfficum, from the stomach to the pelvis; many coils lie against the right flank and 
on the posterior part of the floor of the abdomen. The opening of .the bile duct is 
about one or two inches (ca. 2.5 to 5 cm.) from the pylorus, and that of the pan- 
creatic duct about six inches (ca. 15 cm.) beyond it. Aggregated lymph nodules 
or Peyer's patches and solitary nodules are numerous and very distinct. The 
patches are usually band-like and prominent; their number has been found to vary 
from 16 to 38. They begin 8 to 20 inches (ca. 20-50 cm.) from the pylorus. The 
last long one is continued a variable distance in the csecum. The solitary nodules 




Fig. 427. — Cecum and Colon of Pig; Left Ventral View. 
i, Apex of spiral coil of colon; 2. apes 



are distinct (except in the duodenum), but are only about a millimeter high. The 
duodenal glands extend some 10 to 16 feet (ca. 3-5 m.) from the pylorus. 

The large intestine is about 12 to 15 feet (ca. 4 to 4.5 meters) in length, and is 
for the most part much wider than the small intestine; it is connected by a mesen- 
tery with the dorsal abdominal wall between the kidneys. The caeciun is cylin- 
drical, about 8 to 12 inches (ca. 20 to 30 cm.) long, and 3 to 4 inches (ca. 8 to 10 cm.) 
wide. It lies against the upper and anterior part of the left flank, and extends 
ventrally, backward, and medially behind the coiled part of the colon, so that its 
ventral blind end usually lies on the floor of the abdomen, near the median plane, 
and at a variable point between the umbilicus and the pelvic inlet (Fig. 423). Its 
dorsal end is directly continued by the colon, the line of demarcation being indi- 
cated by the termination of the small intestine. The ileum joins the csecum 



488 DIGESTIVE SYSTEM OF THE PIG 

obliquely and projects considerably into the latter. A fold of mucous membrane 
(Frenulum ilei) passes from each side of the ileo-csecal opening. The colon has at 
first about the same caliber as the csecum, but becomes gradually smaller. It lies 
chiefly to the left of the median plane, behind the stomach. Most of it is arranged 
in three close, double spiral coils in the mesentery, in relation with the floor of the 
abdomen ventrally, the stomach and liver in front, the csecum and small intestine 
behind, and the small intestine on the right. On emerging from this spiral laby- 
rinth it passes at first forward in the sublumbar region to the right of the median 
plane, and, on reaching the stomach and right end of the pancreas, turns to the left. 
It then passes backward, on the ventral surface of the pancreas, and in relation to 
the medial part of the left kidney, inclines medialh', and is continued at the pelvic 
inlet by the rectum. This terminal part is closely attached by a short mesentery to 
the sublumbar region. The rectum is usually surrounded by a quantity of fat. 
The cfficum has three longitudinal muscular bands and three rows of sacculations, 
which are continued a short distance on the colon. The spiral colon has two bands 
and two series of sacculations, which, however, gradually disapj^ear in the centrif- 
ugal part. The solitary nodules are numerous, and appear as round prominences, 
2-3 mm. in diameter, often with a crater-like depression. The last Peyer's patch, 
of the small intestine is continued a variable distance in the csecum, and there are 
often patches in the first part of the colon. 



THE LIVER 

The liver is relatively large, its average weight in the adult being about four 
pounds (ca. 1.5-2 kg.). It is thick centrally, but the circumference is thin. It is 
divided by three deep interlobar incisures into four principal lobes — right lateral, 
right central, left central, left lateral; the last of these is usually considerably the 
largest. On the upper part of the right lateral lobe, is the caudate lobe, which is 
clearly marked off by a fissure and is often partially subdivided by a secondary 
fissure. That part of the right central lobe which lies below the portal fissure and 
to the left of the gall-bladder and cystic duct is homologous with the quadrate lobe 
of man. Much the greater part is to the right of the median plane. The parietal 
surface is extremely convex in conformity with the curvature of the diaphragm, to 
which it is chiefly related.^ A small part of the surface is in contact with the 
abdominal floor in the xiphoid region and ventral to the right costal arch. Its 
most anterior part reaches to a transverse plane through the ventral part of the 
sixth rib or intercostal space. The visceral surface is deeply concave; most of it 
is related to the stomach, for which there is a correspondingly large and deep gastric 
impression. There may be a duodenal impression on the upper part of the right 
lateral lobe, but no renal impression exists, as the right kidney does not touch the 
liver. The fossa for the gall-bladder (Fossa vesicae fellese) is mainly on the right 
central lobe, but also in part on the adj acent surface of the left central lobe. The pos- 
terior vena cava enters the dorsal border of the caudate lobe and soon becomes entirely 
embedded in the gland substance, emerging only at its passage through the dia- 
phragm. The oesophageal notch is large and is occupied mainly by the large right 
crus of the diaphragm. The right lateral border extends backward to the upper 
part of the last intercostal space. The left lateral border is opposite the ninth 
intercostal space and eighth rib. The ventral border lies on the abdominal floor 
a short distance (ca. 3-5 cm.) behind the xiphoid cartilage. 

The coronary ligament resembles that of the hor.se. The falciform ligament is 
very short or absent in the adult, and is attached to the diaphragm just below the 

' The description here given is based on the appearance of the organ as hardened in silit, 
which differs radically from that of the soft organ. It also differs much in shape in young and 
adult subjects. 



THE LIVER 



489 



■« -h 





490 



DIGESTIVE SYSTEM OF THE PIG 



foramen venae cavce. The round ligament is present in the young subject. Neither 
lateral nor caudate ligaments are present. 

The gall-bladder is attached in the fossa vesicae felleae; its fundus does not 




Fig. 430. — Projection of Viscera of Pig on Body-wall; Left Side. 
D, Costal line of diaphragm; V, ureter; V.S., vesicula seminalis; E.g., bulbo-urethral gland; P, penis. 

reach to the ventral border. The cystic tluct joins the hepatic duct at an acute 
angle immediately after the emergence of the latter from the portal fissure. The 
bile duct (Ductus choledochus) opens at the papilla duodeni about one or two inches 
(ca. 2. .5 to 5 cm.) from the pylorus; an ampulla may be formed. 



''0i?MM?a> 




Fig. 431. — Projection of Viscera of Pig on Body-wall; Right Side. 

D, Costal line of diaphragm: O, ovary. The pancreas and duodenum are not in contact with the flank, as would 

naturally be inferred from this figure, but are situated moi'e medially and are covered laterally by small intestine. 



Owing to the large amount of interlobular tissue, the lobules are mapped out 
sharply; they are polyhedral in form, anil are 1 to 2.5 mm. in diameter. For the 
same reason the gland is much less friable than that of the other animals, from which 
it is easily distinguished. 



DIGESTIVE SYSTEM OF THE DOG THE MOUTH 



491 



THE PANCREAS 

The pancreas extends across the dorsal wall of the abdominal cavity behind 
the stomach. It is triradiate or triangular. The right extremity is attached to the 
first curve (Flexura portalis) of the duodenum, and here the duct passes to the 
bowel. The left extremity is related to the left extremity of the stomach, the 
dorsal end of the spleen, and the anterior pole of the 
left kidney. The middle or posterior extremity or 
lobe is practically median and is related to the portal 
vein and the root of the mesentery. The pancreatic 
duct passes from the right extremity directly through 
the duodenal wall, opening about four or five inches 
(ca. 10-12 cm.) from the pylorus. The interlobular 
tissue usually contains a good deal of fat. 



THE SPLEEN 
The spleen is long and narrow. Its long axis is 
nearly dorso-ventral in direction, and is curved to con- 
form to the left part of the greater curvature of the 
stomach. The dorsal end lies under the vertebral 
ends of the last three ribs; it is related to the 
stomach in front, the left kidney behind, and the 
left extremity of the pancreas medially. The visceral 
surface has a longitudinal ritlge on which the hilus is 
situated; this divides the surface into nearly equal 
gastric and intestinal areas, which are in contact with 
the stomach and colon respectively. The parietal 
surface is convex and is related to the left lateral and 
ventral wall of the abdomen. The ventral end is 
smaller than the dorsal one; it lies on the abdom- 
inal floor, usually in the umbilical region. The spleen 
is attached so loosely to the stomach that it may be 
regarded as being intercalated in the great omentum. 
In large subjects it may reach a length of about 25 
inches (ca. 60 cm.) and a width of 3 to 4 inches (ca. 8 
to 10 cm.), and a weight of 10-15 ounces (ca. 350 gm.). 

The position of the spleen varie.s according to the fulness 
of the stomach and its own size. The dorsal end varies little. 
But the ventral end has a wide range, as might be expected; it 
may be in contact with the left lobe of the liver or may be cen- 
trally situated just in front of the umbilicus. As in other ani- 
mals, the size of the spleen is extremely variable. Even in a 
large adult it may be only a httle more than a foot (ca. 35 cm.) 
and weigh six or seven ounces (ca. 200 gm.). 




Fig. 432. — Spleen of Pig; Visceral 
Surface. 
1. Dorsal end; 2, ventral end; 3, 
stumps of splenic vessels; 4, gastric 
surface; 5, hilus wnth vessels. 

long, two and a half inches wide, 



DIGESTIVE SYSTEM OF THE DOG 

THE MOUTH 

The size and form of the mouth vary greatly in different breeds, the cavity 
being in some long and narrow, in others short and wide. The rima oris is very 
extensive, so that the labial commissure is opposite the third or foiu'th cheek tooth. 
The lips are thin and mobile, and present numerous tactile hairs. The upper lip 



492 



DIGESTIVE SYSTEM OF THE DOG 



has a small, central, bare area which forms part of the muzzle, and is marked by a 
central groove, the philtrum, or (as in the bull-dog) a fissure, giving the appearance 
of harelip. The lateral borders of the lower lip are flaccid and denticulated. The 
mucous membrane is usually pigmented and forms distinct frena labiorum. The 
labial glands are small and scanty. 

The cheeks are loose and capacious, and their mucous lining is smooth and 
more or less pigmented. The parotid duct opens usually opposite the third upper 
cheek tooth. Near the last tooth are the openings of the four or five ducts from 
the zygomatic gland. This gland may be regarded as the homologue of the dorsal 




i of the mandible and cutting 



Fig. 433. — Palate of Dog. 

The lower jaw and related structures have been removed by sawing through the i 
the soft structures horizontally. 

1, Raph4 of palate: 2, ridges of palate: 3, papilla inrisiva: 4, soft palate; 5, tonsil: 6, meatus naso-pharyngeus: 7, 
dorsal wall of pharynx: 8, parotid gland: 9, mandibular gland; 10, pharyngeal lymph gland; 11, m. occipito- 
mandibularis (cut); 12, m, masseter (cut); 13, cheek (cut); 14, ramus of mandible (section); 15, parotid lymph gland; 
16, carotid artery; I, incisor teeth; C, canine tooth; P, premolar teeth; M, molar teeth. 



buccal glands of the other animals; it will be described later. The ventral buccal 
glands are opposite the cheek teeth and in series with the inferior labial glands. 

The hard palate is widest between the fourth pair of cheek teeth. It has 
eight to ten curved ridges on either side of the median raphe; the latter may be 
indistinct or scarcely recognizable. Behind the first pair of incisor teeth is the 
rounded or triangular papilla incisiva, at which the incisive or naso-palatine ducts 
open. The mucous membrane is usually pigmented. 

The soft palate (Figs. 433, 488) is thick, except at its margins. In the resting 
state of the parts it comes in contact with the epiglottis.' Between its anterior and 

1 It is usually stated that it is in contact with the oral surface of the epiglottis, but the epi- 
glottis may be ventral to the soft palate (Fig. 488). 



THK TEETH 



493 




posterior pillars on either side is a marked tonsillar sinus, in which an 

fusiform tonsil is situated ; this is reddish in color, 

about an inch long, and is largely or completely 

concealed between two folds of mucous membrane. 

The posterior pillar is double; the upper fold passes 

to the dorsal wall of the pharynx, where it subsides; 

the lower fold goes to the side of the epiglottis. 

The tongue is wide and thin in front, thicker 
posteriorly; it is very mobile. It is not pigmented, 
but has a bright red color. The dorsum is marked 
by a median groove (Sulcus medianus linguse), and 
is thickly beset with short, pointed, filiform papillae, 
the free ends of which are directed backward. On 
the root there are long conical papillae which are 
soft, and point backward; similar papillae occur 
on the lateral walls of the isthmus faucium. The 
fungiform papillae are small, and are scattered over 
the dorsum and sides of the tongue, but are absent 
on the posterior part of the dorsum and on the 
root, where the conical papillae occur. There are 
usually two or three vallate papillae on either side 
on the posterior part of the dorsum, where the 
conical papillae begin. Small foliate papillae are 
also present just in front of the anterior pillars of 
the soft palate; they are oval and are crossed by 
about half a dozen fine fissures. In the inferior 
part of the tip of the tongue is the lyssa, a fusiform 
cord, composed of fibrous tissue, muscular tissue, 
and fat. In large dogs it is about two inches (ca. 
4 to 5 cm.) long. The lingual muscles present no 
remarkable special characters. 



elongated, 




THE TEETH 



The formula of the permanent teeth is: 



/ 3 1 4 2\ 
I I-C-P-M- I 
V 3 1 4 3/ 



= 42 



All of the teeth have short crowns and dis- 
tinct necks; they erupt rapidly. The cro\vns are 
white, being destitute of cement.^ 

The incisors are placed almost vertically and 
close together in the jaw Isones. They do not cor- 
respond to an opposing tooth, but rather to parts 
of two teeth of the other jaw. They increase in 
size from the ^first to the third. The crowns are 
trituberculate, the central projection being the 
largest. The labial surface is convex; the lingual 
surface is slightly concave, and is marked off from 
the neck by a V-shaped ridge, the cingulum. The 
roots are narrow transversely. The lower incisors 
are smaller than the ujiper ones. One or two supernumerary teeth may be present. 

The canine teeth are large, conical, and curved. The upper canine is separated 

1 Other figures which illustrate the teeth are to be found in the description of the skull. 



Fig. 434. — Tomjue, Phauynx, Larvnx, 
ETC., OF Dog; Dorsal View. 

The pharynx and soft palate have 
been cut niecUally and reflected, and the 
oesophagus cut off. 

1, Median groove of tongue; 2, Ions 
conical papillse of root of tongue; 3, val- 
late papiilse; 4, tonsil (drawn out of ton- 
sillar sinus; 5, fioor of pharynx (promi- 
nence here caused by cricoid cartilage 
and m. crico-arytenoideus dorsalis) ; 7, 
vestibule of larynx; 8, epiglottis; 9, ary- 
tenoid cartilage; 10, trachea (membran- 
ous part); 11, 11, lateral lobes of thyroid 
gland; 12, 12', anterior and posterior thy- 



494 



DIGESTIVE SYSTEM OF THE DOG 



from the corner incisor by an interval into which the lower canine is received when 
the jaws are closed.' The lower canine is close to the corner incisor. The root is 
about an inch (ca. 2 to 3 cm.) long and is flattened laterally. 

The cheek teeth are typically f, but in brachycephalic breeds they are com- 
monly reduced to f , and in extreme cases even to f . The reduction occurs at either 
end or at both ends of the series.^ The first tooth appears only once. The fourth 
tooth of the upper row and the fifth of the lower row are much larger than the rest, 
and are termed sectorial or camassial teeth. From these the teeth diminish in size 
both forward and backward. The upjwr and lower teeth do not correspond, but 
rather dovetail. The teeth liehind the sectorial ones are tuberculate, i. e., have 




Fig. 435.— Skdl 



' Adult St. Bern.\rd Dog, Sculpture 
Il-J. In 



> to Show the Embedded Parts of the Teeth. 
emolars; Mt-3, molars. 



rounded eminences on the masticatory surface. The others are all sectorial in 
character, i. e., have sharp-edged, pointed projections, the middle one being the 
most prominent. The premolars are laterally compressed, and are separated liy 
intervals from the canines and from each other, except in the brachj'cephalic 
breeds. The upper molars have wide, somewhat quadrangular crowns, and three 
roots. The crown of the upper fourth premolar (Dens sectorius) is divided into 
two pointed lobes and has an antero-medial tubercle; it has three roots. The 

' In the bull-dog, which is very prognathic ("undershot"), the lower canines are opposite 
to or slightly in front of the plane of the upper incisors, and the upper canines are about opposite 
to the first lower cheek teeth. In the epignathic ("overshot") dachshund the lower canines are 
under or slightly behind the upper ones. 

- Increase in number also occurs, the supernumerary teeth being at either end of the series. 
The occurrence of a third upper molar is not rare. 



THE SALIVARY GLANDS 



495 



crown of the first lower molar (Dens sectorius) is compressed laterally and has two 
pointed, sharp-edged lobes, behind which are one or two tubercles: it has two roots. 
The average periods of eruption are given below. 



Tooth Ertjption 

Ii 4 to 5 weeks 

I2 4 to 5 weeks 

I3 4 weeks 

C 3 to 4 weeks 

Pi 4 to 5 months 

Pa 4 to 5 weeks 

Ps 3 to 4 weeks 

F, 3 to 4 weeks 

Ml 4 months 

/ upper 5 to 6 months 
\ lower 43-^ to 5 months 
Ms 6 to 7 months 



4 to 5 months 
4 to 5 months 



5 to 6 months 



M,. 




Il-S, I: 



Fig. 43G. — Base of Skull of Cocker Spaniel. 

PI-4, premolars: Ml-B, molars. Note the crowding of the 

account of the shortness of the jaw. 



THE SALIVARY GLANDS 

The parotid gland is small and is irregularly triangular. Its dorsal end is wide 
and is divided into two parts by a deep notch into which the base of the ear is 
received. The ventral end is small and overlaps the mandibular gland. The 
parotid duct leaves the gland at the lower part of the anterior Ijorder, crosses the 
masseter muscle, and opens into the mouth opposite the thiril upper cheek tooth. 



496 



DIGESTIVE SYSTEM OF THE DOG 



Small accessory parotid glands (Glandulse parotidese accessorise) are sometimes 
found along the course of the duct. 

The mandibular gland is usually larger than the parotid. In large dogs it 
is about two inches (ca. 5 cm.) long and an inch or more (ca. 3 cm.) wide. It is 
rounded in outline, pale yellow in color, and is enclosed in a fibrous capsule. Its 
upper part is covered by the parotid, but it is otherwise superficial, and is palpable 
in the angle of junction of the jugular and external maxillary veins. The 
mandibular duct leave.s the deep face of the gland, passes along the surface of 
the occi])ito-mandibularis and stylo-glossus, and opens into the mouth on a very 
indistinct papilla near the frenum linguae. 

The sublingual gland is pink in color and is divided into two parts. The 
posterior part (Glandula sublingualis grandicanalaris) lies on the occipito-man- 





FiG. 437. — Dissection of Head of Doq, Showing Salivary Glands, etc. 
a, Ocular muscles; 6, pterygoideus medialis (cut) ; o, stylo-glossus; d, occipito-mandibularis (cut) ; c, genio-glossus; 
/, genio-hyoideus; g, hyo-glossus; h, thyro-pharyngeus; i, crico-pharyngeus; *:, thyro-hyoideus; (, zygomatic process 
of temporal (sawn off) ; i, parotid gland; S, mandibular gland; 3, posterior part of sublingual gland; 3', anterior part 
of same; .(, mandibular duct; a, ductus sublingualis major; 6, palatine glands; 7, zygomatic gland; S, ducts of 7; S, 
lacrimal gland. (Ducts colored red.) (After EUenbcrger, in Leisering's .\tlas.) 



dibularis muscle in intimate relation with the mandibular gland, but is clearly separ- 
able from it after removal of the common fibrous capsule. It has a pointed anterior 
process. Its duct (Ductus sublingualis major) accompanies the mandibular duct, 
and either opens beside it or joins it. The anterior part (Glandula sublingualis 
parvicanalaris) is long and narrow; it lies between the mucous membrane of the 
mouth and the mylo-hyoideus, dorsal to the stylo-glossus muscle. It has a number 
(8 to 12) of small ducts (Ductus .sublinguales minores), some of which open directly 
into the mouth, while others join the large duct. 

The zygomatic gland (Glandula zygomatica)' (Fig. 437) is situated in the 
anterior part of the pterygo-palatine fossa. It is related superficially to the zygo- 
matic arch and the masseter and temporal muscles. Its deep face is in contact 
with the periorbita, the pterygoid muscle, the internal maxillary artery, and the 

1 Also known as the orbital gland. 



THE PHARYNX — THE (ESOPHAGUS — THE STOMACH 497 

maxillary nerve. It has four or five ducts which open near the last upper cheek 
tooth; one of them (Ductus glandulse zygomaticse major) is almost as large as the 
parotid duct; the others (Ductus glandule zygomaticse minores) are small. 

THE PHARYNX (Fig. 434) 

The fornix is narrow. The pharyngeal orifices of the auditive or Eustachian 
tubes are small and slit-like; the end of the tube causes a rounded projection of the 
mucous membrane (Torus tubarius). The oesophageal aditus is relatively small 
and is well defined by a transverse fold of the mucous membrane. The muscles 
present no marked differential features, but the hyo-pharvngeus muscle is clearly 
divided into a kerato-pharyngeus and a chondro-pharyngeus. 



THE (ESOPHAGUS 
The oesophagus is relatively wide and dilatable except at its origin, where there 
is a constriction termed the isthmus oesophagi. This initial narrowness of the 
lumen is caused by a prominence of the ventral part of the mucous membrane, 
underlying which is a thick layer of mucous glands (Fig. 490). The cervical part 
is at first median and is dorsal to the trachea, but in the posterior part of the neck 
it lies to the left of the trachea. The thoracic part continues in this position and 
ventral to the left longus colli to the base of the heart; here it inclines medially, 
having the aortic arch on its left, and passes back over the bifurcation of the trachea. 
Continuing backward between the lungs it usually inclines slightly to the left, 
passes through the hiatus cesophageus, and joins the stomach just to the left of the 
median plane and ventral to the eleventh or twelfth thoracic vertebra. The 
muscular tissue is striated and consists mainly of two layers of spiral fibers which 
cross each other ; near the cardia, however, the fibers are longitudinal and circular. 
There are tubulo-alveolar glands (Gl. oesophagie) in the submucosa throughout. 

THE STOMACH 
The stomach is relatively large. Its capacity in a clog weighing about 40 
pounds is about six to seven pints. 

Colin estimates the average capacity at about 3 liters (ca. 6}-^ pints), with a range between 
0.6 and 8 liters (ca. ly^ to 173^2 pints). Neumayer gives the capcaity as 100 to 2.50 c.c. per kilogram 
of body-weight (ca. 2.7 ounces per pound). The average capacity of the human stomach is esti- 
mated at 1.2 liters (23^ pints) — not much more than a third of that of a dog of medium size. 

When full, it is irregularly piriform. The left or cardiac part (Fundus et corpus 
ventriculi) is large and rounded, while the right or pyloric part (Pars pylorica) is 
small and cylindrical. When empty, or nearly so, the left sac is strongly contracted; 
the p.yloric part is much less affected by variations in the amount of ingesta. 

The parietal surface of the full stomach is very extensive, strongly convex, 
and faces partly forward, but largely ventrally and to the left. It is related to the 
liver, the left part of the diaphragm, and the left and ventral abdominal wall as far 
back as a transverse plane through the second or third lumbar vertebra. The 
visceral surface is much less extensive and is considerably flattened ; it faces chiefly 
dorsally and to the right, and is related to the intestine, pancreas, and left kidney. 

The upper part of the lesser curvature is nearly straight and vertical, but the 
lower part forms a deep, narrow angle (Incisura angularis), due to the fact that the 
pyloric part is directed sharply forward and upward. The greater curvature is 
nearly four times as long as the lesser curvature. In the full stomach it extends 
considerably behind the left costal arch; ventrally it lies on the abdominal wall 
about midway between the xiphoid cartilage and the pubis. 
32 



498 



DIGESTIVE SYSTEM OF THE DOG 



(Esophagus 



Pyl 



The left extremity or fundus is large and rounded; it is the most dorsal part 
of the organ, and lies under the vertebral ends of the eleventh and twelfth ribs. 

The pyloric extremity is small 
and is directed forward and dor- 
sally; it lies usually opposite to 
the ventral part of the ninth 
or tenth intercostal space, and 
about an inch (ca. 2-3 cm.) to 
the right of the median plane. 
It is related to the portal fissure 
of the liver and to the pancreas. 
The cardia is situated about two 
to three inches (ca. 5 to 7 cm.) 
from the left extremity, and is 
oval; it lies just to the left of 
the median plane, ventral to the . 
eleventh or twelfth thoracic ver- 
tebra. 

When empty, or nearly so, 
the stomach is separated from 
the ventral abdominal wall by 
the liver and intestine, and the 
greater curvature extends back 
on the left side to the eleventh 
or twelfth rib. In this state there is not rarely a marked constriction between the 
right and left parts. 

The preceding topographic statements are based on observations made on a considerable 
number of formahn-hardeued subjects, and are to be regarded as average findings in dogs of 




Fig. 43S. — Stom. 

Organ fixed 



Left extremity 



(Esophagus 




Greater Attachment i>f 
curvature greater omentum ■ 

Fig. 439. — Stomach of Dog; Visceral Surface. 
Organ fixed in situ when it contained small amount of ingesta. 



medium size. The cardiac and pyloric ends vary least in position, but the former varies the 
length of one vertebra and the latter as much as two intercostal spaces. This variation a,ppears 
to be due, not only to tlie amount of ingesta in the stomach, but also to the phase in which the 
diaphragm is fixed. 



THE STOMACH 



499 



The serous coat is almost complete. Along the curvatures it leaves the stom- 
ach to form the omenta. The longitudinal muscular fibers are chiefly along the 
curvatures and on the pyloric part; they are continuous with the external layer 
of the CESophagus. The oblique fibers are arranged in two layers: the external layer 
is largely a continuation of the longitudinal fibers of the oesophagus to the body 
and fundus. The circular layer covers the whole stomach except the fundus, and 
forms a pyloric sphincter and an antral sphincter. The internal oblique layer is 
arranged as in the horse, and forms a similar loop-like, cardiac sphincter. Three 
regions of the mucous membrane exist. Cardiac glands are found in a very narrow 
pale zone around the cardiac opening, and also scattered along the lesser curva- 




FiG. 440. — SrnMAc II <iv Dog; Frontal Section 
1, Fundus gland region; 2, pyloric part; 3, It'saer curvature; 4, cardia; 5, pylorus; 6, oesophagus; 7, duodenum. 



ture. The fundus gland region has a thick, reddish-bro^vn mucous membrane, 
which lines about two-thirds of the organ. The pyloric mucous membrane is 
thimicr ami pale; in the dead subject it is often stained by regurgitated bile. 

The greater omentiun is very extensive, and in well-nourished subjects it con- 
tains much fat arranged in interlacing strands. Viewed ventrally it covers the 
entire intestinal mass, extending from the greater curvature of the stomach to the 
pelvic inlet. It is attached to the greater curvature of the stomach, the left part 
of the colon, the left liranch of the pancreas, and the hilus of the spleen. 

The lesser omentum extends from the lesser curvature of the stomach to the 
portal fissure ; to reach the latter it passes in great part between the papillary and 
left lateral lobes of the liver. 



500 



DIGESTIVE SYSTEM OF THE DOG 



THE INTESTINE 

The intestine is short — onlj' about five times the length of the body. 

The small intestine has an average lengtli of about thirteen feet (ca. 4 meters). 
It occupies most of tlie abdominal cavity behind the liver and stomach. The duo- 
denum begins at the pjdorus and passes backward and somewhat dorsally, at first 




Fig. 441. — Abdominal Viscera of Dog. 
Ventral view after removal of greater omentum. The stomach 
a. Cartilage of Last rib; 6, duodenum; j:, xiphoid cartilage 



on the visceral surface of the liver, then in contact vnth the right flank. Near the 
pelvis it turns medially and passes forward along the medial side of the left part of 
the colon and the left kidney, bends ventrallj% and joins the jejunum to the left of 
the root of the mesentery.' The mesoduodenum is given off from the right side of the 

1 The duodenum might be regarded as consisting of a right or retrograde part, an iliac flexure, 
and a left or recurrent part; the terminal bend i.s the duodeno-jejunal flexure. 



THE INTESTINE 



501 



common mesentery; it is a relatively wide fold. The left part of the duodenum is 
connected with the mesocolon by a peritoneal fold; this fold has a free posterior 
border which is clearlj' seen when the posterior flexure of the duodenum is drawn 
away from the sublumbar region. The first part of the mesoduodenum contains 
the right branch of the pancreas. Its root is blended with the mesocolon to form a 
common mesentery. The remainder of the small intestine forms numerous coils, 
and is attached by a ■wide mesentery to the sublumbar region. The terminal part 
(ileum) passes forward in the sublumbar region along the medial surface of the 
caecum and opens into the beginning of the colon at the ileo-colic orifice (Ostimn 




Fig. 442. — Deep Dissection of Abdominal Viscera of Dog (Female). 

Bl., Bladder; B, body, C, C, cornua of uterus; O, O', ovaries; L. k., left kidney. The concealed part of the colon 

is indicated by dotted lines. The spleen is drawn backward and outward. 



ileocolicum). The bile duct and smaller pancreatic duct open into the duodenum 
about two or three inches (ca. 5 to 8 cm.) from the pylorus; the larger pancreatic 
duct opens an inch or two (ca. 2.5 to 5 cm.) further back. The mucous membrane 
has very long, thin villi. The duodenal glands occur only close to the pylorus. 
Aggregated Ij'mph nodules or Peyer's patches are numerous (about twenty in 
young subjects), and Ijegin in the duodenum. They are usually elliptical in out^ 
line, but the last one is band-like, reaches to the end of the ilemn, and is four to 
sixteen inches (ca. 10 to 40 cm.) long in young dogs (Ellenberger). There is an ileo- 
colic valve. 1 The muscular coat is relatively thick. 

' The valve does not seem always to be efficient, since experience shows that rectal injections 
can be made to pass beyond it. This may be partly due also to the fact that the terminal part of 
the ileum runs horizontally forward, and its orifice faces forward into the beginning of the colon. 



502 



DIGESTIVE SYSTEM OF THE DOG 



The large intestine is two to two and a half feet (ca. 60 to 75 cm.) long in 
average. Its caliber is about the same as that of the small intestine, and it has 
neither longitudinal bands nor sacculations. 

The caecum averages about five or six inches (ca. 12.5-15 cm.) in length, and 
is flexuous (Fig. 442). The flexures are maintained by the peritoneum, which 
attaches it also to the ilemn. It is situated usually about midway between the 
right flank and the median plane, ventral to the duodenum and the right branch of 
the pancreas.' Its anterior end opens into the origin of the colon, lateral to the 
ileo-colic orifice. The other end is pointed and blind. 

The colon is attached to the sublumbar region by a mesentery — the mesocolon. 
It presents three parts, which correspond to the ascending, transverse, and descend- 
ing colon of man. The first or right part (Colon 
dextrum s. ascendens) is very short. It passes for- 
ward along the medial surface of the first part of the 
duodenum and the right branch of the pancreas till 
it reaches the pyloric part of the stomach; here it 
turns to the right and crosses the median plane, 
forming the transverse part (Colon transversum). 
The third or left part (Colon sinistrum s. descen- 
dens) passes backward in the sublumbar region 
along the medial border or ventral surface of the 
left kidney; it then inclines toward the median 
plane and is continued by the rectum. The cali- 
ber of the colon is about the same throughout. It 
has no bands nor sacculations. The mesen- 
tery of the colon is termed the mesocolon; it is 
given off from the left side of the common mesen- 
tery. ^ 

The mucous membrane of the caecum con- 
tains numerous solitary lymph nodules which are 
circular, with a central depression; some are 
present also in the first part of the colon. 

The rectum is almost completely covered with 
peritoneum, the line of peritoneal reflection being 
under the second or third coccygeal vertebra. At 
the junction of the rectum and anus the mucous 
membrane has a stratified squamous epithelium, 
and contains the anal glands. A small opening on 
either side leads into two lateral anal sacs (Sinus 
paranales) ; these are usually about the size of a 
hazel-nut, and contain a dirty gray, fatty substance, 
which has a peculiar and very unpleasant odor. 
The skin which lines these pouches contains coil-glands. Further back the skin 
contains large sebaceous glands and peculiar circumanal glands. 

The retractor ani muscle is extensive. It arises from the shaft of the ilium, 
the pubis, and the sjanphysis pelvis, and passes upward and backward to end on the 




Fig. 443. — Sectional View of Ileum, 

Cecum, and Colon of Dog. 

1, Ileo-colic orifice: 2, cgeco-colic orifice 

3, apes of csecum. 



^ In large dogs (e. g., St. Bernard or Great Dane) the caecum may reach a length of 4.5 cm. 
(measured along its curves) and a diameter of 3 cm.. Its position is somewhat variable. It may 
be closer to the lateral wall, or more medial than is stated above. Its anterior end is usually 
in a transverse plane through the ventral end of the last rib if the stomach is not very full. 

^ The arrangement of the colon is variable. The transverse part may be quite long and 
extend across from the angle of junction of the two branches of the pancreas to the dorsal end of 
the spleen. On tlie other hand, a transverse part may be absent, the colon forming instead an 
acute angle or flexure. WTien the stomach is empty and contracted, the transverse part of the 
colon may be separated from the ventral wall by the omentum only. 



THE LIVER 



503 



first coccygeal vertebrae and the sphincter ani externus. The retractors, together 
with the coccygei, form a sort of pelvic diaphragm, analogous to that of man. 



THE LIVER 
The liver is relatively large, weighing usually al;)out 3 per cent, of the body- 
weight. It is divided into five chief lobes by fissures which converge at the portal 
fissure. When the gland is ex- 



ieduct 



amined in the soft condition poit.miacMo. 

the lobes may be spread out so 
as to be all visible (Fig. 444), 
but when the organ is hard- 
ened in situ the lobes overlap 
to a considerable extent (Figs. 
445, 446). 

The left lateral lobe is the 
largest, and is oval in outline. 
The left central lobe is smaller 
and is prismatic. The right 
central lobe is second in size, 
and j)resents a somewhat 
tongue-shaped quadrate lobe, 
marked off by the deep fossa 
in which the gall-bladder lies. 
The right lateral lobe is third 

in size, and is oval in outline. On its visceral surface is the large caudate lobe; 
this consists of two parts — on the right, the caudate process, on the left, the papil- 
lary process, both often being subdivided by secondary fissures. 




Fig. 444. — Liver of Dog. 
Soft specimen sketched with lobes drawn apart. 



Right lateral lobe 




Left central lobe 



Gall-bladder Quadrate lobe 
Fig. 445. — Liver of Dog; Parietal Sdbface. 
3 opening into posterior vena cava; 2, coronary ligament; 3, falciform ligament. 



504 



DIGESTIVE SYSTEM OF THE DOG 



When hardened in situ, the gland presents the following characters: The 
parietal surface is strongly convex in conformity with the curvature of the dia- 
phragm and the adjacent part of the ventral wall of the abdomen, with which it is 
in contact. 

The visceral surface is in general concave, but is irregular in adaptation to the 
viscera in contact with it. The largest of these is the stomach, and the configuration 
of the liver varies greatly in accordance with the degree of fulness of that viscus. 
When the stomach is well filled, there is a ridge on the liver which corresponds to 
the lesser curvature. To the left of this is a large concavity adapted to the body 
and fundus of the stomach ; and on the right is a smaller impression of the pyloric 
part of the stomach, the first part of the duodenum, and the anterior part of the 



(Esophageal notch 



Posterior vena cava 




Right central lobe 



Fig. 446. — Liter of Dog, Visceral Surface; Hardened in situ. 
Left central lobe, gall-bladder, and great part of right central lobe not visible. 



right branch of the pancreas. Dorsal to the cavity for the pyloric part of the 
stomach is a deep depression, and at the bottom of this is the portal fissure. To 
see the latter the papillary and caudate lobes must be drawn apart. The hepatic 
artery enters the liver at the dorsal part of the fissure, the portal vein enters cen- 
trally, and the hepatic duct emerges at the ventral part. The gall-bladder is 
usually not visible till the right lateral and central lobes are drawn apart. 

When the stomach is empty and contracted, the visceral surface of the liver is strikingly 
different. There is then a shallow impression for the left part of the stomach on the left lobe 
and a large convex area, related to the small intestine and a mass of omentum. The pyloric and 
duodenal impressions are not much changed. 

The dorsal border presents a deep renal impression on its right part. The 
posterior vena cava passes ventrally antl forward, at first in a deep groove on the 
caudate lobe, then largely embedded in the parietal surface of the right lateral lobe; 
it receives two or three large hepatic veins just before piercing the diaphragm. 



THE PANCREAS 



505 



Dorsal end 



The oesophageal notch is large, and is occupied on the right by the thick margin of 
the hiatus oesophagus. The remainder of the circumference is thin, and is cut into 
l)y deep fissures which separate the lobes. The ventral border lies on the abdominal 
wall, a variable distance behind the xiphoid cartilage. The left border is also 
Variable, but usually extends back ventrally as far as the tenth intercostal space 
or eleventh rib. The right border corresponds more or less closely in direction 
with the costal arch ; the end of the caudate process is ventral to the right kidney, 
opposite to, or a little behintl, the last rib. 

The gall-bladder lies in the fossa vesicae fellese, between the two parts of the 
right central lobe; it does not reach to the 
ventral border of the liver. The cystic duct 
joins the hepatic duct at the ventral part of 
the portal fissure, forming with it the bile 
duct (Ductus choledochus) ; the latter passes 
to the right and opens into the duodenum, 
about two or three inches (ca. 5 to 8 cm.) 
from the pylorus. 

Of the ligaments, the coronary and right 



Gastric 
surface 




Ventral end 



Dog; Paeii 



Fig. 448.— Sp 



Fig. 447. — Splees o 

Surface. 
Fig. 447 is from subject in which the stomach was full, yhile the organ shown in Fig. 448 i 
stomach contained httie food. 




Ventral 
end 



lateral are well developed, but the left lateral and falciform are small; a ligament 
extends from the caudate process to the right kidney. 



THE PANCREAS 
The pancreas is V-shaped, consisting of two long narrow branches, which 
meet at an acute angle behind the pylorus. The right branch extends backward 
above the first part of the tluodenum, below the caudate lobe of the liver and the 
right kidney, and ends usually a short distance behind the latter; it is enclosed by the 
mesoduodenum. The left branch passes to the left and backward between the 



506 



DIGESTIVE SYSTEM OF THE DOG 



visceral surface of the stomach and the transverse colon, and ends at the anterior 
pole of the left kidney. There are usually two pancreatic ducts. The smaller one 
opens into the duodenum ^vith the bile duct or close to it; the larger one opens into 
the bowel an inch or two (ca. 3-5 cm.) further back. 

THE SPLEEN 
The spleen is bright red in color in the fresh state. It is somewhat falciform, 
long, and narrow; the ventral part is the widest. Its weight in a dog of medium 




Fig. 449. — Projection of Viscera of Dog (Male) on Body Wall; Left Side. 
D, .\pical, cardiac, and diaphragmatic lobes of lung: P, pericardium; Pr, prostate. Costal attachment and 
median Une of diaphragm are dotted. 




Fig. 450. — Projection of Viscera of Dog (Fem.ale) on Body Wall; Right Side. 
A, C, D, Apical, cardiac, and diaphragmatic lobes of right lung; P, pericardium; K, right kidney; Pan., right 
branch of pancreas; O, ovary; U, cornu of uterus. Costal attachment and median line of diaphragm are dotted; also 
posterior contour of stomach. 



size is 13^-2 ounces (ca. 50 gm.). It is freely movable, and, with the exception 
of its tlorsal end, varies much in position and shape. The dorsal end is ventral to 



THE SPLEEN 507 

the vertelaral end of the last rib and the first lunibar transverse process; it fits into 
the interval between the left crus of the diaphragm, the left end of the stomach, 
and the left kidney. When the stomach is full, the long axis of the spleen corre- 
sponds to the direction of the last rib. Its parietal surface is convex and lies largely 
against the left flank. The visceral surface is concave in its length, and is marked 
by a longitudinal ridge, on which the vessels and nerves are situated, and to which 
the greater omentum is attached. The spleen is so loosely attached by the omen- 
tum as to be regarded as an appendage of the latter. 

The dorsal end of the spleen does not vary in position, but the rest of the organ is very 
variable. When the stomach is full, the part of the visceral surface of the spleen in front of the 
hilus is usually in apposition with the left part of the greater curvature of the stomach (as in the 
horse). It may have a similar position when the stomach is not full, and may be in contact with 
the latter only to a small extent dorsally. It is not rare to find the spleen lying along the dorsal 
part of the left fl.ank, with its long axis almost longitudinal; this is liable to be the case when the 
stomach is empty and contracted. In this condition the spleen shuts the left kidney entirely off 
from contact with the flank. 



THE RESPIRATORY SYSTEM 

The respiratory apparatus (Apparatus respiratorius) comprises the nasal 
cavity,^ the pharynx, the larynx, the trachea, the bronchi, and the lungs. The 
lungs are the central organs in which the exchange of gases between the blood and 
the air takes place; the other parts of the system are passages by which the air 
passes to and from the lungs. The nasal cavity opens externally at the nostrils, 
and communicates behind witli the pharynx through the choanse or posterior nares; 
it contains the peripheral part of the olfactory apparatus, which mediates the sense 
of smell. The pharynx is a common passage for the air and food — a remnant of the 
primitive embryonic arrangement; it has been described with the digestive tube. 
The larynx is a complex valvular apparatus which regulates the volume of air pass- 
ing through the tract; it is also the chief organ of voice. The trachea and the 
bronchi formed by its bifurcation are permanently open conducting tubes. The 
thorax, the pleural sacs which it contains, and the muscles which increase or di- 
minish the size of the cavity are also parts of the system. The bones, joints, and 
muscles of the thorax have already been described. 

For topographic reasons two ductless glands, the thyroid and the thjinus, are 
usually described in this section, although they are in no sense a part of the respira- 
tory system. 



RESPIRATORY SYSTEM OF THE HORSE 
THE NASAL CAVITY 

The nasal cavity (Cavum nasi), the first segment of the respiratory tract, is a 
long, somewhat cylindrical passage, enclosed by all the facial bones except the 
mandible and hyoid. It is separated from the mouth ventrally by the palate. 
It opens externally at the nostrils, and communicates posteriorly with the pharynx 
through the posterior nares or choanse. 

The nostrils (Nares) are somewhat oval in outline, and are placed obliquely, 
so that they are closer together below than above. They are bounded by two alae or 
wings (Alse nasi), which meet above and below, forming the commissures. The 
lateral ala is concave; the medial one is convex above, concave below. The 
prominence of the medial ala is caused by the lamina of the alar cartilage; this 
prominence, togetlier with the alar fold which extends backward from it, partially 
divides the nostril into a large lower part and a small upjier part, which are pop- 
ularly distinguished as the "true" and "false" nostril.- The superior commissure 
is narrow, the inferior one mde and rounded. If the finger is passed into the nostril 
at the U]3pcr commissure, it enters a blind cutaneous pouch. This cul-de-sac, the 
diverticulum nasi, extends backward to the angle of junction of the nasal bone and 
the nasal iir(jcess of the premaxilla. In order to enter the nasal cavity the finger 
should be introduced at the inferior commissure and directed toward the septum 
nasi. The naso-lacrimal orifice (Ostium nasolacrimale), the external opening of 

' A nose (Nasus extemus), such as exists in man, forming a projection distinctly marked 
off from the rest of the face, does not exist in the domesticated animals. 

- These terms should be abandoned, as they tend unnecessarily to complicate the description 
as well as to misconception with regard to function. 

508 



THE NASAL CAVITY 



509 



the naso-lacrimal duct, is seen when the nostril is thlated; it is situated on the floor 
of the vestibule, aoout two inches (ca. 5 cm.) from the lower commissure, perforat- 
ing the skin close to its junction \^'ith the mucous membrane. (It is not rare to find 
one or two accessory orifices further back.) 

Structure. — The skin around the nostrils presents long tactile hairs as well as 
the ordinary ones. It is continued around the alse and lines the vestibule. The 
skin of the diverticulum is thin 

and usually black, and is cov- y^--/- — i 

ered Avith very fine hairs; it is '- ■■''-:-'~- ^^■^?^»^ 

provided ■with numerous seba- ////; a ^^^^ Z ^^^ 

ceous glands. The medial wing /a7\ ^^^^B\ l^Biw* 

is sujiported by the alar cartil- / //Ak&\ ^^^H; '^^^k 

age (Cartilage alaris), which is 





Fig 451. — Cast of Left Nostbil. Nasal 

Diverticulum, and Nasal Vestibule 

OF Horse; Dorsal View. 

N, Nostril; U, diverticulum; 1, super- 

; of nostril: 2, inferior com- 

3, space occupied by alar fold; 4, 

groove occupied by dorsal turbinate fold; 

5, dorsal meatus. 



Fig. 452. — Cross-section of Nasal Region of Horse. 
The section is cut about two inches (5 cm.) behind the nostrils and a 
little more than half an inch behind the labial commissure, 
a, Dorsal meatus; b, middle meatus; c, ventral meatus; d, diver- 
ticulum nasi; e, dorsal turbinate fold; /. ventral turbinate fold; ff, 
prominence caused by venous plexus which extends back on lower part 
of ventral turbinate; 1, nasal bone; 2, cartilage of septum nasi; 3, 4, 
palatine and nasal processes of palatine bones; 5, maxilla; 6, tendon of 
levator labii superioris proprius; 7, part of lateralis nasi muscle which 
goes to cartilage of ventral turbinate; S, S', levator nasolabialis; 9. dila- 
tor naris lateralis; 10, buccinator; 11, vomero-nasal organ; 12, naso- 
lacrimal duct (wide part); 13, lateral nasal artery; 14, 14', branches of 
superior labial artery; 15, palatine artery; 16, labial branches of infra- 
orbital nerve; 17, external nasal nerve; 18, hard palate; 19, cheek; 20, 
superior labial vein. The veins (black) are filled by a natural injec- 
tion. 



shaped somewhat like a com- 
ma, the convex margin being 
medial (Fig. 453) . The cartil- 
ages are attached by fibrous 
tissue to the extremity of the 
septal cartilage. Each consists 

of an upper, quadrilateral curved plate, the lamina, and a narrow comu which curves 
ventro-laterally, supporting the medial wng and the inferior commissure, but not en- 
tering into the formation of the lateral wing. The lamina causes the projection of the 
upper part of the medial wing, from which the thick alar fold (Plica alaris) passes 
backward along the lateral wall of the nasal cavity to join the mucous fold which 



510 



RESPIRATORY SYSTEM OF THE HORSE 



encloses the cartilaginous prolongation of the ventral turbinate bone.' The extrem- 
ity of the cornu usually causes a slight projection of the skin a short distance behind 
and below the inferior commissure. 

The muscles of the nostrils have been described (p. 258). 

Vessels and Nerves. — The arteries are branches of the palato-labial, superior 
labial, and lateral nasal arteries, and the blood is conveyed away by corresponding 
veins. The lymph vessels go to the mandibular lymph glands. The nerves are 
derived from the infraorbital nerve (sensory) antl from the facial nerve (motor) . 

The nasal cavity is divided into two symmetrical halves by the median septum 
nasi (Figs. 452, 455, 456). The osseous septum (Septum nasi osseum) is formed 
behind by the perpendicular plate of the ethmoid and ventrally by the vomer. A 
few ridges on the former correspond to the ethmoidal meatuses. The major part 

of it, however, is formed by the 
cartilage of the septum nasi (Car- 
thago sppti nasi). The surfaces 
of the cartilage are marked by 
faint grooves for the vessels and 
nerves which course over it. The 
dorsal border is attached along 
the frontal and nasal sutures, and 
extends beyond the apices of the 
nasal bones about two inches (ca. 
5 cm.). From this border a thin, 
narrow plate, the parietal cartil- 
age (Cartilago parietalis) curves 
outward for a short distance on 
either side. Near the nostrils 
these plates are somewhat wider, 
partially making good the tlefect 
(naso-maxillary notch) in the 
bony wall of the cavity in this 
situation. The ventral border is 
thick and rounded; it lies in the 
groove of the vomer and the pala- 
tine processes of the premaxillae; 
its anterior part occupies the 
space between the premaxillary 
bones. A process from it extends 
into the palatine fissure, which it 
almost completely fills; the pala- 
tine end of the process lies in the 
submucous tissue of the hard palate, and the palatine artery turns medially between 
the cartilage and the bone. The posterior border is continuous with the perpen- 
dicular plate of the ethmoid bone.^ The alar cartilages are attached to the anterior 
extremity by fibrous tissue in such a manner as to allow very free movement — in 
fact an actual joint may be present. The ventral part of the cartilage is about 
half an inch (ca. 1 cm.), the middle part about one-tenth of an inch (ca. 2.5 mm.), 
and the dorsal part about a quarter to a third of an inch (ca. 6 to 8 mm.) in 
thickness. 

1 When the nostril is fully dilated it is circular in outline, and the so-called false nostril is 
effaced by the lamina of the alar cartilage being brought in contact with the superior commissure. 

" The cartilage is to be regarded as an unossified part of the mesethmoid. It will be noted 
that the line of demarcation between the bone and the cartilage is irregular and varies with age; 
extensive ossification (or calcification) of the cartilage is commonly found in old animals. The 
process often results in the formation of calcareous islands in the cartilage. 




Fig. 453. — Nasal Cartilages of Horse; Dorsal View. 
Anterior extremity of cartil.age of septum nasi; 2, foran 



THE NASAL CAVITY 



511 



The two turbinate bones project from the lateral wall, and divide the outer 
part of the cavity into three meatuses — dorsal, middle, and ventral (Figs. 454, 
455,456). 

The dorsal nasal meatus (Meatus nasi dorsalis) is a narrow passage, bounded 
dorsally by the roof of the cavity, and ventrally by the ventral turbinate bone; its 
posterior end is closed by the junction of the inner plate of the frontal bone with the 
cribriform plate and lateral mass of the ethmoid. It transmits air to the olfactory 
region. 

The middle nasal meatus (Meatus nasi medius) is between the two turbinate 
bones. It is somewhat larger than the dorsal meatus, and does not extend back 
so far; it ends near the great ethmoturbinate and the ethmoidal meatuses. In 
its posterior part is the extremely narrow, slit-like interval by which the max- 
illary sinus communicates with the nasal cavity — the naso-maxillary opening 
(Aditus naso-maxillaris) . The opening, which is normally a mere fissure, is not 
visible from the nasal side, being concealed by the overhanging dorsal turliinate. 
A fine flexible probe, passed outward and somewhat backward between the turliinate 



Dorsal p.. 

Ventral • turbinate ^ £(«"»"- Septum between 

turbinate Middle . Dorsal turbinates frontal sinuses 

Ventral \ meatus \ meatus 

meatus 




/'■■.- 



Fig. 454. — Nasal Cavity of Horse; Sagittal Section with Septum Removed. 
1, Dorsal turbinate fold; 2, alar fold, containing cartilaginous prolongation of ventral turbinate; 3, arrow pointing 
to naso-maxillary opening, which is concealed by dorsal turbinate bone; 4, cranial cavity; 5, sphenoidal sinus; 6', 
hamulus of pterygoid bone. The olfactory mucous membrane is shaded. Dotted lines indicate anterior Urait of 
uncoiled parts of turbinate bones, which inclose parts of frontal and maxillary 



bones, enters the maxillary sinus; if introduced a little further in the same direction, 
it usually passes through the orifice of communication between the maxillary 
sinus and the frontal sinus and enters the latter. A small part of the fissure usually 
brings the anterior division of the maxillary sinus into communication with the 
nasal cavity. The spaces enclosed by the coiled parts of the turbinates also open 
into the middle meatus. This passage may be characterized as the sinus-meatus, 
but it also conducts air to the olfactory region. 

The ventral nasal meatus (Meatus nasi ventralis) is situated between the 
ventral turbinate antl the floor of the cavity. It is much larger than the other two, 
and is tlie tlirect passage between the nostrils and the pharynx. The small, slit- 
like orifice of the vomero-nasal organ and the incisive or naso-palatine duct is 
situated in the floor of the anterior end of the meatus. 

The common nasal meatus (Meatus nasi communis) is situated between the 
septum and the turbinates, and is continuous laterally with the other meatuses. 
It is very narrow dorsally, but widens ventrally. 

The lateral masses of the ethmoid bone project forward into the posterior 
part (fundus) of the nasal cavity. Between the ethmoturbinates, of which each 



512 



RESPIRATORY SYSTEM OF THE HORSE 



mass IS composed, there are three principal and numerous small passages, the 
ethmoidal meatuses (Meatus ethmoidales). 

The choanse or posterior nares are two elliptical orifices by which the nasal 
cavity and pharynx connnunicate. They are in the same plane as the floor of the 




Fig. 455. — Cross-section of Head of Hokse. 
The section is cut midway between the medial canthus and the anterior end of the facial crest and i 



L front ^ 



1, Septum nasi; 2, 3, 4, dorsal, middle, and ventral meatus nasi; 5, common meatus nasi; 6, canity of dorsal 
turbinate bone (^ e., turbinate part of frontal sinus) ; 7, cavity of ventral turbinate bone (i. e., turbinate part of maxillary 
sinus); S, maxillary sinus; 9, communication between 7 and 8 over infraorbital canal; 10, naso-lacrimal duct; 11, 
infraorbital nerve and canal; 12, m. levator labii superioris proprius; 13, mouth cavity; 14, palatine artery; 15, fifth 
upper cheek tooth (posterior part); 16, sixth lower cheek tooth (anterior part); 17, m. buccinator; IS, hard palate; 19, 
vena refiexa; 20, superior buccal glands; 21, buccinator vessels and nerve; 22, alveolar vessels and nerve of mandible; 
23, lingual artery; 24, mm. genio-glossi ; 25, m. hyo-glossus (number placed between two radicles of lingual vein) ; 26, 
m. stylo-glossus; 27, m. mylo-hyoideus ; 2S, m. genio-hyoideus; 29, Ungual nerve; 30, hypoglossal nerve; 31, sub- 
lingual artery ; 32, m. digastricus (anterior belly) . The mandibular duct is shown in the fat lateral to the genio-hj oideus 
but is not marked. 



nasal cavity, and are separated from each other by the vomer. They are, taken 
together, al^out two inches (ca. 5 cm.) wide and three to four inches (ca. 8 to 10 
cm.) long. 

The nasal mucous membrane (Membrana mucosa nasi) is thick, highly vas- 
cular, and is, in general, firmly attached to the underlying periosteum and peri- 



THE NASAL CAVITY 



513 



chondrium. It is continuous in front with the skin which Hues the nostrils, and 
behind with the mucous membrane of the pharynx. It is also continuous at the 
naso-niaxillary opening with the very thin and much less vascular mucous mem- 
brane which lines the paranasal sinuses. In the anterior jjart of the cavity it forms 
prominent thick folds on the lateral wall, which extend from the turbinate bones to 
the nostril. There are usually two dorsal turbinate folds which unite anteriorly. 



Dorsal mealiis 



Septum nasi 



Lacrimal sac 




Transverse 
facial vessels 

I'lilatine artery 

\'ena reflexa 
Palatine vein 
liiirciiiator and 

l)i l>. labii inf. 
iJiiaiiiator 

vessels and 

nerve 



Lingual nerve 

- Lingual artery 

Lingual vein 

Mandibular 
iluct 

Hypoglossal 
nerve 



Digastricus (ant. belly) 



Parotid duct 



Fig. 45G. — Cross-section of Head of Horse. The S 



^, Mylo-hyoideus; :2, stylo-glossus; 5, hyo-glossus; -J, genio-glossus; 5, lingual process of hyoid bone. An arrow 
points to the naso-maxillary opening. The projecting edge just above the arrow point is the anterior margin of the 
fronto-maxillary opening. 



The upper one encloses a thin plate of cartilage which is continuous with the dorsal 
turbinate bone. The ventral turbinate fold is curved, and encloses an ''%_' shaped 
cartilaginous plate which prolongs the ventral turbinate lione; this fold is con- 
tinuous with the alar fold of the nostril, and forms with it the upper margin of the 
entrance from the nostril to the nasal cavity. Below this there is a rounded ridge 
produced by the nasal process of the premaxilla. The mucous membrane of the 
33 



514 RESPIRATORY SYSTEM OF THE HORSE 

greater part oi the cavity (Regio rcspiratoria) is red in color, and is covered with a 
stratified ciliated epithelium. It contains numerous tubulo-alveolar nasal glands 
(Glandulse nasales). The submucosa contains rich venous plexuses which form 
in certain situations a sort of cavernous tissue (Plexus cavernosus nasalis), composed 
of several strata of freely anastomosing veins, between which there are unstriped 
muscle-fibers. This arrangement is most marked in the turbinate folds, on the 
lower part of the ventral turbinate bone, and the lower part of the septum. The 
mucous membrane of the vestibule presents numerous small depressions (openings 
of gland ducts), and is covered with stratified squamous epithelium. On the 
posterior part of the lateral masses of the ethmoid and the adjacent part of the 
dorsal turbinate and the septum (Regio olfactoria) the mucous membrane is brown- 
ish-yellow in color and thicker; it contains the olfactory nerve-endings in a special 
non-ciliated epithelium. In it are numerous olfactory glands (Glandulte olfactorite) ; 
these are long, tul^ular, and often branched. 

The vomero-nasal organ (Organon vomeronasale)' is situated on the floor of 
the nasal cavity, on either side of the ventral border of the septum (Fig. 452). 
It consists of a tubular cartilage (Cartilago vomeronasalis) lined with mucous 
membrane (Ductus vomeronasalis) , to which fibers of the olfactory nerve may be 
traced. Its anterior part communicates with the nasal cavity by a slit-like orifice 
in common with the incisive or naso-palatine duct. The posterior blind end is in a 
transverse plane through the second or third cheek tooth. The average length of 
the organ is about five inches (ca. 12 cm.). 

The ductus incisivus (or naso-palatine duct) is a small mucous tube, an inch 
or more (ca. 2.5-3 cm.) in length, which extends obliquely through the palatine 
fissure. Its nasal end communicates wth the nasal cavity through a slit-like 
opening in common -^^ith the vomero-nasal organ. The palatine extremity ends 
blindly in the submucous tissue of the hard palate. 

The paranasal sinuses are described in the Osteology. 

Vessels and Nerves. — The arteries are l^ranches of the ethmoidal, spheno- 
palatine, palatine, superior labial, and lateral nasal arteries. The blood is carried 
away by corresponding veins. The lymph vessels go to the mandibular and 
pharyngeal lymph glands. The nerves come from the olfactory and trigeminal 
nerves. 

THE LARYNX 

The larynx is a short tube which connects the pharynx and trachea. It is a 
complex valvular apparatus, which regulates the volume of air in respiration, 
prevents aspiration of foreign bodies, and is the chief organ of voice. 

It is situated parti}' between the medial pterygoid muscles, partly in the neck 
between the parotid glands.^ Its long axis is practically horizontal in the ordinary 
position of the head and neck. It is related dorsally to the pharynx and the origin 
of the oesophagus. Ventrally it is covered by the skin, fascia, and sterno-hyoid 
and omo-hyoid muscles. Laterally it is related to the parotid and mandibular 
glands and to the medial pterygoid, occipito-mandibularis, digastricus, stylo-hyoid, 
and pharyngeal constrictor muscles. It is attached to the body and thyroid cornua 
of the hyoid bone, and thus indirectly to the base of the cranium. Its cavity 
communicates dorsally with the pharynx, posteriorly with the trachea. The 
skeleton of the larynx consists of a frameWork of cartilages, which are connected by 
joints and ligaments or membranes, and moved by extrinsic and intrinsic muscles. 
It is lined with mucous membrane. 

• Commonly known as the organ of Jacobsofi. 

' In the ordinary position of the head and neck, and wliile the parts are at rest, about half 
of the larynx lies between the branches of the mandible; when the head and neck are extended, 
proportionately more of the larynx lies behind a plane through the posterior borders of the rami. 



CARTILAGES OF THE LARYNX 



515 



Cartilages of the Larynx 

There are three single cartilages and one pair; the single cartilages are the 
cricoid, tliyroid, and epiglottic; the arytenoid cartilages are paired. 

The cricoid CJirtilage (Cartilago cricoidea) is shaped like a signet ring. The 
dorsal part is a broad, thick, quadrilateral plate termed the lamina; the external 
(dorsal) surface of this is marked by a median ridge (Crista mediana) separating two 
shallow cavities, from which the dorsal crico-arytenoid muscles arise. On either 
side of these depressions are two articular facets. The anterior facet (Facies articu- 
laris ar\i;£enoidea) is at the anterior border, is oval and convex, and articulates 
with the arytenoid cartilage. The posterior facet (Facies articularis thyreoidea) is 
situated on the front of a ridge, a short distance from the posterior border; it is 
concave, and articulates with the posterior cornu of the thyroid cartilage. The 
ventral and lateral parts of the ring are formed by a curved band, called the arch 
(Arcus), which is narrowest ventrally. The lateral surfaces of the arch are grooved 



Muscular process 



Apex 




Crico-thyroiil 
membrane 



Laryngeal prominence 



Fig. 457. — Laryngeal Cartilages and Part of Trachea of Horse; Right Vi 
For "thyroid wing" read "thyroid lamina." 



for the crico-thyroid muscle. The anterior border of the lamina is thick and 
slightly concave; the posterior border is thin and irregular. The anterior border 
of the arch is concave ventrally and gives attachment to the crico-th.vroid membrane ; 
laterally it is thicker and gives attachment to the crico-arytenoideus lateralis 
muscle. The posterior border of the cartilage is attached to the first ring of the 
trachea by the crico-tracheal membrane. The internal surface is smooth and is 
covered with mucous membrane. 

The thyroid cartilage (Cartilago thyreoidea) consists of a median thickened 
portion, termed the bodj', and two lateral laminje. The body forms ventrally a 
slight prominence (Prominentia laryngea), which can be felt, but is not visible in 
the living subject; it is related dorsally to the base of the epiglottis, which is at- 
tached to it by an elastic ligament. The laminae or wings spring from the body 
on either side and form a large part of the lateral wall of the larynx. Each is a 
rhomboid plate, presenting a slightly convex lateral surface, which is divided into 
two areas by an oblique line (Linca obliqua), on which the thyro-hyoid and th.yro- 
pharyngeus muscles meet. The dorsal iiorder is nearly straight; it gives attach- 
ment to the pharyngeal fascia and the palato-phar\aigeus muscle, and bears a cornu 
at each end. The anterior cornu (Cornu orale) articulates with the cartilage of the 



)1C 



RESPIRATORY SYSTEM OF THE HORSE 



thjToid cornu of the hj'oid Isone ; below it is a notch (Fissura thyreoidea) , wliich is? 
converted into a foramen (Foramen thyreoideum) by a fibrous band, and trans- 
mits the anterior larjaigeal nerve to the interior of the larynx. The posterior cornu 
(Cornu aborale) articulates with the cricoid cartilage. The ventral Ijoriler joins 
the body in front, and behind diverges 
from its fellow to inclose a triangular ^^^^ 

space, the thyroid notch (Incisura thy- 
reoidea aboralis), which is occupied by / ' ^^ 
the crico-thyroid membrane. The anter- 

Median ridge Lamina 




Posterior cornu 
Surface for 
cricoid 

Fig. 45S.— Cricoid Cartilage of Horse; Left Axtero- Fig. 459.— Thyroid Cartilage of Horse; Ventral 



ior border is slightly convex, and is attached to the hyoid bone by the thyro-hyoid 
membrane. The posterior border overlaps the arch of the cricoid cartilage, and 



Pharyngeal surface 



Medial angle of base 



Aj)e.r 




Cuneiform process 

Fig. 460. — Epiglottic Cartilage of Horse; Right 
Lateral View. 



Vocal process 



' Fig. 461. — Left Arytenoid Cartilage of Horse; 
jMedio-ventral View. 



gives attachment to the crico-thyroid muscle. The medial surface is concave, 
and is partly covered by mucous membrane. 

The epiglottic cartilage (Cartilago epiglottica), usually called the epiglottis for 
the sake of brevity, is situated above the body of the thyroid cartilage and curves 



JOINTS, LIGAMENTS, AND MEMBRANES OF THE LARYNX 517 

toward the root of the tongue. It is shaped somewhat like a pointed ovate leaf, 
and presents two surfaces, two borders, a base, and an apex. The oral (or anterior) 
surface is concave in its length, convex transversely; the pharyngeal (or posterior) 
surface has the reverse configuration. The borders are thin, irregular, and some- 
what everted. The base is thick, antl is attached to the dorsal surface of the body 
of the thyroid cartilage by elastic tissue. From each side of it a cartilaginous bar 
projects upward and backward; these are the cuneiform processes (Processus 
cuneiformes) and correspond to the cuneiform cartilages of man. The apex is 
pointed and curved ventrally. Nearly all of the epiglottic cartilage is covered with 
mucous membrane. It usually projects into the isthmus fauciiun, but is often 
on the pharyngeal side of the soft palate. 

The arytenoid cartilages (C'artilagincs arj'tenoideae) are situated on either side, 
in front of the cricoid, and partly medial to the laminee of the thyroid cartilage. 
They are somewhat pyramiilal in form, and may be described as having three 
surfaces, three borders, a base, and an apex. The medial surface is concavo- 
convex, but very slightly curved, and is smooth and covered Ijy mucous membrane. 
The lateral surface is concave and is separated fro'm the lamina of the thyroid 
cartilage by the crico-arytenoideus lateralis and vocalis muscles, and the laryn- 
geal saccule. The dorsal surface is ^Iso concave, and is covered by the aryte- 
noideus muscle, which is attached to it. The dorsal and lateral surfaces are 
separated (except in front) by a ridge which increases in size toward the lateral 
angle of the base, where it forms a rounded prominence, the muscular process 
(Processus muscularis). The anterior and posterior borders are convex; they 
converge ventrally to a thin, wide angle, the vocal process (Processus vocalis). 
The process is so named because it furnishes attachment to the vocal ligament. 
The dorsal border forms a deep notch with the apex. The base is concave and 
faces chiefly backward; it presents laterally an oval concave facet (Facies artic- 
ularis) for articulation with the anterior border of the lamina of the cricoid carti- 
lage. The medial angle of the base is attached to its fellow by the transverse 
arj-tenoid ligament. The apex (Cartilago corniculata) curves upward and back- 
ward, forming with its fellow the pitcher-shaped lip from which the cartilages derive 
their name. 

The cricoid and thyroid cartilages and the greater part of the arj-tenoid 
cartilages are hyaline. The apices and vocal processes of the aiytenoid and the 
epiglottis (including the cuneiform processes) consist of elastic cartilage; they 
show no tendency toward ossification at any age. The thyroid and cricoid carti- 
lages regularly undergo considerable ossification; the process begins in the body of 
the thyroid, and often involves the greater part of the cartilage.^ 

Joints, Ligaments, and Membranes of the Larynx 

The crico'-Hhyroid joints (Articulationes crico-thyreoidese) are diarthroses 
formed liy the apposition of the convex facets on the ends of the posterior cornua 
of the thyroid cartilage with corresponding facets on the sides of the cricoid car- 
tilage. The capsule is thin, but is strengthened by accessory bands dorsally, 
laterally, and medially. The movements are chiefly rotation around a trans- 
verse axis passing through the centers of the two joints. 

The crico-arytenoid joints (Articulationes crico-arytaenoidea) are also diar- 
throdial. They are formed by the apposition of the convex facets on the anterior 
border of the cricoid cartilages with the concave facets on the bases of the arjienoid 
cartilages. Each has a very thin, loose capsule, strengthened by accessory bundles 

1 Calcareous deposits are present in the body of the thyroid cartilage, even before adult age 
is reached. Scheier (by use of A'-rays) found complete calcification of the thyroid in two mares 
eight and ten years of age; in the former the process also involved a large part of the lamina and 
the adjacent part of the arch of the cricoid. 



518 RESPIRATORY SYSTEM OF THE HORSE 

dorsally and medially. The most important movement is rotation of the arytenoid 
cartilage about a longitudinal axis so that the vocal process swings outward (ab- 
duction) or inward (adduction), carrying the vocal cord with it. Another move- 
ment here is rotation about a transverse axis, in which the apical part of the carti- 
lage is raised or lowered. The arytenoid is also capable of slight inward or outward 
gliding movement. 

The thyro-hyoid joints (Articulationes hyo-thyreoidese) are formed by the 
anterior cornua of the thyroid cartilage and the cartilaginous extremities of the 
thyroid cornua of the hyoid bone. They are diarthroses and the joint capsule is 
reinforced by a relatively strong thyro-hyoid ligament. The thyroid cornu has 
here a cartilaginous prolongation about a quarter of an inch (ca. 6 mm.) in length. 
The chief movement is rotation around a transverse axis passing through the two 
joints. 

The crico-th3rroid membrane (Membrana crico-thyreoidea) occupies the thy- 
roid notch and extends backward to the arch of the cricoid cartilage. It is tri- 
angular in form, and is attached by its base to the anterior border of the arch of 
the cricoid cartilage, while its borders are attached to the margins of the thyroid 
notch. It is strong, tightly stretched, and composed largely of elastic tissue. It 
is reinforced ventrally by longitudinal fibers, dorsally by fibers which stretch across 
the thyroid notch. 

The th3rro-hyoid membrane (Membrana hyo-thjrcoidea) connects the body 
and anterior borders of the thyroid cartilage with the body and thyroid cornua of 
the hyoid bone. 

The hyo-epiglottic ligament (Lig. hyo-epiglotticum) attaches the lower part 
of the oral surface of the epiglottis to the body of the hyoid bone. It forms an 
elastic sheath for the hyo-epiglottic muscle. Ventrally it blends with the thyro- 
hyoid membrane, and dorsally it is not well defined. 

The thjrro-epiglottic ligament (Lig. thyreo-epiglotticumj is strong and thick; 
it is composed chiefly of elastic tissue. It connects the base of the epiglottis with 
the body and the adjacent medial surfaces of the laminae of the thyroid cartilage. 
Other fibers attach the cuneiform processes somewhat loosely to the thyroid lamina;. 

The transverse ar3d;enoid ligament (Lig. arytsenoideum transversum) is a 
slender band which comiects the medial angles of the bases of the arytenoid carti- 
lages. 

The vocal (or posterior thyro-arytenoid) ligament (Lig. vocale) underlies and 
is intimately adherent to the mucous membrane of the true vocal cord. It is thin 
and elastic and is attached ventrally to the body of the thyroid cartilage and the 
crico-thyroid membrane close to its fellow of the opposite side, and ends dorsally 
on the processus vocalis of the arytenoid cartilage. 

The ventricular (or anterior thyro-arytenoid) ligament (Lig. ventriculare) is 
included in the false vocal cord. It consists of loosely arranged bundles which 
arise chiefly from the cuneiform process and end on the lateral surface of the pro- 
cessus vocalis and adjacent part of the arytenoid cartilage. 

The crico-tracheal membrane (Membrana crico-trachealis) connects the cri- 
coid cartilage with the first ring of the trachea. 

Muscles of the Larynx 
A. Extrinsic Muscles 
The stemo-th5TO-hyoideus is described on p. 268. 

The thyro-hyoideus (M. hyo-thyreoideus) is a flat, quadrilateral muscle, which 
lies on the lateral surface of the thyroid lamina and the lateral part of the thyro- 
hyoid membrane. It arises from the body and thyroid cornu of the hyoid bone 
(almost meeting the opposite muscle), and ends on the oblique line on the lamina 



MUSCLES OF THE LARYNX 



519 



of the thyroid cartilage. Its action is to draw the larj'nx toward the root of the 
tongue. It is related laterally to the external maxillary vein and the anterior part 
of the mandibular gland. 

The hyo-epiglotticus (M. hyo-epiglotticus) is a feeble muscle which occupies a 
median position above the central part of the thyro-hyoid membrane, enclosed by 
an elastic sheath, the hyo-epiglottic ligament. It arises from the body of the hyoid 
bone by two branches which unite and are inserted into the front of the base of the 
epiglottis. Its action is to draw the epiglottis toward the root of the tongue. 

B. Intrinsic Muscles 

The crico-thyroideus (M. crico-thyreoideus) is a short muscle which fills the 

groove on the lateral surface of the cricoid cartilage ; its fibers are directed dorsally 

and somewhat forward. It arises from the ventral part of the lateral surface and 

posterior edge of the cricoid cartilage, and is inserted into the posterior border and 




Fig. 462. — Laryngeal MnscLES of Horse, Seen from Left Side After Removal of Major Part of Lamina of 

Thyroid Cartilage. 
a, Kerato-hyoideus; b, thyro-hyoideus; c, crico-thyroideus; d, sterno-thyroideus ; e, ventricularia; /, vocalis; g, 
crico-arytenoideus lateralis; h, crico-arytenoideua dorsalis; i, arytenoideus transversus; t, lingual process; B, small 
cornu, 3, thyroid cornu, of hyoid bone; 4> thyroid cartilage; o, cricoid cartilage; 6, epiglottis; 7, apex of arj'tenoid 
cartilage; 5, trachea; P, muscular process of arytenoid; /(?, lateral lobe of thjToid gland; iO', isthmus of thyroid gland; 
11, laryngeal saccule. The saccule is larger than it is represented in this figure, and extends almost to the vocal 
process. (Ellenberger-Baum, Anat. d. Haustiere.) 



adjacent part of the lateral surface of the lamina of the thyroid cartilage. Its 
action is to draw the thyroid cartilage and the ventral part of the cricoid cartilage 
together. In this action the cricoid cartilage is probably rotated about a trans- 
verse axis through the crico-thyroid joints, carrying the bases of the arytenoid 
cartilages with it and thus tensing the vocal cords. 

The crico-arjrtenoideus dorsalis (M. crico-arytaenoideus dorsalis)' is 'a strong, 
somewhat fan-shaped muscle, which, with its fellow, covers the dorsal surface of 
the lamina of the cricoid cartilage. It is partially divisible into two layers. It 
has a broad origin on half of the lamina of the cricoid cartilage, including the me- 
dian ridge, and its fibers converge to be inserted into the processus muscularis of 
the arytenoid cartilage. Its action is to dilate the rima glottidis by rotating the 
arytenoid cartilage so as to carrj' the vocal process and cord outward (abduction) . 

The crico-arytenoideus lateralis (M. crico-arytsenoideus lateralis) lies on the 
medial face of the thyroid lamina. It arises from the anterior border of the lateral 
part of the arch of the cricoid cartilage. The fibers pass in a dorsal direction and 
converge on the processus muscularis of the arytenoid cartilage. It closes the 
rima glottidis by rotating the arytenoid cartilage inward (adduction). 
' Also known as the crico-arytenoideus posterior s. posticus. 



520 



RESPIRATORY SYSTEM OF THE HORSE 



The arytenoideous transversus (M. arytfenoideus transversus) is an unpaired 
muscle which stretches across the concave dorsal surface of the arytenoid cartilages. 
Its fibers are attached on either side to the processus muscularis and the ridge which 
extends forward from it. The right and left parts of the muscle meet at a fibrous 
raphe, which is coimected with the transverse arytenoid ligament. Fibers of the 
ventricularis muscle overlap its anterior part. It narrows the rima by draw- 
ing the arytenoid cartilages together (adduction). 

The ventricularis^ lies in the lateral wall of the larynx, covered by the lamina of 
the thyroid cartilage. It arises from the anterior part of the crico-thyroid membrane 
and the ventral border of the thyroid lamina. Its fibers pass upward and backwartl 



Salpingo-pharyngcal 
fold 

Epiglottis 

Aryteno-epiglottic 
fold 




Root of tongue 
Soft palate {cut) 



Wall of pharynx 
Arytenoid cartilage {apex) 

Posterior pillar of soft palate 

Position of cricoid 
cartilage under oesophagus 



Thyroid gland 
Trachea 
- Oesophagus 



Fig. 463. — Aditus Lartngts of HnnaE, Exposed by Opening Pharynx ani 

Median Dorsal Line. 
1, False vocal cord; ^, lateral ventricle; 3, true vocal cords 



Beginning of (Esophagus Along 
4, rima glottidis. 



to end partly on the processus muscularis, partly on the arytenoideus transversus, 
meeting its fellow. 

The vocalis' is also medial to the lamina of the thyroid cartilage, and is in part 
separated from the preceding muscle by the laryngeal saccule. It has an extensive 
origin on the crico-thjToid membrane. Its direction corresponds with that of the 
true vocal cord. It is inserted into the lateral surface of the arytenoid cartilage 
below the processus muscularis. 

The two preceding muscles close the rima glottidis antl slacken the vocal cords. 
With the arytenoideus transversus and cri'co-arytenoideus lateralis they form a 
sphincter which closes the entrance to the larynx. 

' These two muscles were formerly taken together as parts of the thyro-arytenoideus muscle. 



CAVITY OF THE LARYNX 



521 



The ventricularis rotates the arytenoid so as to bring the apical part of the cartilage do'mi- 
ward and forward. 

In some cases there is a small thyro-arytenoideus extemus muscle which arises from the 
medial face of the lamina of the thyroid cartilage near the dorsal border, passes upward and 
backward, and blends with the arytenoideus transversus. 

Cavity of the Larynx 
The cavity of the larynx (Cavum laryngis) is smaller than one would naturally 
expect from its external appearance. On looking into it through the pharyngeal 
end two folds are seen projecting from each lateral wall. These are termed the 




Fig. 404. — Part of .S.\gittal Section of Head of Horse. 
Section is cut just to left of median plane. 
1, Epiglottis; 2, body of thyroid cartilage; 3, arytenoid cartilage; 4. 4', lamina and arch of cricoid cartilage; 5, 
ary-epiglottic fold; 6, vocal cord (labium vocale) ; 7, ventricular fold or false vocal cord (plica ventricularis) ; S, lateral 
ventricle of larynx: 8', dotted line indicating contour of laryngeal saccule; 9, middle ventricle of larynx; 10, m. crico- 
arytenoideus dorsalis; 11, oesophagus; 12, septum of areolar tissue between guttural pouches; 13, m. rectus capitis 
ventralis; 14, body of sphenoid bone; 15, pharyngeal recess; 16. arrow points into nasal cavity; 17, pharyngeal open- 
ing of auditive or Eustachian tube; IS, posterior pillars of soft palate united over aditus cesophagi; 19, arrow points 
into vestibule of larynx: 20, soft palate; 21, tonsil: 22, root of tongue: 23, m. hyo-epiglotticus; 24, hyoid bone; 25, 
mandibular lymph glands; 26, mm. omo-hyoideus and sterno-hyoideus; A, vestibule of larynx; B, glottis; C, post- 
glottic part of larynx; D, trachea; E, pharynx, F, isthmus faucium. 



vocal cords, and the narrow part of the cavity between them is the ritna glottidis. 
Thus it is convenient to recognize three divisions of the cavity. 

The aditus laryngis, or pharyngeal aperture, is a large, oblique, oval opening, 
which faces into the ventral part of the pharynx. It is bounded in front by the 
epiglottis, behind by the arytenoid cartilages, and laterally by the aryteno-epi- 
glottic folds of mucous membrane (Plicffi aryepiglotticEe), which stretch between 
the edges of the epiglottis and the arytenoid cartilages. 



522 



RESPIRATORY SYSTEM OF THE HORSE 



The vestibule of the larynx (Vestibulum laryngis) is that part of the cavity 
which extends from the aditus to the vocal cords. On its lateral walls are the false 
vocal cords (Plicae ventriculares), each of which consists of a fold of mucous mem- 
brane covering the ventricular ligament and the cuneiform process. Between the 
false and true vocal cord there is a pocket-like depression termed the lateral ven- 
tricle of the larynx (Ventriculus lateralis laryngis). This is the entrance to the 
laryngeal saccule (Sacculus laryngis), a cul-de-sac of the mucous membrane which 
is an inch or more (ca. 2.5 to 3 cm.) long and extends upward and backward on the 
medial surface of the thyroid lamina. There is a small middle ventricle (Ventric- 
ulus laryngis medianus) at the base of the epiglottis. 

The term "laryngeal saccule" seems decidedly preferable to the "appendix ventrieuli lar- 
jmgis" of the B. N. A. The saccule is m relation with the ventricular and vocal muscles, and 



Body of thyroid 
curtilage 





Fig. 466. — Cast of Right Lateral Ventricle 

AND Saccule of Horse; Medial View. 

1, Ventricle; 2, saccule. Figure is a little less than 

three-fourths of natural size. 




Fig. 465. — Section op Larynx of Horse. 
The section cut is parallel with the vocal cords. 



Fig. 467. — Cast of Left Lateral Ventricle and 

Saccule of Larynx of Horse; Lateral View. 

1, Ventricle; 2, saccule; 3, impression of ventricu- 

laris muscle; 4, impression of voealis muscle. 



when the latter are atrophic (as in hemiplegia lar>Tigis or "roaring"), the pouch is considerably 
larger on the affected side, having occupied the space vacated by the muscles. The blind end of 
the saccule lies just below the level of the muscular process of the arytenoid cartilage. It is loosely 
attached to the contiguous structures. The average capacity of the saccule is about 5 to 6 c.c. 

The middle, narrow part of the cavity is termed the glottis or rima glottidis. 
It is bounded on either side by the true vocal cord and the medial surface of the ary- 
tenoid cartilage. The true vocal cords (Labia vocales) are situated behind the 
false cords and the lateral ventricles. They extend from the angle of junction of 
the body and laminae of the thyroid cartilage to the vocal processes of the arytenoid 
cartilages. They are prismatic in cross-section, and their free edges look forward 
and somewhat upward. The mucous membrane of the cord (Plica voealis) is very 
thin and smooth, and is intimately attached to the underlj-ing vocal ligament. In 



THE TRACHEA 523 

ordinary breathing the rima is somewhat lanceolate in form (Fig. 465) ; when dilated, 
it is diamond-shaped, the widest part being between the vocal processes. The 
narrow part of the glottis between the vocal cords is termed the glottis vocalis (Pars 
intermenabranacea) , while the wider part between the arytenoid cartilages is the 
glottis respiratoria (Pars intercartilaginea). 

In the revised nomenclature the terms "true" and "false" vocal cords have been replaced 
by "labium vocale"and " plica ventricularis. " The labium vocale consists of the plica vocalis, 
lig. vocale, and m. vocalis; the last forms the bulk of the projection. 

The posterior compartment of the laryngeal cavity is directly continuous with 
the trachea. It is enclosed by the cricoid cartilage and the crico-thyroid membrane. 
It is clearly marked off laterally by the vocal cord and the projection caused by the 
posterior border of the arytenoid cartilage. It is oval in form, the transverse 
diameter being an inch and a half to two inches (ca. 4 to 5 cm.), and the dorso- 
ventral diameter two to two and a half inches (ca. 5 to 6 cm.). 

The mucous membrane of the larynx (Tunica mucosa laryngis) is reflected 
around the margin of the aditus to become continuous with that of the pharjTix, 
and is continuous behind with that which lines the trachea. It is closely attached 
to the epiglottis, except at the base, but elsewhere in the aditus and vestibule it is 
loosely attached by submucous tissue which contains many elastic fibers. It is 
thin and very closely adherent over the vocal cords and the medial surfaces of the 
arytenoid cartilages. The epithelium is of the stratified squamous type from the 
aditus to the glottis, beyond which it is columnar ciliated in character. There are 
numerous mucous larjmgeal glands (Glandulse laryngeae), except in the glottis and 
the pharyngeal surface of the epiglottis, in which situations they are scanty. LjTnph 
nodules (Noduli lymphatici laryngei) are also present, especially at the lateral 
ventricle. 

Vessels and Nerves. — The arteries are derived from the laryngeal and ascend- 
ing pharjaigeal arteries. The veins correspond to the arteries. The lymph- 
vessels go to the anterior cervical and pharyngeal lymph glands. The nerves 
come from the vagus. The recurrent or posterior laryngeal is the motor nerve to 
the muscles with the exception of the crico-thyroideus. The anterior laryngeal 
is the sensory nerve; it commonly supplies the nerve to the crico-thyroideus. 



THE TRACHEA 

The trachea extends from the larynx to the roots of the lungs, where it divides 
into the right and left bronchi. It is kept permanently open by a series of fifty to 
sixty mcomplete cartilaginous rings embedded in its wall. It occupies a median 
position, except near its termination, where it is pushed a little to the right by the 
arch of the aorta. It is approximately cylindrical, but its cervical part is for the 
most part depressed dorso-ventrally by contact with the longus colli muscle, so 
that the dorsal surface is flattened. Its average length is about 30 to 32 inches (ca. 
75 to 80 cm.). The average caliber is about two to two and one-half inches (ca. 5 to 
6 cm.), but in the greater part of the neck the transverse diameter is greater and the 
dorso-ventral smaller.' It is enclosed by a fascia propria. 

In its cervical part (Pars cervicalis) the trachea is related dorsally to the 
oesophagus for a short distance, but chiefly to the longus colli muscles. It is related 
laterally to the lateral lobes of the thyroid gland, the carotid artery, the jugular 
vein, the vagus, sympathetic, and recurrent laryngeal nerves, and the tracheal 

'■ At its origin the trachea is almost circular in cross-section and the average diameter is 
about two and a quarter mches (ca. .5.5 cm.). It soon becomes flattened dorso-ventrally, so that 
the transverse diameter may be nearly three inches (ca. 7 cm.) and the dor.so-ventral about two 
inches (ca. 5 cm.). In the thorax the diameters become more nearly equal, and sometimes the 
dorso-ventral diameter is the greater; this is the case where the aorta crosses the trachea. 



524 



RESPIRATORY SYSTEM OF THE HORSE 



lymph ducts and cervical lymph glands. The oesophagus lies on its left face from 
the third cervical vertebra backward. The sterno-cephalicus muscles cross it very 
obliquely, passing from the ventral surface forward over its sides, and diverging to 
reach the angles of the jaw. The omo-hyoidei also cross it very obliquely, passing 
over the lateral surfaces of the tube, and converging ventrally in the laryngeal 
region. The sterno-thyro-hyoideus lies on the ventral surface.' The scaleni lie on 
either side near the entrance to the thorax. 

The thoracic part (Pars thoracalis) of the trachea (Figs. 553, 554) passes back- 



Obliquus 
capiiis 
posterior 
hUerlrans- 
versalis 
Luiigissimus ,, 
capiiis et atlantis ' 
T 



Rectus capitis 

ventralis miijor 

Brnchiocephalicus 

humcralis 



Vagosympa- 
thetic trunk 
Carotid artery 

Recurrent nerve 
Jugular vein 



Sterno- 
cephalicus 




Omo-liyoideus 



Stemo-thyroideus Sterno-hyoideus 



Fig. 4GS. — Cross-sectiox of Ventral Part of Neck of Horse. 
This section is cut at right angles to the iong axis of the neck, passing througii the junction of the second and third 
cervical vertebrae. .S.c. Spinal cord; 5.f., spinal vein; T'.t'., V. a., vertebral vein and artery; r.p., transverse process 
(tip); F, intervertebral fibro-cartilage ; T, atlantal tendon common to brachiocephalicus, splenius, and longissimus 
atlantis; ilf, digitation of brachiocephahcus inserted by T. 



ward between the pleural sacs and divides into two bronchi over the left atrium of the 
heart. It is related dorsally to the longus colli for a short distance, and beyond this to 
the oesophagus. Its left face is crossed by the aortic arch, the left brachial artery, and 
the thoracic duct. Its right face is crossed by the vena azygos, the dorso-cervical 
and vertebral vessels, and the right vagus rierve. Ventrally it is related to the 
anterior vena cava, the brachiocephalic and common carotid trunks, and the car- 
diac and left recurrent nerves. 

1 The arrangement of the muscles should be noted, since the space enclosed by the divergence 
of the stemo-cephahci and the convergence of the omo-hyoidei is the area of election for the opera- 
tion of tracheotomy. 



THE BRONCHI THE THORACIC CAVITY 525 

The bifurcation of the trachea (Bifurcatio trachese) is situated opposite to the 
fifth rib or intercostal space, and about four or five inches (ca. 10 to 12 cm.) ventral 
to the vertebral column. 

The trachea is composed of — (1) the cartilaginous rings; (2) a fibro-elastic 
membrane which encloses and connects the rings; (3) a muscular layer; (4) the 
mucous membrane. The elastic membrane is intimately attached to the peri- 
chondrium of the rings. In the intervals between the latter it constitutes the 
tracheal annular ligaments (Ligamenta annularia trachealia). The rings of the 
trachea (Cartilagines trachealcs) are composed of hyaline cartilage. They are 
incomplete dorsally, and when their free ends are drawn apart, resemble somewhat 
the letter C. In the cervical part the free ends overlap, while in the thoracic part 
they do not meet; here the deficiency is made up by thin plates of variable size 
and form, embedded in a membrana transversa. Ventrally the rings are about 
one-half inch (ca. 1.5 cm.) wide, while dorsally they are wider and thinner. The 
first ring is attached to the cricoid cartilage by the crico-tracheal membrane, and is 
often fused dorsally with the second ring. Various irregularities, svich as partial 
bifurcation or partial or complete fusion of atljacent rings, are conmion. The 
arrangement in the terminal part is very irregular. The trachealis muscle (AI. 
trachealis) consists of unstriped fibers which stretch across the dorsal part of the 
tube. It is separated from the ends of the rings and the membrana transversa by 
a ciuantity of areolar tissue. When it contracts the caliber of the tube is diminished. 
The mucous membrane is pale normally, and presents numerous fine longitudinal 
folds, in which are bundles of elastic fibers. The epithelium is stratified columnar 
ciliated. Numerous tracheal glands (Glandulse tracheales) are present; they are 
tulDulo-alveolar and mixed in t\'pe. 

Vessels and Nerves. — The arteries are derived chiefly from the common 
carotid arteries, and the veins go mainly to the jugular veins. The lymph-vessels 
go to the cervical and mediastinal lymph glands. The nerves come from the vagus 
and sympathetic. 

THE BRONCHI 

The two bronchi, right and left (Bronchus dexter, sinister), are formed by the 
bifurcation of the trachea. Each passes backward and outward to the hilus of 
the corresponding lung. The right bronchus is a little larger and less oblique in 
direction than the left. They are related ventrally to the divisions of the pulmon- 
ary artery, and dorsally to the branches of the bronchial artery and the bronchial 
lymph glands. Their structure is similar to that of the trachea, but the cartilagi- 
nous framework consists chieflj' of plates instead of rings. 



THE THORACIC CAVITY 

The thoracic cavity (Cavum thoracis) is the secontl in point of size of the body 
cavities. In form it is somewhat like a truncated cone, much compressed laterally 
in its anterior part, and with the base cut off very obliquely. The dorsal wall 
or roof is formed by the thoracic vertebrae and the ligaments and muscles connected 
with them. The lateral walls are formed by the ribs and the intercostal muscles. 
The ventral wall or floor is formed by the sternum, the cartilages of the sternal 
ribs, and the muscles in connection therewith. It is about one-half as long as the 
dorsal wall. The posterior wall, formed by the diaphragm, is very oblique and is 
strongly convex. The anterior aperture or inlet (Apertura thoracis cranialis) is 
relatively small, and of narrow, oval form. It is bounded dorsally by the first 
thoracic vertebra and laterally by the first pair of ribs. It is occupied bj^ the longus 
colli muscles, the trachea, cesophagus, vessels, nerves, and lymph glands. 

A longitudinal septum, termed the mediastinum thoracis (Septum medias- 



626 BESPIRATORY SYSTEM OF THE HORSE 

tinale), extends from the aorsal wall to the ventral and posterior walls, and divides 
the cavity into two lateral chambers. Each of these chambers is lined by a serous 
membrane called the pleura, and is termed a pleural cavity (Cavum pleuree) . The 
mediastinum is, for the most part, not median in position, as might be inferred 
from its name; this is chiefly due to the fact that the largest organ contained in it, 
the heart, is placed more on the left side than on the right; consequently the right 
pleural cavity and lung are larger than the left. Practically all of the organs in 
the thorax are in the mediastinal space, with the exception of the lungs, the posterior 
vena cava, and the right phrenic nerve. The part in which the heart and the peri- 
cardium are situated, together with that dorsal to it, is usually called the middle 
mediastinal space (Cavum mediastinale medium); the parts before and behind 
this are termed respectively the anterior and posterior mediastinal spaces (Cavum 
mediastinale craniale, caudale). 



THE PLEURS: 

The pleurae are two serous membranes, right and left, which enclose on each 
side a pleural cavity (Cavum pleura?) . They line the walls of the thorax, form the 
lateral laminae of the mediastinum, and are reflected from the latter upon the lungs. 
We therefore distinguish parietal, mediastinal, and pulmonary or visceral parts of 
the pleurae. 

The parietal pleura (Pleura parietalis) is attached to the thoracic wall by the 
endothoracic fascia. On the lateral thoracic wall it is adherent to the ribs and 
intercostal muscles and is termed the costal pleura (Pleura costalis) . Behind it is 
closely attached to the diaphragm, forming the diaphragmatic pleura (Pleura 
diaphragmatica) . 

The mediastinal pleura (Pleura mediastinalis) covers the organs in the medi- 
astinal space and is in part in apposition with the opposite sac. Where this layer 
is adherent to the pericardium, it is distinguished as pericardiac pleura (Pleura 
pericardiaca).^ 

From the mediastinum each pleura is reflected upon the corresponding lung, 
which it covers, constituting the pulmonary or visceral pleura (Pleura pulmonalis). 
The reflection occurs around and behind the hilus of the lung, and is in great part 
direct, so that a portion of the mediastinal surface of each lung has no pleural 
covering. Behind the hilus of the lung a considerable triangular area is not covered 
by the pleura, the two lungs being attached to each other by a thin layer of con- 
nective tissue in this situation.- Posteriorly the reflection is not direct, so that 
there is a fold formed by the reflection of the pleura from the mediastinum and the 
diaphragm to the lung, behind the triangular area of adhesion just mentioned; it 
is seen when the base of the lung is dra\vn outward. This is the pulmonary liga- 
ment (Lig. pulmonale) ; it consists of two layers of pleura, between which there is 
elastic tissue, especially abundant in its posterior part. 

The right pleura forms a special sagittal fold about a nandbreaatn to the right 
of the median plane, which encloses the posterior vena cava in its upper edge; it is 
therefore called the fold of the vena cava (Plica venae cavae). It gives off a small 
accessory fold for the right phrenic nerve. Tlie fold arises from the thoracic floor 
and from the diaphragm l^elow the foramen venae cavae, and intervenes -between the 
intermediate lobe and the body of the right lung. It is delicate and lace-like. 

The posterior mediastinum is very delicate ventral to the oesophagus, and 

• The student should bear in mind that these terms are employed simply as a matter of 
convenience in description; all the parts of each pleural sac, though differently named, form a 
continuous whole. 

' Here the mediastinal pleura does not extend continuously from the dorsal to the ventral 
wall, but consists of dorsal and ventral parts. 



THE PLEURA 



527 



Dorso-scapular ligament 



Cartilage of scapula 



'amentum nucha: 



Trapezius 
Rhomboideus 




Longissimus dorsi 
Multifidus 
Serratus venlralis 

Longissimus 
costarum 
Levator costce 

Subscapularis 
ifrasjnnatus 



Teres major 

Delloideus 
Triceps 
(c. longum) 



Triceps 
{c. laterale) 

Curaco-brachiaUs 

Brachialis 
Pecloralis prof. 
(p. humeralis) 
Extensor carpi 
rndialis 
Biceps brachii 



Pecloralis profundus Pecloralis superJiciaLs 
{p. scapularis) (p. transversa) 

Fig. 469. — .Section of Thor.oc of Horse. 

The section is cut in an oblique direction corresponding with the .spine of the scapula. It passes through the fourth 
thoracic vertebra and a little more than an inch behind the shoulder joint. The pleural cavities, indicated by wide 
black lines, are exaggerated for the sake of clearness. 

1, Pleural cavities (number is placed in mediastinum) : 2, 2', lungs: 3, oesophagus; 4, trachea: 5, brachioceph-ilic 
trunk; 6, anterior vena cava; 7, thoracic duct; 8, 8', vagi; 9, left recurrent nerve; 10, 10', phrenic nerves; 11, internal 
thoracic vessels; 12, sympathetic trunk; 13, subcostal vessels; 14, external thoracic vessels; 15, brachial vein; 16, 
brachial artery; 17, radial nerve; 18, ulnar nerve; 19, musculo-cutaneous nerve; 20, median nerve; 21, subscapular 
vessels; a, m. longus colli; 6, m. rectus thoracis; c, m. transversus thoracis; d, m. intercostalis internus; ,S, sternum; 
H, humerus. Ventral to the trachea there are shown, but not marked on account of lack of space, two cardiac nerves 
and a mediastinal lymph gland. 



528 



RESPIRATORY SYSTEM OF THE HORSE 



Trapezius 



Rhomboideus 

Spintilis 

Multifidus 

Cartilage of scapula 

Longissimus dorsi 

Serratus dorsalis 
Levator costce 

intercost. ext. 
Longissimus costarnm 
Inlercostales 

Serratus ventrolis 

Latissimus dorsi 




Triceps (c. longuni) 



Pectoralis superficialis 
{p. transversa) 

Fig. 470. — Sectiox of Thor.vx of Horse. 

The section is cut in an oblique direction corresponding witli the spine of the scapula. It cuts the body of the 
seventh thoracic vertebrse and the seventh rib dorsally and the fourth rib and its cartilage ventrally. The pleural 
and pericardiac cavities, represented by wide black lines, are exaggerated for the sake of clearness. 

L, L', lungs; 1. aorta; 2, oesophagus; 3, thoracic duct; 4, vena azygos; 5, 5', bronchi; 6, bifurcation of pulmonary 
artery; 7, 7', right and left atria; S, right ventricle; 9, tricuspid valve; 10, origin of aorta; 11, right coronary artery; 
12, left coronary artery (circumflex branch) and satellite vein; 13, internal thoracic vessels; 14, external thoracic 
vessels; S, sternum; (7. ulna. The following structures are shown, but not marked on account of lack of space: The 
right vagus is on the cesophagus and ventral to the vena azygos. The phrenic nerves are on the upper part of the peri- 
carditun on each side. The sympathetic trunks are on each side of the body of the vertebra. The number 10 is placed 
on the ventricular septum. Bronchial lymph-glands are shown ventral to the oesophagus and the left bronchus. 



THE PLEURAE 



529 



Trapezius 



Rhoniboideus 

Longissimiis dorsi 
MuUifidus 
Dorsal vessels 



iilage of scapula 

Longissimiis 

costarum 

Latissimus 

dorsi 

Iniercostalis 

externus 




Phrenico-costal 
sinus 



Cidaneus 
External 
thoracic vessels 

ilidinia iihiloin- 



Anterior abdominal vessels 



Muscalo-phi 
vessels 
Transrersit.^ thoracis 



illlC 



Rectus abdominis 
Pectoralis profundus 
{p. hwneralis) 



Fig. i"l. — Cross-section of Body of Horse. 

The section is cut through the eighth thoracic vertebra and the anterior part of the xiphoid cartilage. It cuts the 
vertebral end of the eighth rib and a little more than half of the seventh rib. The flexures of the great colon and a small 
part of the Uver, which lay in the concavity of the diaphragm, have been removed. The dotted hnes indicate the con- 
tour of the bases of the lungs and the apex of the heart, which are concealed by the diaphragm. The pleural cavities, 
indicated bv wide black lines, are exaggerated for the sake of clearness. 

1 1' Lungs; 2, aorta: 3, oesophagus; 4, i' stem bronchi; 5, 5', pulmonary arteries; 6, 6', large pulmonary veins: 
7 posterior vena cava; 8, 8', phrenic nerves; 9, vena azygos; 10, falciform and round ligaments of liver; Imposition 
of apex of heart; 12 (placed on cut surface of sternal part of diaphragm), xiphoid cartilage. The sympathetic trunks 
(not marked) are shown on each side of the body of the vertebra. The oesophageal trunks of the vagi (not marked) are 
shown in relation to the oesophagus. The thoracic duct is ventral to the vena azygos. 



34 



530 RESPIRATORY SYSTEM OF THE HORSE 

usually appears fenestrated; when these apertures are present, lae two pleural 
cavities communicate with each other.^ 

The pleural sacs contain a clear serous fluid, the liquor pleurae ; in health there 
is only a sufficient amount to moisten the surface, but it acciunulates rapidly after 
death. 

It should be borne in mind that the pleural cavity is normally a capillary space between the 
parietal and visceral parts of the pleura, and contains a film of serous fluid. In illustrations it is 
necessary, for the sake of clearness, to exaggerate the space. 

The pleura resembles the peritoneum in structure and appearance. It is 
attached to the structures which it covers by subserous tissue, which is elastic and 
in some situations contains fat. In the case of the parietal pleura the subserous 
tissue is termed the endothoracic fascia. This lines the thoracic walls, but is 
practically absent over the tendinous center of the diaphragm. A strong layer 
descends from it in the mediastinum and blends with the fibrous part of the peri- 
cardium. The subserous tissue of the pulmonary pleura is continuous with the 
interstitial tissue of the lung. 

The pleura receives an abundant blood supply which is derived chiefly from 
the intercostal, internal thoracic, and bronchial arteries. Lymph vessels are very 
numerous in the pleura and subserous tissue; they go chiefly to the intercostal and 
mediastinal glands. 

The parietal pleura is reflected along three lines which are known as the lines of pleural re- 
flection; these may be termed vertebral, sternal, and diaphragmatic. The vertebral line of 
pleural reflection is that along which the costal pleura turns ventrally to form the mediastinal 
pleura; it extends along the longus colli and the bodies of the thoracic vertebra,' to the vertebral 
end of the last intercostal space, where it joins the \me of diaphragmatic reflection. The 
sternal line of pleural reflection is that along which the costal pleura is reflected dorsally 
to l)ecome the niciliaslinal plciu-a. Anteriorly the two lines are close together along the middle of 
the floor of the thorax, but furtlicr back they diverge to each side of the sternal attachment of the 
pericardium. The rcllcctiim is at an acute angle and the narrow angular recess of the pl(Miral cav- 
ity here is termed the costo-mediastinal sinus (Sinus costomediastinalis). The diaphragmatic 
line of pleural reflection is that along which the costal pleura passes from the lateral wall 
to the diaphragm. This line is important clinically, since it is, from the standpoint of physical 
diagnosis, the demarcation between the thoracic and abdominal cavities. It extends along the 
eighth and ninth costal cartilages, crosses the sternal end of the ninth rib, and passes backward and 
upward in a gentle curve and at a gradually increasing distance from the stenial ends of the ribs, 
so that its most posterior part is about the middle of the anterior border of the last rib ; this is the 
posterior limit of the pleural cavity. Here it turns medially and a little forward and ends at the 
vertebral end of the last intercostal space. This reflection is alsd at an acute angle and the costal 
and diaphragmatic pleura are in contact over an area of variable width aliuii!; this line. The nar- 
row angular recess of the pleiu'al cavity here is termed the phrenico-costal sinus (Sinus phren- 
icocostalis). 

The apex of each pleural sac (Cupula pleurae) lies at the anterior aperture of the thorax. 
On the right side it forms two culs-de-sac; one of these may extend forward more than an inch 
(ca. 3 cm.) beyond the first rib in contact with the deep face of the scalenus; the other is ventral 
to the anterior vena cava and may extend about an inch (ca. 2.5 cm.) beyond the first rib. The 
apex of the left pleura usually does not extend beyond the plane of the first rib. 



THE LUNGS 
The lungs, right and left (Pulmo dexter, sinister), occupy much the greater 
part of the thoracic cavity. They are accurately adapted to the walls of the 
cavity and the other organs contained therein. The two lungs are not alike in 
form or size, the right one being considerably larger than the left; the differ- 
ence is chiefly in width, in conformity with the projection of the heart, to the 
left. The lung is soft, spongy, and highly elastic. It crepitates when pressed 
between the finger and thumb, and floats in water. When the thoracic cavity of 
the unpreserved subject is opened, the lung collapses immediately to about one- 

^The apertures do not exist in the foetus, and are sometimes absent in the adult subject. 
Some of them are doubtless produced in dissection by the necessary disturbance of the parts. The 
character of the pleura here probably explains the clinical observation that in the horse fluid exu- 
date resulting from imilateral pleurisy is usually present in both pleural sacs in like amount. 



THE LUNGS 531 

third of its original size, and loses its proper form; this is due to its highly elastic 
character and the fact that the tension of the lung tissue caused by the air pressure 
in its cavities has been relieved by the external air pressure.' The color varies 
according to the amount of blood contained in the lung. During life the lung has a 
pink color, but in subjects which have been bled for dissection it is light gray or 
faintly tinged with red. In unbled subjects it is dark red ; the depth of color varies, 
and is often locally accentuated by gravitation of blood to the most dependent parts 
(hypostasis). The foetal lung, since it contains no air and has a relatively small 
blood-supply, differs from that of an animal which has breathed in the following 
respects: (1) It is much smaller; (2) it is firmer and does not crepitate; (3) it sinks 
in water; (4) it is pale gray in color. In form the lungs are like casts of the cavities 
in which they are situated. When well hardened in situ, their surfaces present 






d e r 






Apex 



Fig. 472. — Right Lung of Horse: Cost.^l Surface. 
Specimea hardened in filu. 

impressions and elevations corresponding exactly to the structures with which they 
are in contact. Each lung presents two surfaces, two borders, a base, and an apex. 

The costal surface (Facies costalis) is convex, and lies against the lateral 
thoracic wall, to which it is accurately adapted. 

The mediastinal surface (Facies mediastinalis) is much less extensive than the 
costal surface. It is moldetl on the mediastinum and its contents. It presents a 
large cavity adapted to the pericardium and heart; this is termed the cardiac 
impression (Impressio cardiaca), and is larger and deeper on the left lung than on 
the right. Above and behind this is the hilus of the limg (Hilus pulmonis), at which 
the bronchus, vessels, and nerves enter the lung; the bronchial lymph glands are 
also found here. Behind this the two lungs are adherent to each other over a 
triangular area. Above this there is a groove for the oesophagus, which is deepest 
on the left lung. A groove for the aorta (Sulcus aortis) curves upward and back- 
ward over the hilus, and passes backward near the dorsal border of the lung; the 

'No idea of the natural form and size of the kuig can be obtained from a specimen in this 
state, nor can an accurate conception be gained by examination of the soft inflated organ. The 
lungs should be hardened in situ for this purpose, and if the process has been successful they con- 
form in every detail to the structures with which they were in contact. 



532 



RESPIRATORY SYSTEM OF THE HORSE 



curved part of the groove for the aortic arch is absent on the right lung, on which 
there is a groove for the vena azygos. Anteriorly there are grooves for the trachea, 
the brachiocephalic trunk, the anterior vena cava, and other vessels. 



Dorsctl bonder 




Fig. 473. — Left Lung of Horse; Costal Sub 
Specimen bardened in situ. 

Pulmonnrji 

Grnnvefor artery Bronchus 

anterior c.d. \ ', Groove for vena azygos 

vena cava i\ i \ \ 

I ' \ MWaJW^ Dor-'sai' hofcf^er 

Croofe ^or '^'^^'^ 

Area of 

adhesion Jk 



Ligament of lung (cut) 




Pulmonary veins 



Line of reflection of pleura 



Fig. 474. — Right Lung of Horse; Mediastix.vl and Diaphragmatic Surfaces. 
Organ hardened in situ, c, d, Groove.s for deep cervical and dorsal veins. Arrows indicate canal for posterior 
vena cava between intermediate lobe and main part of lung. B.^■ an oversight the impression of the trachea is un- 
marked; it is dorsal to the groove for the vena cava. 



The dorsal border (Margo dorsalis) is long, thick, and rounded; it lies in the 
groove alongside of the bodies of the thoracic vertebrae. "^ 

1 In some cases this border is cut into by a fissure which partly marks off the apex from the 
body of the king. 



THE LUNGS 



533 



The ventral border (Margo ventralis) is thin and short ; it occupies the angular 
space between the mediastinum and the ventral parts of the sternal ribs (Recessus 
costo-mediastinalis). It presents, opposite to the heart, the cardiac notch (Incisura 
cardiaca). On the left lung this notch is opposite to the ribs from the third to tlie 
sixth, so that a considerable area of the pericardium here lies in direct contact with 
the chest-wall. On the right lung the notch is much smaller, and extends from the 
third rib to the fourth intercostal space. 

The left cardiac notch is usually quadrilateral; its highest part is about four to five inches 
(ca. 10-12 cm.) above the sternal ends of the fourth and fifth ribs. The right notch is usually- 
triangular; its apex is about three inches (ca. 7-8 cm.) above the level of the sternal end of the 
ribs at the third intercostal space. In some cases a fissure partially marks off the apex from the 
body of the lung. 

The base of the lung (Basis pulmonis) is oval in outline; its surface (Facies 



Ligament of lung {cut) 



Bronchial artery 
I Bronchus 
Pulmonary I i Pulmonary Vascular 
veins j j artery impression 

^''^<'<'^ /or aori/x ' I '',,.'■ 
oesophagus < . ,' ' / - 




lAne of reJlectio7i 
of pleura 



Fin. 475. — Left LrxG of Horse; Mediastinal and Diaphhagmatic Surfaces. 
Organ hardened in situ. Vascular impression for common dorso-cervico-vertebral ^ 



diaphragmatica) is deeply concave in adaptation to the thoracic surface of the 
diaphragm. Laterally and dorsally it is limited by a thin convex basal border 
(Margo basalis) which fits into the narrow recess (Sinus phrenico-costalis) between 
the diaphragm and the lateral chest-wall. The position of this border, of course, 
varies during respiration. In the deepest inspiration it may reach the bottom of 
this recess. 

In dissecting-room sulDJects the distance between the border and the diaphrag- 
matic line of reflection of the pleura increases from about two inches (ca. 5 cm.) at 
the seventh rib to aljout six or seven inches (ca. 16-18 cm.) at the fifteenth, and 
then decreases. The dorsal end of the base is usually at the vertebral end of the 
sixteenth intercostal space or seventeenth rib.^ 

The apex of the lung (Apex pulmonis) is prismatic, narrow, and flattened 
transversely. It is partially marked off from the rest of the limg by the cardiac 

1 The ventral and basal borders may be taken together under the term margo acutus. 



534 RESPIRATORY SYSTEM OF THE HORSE 

notch. It curves do^vn\vard, and is related deeply to the anterior mediastinum and 
the anterior part of the pericardium. 

The lungs of the horse are not divided into lobes by deep fissures, as is the case 
in most mammals. The left lung may be regarded as consisting of a chief part, 
the body of the lung (Corpus pulmonis), ancl the apex (Apex puhnonis). But 
the right lung has in addition an intermediate lobe (Lobus intermedius),^ which is 
se])arated from the body of the lung by a fissure which forms in its dorsal part a 
canal for the posterior vena cava and the right phrenic nerve, enclosed in a special 
fold of the right pleura. - 

The root of the lung (Radix pulmonis) is composed of the structures which 
enter or leave the lung at the hilus on the mediastinal surface. These are: (1) 
Tlie bronchus; (2) the pulmonary artery; (3) the pulmonary veins; (4) the bron- 
chial artery; (5) the pulmonary nerves; (6) the lymph vessels, which go to the 
bronchial lymph glands. The bronchus is situated dorsally, with the bronchial 
artery on its upper surface and the pulmonary artery immediately below it. The 
pulmonary veins lie chiefly below and behind the artery. 

The lobulation of the lungs is not very evident on account of the small amount 
of interlobular tissue. The lobules appear on the surface or on sections as irregular 
polygonal areas of different sizes. ^ 

Bronchial Branches. — Each bronchus at its entrance into the lung gives off a 
branch to the apex of the lung (Bronchus apicalis). It is then continued backward 
as the mam stem bronchus, parallel with the dorsal border of the lung, giving off 
branches (Rami bronchiales) in monopodic fashion; these branch similarly and 
reach all parts of the lung. The right bronchus gives off a special branch to the 
inteiTnediate lobe. The apical bronchus of the right lung is larger than that of 
the left lung. A large ventral bronchial branch is given off from each stem 
bronchus to the part of the lung which is homologous with the cardiac lobe of other 
animals. 

The structure of the larger bronchial tubes is, in general, similar to that of the 
trachea. Their walls contain irregular plates of cartilage instead of rings. There 
is a continuous layer of unstriped muscle, composed of circularly arranged bundles. 
The mucous membrane presents numerous longitudinal folds; it contains many 
elastic fillers, mucous glands, and lymph nodules, and is lined by ciliated columnar 
epithelium. As the tubes diminish in size the coats become thinner and the car- 
tilages smaller; in tubes about 1 mm. in diameter the cartilages and mucous glands 
are absent. 

By repeated branching the interlobular bronchi are fonned, and from these 
arise the lobular bronchioles. The latter enter a lobule and branch within it, 
forming the respiratory bronchioles (Bronchioli respiratorii) ; these give off the 
alveolar ducts (Ductuli alveolares), the walls of which are pouched out to form 
hemispherical diverticula, the alveoli or air-cells. 

A pulmonary lobule (Lobulus pulmonis), the unit of lung structure, is made up 
of a lobular bronchiole with its branches, and their air-cells, blood- and lymph- 
vessels, and nerves. Between the lobules is the interlobular tissue, which forms 
the supporting framework of the lung. 

Vessels and Nerves. — The branches of the pulmonary artery carry venous 
blood to the lungs. They accompany the bronchi, and form rich capillary plexuses 

' This is also commonly called the mediastmal lobe. 

''■ Some authors consider each lung to be divided into anterior and posterior lobes by the 
cardiac notch, so that the right lung would have three lobes and the left lung two lobes. Not 
rarely a fissure or notch in the dorsal border partially marks off the apex from the body of the lung, 
and in some cases there is a corresponding Hssinc in the \('iitial border. 

' In fcetal lung the lobulation is much more distinct. Pigmentation of the lung is sometimes 
seen in horses, and in such cases the pigment is deposited mainly m the mterlobular tissue, thus 
mapping out the lobules. 



THE THYROID GLAND 535 

on the walls of the alveoli. Here the l)loocl is arterialized, and is returned to the 
heart by the pulmonary veins. The bronchial arteries are relatively small vessels 
which carry arterial blood for the nutrition of the lungs. The branches of these 
arteries accompany the bronchial ramifications as far as the alveolar ducts, but 
do not extend to the alveoli. The oesophageal branches of the broncho-cesophageal 
and gastric arteries also supply pulmonary branches (in the horse) which reach the 
lung by way of the ligament of the latter. These branches vary much in size, and 
ramify chiefly in the subpleural tissue of the basal part of the lungs.' The lymph 
vessels are numerous, and are arranged in two sets. The superficial set forms 
close networks in and under the pleura, while the deep set accompanies the bronchi 
and puhnonary vessels. Most of them converge to the root of the lung and enter 
the bronchial lymph glands, but some go to the mediastinal lymph glands. The 
pulmonary nerves come from the vagus and sympathetic nerves. They enter at 
the hilus and supply branches to the bronchial arteries and the air-tubes. 



THE THYROID GLAND 

The thyroid gland (Glandula thyreoidea) is situated on the anterior part of the 
trachea, to which it is loosely attached. It is a very vascular ductless gland, and 
is firm in texture and dark red-bro^vn in color. It consists of two lateral lobes and 
a very narrow connecting isthmus (Figs. 3.32, 649). 

The lateral lobes (Lobus dexter, sinister) are situated on each side of the trachea 
near to or in contact with the larynx. Their position is indicated approximately 
by the angle of junction of the jugular and external maxillary veins. Each is oval 
in outline and is about as large as a plum of medium size. The superficial surface 
is convex and is covered by the cervical angle of the parotid gland and the sterno- 
cephalicus and omo-hyoideus. The deep surface is adapted to the trachea. About 
the lobe are the anterior cervical lymph glands. The anterior pole is large and 
rounded, while the posterior is smaller and often tapers to a tail-like process which 
is continuous with the isthmus. 

The isthmus (Isthmus gl. thyreoidese) extends across the ventral face of the 
trachea, coimecting the two lobes. It is usually extremely narrow in the adult 
horse and is often reduced in great part to a small strand of fibrous tissue. 

The lateral lobes are very variable in size and position, and are usually unsymmetrical. The 
average length is about two inches (ca. 5 cm.). The greatest height averages a little more than an 
inch (ca. 2.7 cm.), and the greatest width a little less than an inch (ca. 1..5-2 cm.). The average 
weight is about half an ounce (ca. 1.5 gm.). The right lobe is commonly in contact with the crico- 
pharyngeus or crico-thyroideus, but may be about a finger's breadth from the larynx. The left 
lobe may be an inch or more (ca. 4 cm.) from the larynx, but in some cases is in contact with it. 
The position varies considerably in the dorso-ventral direction also, irrespective of the ventral dis- 
placement noted m enlargement of the gland. The most common form is oval, with a smaller 
posterior pole which tapers to the isthmus. But the isthmus is sometimes comiected with the 
middle of the ventral border of one lobe or both, so that the two poles are about alike. Many ir- 
regularities may be observed. Cases occur in which a variable posterior process is comiected with 
the body of the gland by a sort of neck. A complete glandular isthmus is not rare, although it is 
usually very narrow and may easily escape notice; in quite exceptional cases it may be 6-8 mm. 
in width. Its connection with the lateral lobes and crossing of the trachea are quite variable. 
Most often it is connected with the posterior jioles and passes almost directly between the two. 
But it may run backward and cross much further liack; in one case (personal obser\'ation) the 
crossing was. at the space between the nin(h and tenth tracheal rings. In the foal the isthmus is 
relatively large and entirely glandular. In the ass and mule there is almost always a well-developed 
isthmus. Extending from it there is sometimes a narrow band of thyroid tissue which reaches to 
the body of the hyoid bone; this is the lobus pyramidalis. 

Structure. — The gland is enveloped by a thin fibro-elastic capsule, from which 
trabeculffi pass into the substance of the organ. The gland tissue is compact and 

' It must not be inferred from the necessarily brief accoimt here given that the two sets of 
vessels are quite distinct. On the contrary, competent observers state that numerous small 
branches of the bronchial arteries anastomose with pulmonary vessels. 



536 RESPIR.\TORY SYSTEM OF THE HORSE 

consists of lobules (Lobuli gl. thyreoideae), which are embedded in a stroma of 
strands of fibrous tissue. The stroma contains nmnerous vessels. The lobules 
consist of non-commimicating alveoli or follicles of varying form and size. The 
alveoli are lined by cubical or columnar epithelium, and contain a viscid colloid 
substance. 

Vessels and Nerves. — The arteries are relatively very large; there are usually 
two thyroid arteries, which arise from the carotid; their branches enter the gland 
chiefly at or near the ends and the dorsal border. The veins are also large; they 
go to the jugular vein; the largest one leaves the gland at its posterior pole. The 
lymph vessels go to the cervical lymph glands. The nerves are derived from the 
sympathetic system. 

Nodules of thyroid tissue of variable size, sometimes as large as a pea, may be 
found near the anterior extremity of the lateral lobes, on the course of the anterior 
thyroid artery or on the trachea, even at a considerable distance from the thyroid 
region. They are termed accessory thyroids (Glandulse thyreoidese accessorise). 

The parathyroids are small glandular bodies found in the thyroid region. 
The.y are paler and not so dense as the thyroid tissue, but often cannot be differen- 
tiated by their naked-eye appearance. In the horse there is usually only one on 
each side in the connective tissue over the dorsal border or anterior extremity of the 
lateral lobe of the thyroid. One may be embedded in the deep face of the lateral 
lobe of the thyroid. They resemljle in structure embryonic thyroid tissue. 



THE THYMUS GLAND 

The th3Tnus is a ductless gland which has a close resemblance to the IjTnphoid 
tissues. It is well developed only in late fcetal life and for a few months after birth. 
After this it undergoes rapid atrophy, fatty infiltration, and amyloid degeneration, 
so that in the adult it is usually represented by a thin remnant in the ventral part 
of the anterior mediastinum or has entirely disappeared. In the new-bom foal 
it is of a grayish-pink color, and consists of right and left lobes (Lobus dexter, 
sinister). The greater part of the gland is situated in the anterior mediastinum 
ventral to the trachea and large vessels, but the two lobes are continued into the 
neck by a chain of lobules which lie on the trachea along the course of the carotid 
artery, extending sometimes as far as the thyroid gland. ^ 

Structure. — The thymus is enclosed in a thin and loose fibro-elastic capsule, 
and consists of secondary lobules (Lobuli thymi), of varying shape and size, held to- 
gether by areolar tissue and fat, and coimected with a strand of comiective tissue 
termed the tractus centralis. These lobules are subdivided into polyhedral primary 
lobules, which are composed of lymphoid tissue, and present a dark, vascular cor- 
tex, and a lighter medulla that contains small masses of concentrically arranged, 
flattened cells; these are kno\\ni as concentric corpuscles. 

Vessels and Nerves. — The arteries are derived from the internal thoracic and 
common carotid. The nerves come from the sympathetic and vagus. 

1 The cervical part of the gland is very variable. The thoracic lobe of one side may have 
no cervical continuation; the other lobe may then give olT a single prolongation which bifurcates. 
The thoracic part in the new-born foal occupies most of the space which is later taken up by the 
apices of the lungs. Its two lobes are in (-(.til ad , :ni(l its deep surface is molded on the anterior 
part of the pericardium and the large vessels. In rxcipl idiial cases a considerable remnant of the 
thymus is present in adult or even old suli.ii'rl>'; this is usually true only of the thoracic part, but 
it "may extend into the neck a short distance; but a large lymph gland must not be mistaken for 
thymus. 



RESPIRATORY SYSTEM OF THE OX — THE NASAL CAVITY 



537 



RESPIRATORY SYSTEM OF THE OX 

THE NASAL CAVITY 

The nostrils (Fig. 379), situated on either side of the muzzle, are relatively 
small, and are much less dilatable than those of the horse. The alse are thick and 
finn. The superior commissure is narrow. There is no diverticulum nasi. The 
skin is smooth, bare, and moist, and there is no clear line of demarcation between 
it and the nasal mucosa. The opening of the naso-lacriiual duct is not visible, as 



Frontal eminence 



Great clhmo-lurbinate 



Dorsal turbinate 



Dorsalmeatus 
Middle meatus 



Ventral 
turbinate 




Ventral 
meatus 



Genio- 
hjjoidius 



Thyroid cartilage 



Fig. 476. — Sagittal Section of Head of Cow. 
I, Cerebral hemisphere: 3. lateral ventricle; 3. thalamus, .f, corpora quadrigemina; .5. optic chiasma; ff, pituitary 
body; 7. pons; S, medulla oblongata; 0, cerebellum; 10, spinal cord; 11, ventral straight muscles; 13, pharyngeal 
lymph gland; ij, arytenoid cartilage; /.(.epiglottis; iJ, cricoid cartilage; iS, vocal cord; 7 r, palatine sinus; iS, soft 
palate; 19, Eustachian opening; CI, C2, C3, first, second, and third cervical vertebrse: B.o., basioccipital; Sp., pre- 
sphenoid. 



it is on the lateral wall of the nostril, and is concealed by the cartilaginous pro- 
longation of the ventral turbinate. There are two parietal cartilages on either 
side, united by fibrous tissue. The dorsal cartilages are thin lamina^ which curve 
ventro-laterally from the dorsal margin of the septal cartilage; they are prolonga- 
tions of the nasal iDones, and carry the alar cartilages on their anterior extremities. 
The ventral pair are lateral continuations of the basal lamella of the ventral tur- 
Ijinates. They lie along the nasal processes of the premaxilla;; anteriorly they 
l)ecome thicker, turn a little upward, and each blends with the cartilaginous pro- 
longation of the upper coil of the ventral turbinate. The alar cartilages are of 



538 



RESPIRATORY SYSTEM OF THE OX 



peculiar form. The lamina is oblong, and curves ventro-laterally from the anterior 
extremity of the dorsal parietal cartilage, with which it is connected. The cornu 
springs from the lateral part of the lamina and curves dorso-laterally into the outer 
wing of the nostril ; it carries on its extremity a small transverse bar, thus having 
some resemblance to the fluke of an anchor. 

The nasal cavity is short, wide anteriorly, narrow behind. It is not com- 
pletely dividetl by the septum, which in its posterior third is separated from the 
floor of the cavity by an interval that increases from Vjefore backward (Figs. 140, 
141). The middle meatus is very narrow, and divides posteriorly into two branches; 
the upper division leads to the ethmoidal meatuses, and communicates with the 
frontal sinus and the cavity of the dorsal turbinate. Anterior to the division are 
communications with the upper cavity of the ventral turbinate and the maxillary 
sinus. The main facts in regard to the sinuses were stated in the Osteology. 



THE LARYNX 
The lar3mx is more compact than in the horse, and presents numerous differ- 
ential features. The cricoid cartilage is compressed laterally. The lamina is not 
distinctly marked off from the arch ; it slopes do\vnward and backward and has a 



Arytenoid Processus Lamina of Lateral lobe 
cartilage muscularis cricoid cartilage , thvroid 



Epiglottis 




Isthmits of 
thyroid 



Thyroid Laryngeal Arch of cricoid 
cartilage prominence cartilage 

Fig. 477. — Cartilages of Larynx and Part of Trachea of Ox; Left View. 

Outline of thyroid gland indicated by dotted line. 

1, Anterior cornu of tliyroid cartilage: 2. thyroid foramen; 3, ligament converting notch into foramen; 4, posterior 

cornu of thyroid cartilage; 5, capsule of thyro-arytenoid joint. 



large median ridge. The thyroid cartilage is complete ventrally, i. e., the laminse 
are united to form a long plate which is notched in front and behind; the laryngeal 
prominence is small and is situated posteriorly. The height and thickness of the 
cartilage increase from before backward. The posterior cornua are curved and are 
about an inch long; they form syndesmoses with the cricoid cartilage. The short 
anterior cornua unite similarly with the hyoid bone; near them there is a foramen 
or a notch on each side for the passage of the anterior laryngeal nerve. The epi- 
glottis is short, oval in outline, and its apex is rounded; its base rests on the thyro- 
hyoid membrane, to which it is rather loosely attached. The cuneiform cartilages 
are absent. The ar5rtenoid cartilages present only slight differences. The muscular 



THE LARYNX 



539 



process is well developed, and the vocal process is narrow and long. The vocal 
cords are short and project very little from the wall, so that the rima glottidis is 
witle; the vocal ligament is attached ventrally to the crico-thyroid membrane, it 
has the form of a half tube, open behind. The lateral ventricle is represented by a 
very shallow depression, and the saccule is absent. The thyro-arytenoideus muscle 




Fig. 478. — Aditus L.a.ryngis .\nd Adjacent Structures of Ox. 
The pharynx, soft palate, and origin of cesophagua have been cut along the dorsal median tine and reflected. 
1, Epiglottis: 2, aditus laryngis: 3, 3', apices of arytenoid cartilages; 4, posterior pillar of soft palate; 5, cut sur- 
face of soft palate; 6, pharynx; 7, limen oesophagi; 8, oesophagus; 9, trachea; 10, glosso-epiglottic space; 11, tonsil- 
lar sinus; 12, root of tongue; 13, vallate papiliEe; 14, dorsum linguee. 



is equivalent to the vocalis and ventricularis of the horse; it is fan-shaped, thick, 
and narrow dorsally; it is attached ventrally to the base of the epiglottis, the angle 
of the union of the thyroid lamin£B, and the crico-thyroid membrane. The hyo- 
epiglotticus muscle is large and bifid ; it arises from the small cornua and at their 
articulation with the body of the hyoid bone, and thus may take the place of the 
hyoideus transversus in its action on the small cornua. 



540 RESPIRATORY SYSTEM OF THE OX 



THE TRACHEA 

The trachea is shorter than that of the horse, the average length being about 
26 inches (ca. 65 cm.). Its cahber is relatively small, the width being about an 
inch and a half (ca. 4 cm.) and the height about two inches (ca. 5 cm.). The rings 
are smaller, and number about fifty. At the beginning of the tube their free ends 
are separated by a varj'ing interval, so that the tube is flattened and membranous 
dorsally; but further l^ack the ends are in apposition, so that they fonn a ridge 
dorsally. The trachea is adherent to the right lung from the second rib backward. 
The bifurcation is opposite the fifth rib, about the junction of its middle and ventral 
thirds. 

In the sheep the average length of the trachea is about nine or ten inches (ca. 
25 cm.) and its caliber a little less than an inch (ca. 2 cm.). 



THE BRONCHI 

There are three chief bronchi. The bronchus for the apical lobe of the right 
lung (Bronchus apicalis) is detached from the trachea opposite to the third rib, 
i. e., at a considerable distance anterior to the bifurcation. 



THE THORACIC CAVITY AND PLEURA 

The thoracic cavity is relatively small; it is especially short dorsally, and is 
diminished laterally by the mode of attachment of the diaphragm to the ribs {vide 
Myology). The endothoracic fascia is better developed than in the horse, and is 
distinctlj^ elastic. The pleura is also thick, and there are no perforations of the 
mediastinum. The pleural sacs are even more unequal in extent than in the horse, 
and the ventral part of the mediastinum is further to the left; m front of the peri- 
cardium it is for the most part in contact with the left wall of the chest. 

The diaphragmatic line of pleural reflection differs considerably from that of the horse in 
conformity with the difference in the costal attachment of the diaphragm. It begins over the 
space between the seventh and eighth costal cartilages, crosses the ventral end of the eighth rib, 
and extends in a very slight curve upward and backward, so that it crosses the twelfth rib a little 
above its middle and reaches to the last rib a short distance from its vertebral end. 

The pleura forms a cul-de-sac alongside of the body of the last thoracic vertebra. The right 
pleural sac extends forward on the deep face of the scalenus a short distance beyond the fii'st rib. 



THE LUNGS 

The difference in size between the two lungs is greater than in the horse, the 
right lung weighing about half as much again as the left one. The average weight 
of the lungs is about 73^ pounds (ca. 3 to 4 kg.) ; they form about j-i-n- of the body 
weight. They are divided into lobes by deep interlobar fissures (Incisurse inter- 
lobares). The left lung is divided into three lobes, named from before backward 
apical, cardiac, and diaphragmatic (Lobus apicalis, cartliacus, diaphragmaticus). 
The right lung may be r(>garded as having either four or five lobes. The apical 
lobe is much larger than that of the left hmg, and occupies the space in front of 
the pericardium, pushing the mediastinum against the left wall ; it is usually sub- 
divided into anterior anfl posterior parts by a deep fissure. The other lobes are 
the cardiac, diaphragmatic, and intermediate, the last resembling that of the horse.^ 

' It has been customary to consider the cardiac lobe to consist of two parts, as sho'mi in Fig. 
479. But the apical bronchus divides into two branches, the posterior of which goes to that 
division of the lung which has been regarded as belonging to the cardiac lobe; furthermore, these 
parts of the lung are sometimes fused. It therefore appears desirable to include both as apical 
lobe. 



THE LUNGS 



541 



The apical lolie of the right hing receives a special bronchus from the trachea oppo- 
site the third ril), and is adherent to the trachea from the second rib baclcward. 
The two lungs are not adherent to each other behind the root as in the horse, but 



hordei- 




Hardened in silu 



Fig. 479. — Right Lung of Ox; Costal Surf.\ce. 
■ the inscription "cardiac lobe" extends forward upon what J 
lobe. 




V iioriJJ «««», 



oy^e for Acr^a 

'Groove for OeSOpho^'^^ 



•w 




Fig. 480. — Right Ll'xg of Ox; Medi.\l \'iew. 
Hardened m s?7w. J, Left bronchus: 5, pulmonary veins; 3, pulmonary artery. Mediastinal lobe = inte 



are in contact with the oesophagus; above and lielow the latter the pleura is re- 
flected, as shown in Fig. 480. 

The interlobar fissures begin at the ventral margin of the lung and pass toward the root. 
Those of the left limg lie opposite to the fourth and sixth ribs. The diaphragmatic lobe is the 



542 



EESPIRATORY SYSTEM OF THE OX 



largest, and has the form of a three-sided pyramid with its base resting on the diaphragm. The 
cardiac lobe is prismatic and forms the posterior margin of the cardiac notch; its long axis corre- 
sponds to the fifth rib. The apical lobe of the left lung is small and pointed; its ventral margin 

Dorsal border 




Cardiac lobe 



Fig. 4S1. — Left Lung of Ox; Lateral Vie 
Arrows indicate interlobar fissures. 



Dorsal border 




Apical lobe 
Cardiac impression 



Diajtiiragi/ialic lobe 
and surface 



Fig. 482. — Left Lung of Om Meiuai, View. 
i, Stem broncliu.'s; i', bronchial branch for apical and cardiac lobes; ^.pulmonary artery; 5, 3, 5, pulmonary 
4, groove for aorta; o, groove for oesophagus. Arrows indicate interlobar fissures. 



lies on the pulmonary artery and the anterior aorta; below this the space in front of the heart 
is occupied by the apical lobe of the right lung. In some cases additional fissures partially sub- 
divide the apical lobe, and on the other hand the apical lobe of the right lung may be undivided. 



THE LUNGS 



543 



— Apical lobe 



Cardiac lobe 




Intermediate lobe 



Diaphragmatic lobe 

Posterior mediastinal lymph gland 

Fig. 483.— Lungs an-d Heart of Sheep; Ventral View. 
Specimen hardened in situ. Space between heart and lungs was occupied by pericardium and fat. 



Apical lobe 

\ 



J)or^ 



^'^-^^---^^ ^i^: 




~- Diaphragmatic surface 



Apex 
Cardiac notch 

Fig. 484. — Right Lung of Sheep; Mediastinal Aspect. 
1. B, Bronchus; P.a., pulmonary artery; P.v., pulmonary vein; I'.i-., posterior vena cava; L.i 
bronchial lymph gland. Mediastinal Iobe=intermediate lobe. 



544 RESPIRATORY SYSTEM OF THE OX 

On the left side the cardiac notch leaves the greater part of the pericardium in contact with the 
chest wall as far back as the fourth intercostal space. On the right side the lung commonly covers 
the pericardium, so that the latter has no contact with the lateral wall of the thorax. But in some 
cases (as in the annexed figures) there is a small cardiac notch at the ventral part of the third rib 
and intercostal space. In dissecting-room subjects the basal border usually begins at the space be- 
tween the fifth and sixth costal cartilages, crosses the ventral part of the sixth rib, and is then 
about parallel with the diaphragmatic line of pleural reflection. It crosses the ninth rib about 
its middle and ends at the vertebral end of the eleventh intercostal space. 

The lobulation is very distinct on account of the extremely large amount of 
interlobular tissue. 

In the sheep the lungs resemble those of the ox in lobation, but differ from 
them considerably in shape. They are relatively somewhat longer, and the basal 
border differs in conformity with the diaphragmatic line of pleural reflection. 
There is usually a small triangular cardiac notch on the right lung opposite to the 
■ventral part of the fourth and fifth ribs; its greatest height is about two inches 
(ca. 5 cm.). The left lung leaves the greater part of the pericardium uncovered as 
far back as the fifth intercostal space. The lobulation of the lung is much less 
distinct than in the ox. The pleural sacs form a cul-de-sac on each side of the first 
lumbar vertebra. 

In the sheep the diaphragmatic line of jilein-al reflection differs fi'om that of the ox. It ex- 
tends along the seventh and eighth costal cartilages, crosses the ninth cartilage close to the rib, 
the ventral ends of the tenth and eleventh ribs, the twelfth rib about an inch (ca. 2-3 cm.) from 
its ventral end, and the thirteenth rib about two mches (ca. 5 cm.) from its ventral end. It 
reaches as far back as the anterior border of the first lumbar transverse process. 

THE THYROID GLAND 

The thyroid gland is softer in texture than in the horse and is pale in color in 
the adult; in the calf it is dark red in color. The lateral lobes are irregularly 
triangular in outline and are more extensive and flatter than in the horse. In 
addition to their contact with the trachea they are related deeply to the oesophagus 
and the crico-pharyngeus muscle to a varying extent. The superficial face is 
related to the sterno-thyro-hyoideus, sterno-cephalicus, the carotid artery, internal 
jugular vein, and the vagus and sympathetic nerves. The isthmus is constantly 
present and glandular; it is band-like and is commonly a quarter to half an inch 
(ca. 0.5-1 cm.) in •^^'idth. 

The lateral lobes average about three inches or more (ca. 8 cm.) in length and about half an 
ounce (ca. 14-1.5 gm.) in weight. They are so soft and loose m texture that their true shape is 
seen only in specunens hardened in situ. In soft material they appear o\'al in outline. The 
isthmus may be connected with the ventral margin or the posterior end of the lateral lobes; it is 
relatively large in the calf, and is very evident on account of its dark color. 

In the sheep the thyroid gland is dark red in color. The lateral lobes have a 
long clliiJtical outline and lie on each side of the first six or seven rings of the trachea; 
they are two inches or more (ca. 5-6 cm.) in length and half an inch or more (ca. 
1.5 cm.) in height. They are connected by a flat glandular isthmus a quarter of 
an inch or more (ca. 6-8 mm.) in width; the isthmus is connected with the lateral 
lobe at or near the posterior end of the latter, and crosses the trachea about the fifth 
ring. 

Accessory thyroids may be found, and parathyroids also occur near the pos- 
terior extremity or on the deep surface of the lateral lobes of the thyroid. 



THE THYMUS GLAND 
The thymus is pale and distinctly lobulated. It is much larger in the calf 
than in the foal, weighing at five or six weeks about 15 to 25 ounces (ca. 425 to 600 
grams). At the period of its greatest development it occupies the greater part of 
the anterior mediastinal space, reaching back to the pericardium, pulmonary artery, 
and aortic arch. Its left face (covered by the mediastinal pleura) is in contact 



EESPIRATOEY SYSTEM OF THE PIG — THE NASAL CAVITY 545 

with the chest-wall and apical lobe of the left lung as far back as the thirti rib. 
Its right face is largely molded on the great vessels in front of the heart. The 
cervical part forms the l)ulk of the gland; it consists of right and left lobes which 
extend along the trachea anrl oesophagus from the thoracic inlet to the thyroid 
gland. The two lobes are large at the root of the neck, where they are in apposition 




FiQ. 485. — Thy-mub of Young Calf. 

a, Thymus (cervical part) : 6, trachea; c, isthmus of thyroid gland; d, laryngeal prominence; ?, apical lobe of right lung; 
;2, heart (left ventricle) ; 5, pulmonary artery ; 4i aorta; J, i', oesophagus: '>', m. iongus colli; 7, diaphragm. 

and cover the trachea, oesophagus, carotid arter}', and vago-sympathetic trunk. 
Further forward they gradually diminish in size and diverge to the sides of the 
trachea. They are related superficially to the sterno-cephalicus, sterno-thyro- 
hyoideus, and external jugular vein. It undergoes atrophy slowly and remnants 
of the thoracic part often remain even in advanced age. 



RESPIRATORY SYSTEM OF THE PIG 
THE NASAL CAVITY 

The nostrils are small, and are situated on the flat anterior surface of the 
rostrum or snout (Rostrum suis). The latter is a short cylindrical projection, 
with which the upper lip is fused, and is circumscribed by a prominent circular 
margin. The skin on the snout is thin and highly sensitive; it presents small 
pores, and scattered over it are fine short hairs. In the snout between the nostrils 
is the OS rostri, which is to be regarded as a special development of the extremity of 
the septum nasi in adaptation to the habit of burrowing or rooting. A plate of 
cartilage, representing the lamina of the alar cartilage of the horse, curves ventro- 
laterally from the dorsal part of the os rostri, and a pointed bar of cartilage curves 
upward from the lower part of the bone in the lateral wing of the nostril. The 
notch between the nasal bone and the premaxilla is closed in l)y parietal cartilages 
which resemble those of the ox. 

The nasal cavity (Fig. 180) is long and narrow. It is divided behind by the 
lamina transversalis into an upper olfactory part, which leads to the ethmoidal 
meatuses, and a lower respiratory part, which is a direct continuation of the ventral 
meatus. The posterior part of the septum is membranous. The turbinate bones 
resemble in general those of the ox. The dorsal meatus is exceedingly small. The 
middle meatus is a deep fissure between the two turbinates: it divides posteriorly 
35 



546 RESPIRATORY SYSTEM OF THE PIG 

into two branches : one of these extends upward and backward between the lateral 
mass of the ethmoid bone and the dorsal turbinate; the other widens and joins the 
ventral meatus. The opening l^etween the maxillary sinus and the middle meatus 
lies in a transverse plane through the last cheek teeth. The middle meatus is 
continuous with the space enclosed l:>y the dorsal part of the ventral turbinate and 
with the cavity of the dorsal turl.iinate. The dorsal division of the middle meatus 
presents several openings into the frontal sinus. The ventral meatus is relatively 
roomy; it communicates with the space enclosed by the lower coil of the ventral 
turbinate. The opening of the naso-lacrimal duct is in the posterior part of the 
ventral meatus. The incisive duct and the vomero-nasal organ resemble those of 
the ox. 

THE LARYNX 
The larynx is remarkable for its great length and mobility. The cartilages 
are more loosely attached to each other than in the other animals. The cricoid 
cartilage is thick and compressed laterally; its lamina is long and narrow; its 
arch is directed obliquely downward and backward. The thyroid cartilage is very 
long; its laminae are united ventrally and form a median ridge. The anterior 
cornua are absent, and no joints are formed with the hyoid bone. The posterior 
cornua are broad, bent inward, and articulate with the cricoid cartilage. The 
epiglottis is relatively very large, and is more closely attached to the hyoid bone 
than to the rest of the larynx. The middle part of its base is turned forward, and 
rests on the thyro-hyoid membrane; it is closely connected with the body of the 
hyoid bone by the hyo-epiglottic ligament and the strong hyo-epiglottic muscle.^ 
The apex of the arytenoid cartilage is very large, and is divided into two parts at 
its extremity; the medial part is fused with that of the opposite cartilage. There 
is a small interarytenoid cartilage in the transverse ligament. The rima glottidis 
is very narrow. The vocal cords are directed oljliquely downward and backward; 
and each is pierced by a long, slit-like opening, which leads into the large larjmgeal 
saccule. The vocal ligament is similarly divided into a larger anterior and a smaller 
posterior part. There is a middle ventricle near the base of the epiglottis. The 
thyro-arytenoid muscle is very strong and is undivided; it is equivalent (as in the 
ox) to the vocalis and ventricularis muscles of the horse. The arytenoideus trans- 
versus is very small. The crico-thyroid consists of two strata: the superficial 
layer corresponds to the muscle of the other animals; the deep part consists of 
transverse fibers. 

TRACHEA AND BRONCHI 
The trachea is about six to eight inches (ca. 15-20 cm.) long, and contains 
thirty-two to thirty-five rings, which overlap dorsally. It is slightly depressed 
dorsally, except the terminal part, which is circular in cross-section. A special 
bronchus is detached for the apical lobe of the right lung, as in the ox. In the 
right lung the stem-bronchus sends branches (one each) to the cardiac and inter- 
mediate lol^es and continues backward in the diaphragmatic lobe, in which it 
ramifies. In the left lung the stem-bronchus gives off a bronchus which divides 
into two branches for the anterior part of the lung (fused apical and cardiac lobes'), 
and continues backward in the diaphragmatic lobe. 

^ The arrangement here is one of the most striking features of the pig's lar>Tix. Tlie short 
and thick middle hyo-epiglottie ligament and the anterior part of the thyro-hyoid membrane are 
inelastic, wliilc tlic posterior part of the membrane is thin and elastic and allows the epiglottis 
to be separated by a considerable interval from the thyroid cartilage. Moreover, the borders of 
the epiglottis are comieeted with the thyroid cornua of the hyoid bone by lateral hyo-epiglottic 
ligaments. 



THE THORAX AND PLEURA — THE LUNGS 



547 



THE THORAX AND PLEURA 

The ribs are in general strongly curved in most of the improved breeds, so that 
the thorax is rounded. The pleural sacs extend forward to the first intercostal 
space. The diaphragmatic line of pleural reflection begins at or a little above the 
sternal end of the seventh rib, and extends in a gentle curve to about the middle of 
the last rib, along the medial face of which it continues. (When a fifteenth rib is 
present — a very common occurrence — it does not affect the arrangement of the 
pleura or diaphragm). 

Trachea (Esophagus 



Apical lobe 




. 4SG.— Lu.NGS A.ND Heart of Pig; Ventral View. 
L.i., Intermediate lobe of right lung: F. d., diaphragmatic surface of lungs; /, left brachial arterj'; S, brachio- 
cephalic artery ; 5, apex of heart; .}, pericardium (cut edge) ; 5, plica venae cavse; 5, posterior vena cava; : 
5, ventral oesophageal nerve trunk; 9, aorta. 



THE LUNGS 
The right lung has four lobes — apical, cardiac, diaphragmatic, and intermedi- 
ate. In some cases the apical lobe is ilivided by a fissure into two parts ; sometimes 
it is fused with the cardiac lobe. The left Ixmg may be regarded as having two or 
three lobes. The diaphragmatic lobe is clearly marked off by a fissure. The part 



5-18 RESPIRATORY SYSTEM OF THE DOG 

anterior to the fissure represents the apical and cardiac lobes, which are, however, 
separated only Ijy the cardiac notch, not by an interlobar fissure, as is usual in the 



Trachea 




Apical lobe 



Cardiac lobe Intermediate lobe 



Fig, 487. — Right Lung of Pig; Medial View. 
1, Left bronchus (cut off) ; ^, 2, pulmonary arteries; 3, 3, 3, pulmonary veins; 4, posterior vena cav.-!; o, groove for 
anterior vena cava; ff, groove for vena azygos; 7, groove for aorta; 5 (placed on groove for cesophagus), lines of pleural 
reflection. Arrows indicate interlobar fissures. 

right lung. The lobulation is distinct, but the interlobular septa are thinner than 
in the ox. 

THE THYROID GLAND 

The thjToid gland is large and is situated usually at a considerable distance 
from the larynx, but may be in contact with it. The lateral lobes are irregularlj^ 
triangular in outline, and are two inches or more (ca. 5-6 cm.) in length in a large 
adult. They are united to a considerable extent ventrally, so that an isthmus 
cannot be distinguished. The gland is related deeply to the sides and ventral face 
of the trachea, and is in contact dorsally with the oesophagus. The chief artery 
enters at the posterior extremity. 

THE THYMUS 

The thymus in young subjects is very large, extending to the larynx or even to 
the mandibular space. 



RESPIRATORY SYSTEM OF THE DOG 
THE NASAL CAVITY 
The nostrils are situated on the muzzle, with which the upper lip blends. They 
are shaped somewhat like a comma, with the broad part next to the septum and 
the narrow part directed backward and outward. The skin around the nostrils 
is bare, usually black, and in health moist and cool. The muzzle is marked by a 
median furrow (philtrum), or a deep fissure in some breeds. The cartilaginous 



THE NASAL CAVITY 



549 



framework is formed essentially by the septal cartilage antl the parietal cartilages 
which proceed from it. The septal cartilage projects beyond the premaxilla, and 




Fig. 488. — Sagittal Section of Head and Part of Ne 



porsal meatus 
Middle meatus 
V, '' Ventral meatus 




Fig. 489. — Key to Preceding Figure. 



is much thickened at its extremity; it gives off from its margins the two parietal 
cartilages, which curve laterally and toward each other. A grooved plate extends 



550 



RESPIRATORY SYSTEM OF THE DOG 



outward from the septal cartilage in the floor of the nostril, and another lamina 
supports the alar fold of the ventral turbinate bone; these may be termed accessory 
nasal cartilages (Cartilagines nasi accessorise). 

The length of the nasal cavity varies greatly in different breeds, correspond- 
ing, of course, to the length of the face. The cavity is roomy, but is very largely 
occupied by the turbinates and the lateral masses of the ethmoid bone. The 
middle meatus is short and narrow, and divides posteriorly into two branches: the 
upper branch leads to the ethmoidal meatuses; the lower branch joins the ventral 

meatus. The ventral meatus is very small in 
its middle part, owing to the great develop- 
ment here of the ventral turbinate. The 
posterior part of the nasal cavity is divided 
by the lamina transversalis into an upper olfac- 
tory part and a lower respiratory part. The 
sinuses have been described {vide Osteology). 



THE LARYNX 

The larynx is relatively short. The lamina 
of the cricoid cartilage is wide; the arch is 
grooved laterally. The laminae of the thyroid 
cartilage are high, but short; they unite ven- 
trally to form the body, on which there is an- 
teriorly a marked prominence, and posteriorly 
a deep notch. The oblique line on the lateral 
^^^^ surface of the lamina is prominent. There is 

'^f]<^^F^'^''^^^™^'' "^^ '^ V a rounded notch (Fissura thyreoidea) below the 
"'" ^ short anterior cornu for the passage of the an- 

terior laryngeal nerve. The posterior cornu is 
strong, and has a rounded surface for articula- 
tion with the cricoid cartilage. The arytenoid 
cartilages are relatively small, and have Ix'tween 
them a small interarytenoid cartilage. The 
epiglottis is quadrilateral; its lower part or 
stalk (petiolus) is narrow, and fits into the 
angle of the thyroid cartilage. The cimeiform 
cartilages (Cartilagines cuneiformes) are large 
and somewhat crescent shaped; they are not 
fused with the epiglottis. 

The false vocal cords extend from the 
cuneiform cartilages to the thyroid. The true 
vocal cords arc large and prominent. The 
large lateral ventricle is a long slit parallel with 

the anterior margin of the true vocal cord. The laryngeal saccule is extensive and 

lies lateral to both true and false vocal cords. 

The crico-thyroid muscle is thick. The hyo-epiglotticus is well developed, 

and is double at its hyoid attachment. The ventricularis or anterior part of the 

thyro-arytenoideus arises on the cuneiform cartilage. Hence Lesbre has suggested 

the name cuneo-arytenoideus for it. 




Fig. 490. — Aditus Lastngis and Related 

Structures of Dog. 
The pharynx and oesophagus have been cut 

along the mid-dorsal line and reflected. 

It Epiglottis; 2, 2, corniculate cartilages; 
S, S, arytenoid cartilages; 4^ glottis; 5, wall of 
pharynx; 6, cesophagus; 7, limen cesophagi; S, 
posterior pillar of soft palate; 5, median sulcus 
of tongue; 10, vallate papilla; 11. conical pa- 
pilite of root of tongue; 12, 12, tonsils (shown 
by opening up tonsillar sinus). 



THE TRACHEA AND BRONCHI 
The trachea is practically circular in cross-section at its ends, but the inter- 
vening part is very slightly flattened dorsally. It contains about forty to forty- 



THE LUNGS 



551 



five U-shaped rings; the ends of the rings do not meet dorsally, so that here the 
trachea has a membranous wall (Paries membranacea), and is composed of a layer 
of transverse smooth muscle-fibers outside of the rings, the fibrous membrane, and 
the mucous membrane. 

The stem-bronchi diverge at an obtuse angle, and each divides into two 
branches before entering the lung, but the ramification differs in the two lungs. 
In the right lung the anterior bronchus goes to the apical lobe, and the stem- 
bronchus gives off a branch to the cardiac lobe and another to the intermediate lobe. 
In the left lung the anterior bronchus divides into two branches for the apical and 
ardiac lobes. The anterior branch of the left bronchus crosses under the pul- 
monary artery. 

THE LUNGS 

The lungs differ in shape from those of the horse and ox in conformity with 
the shape of the thorax, which is relatively very wide in the dog ; the lateral thoracic 
walls are strongly curved, and the costal surface of the lungs is correspondingly 
convex.' 

The right lung is much (ca. 25 per cent.) larger than the left. It is divided 



Bursal border 




Cardiac notch 



Fig. 491. — Right Lung of Dog; Medial View. 
Z/. a., Apicallobe; I*, c, cardiac lobe; i. d., diaphragmatic lobe; L. i., intermediate lobe; i, stem-bronchus; 2,B', 
bronchi of apical lobe; 3, 3', divisions of pulmonary artery; 4-^. pulmonarj' veins; 5, groove for anterior vena cava; 
9, groove for vena azygos; 10, groove for oesophagus; 11, groove for trunk of vertebral, cervical, and dorsal veins; 12^ 
groove for internal thoracic vessels. 



into four lobes by deep fissures which extend to the root. The lobes are the apical, 
cardiac, diaphragmatic, and intermediate. The apical lobe extends considerably 
over the median plane in front of the pericardium. The intermediate lobe has the 
form of an irregular, three-sided pj'ramid, with its base against the diaphragm and 
its apex at the root; on its lateral face there is a deep groove which contains the 
posterior vena cava and right phrenic nerve, enclosed in a Special pleural fold. The 
cardiac impression of the right lung is much deeper than that of the left. The 

'The costal attachment of the diaphragm i.s lower than in the other animals, thus further 
increasing the capacity of the thorax (vide diaphragm). 



552 



RESPIRATORY SYSTEM OF THE DOG 



Apex 



Dorsal border 




Apical lobe 



Cardiac lobe 



Fig. 492. — Left Lung of Dog; Costal Surface. 
L. d., Diaphragmatic lobe. Arrows indicate interlobar fis; 



L d 



Diaphragmatic lobe 



Diaphragmolic lobe 




Cardiac lobe 
Cardiac lobe Apex of heart 

Fig. 493. — Diaphragmatic Surface of Lungs .vnd He.uit of Dog. 
1, Aorta; 2, oesophagus; 3, oesophageal nerve trunk; 4, posterior vena cava. 



THE THYROID GLAND THE THYMUS 553 

cardiac notch is triangular and allows the pericardium to come in contact with the 
lateral wall at the fourth and fifth interchonilral spaces. 

The left lung is divided into three lobes — apical, cardiac, and diaphragmatic. 
The cardiac impression is shallow, and a distinct cardiac notch is not jirosent, but 
the pericardium is in contact with the lateral wall along a narrow area at the ventral 
part of the fifth and sixth interchondral spaces. The apical lobe has a small, blunt- 
pointed apex which lies over the manubrium sterni. On account of the small 
amount of interlobular tissue the lobulation is not distinct. Pigmentation of the 
interlobular tissue is usual in dogs kept in town. 

Accessory fissures may partially subdivide some of the lobes; this is most common in re- 
gard to the apical lobe. When the lungs have been successfully hardened in situ, additional mark- 
ings are seen on the mediastinal surface. On the right Iimg there are: (1) A groove for the an- 
terior vena cava in front of the root; (2) a groove tor the vena azygos which curves upward and 
backward over the root; (3) a shallow groove for the aorta aljove the posterior part of the root; 
(i) a groove for the oesophagus behind the root; (.5) a groove for the internal thoracic vessels curv- 
ing do\\^lward and backward over the apex; (6) a groove for the right ])hrenic nerve in the upper 
part of the cardiac impression; (7) grooves for the dorso-cervicLd and vcrleliral veins running from 
the dorsal border to the groove for the vena cava. On the left hmg there are: (1) A well-marked 
groove for the aorta, which curves over the root and runs back just below the dorsal border; (2) 
a shallow groove for the oesophagus bcliind the root; (3) grooves on the apical lobe for the left 
brachial and brachiocephalic arteries; (4) grooves near the apex for the internal thoracic ves- 
sels; (5) a groove for the left phrenic nerve is more or less evident; it passes downward and back- 
ward over the middle of the apical lobe, then rmis backward over the cardiac and diaphragmatic 
lobes. 

The diaphragmatic line of pleural reflection extends along the lower part of the ninth costal 
cartilage, crosses the tenth cartilage a little (ca. 1-2 cm.) below the costo-chondral junction, and 
the eleventh rib at the costo-chondral junction; it then curves up to the last rib, just above its 
middle, and passes medially and backward to the second lumljar transverse process. In a good- 
sized dog (e. g., bull-terrier) the apex of the pleural sac extends about an inch (ca. 2.5 cm.) anterior 
to the plane of the first rib. 

THE THYROID GLAND 

The lateral lobes of the thyroid gland are long and narrow, and have a flat- 
tened, ellipsoidal form; they are situated on the lateral surfaces of the trachea near 
the larjaix, extending along the first six or seven rings (Fig. 434). The extremities, 
are small, the posterior one often being pointed. The isthmus is inconstant and 
variable; in large dogs it has the form of a glandular band which may be nearly 
half an inch (ca. 1 cm.) wide; in medium-sized dogs it is often absent, and in small 
dogs it is usually absent. Accessory thyroids are f requentlj' present ; three or four 
may be found on either side, as well as a metlian one near the hyoicl bone. 

The parathyroids, about the size of millet or hemp seed, are four in number 
usually. Two are situated on the deep face of the thyroid lobes, in which thej^ are 
often embedded ; the others are placed laterally near the anterior extremity of the 
thyroid. 

THE THYMUS 

The thymus is relatively small, and is situated almost entirely in the tliorax. 
The left lobe is much larger than the right, and extends back on the pericardium as 
far as the sixth rib at the time of its greatest size. According to Baum, the gland 
increases in size during the first two weeks after birth, and atrophies rapidly in the 
next two or three months. Traces of it are present at two or three years of age, 
and may be found even in old subjects. 



THE UROGENITAL SYSTEM 

The urogenital apparatus (Apparatus urogenitalis) includes two groups of 
organs, the urinary and the genital. The urinary organs elaborate and remove the 

chief excretory fluid, the urine. The geni- 
tal organs serve for the formation, develop- 
ment, and expulsion of the products of the 
reproductive glands. In the higher verte- 
brates the two apparatus are independent 
except at the terminal part, which consti- 
tutes a urogenital tract, and includes the 
vulva in the female and the greater part of 
the urethra in the male. 



THE URINARY ORGANS 

The urinary organs (Organa uropoiet- 
ica) are the kidneys, ureters, bladder, and 
urethra. The kidneys are the glands which 
secrete the urine; they are red-brown in 
color, and are situated against the dorsal 
wall of the abdomen, being in most ani- 
mals almost sjrmmetrically placed on either 
side of the spine. The ureters are tubes 
which convey the urine to the urinary 
bladder. The latter is an ovoid or piri- 
form sac, which is situated on the pelvic 
floor when empty or nearly so ; it is a reser- 
voir for the urine. The urine accumulates 
in the bladder and is then expelled through 
the urethra. 




Fig. 494. — General Dorsal View of Urinary 
Organs of Horse. 
/, Right kidnev; 1', left kidney; S, 2', ad- tttt- 

renal bodies; 3. 3', ureters; 4, urinary bladder; 4'. THE URINARY ORGANS OF THE 

anterior end of bladder with cicatricial remnant of T-TOl? ^T^ 

urachus; 4", urethra; 6, aorta; 6, 6, renal arteries; 

7, 7, external iliac arteries; S, 8, internal iliac ar- THE KIDNEYS 

teries; 9, 9, umbilical arteries. (After Leisering's 

Atlas.) Each kidney presents two surfaces, 

two borders, and two extremities or poles, 
but they differ so much in form and position as to require a separate description 
of each in these respects. 

The right kidney (Ren dexter) in outline resembles the heart on a playing 
card, or an equilateral triangle with the angles rounded off. It lies ventral to the 
upper ]5arts of the last two or three ribs and the first lumbar transverse process. 
The dorsal surface (Facies dorsalis) is strongly convex; it is 'related chiefly to the 
diaphragm, but also to a small extent posteriorly to the iliac fascia and psoas 



THE KIDNEYS 



555 



muscles. In well-hardened specimens, especially those from thin subjects, impres- 
sions of the last two ribs and the tip of the first lumbar transverse process are 
usually visible. 1 The ventral surface (Facies ventralis) is in general slightly con- 
cave, and is related to the liver, pancreas, caecum, and right adrenal; it either has 
no peritoneal covering, or only a narrow peritoneal area laterally.- The medial 
border (Margo medialis) is convex and rounded; it is related to the right adrenal 
and the posterior vena cava. It presents about its middle a deep notch, the renal 
hilus (Hilus renalis); this is bounded by rounded margins, and leads into a space 
termed the renal sinus (Sinus renalis). The vessels and nerves reach the kidney 
at the hilus, and the sinus contains the renal pelvis or dilated origin of the ureter. 
The lateral border (Margo lateralis) is rounded, and is thimier than the medial one. 







S^:^ 


-^ 


-^ f - 

C L.ir 

— _ 


a 




Oh 




^^"^^..^Z.227^ 






Fig. 495. — Diagram of Position and Dorsal Relations of Kidneys of Horse. 

Areas of direct relations are enclosed b.v continuous lines: parts of skeleton which overlie the kidneys are indicated by 

dotted lines. L.I. — L.IU, lumbar transverse processes. 



It consists of two parts, anterior and posterior, which meet at a lateral angle; the 
anterior part fits into the renal imjDression of the liver. The duodenum curves 
around the lateral border. The anterior extremity (Extremitas cranialis), thick 
and rounded, lies in the renal impression of the liver. The posterior extremity 
(Extremitas caudalis) is thinner and narrower. 

The left kidney (Ren sinister) is bean shaped. It is considerably longer and 
narrower than the right one, and is situated nearer the median plane and further 
back, so that the hilus of the left kidney is usually about opposite to the posterior 
extremity of the right one. It is usually ventral to the last rib and the first two 

' The dorsal surface, being largely in contact with the diaphragm, slopes downward in front; 
thus its anterior part is about three inches (ca. 6-8 cm.) ventral to the dorsal part of the seven- 
teenth rib. 

2 In exceptional cftses a considerable area — as much as the outer and posterior third — of the 
surface may have a peritoneal covering. In the new-bom foal a large part is so covered; this is 
apparently due to the small size of the ceecum and the small area of attachment of its base. 



556 



THE URINARY ORGANS OF THE HORSE 



or three lumbar transverse processes. The dorsal surface is convex, and is related 
to the left crus of the diaphragm, the iliac fascia and i^soas muscles, and the dorsal end 



Riyld adrenal 



Left adrinnl 




u;^^^ i^'f c 



Left ureter 



Fig. 496. — Kidxeys axd Adrenals of Horse; Porsal Vie\ 
Hardened in situ. Impression of seventeenth rib on right kidney is indicated by small i 
little further forward in this subject than is usual. 

Ureters 



The left kidney i 




Anterior mesenteric 
artery {stump) 



Renal arler 



Fig. 497. — Kidneys and Adrenals of Horse; Ventral View. 
Hardened in situ. Left renal vein (not marked) la seen curving round posterior end of left adrenal. 



of the spleen. The ventral surface is convex and irregular; the greater part of it is 
covered by the peritoneum. It is in relation with the origin of the small colon, the 
terminal part of the duodenum, the left adrenal, and the left extremity of the 



THE KIDNEYS 557 

pancreas. The medial border is longer, straighter, and thicker than that of the 
right kidney. It is rehited to the posterior aorta, the adrenal, and the ureter. Tlie 
lateral border is relatetl chiefly to the base of the spleen. The anterior extremity 
extends ahnost to the saccus csecus of the stomach; it is related to tlie left end of 
the pancreas and the splenic vessels. The posterior extremity is usually larger 
than the anterior one. 

The form of the left kidney is variable. In some cases its outline is similar to that, of the 
right kidney, but its ventral surface is convex and is often marked by several fuiTows which diverge 
from the hilus. In well-hardened specimens the thi-ee areas of the dorsal surface are often dis- 
tinct. The psoas area (Impressio muscularis) is flat, parallel with the medial border, and widens 
behind. The diaphragmatic area is small and convex; it is crescentic and is confined to the an- 
terior end. The lateral splenic area is somewhat flattened and is often so extensive and distinct 
as really to constitute a third surface as in Fig. 496. 

Fixation. — The kidneys are held in position chiefly by the pressure of adjacent 
organs and by the renal fascia. The latter is a special development of the sub- 



Renal cn-st 



Cortical substance 

Medullary substance 




Renal artery 



Ureter 



Fig. 49S. — Frontal CHorizostal) Section of Kidney of Horse. 

The renal vein is removed. .\ large accessory* renal artery entered the posterior pole. Sections of arteries in limiting 

layer between cortical and medullary substance are white in figure. 

peritoneal tissue, which splits into two layers to enclose the kidney, together with 
the perirenal fat, which is termed the capsula adiposa.^ On account of its relations 
with the liver, pancreas, and base of the ca?cum, the right kidney is much more 
strongly attached than the left one. It is, therefore, not surprising that the latter 
varies somewhat in position; its posterior extremity may be ventral to the third or 
fourth lumbar transverse process. The position of the right kidney, excluding its 
movements during respiration, seems to be very constant. 

Weight and Size. — The right kidney is usually one or two ounces heavier than 
the left. The average weight of the right kidney is about 23 to 24 ounces (ca. 
700 gm.); that of the left, about 22 to 2.3 ounces (ca. 670 gm.). The relation of 
the weight of both kidneys to the body-weight is about 1 : 300-350. In the new- 
born foal the kidney weighs about 6 ounces (ca. 170 gm.). 

' The amount of perirenal fat varies; in animals in good condition it may entirely conceal the 
kidneys; in such cases the impressions produced by contact of the kidney with contiguous struc- 
tures may be indistinct. 



558 



THE I'RINARY ORGANS OF THE HORSE 



Chauveau gives as an average 750 grams for the right kidney and 710 grams for the left. 
EUenberger and Baum (24 cases) give the right kidney as varying between 430 and 840 grams; 
and the left between 425 and 780; this is an average of 635 grams (about 22}'2 ounces) for the 
right kidney, and 602.5 grams (about 21 ' 2 oimces) for the left. They give the relation of the 
weight of both kidneys to the body-wciKlit ;is 1:255-344. In a Percheron mare weighing about 
2000 pounds the right kidney weighed 4 pounds 3 ounces, and the left one 4 pounds. In a horse 
of medium size the right kidney is about si.x inches (ca. 15 cm.) in length, about the same in width, 
and about two inches (ca. 5 cm.) thick. The left kidney is about seven inches (ca. IS em.) long, 
four to five inches (ca. 10 to 12 cm.) wide, and two to two and a half inches (ca. 5 to 6 cm.) thick. 

Structure. — The surface of the kidney is covered by a thin but strong fibrous 
capsule (Tunica fibrosa), which is in general easily stripped off the healthy kidney; 
it is continued into the renal sinus, where it is attached. Sections through the 
kidney show it to consist of an external cortical substance and an internal meduUarj^ 
substance. The cortical substance (Substantia corticalis) is red bro^vn in color 
and has a granular appearance. It is dotted over with minute dark points; these 
are the renal corpuscles (Corpuscula renis),' each consisting of the dilated origin of 
a uriniferous tubide (Capsula glomeruli), with an invaginated tuft of capillaries 
(Glomerulus) enclosed by it. The medullary substance (Substantia metluUaris) 




Renal crest Pelvis 



Renal Branches Ureter 
vein of renal artery 



Fig. 409. — Transverse Section of Right ICiDNEr of Horse Passing Through the Hilus. 
Posterior portion of organ hardened in sUu. Note curvature of dorsal surface. 



is more resistant and presents a distinct radial striation. Its central part is pale, 
but its periphery, the intermediate zone, is of a deep red color; in the latter are 
seen, at fairly regular intervals, sections of the relatively large arciform vessels, 
which are taken to represent the demarcation between the primitive lobes.^ Be- 
tween the vessels the medulla is prolonged somewhat toward the periphery, forming 
the bases of the renal pyramids (Pyramides renales). These are not very pro- 
nounced in the kidney of the horse, especially as the gland is not papillated. Be- 
tween the bases of the p>'ramiils processes of the cortex dip in toward the sinus, 
forming the renal columns (Cohminse renales).' The inner central part of the 
medulla forms a concave ridge which projects into the pelvis of the kidney. This 
projection is termed the renal crest; it presents nunterous small openings at which 
renal tubules open into the pelvis of the kidney, and hence the surface here is loiown 
as the area cribrosa. 

1 Also known as Malpighian corpuscles. 

^ The fcctal kidney is divided by furrows into a number of polygonal areas, each of which 
is the base of a pyramidal lobe or reniculus. These furrows usually disappear before or soon after 
birth in the foal, although traces of them are sometimes seen in the adult. 

' In the kidney of the horse the renal columns dip in between the pyramids very superficially 
as compared with the arrangement in the human kidney. Breuer states that the pyramids are 
40 to 64 in number, and are arranged in four rows. Only the middle ones are distinct. 



THE KIDNEYS 



559 



Examination with a pocket lens shows that the cortex is imperfectly divided 
into lobules (Lobuli corticales). Each lobule consists of an axial radiate part (Pars 
radiata), surrounded by a convoluted part (Pars convoluta). The former appear 
as ray-like prolongations from the liases of the pyramids (hence also termed medul- 
lary rays), and consist largely of narrow, straight or slightly flexuous tubules (limbs 
of the loops of Henle). The convoluted part is granular in appearance, and con- 
sists largely of the renal corpuscles and convoluted tubules. 

The renal pelvis (Pelvis renalis) is the dilated origin of the excretory duct. 
It lies in the sinus of the kidney, and it is funnel-shaped, liut flattened dorso-ven- 
trally. The renal crest^ (Crista renalis) projects into the outer part of the pelvis 
in the form of a horizontal ridge with a concave free edge. The tubules of the 
middle part of the medullary substance open on this crest into the pelvis. The 
tubules from each end of the kidney do not open into the pelvis proper (Recessus 
medius), but into two long, narrow diverticula (Recessus terminales), which pro- 
ceed from it toward the poles of the kidney. The wall of the pelvis consists of 
three layers. The external fibrous coat or advcntitia is continuous with the sup- 
porting tis.sue of the kidney. The muscular coat consists of longitudinal and 




Fig. 500. — Cast of Right Rena 

CESSES (C, C'), AND Or 

(After Dumont.) 




1. 501. — Cast of Left R 
(c, c'), AND Origin 
(After Dumont.) 



(a), Recesses 
{b) OF Horse. 



circular fibers. The mucous coat does not cover the renal crest nor is it continued 
into the diverticula of the pelvis. It has a yellowish tinge, and forms numerous 
folds. It contains compound tubular glands (Glandula pelvis renalis), which 
secrete the thick, viscid mucus always found in the pelvis.^ 

Renal Tubules. — The parenchyma or proper substance of the kidney is composed of the 
small renal or uriniferous tubules (Tubuli renales), which are very close together and have a 
complicated course. Each tubule begin.s m a thin-walled, spherical dilatation or capsule (Cap- 
sula glomeruli), which is invaginated to receive a tuft of looped capillaries termed a glomerulus; 
these two structures constitute a renal corpuscle; the corpuscles are visible as minute red or 
dark spots in the convoluted part of the cortex. Succeeding this is a short narrow neck, beyond 
which the tubule becomes wide and convoluted, forming the proximal convoluted tubule, and 
enters the radiate portion of the cortex. It then gradually narrows and enters the intermediate 
zone; becoming very narrow and nearly straight, it descends for a variable distance into the medul- 
lary substance, turns sharply upon itself, and returns to the cortex, forming thus the loop of Henle, 
with its descending and ascending limbs. In the convoluted part of the cortex it widens and 
becomes tortuous, constituting the distal convoluted tubule. The tubule then narrows, enters a 
medullary ray, and opens witli oilier tuliules into a straight collecting tubule; this passes axially 
through a pyramid, and unites with other collecting tubules to form the relatively large papillary 
ducts, which open into the renal pelvis. 

Stroma. — The interstitial tissue forms a reticulum throughout which supports the tubules 

1 The crest is the result of fusion of the papillae or apices of the pyramids in the embryo and 
is therefore also known as the papilla communis. 

- There are goblet cells in the epithelium of the pelvis which doubtless concur in the secretion 
of mucus. 



560 



THE VRINARY ORGANS OF THE HORSE 



and blood-vessels. It is very scanty in the cortex, much more abundant in the medulla, in which 
it increases in amount toward the pelvis. 

Vessels and Nerves. — The kidneys receive a large amount of blood through the 
renal arteries which come from the aorta. "^ Branches of these enter at the hilus and 
on tlie ventral surface of the gland, and reach the intermediate zone, where they 
form anastomotic arches (Arterite arciformes). From these arciform arteries 
branches pass into the cortex and medulla. The cortical branches (Arterise inter- 
lobulares) have in general a radial course between the cortical lobules, and give off 
short lateral branches, each of which ends as the afferent vessel (Vas afferens) of a 
renal corpuscle. The lilood is carried from the glomerulus by a smaller efferent 



Arched collecting 
tubule 
Straight collect- 
ing tubule 
Distal convo 
luted tubule 
Renal (Malpig- 
hian) corpuscle 
Proximal convo- 
luted tubule 
Loop of Hcnle 

Collecting tubule 



Artery of capsule 



Arteria arci- 
f or mis 



Large collecting 
tubule 



Papillary duct 




RAMMATic Scheme of Uriniferous Tubules and Blood-a'essels of Kidney. 
I part from the descriptions of Golubew (Bohm, Davidoff, and Huber). 



vessel, which breaks up immediately into capillaries which form networks around 
the tubules. The medullary branches descend in the pyramids, forming in them 
bimdles of straight twigs (Arteriolse rectae). The renal veins are large and thin- 
walled; they go to the posterior vena cava. In the superficial part of the cortex 
the veins form star-like figures (Vense stellatfe) by tiie convergence of several small 
radicles to a common trunk. The lymph-vessels form two networks, capsular or 
superficial, and parenchymatous or deep. On leaving the hilus they go to lymph 
glands in this vicinity which are known as the renal lymph glands. 

The nerves are derived from the renal plexus of the sympathetic, wliich en- 
laces the renal artery. 

1 The occurrence of accessory renal arteries is not at all rare. They may come from various 
branches of the aorta (e. g., posterior mesenteric, spermatic, circumflex iliac) and enter the posterior 
part of the gland. 



THE URETERS — THE URINARY BLADDER 561 



THE URETERS 

The ureter is the narrow part of the excretory duct of the kidney. Each 
begins at the renal pelvis and terminates at the bladder. It is about 3 3 to J^ inch 
(ca. 6 to 8 mm.) in diameter, and its average length is about 28 inches (ca. 70 cm.). 
The abdominal part (Pars abdominalis) of each ureter emerges ventrally from the 
hilus of the kidney, and curves backward and medially toward the lateral face of the 
posterior vena cava (right side) or the aorta (left side). They then pass almost 
straight backward in the subperitoneal tissue on the surface of the psoas minor, 
cross the external iliac vessels, and enter the pelvic cavity. The pelvic part (Pars 
pelvina) passes backward and a little ventrally on the lateral wall of the pelvic 
cavity, turns medially, and pierces the dorsal wall of the bladder near the neck. 
In the male the pelvic part enters the genital fold and crosses the ductus deferens. 
In the female the ureter is situated in most of its course in the dorsal part of the 
broad ligament of the uterus. 

The wall of the ureter is composed of three coats. The external fibrous coat 
(Tunica adventitia) contains many elastic fibers. The muscular coat consists of 
internal and external layers of longitudinal fibers, with a stratum of circular fibers 
between them. The mucous membrane is covered with transitional epithelium; 
glands (Cdandulffi mucosae ureteris) resembling those of the renal pelvis occur in the 
first three or four inches of the ureter. 

The blood-sujiply is derived from the renal and umbilical arteries. The nerves 
come from the solar and pelvic plexuses; many minute ganglia are present. 



THE URINARY BLADDER 

The urinary bladder (Vesica urinaria) (Figs. 366, 369, 370) differs in form, size, 
and position according to the amount of its contents. When empty and contracted, 
it is a dense, piriform mass, about the size of a fist, and lies on the ventral wall of 
the pelvic cavity at a variable distance behind the inlet. When moderately filled, 
it is ovoid in form, and extends a variable distance along the ventral abdominal wall. 
Its physiological capacity varies greatly, but may be estimated appro-ximately at 
about three or four quarts. 

The anterior rounded blind end is termed the vertex ;' on its middle is a mass 
of cicatricial tissue (Centrum verticis), a vestige of the urachus, which in thefcetus 
forms a tubular comiection between the bladder and the allantois. The middle 
part or body (Corpus vesicae) is rounded, and is somewhat flattened dorso-ventrally, 
except when distended. It presents two surfaces, dorsal and ventral, the former 
being the more strongly convex, especially in its posterior part in front of the en- 
trance of the ureters.- The posterior narrow extremity, the neck (Collum vesicae), 
joins the urethra. 

The relations of the bladder vary according to the degree of fulness of the 
organ, and also differ in important respects in the two sexes. The ventral stirface 
(Fades ventralis) lies on the ventral wall of the pelvis, and extends forward on the 
abdominal wall as the bladder fills. The dorsal surface (Facies dorsalis) in the male 
is related to the rectum, the genital fold, the terminal parts of the ductus 
deferentes, the vesiculse seminales, and the prostate; in the female it is in contact 
instead with the body of the uterus and the vagina. The vertex of the full bladder 
has variable relations with coils of the small intestine and small colon, and the pelvic 
flexure of the large colon. 

Fixation. — Displacement of the bladder is limited chiefly by three peritoneal 

' This is often termed the fundus by veterinarians, but is not the homologue of the fundus of 
the human bladder. 

- This would correspond to the fundus vesicie of man. 
36 



562 THE URINARY ORGANS OF THE HORSE 

folds, termed the middle and lateral ligaments (Figs. 352, 370). The middle liga- 
ment (Plica umbilicus media) is a median triangular fold, formed by the reflection 
of the peritoneum from the ventral surface of the bladder on to the ventral wall of 
the pelvis and abdomen. In the new-born animal it is extensive and reaches to the 
umbilicus; in the adult it is usually much reduced in length relatively. It contains 
elastic and muscular fibers in its posterior part. The lateral ligaments (Plicse um- 
bilicales laterales) stretch from the lateral aspects of the bladder to the lateral pelvic 
walls. Each contains in its free edge a round, firm band, the roimd ligament (Lig. 
teres vesicae) ; this is the remnant of the large fcetal umbilical artery, the lumen of 
which in the adult is very small. The retroperitoneal part of the bladder is attached 
to the surrounding parts by loose connective tissue, in which there is a quantity of 
fat. It is evident that the posterior part of the bladder has a definite fixed position, 
while its anterior part is movable. 

Structure. — The wall of the bladder consists of a partial peritoneal investment, 
the muscular coat, and the mucous lining. The serous coat (Tunica serosa) covers 
the greater part of the dorsal surface, from which it is reflected in the male to form 
the genital fold; in the female it passes on to the vagina, forming the vesico- 
genital pouch. Ventrally the peritoneum covers only the anterior half or less of 
the bladder, and is reflected posteriorly on to the pelvic floor. The muscular coat 
(Tunica muscularis) is relatively thin when the bladder is full. It is unstriped, pale, 
and not clearly divided into layers, but has rather a plexiform arrangement. Longi- 
tudinal fibers occur on the dorsal and ventral surfaces, but laterally they become 
oblique and decussate with each other. A distinctly circular arrangement is found 
at the neck, where the fibers form a sphincter vesicae. The mucous coat (Tunica 
mucosa) is pale and thin. It is in general attached by a highly elastic submucosa 
to the muscular coat, and forms numerous folds when the organ is empty and con- 
tracted. It is modified dorsally in the vicinity of the neck over a triangular area, 
termed the trigonum vesicae; the angles of this space lie at the orifices of the two 
ureters and the urethra, which are close together. Here the mucous membrane is 
closely attached and does not form folds. From each ureteral orifice (Orificiuin 
ureteris) a fold of mucous membrane (Plica ureterica) passes backwartl and inward, 
uniting with its fellow to form a median crest (Crista urethralis) in the first part of 
the urethra. The ureteral orifices are a little more than an inch (ca. 3 cm.) apart. 
The terminal part of the ureter, after piercing the muscular coat of the blaiUler, 
passes for a distance of about an inch (ca. 2 to 3 cm.) between the muscular and 
mucous coats before piercing the latter; this arrangement constitutes a valve which 
prevents absolutely the return of the urine from the bladder into the ureter. The 
internal urethral orifice (Orificium urethrae internum) lies at the apex of the tri- 
gonum, and is about an inch and a half (ca. 4 cm.) behind the ureteral orifices. The 
mucous membrane is covered with transitional epithelium like that of the ureter 
and renal pelvis. It contains lymph nodules. 

Vessels and Nerves. — The arteries are derived chiefly from the internal pudic, 
but branches also come from the ol^turator and umbilical arteries. The veins 
terminate chiefly in the internal pudic veins. They form plexuses posteriorly. 
The lymph-vessels form plexuses on both surfaces of the muscular coat. They 
go to the internal iliac and lumbar glands. The nerves are derived from the pelvic 
plexus (sympathetic and ventral branches of thirdand fourth sacral nerves). They 
form a plexus in the submucosa which presents microscopic ganglia. 

In the fcetus and new-bom animal the bladder is situated chiefly in the abdomen. It is 
long, narrow, and fusiform. Its abdominal end lies at the umbiUcus, through which it is con- 
tinued by the urachus to the extra-embryonic part of the allantois. The lateral ligaments also ex- 
tend to the umbilicus and each contains in its edge the large umbilical artery. As the pelvis in- 
creases in size and the large intestine grows, the bladder retracts into the pelvis and changes its 
form. 

The urethra will be described with the genital organs. 



THE ADRENAL BODIES 



563 



THE ADRENAL BODffiS 

The adrenal bodies or glands (Glandulte adrenales)^ are two small, flattened 
organs, which lie in contact witli the anterior part of the medial borrler of the 
kidneys (Figs. 496, 497). They are ductless. In the horse they are red-bro\vTi in 
color, about three and a half to four inches (ca. 9 to 10 cm.) long, one to one and a 
half inches (ca. 3 to 4 cm.) wddc, and about half an inch or more (ca. 1.5 cm.) in 
thickness. The weiglit varies from one to two ounces (ca. 28 to 56 gm.). 

The right adrenal body is related medially to the posterior vena cava, to which 
it is adherent. Its anterior part curves dorsally around the mecHal border of the 
right kidney. Its posterior part is flattened and is related ventrally to the pancreas 
and caecum, dorsally to the right renal vessels. The anterior extremity is con- 
cealed in the renal impression of the liver; the posterior is related to the ureter. 

The left adrenal body is a little shorter than the right one, and its extremities 
are rounded; it is usually curved, so that its medial border partly embraces the 
anterior mesenteric artery. Its dorsal surface is related 
to the kidney, the renal artery, the aorta, and the left 
cceliaco-mesenteric ganglion. The ventral surface is in 
relation -with the left extremity of the pancreas and the 
root of the great mesentery. The posterior extremity 
often curves inward behind the anterior mesenteric 
artery; it is related behind to the left renal vein. 

When hardened in situ the adrenals present several features 
not evident in the soft organs. The anterior pai't of the right 
adrenal is twisted dorso-laterally over the medial margin of the 
kidney, so that this part is prismatic and has three surfaces; of 
these, the concave lateral one is applied to the kidney, the dorsal 
one is related to the right cms of the diaphragm and the liver, 
and the medial one is in contact with the posterior vena cava. 
The anterior mesenteric artery is nearly always more or less en- 
larged as a result of verminous arteritis, and the form and degree 
of curvature of the left adrenal seem to vary in conformity with 
the condition of the artery. 

Structure. — The fibrous capsule adheres intimately 
to the surface of the organ. It contains elastic fibers, 
and in its deep part unstriped muscle-fibers. From it 
trabeculae pass radially into the substance, blending 
with the fine supporting reticulum. The parenchjrma 
consists of a cortical and a meduUaiy part. The cor- 
tical substance (Substantia corticalis) is red-broAvn in 

color, and is clearly distinguishable from the yellow medullary substance (Substantia 
medullaris) . A large central vein (Vena centralis) is visible on cross-sections. 

The cells of the cortex are arranged in chains of one or two rows. In the peripheral portion 
the cells are of high cylmdrical shape, and (he cliaius form connectmg loops; Giinther has pro- 
posed the name zona arcuata for this pari. iii>ii':i(l (if the usual teim zona glomerularis. More 
deeply the chains are distinctly palisade-like, and tliis region is called the zona fasciculata. Next 
to the medulla is the zona reticularis, in wliich the cliains form a network. The cells in these two 
zones are polygonal and contain a brown pigment. The cells of the medulla are arranged in 
irregular groups or form sheaths around the veins. They react to chromic salts by assuming a 
yellow or yellow-brown color, and are termed chromaffin cells; they share this peculiarity with 
certain cells of the sympathetic ganglia and paraganglia, with which they are probably related 
genetically. The alkaloid adrenalin appears to be formed in the medullary cells. 

Vessels and Nerves. — The adrenals receive a relatively large blood-supply 
through the adrenal arteries, which arise from the renal arteries or from the aorta 
directly. The veins terminate in the posterior vena cava and the left renal vein. 

'From the standpoint of comparative anatomy the term ".adrenal" is decidedly preferable 
to "suprarenal." 




Fig. 



Body 



.sec- 



Adrexal 

Horse; Horizo 

TION, Reduced. 

1, Capsule; 5, ^', cortical 
substance; 5, medullary substance: 
4, blood-vessel in section. (From 
Leisering's Atlas, reduced.) 



564 



URINARY ORGANS OF THE OX 



The lymph-vessels go to the renal lymph glands. The numerous nerves are derived 
from the sjaupathetic sj^stem through the solar and renal plexuses. The fibers 
form a rich interlacement, especially in the medullary substance. Ganglion cells 
are found chiefly in the medulla, but also occur in the deeper jjart of the cortex. 



URINARY ORGANS OF THE OX 

The kidneys are superficially divided into polygonal lobes by fissures of vari- 
able depth. The lobes vary in size, and are commonly about twenty in numljer. 
The fissures are filled with fat. 

The right kidney lias an elongated elliptical outline, and is flattened dorso- 
ventrally. It commonly lies ventral to the last rib and the first two or three lumbar 



External border 




Anterior extremity 



Ureter Renal artery 

Fig, 504.— Right Kidney o: 
Organ hardened in ditu. Fat baa been re 



i between lobes. 




Renal artery 



Fig. 505. — Frontal .Section of Kibnet of Ox. 
L, Lobes of cortes; P, papilla;; C, calyx major; c', calyces 



transverse processes, but its e.xtremities may be ventral to the first and fourth 
lumbar transverse processes. The dorsal surface is rounded, and is in contact 
chiefly with the sublumbar muscles. The ventral surface is less convex, antl is 
related to the liver, pancreas, duocienum, and colon. The hilus is situated on the 
anterior part of this surface, near the medial border. The medial Iwrder is 
nearly straight, and lies parallel witli the posterior vena cava. The lateral border 
is convex. The anterior extremity occupies the renal impression of the liver, and 
is capped by the adrenal body. 



rRINAKY ORGANS OF THE OX 565 

The left kidney occupies a remarkable position, and when hardened in situ 
differs strongly in form from the right one. When the rumen is full, it pushes the 
kidnej' backward and across the median plane, so that it is situated on the right 
side, behind, and at a lower level than, the right kidney. It then lies usually 
ventral to the third, fourth, and fifth lumbar vertebrae. When the rumen is not 
full, the left kidney may lie partly to the left of the median plane. It has three 
surfaces. The dorsal surface is convex, and presents on its antero-lateral part the 
hilus, which opens laterally. The ventral surface is related to the intestine. The 
third face is more or less flattened by contact with the rumen, and may be termed 
the ruminal surface. The anterior extremity is small, the posterior large and 
rounded.' 

The kidneys are embedded in a large amount of perirenal fat termed the 
capsula adiposa. The weight of a kidney of an ailult animal is about 20 to 25 ounces 
(ca. 600-700 gm.), the left one being usually an ounce or more the heavier. The 
two form about ^ per cent, of the body-weight. 

The right kidney measures about 8 or 9 inches (ea. 20-22.5 cm.) in length, 4 to 5 inches (ca. 
10-12 cm.) in width, and 23''2 to 3 inches (ca. 5-6 cm.) in thickness. The left kidney is one or 
two inches (ca. 2 to 5 cm.) shorter, but its posterior part is much thicker than the right one. 

Structure. — The hilus is equivalent to the hilus and sinus of the kidney of the 




Fig. 50G. — Cast of Origin of Ureter (a), Calyces Majores, and Calyces Minores (6) of Ox. (After Dumont.) 



horse; in the right kidney it is an extensive elliptical cavity; in the left one it is a 
deep fissure. The pelvis is alisent. The ureter begins at the junction of two wide, 
thin-walled tubes, the calyces majores; the anterior calyx is usuallj^ the larger. 
Each calyx major gives off a number of branches, and these divide into several 
funnel-shaped calyces minores, each of which embraces a renal papilla. The 
space not occupied by the calj'ces and vessels is filled with fat. 

On section through the kidney the renal pyramids are easily made out. The 
blunt apex of each pj^amid, the renal papilla (Papilla renalis), projects into a calyx 
minor. On each papilla are small orifices (Foramina papillaria) by which the 
papillary ducts (Ductus papillares) open into the calyx. The renal colmnns are 
much more distinct than in the horse. 

At the hilus the renal artery is dorsal, the vein in the middle, and the ureter 
ventral; a quantity of fat surrounds these structures in the hilus. 

' The above statements refer to the adult subject, and are based on investigations made on 
livmg subjects, and studies of frozen sections and material hardened in situ. In the new-bom 
calf the kidneys are almost symmetrically placed, but as the rumen grows it pushes the left kidney 
to the right and backward pari passu. It also usually causes a rotation of the kidney, so that the 
primary dorsal surface comes to lie almost in a sagittal plane. Further, the gland is bent so that 
the hilus is largely closed up and faces outward (to the right). In very fat subjects the three- 
sided appearance of the kidney may be absent, and about one-third or more may remain to the left 
of the median plane, even where the rumen is pretty well filled. 



566 



URINARY ORGANS OF THE OX 



The kidneys of the sheep are bean-shaped and smooth, without any superficial 
lobation. The soft organ is regularly elliptical in form, with convex dorsal and 
ventral surfaces and rounded extremities; its length is about 3 inches (ca. 7.5 cm.), 
its width about 2 inches (ca. 5 cm.), and its thickness a little more than 1 inch (ca. 
3 cm.). They arc embedded in fat normally. In position they resemble those of 
the ox, except that the right one is usually a little further back, and lies under the 
first three lumbar transverse processes.' The average weight of each is about four 
ounces. The hilus is in the middle of the medial border. There is a renal crest or 
common papilla formed by the fusion of twelve to sixteen pyramids. 

The ureters are, in general, like those of the horse, except in regard to the 
first part of the left one, which has a peculiar course, in conformity with the remark- 
able position of the kidney. It begins at the ventral part of the hilus (which faces 





-Right Kidney of Sheep; Ventra 
V.V., Branches of renal vein. 



Fig. 508. — Kidney of Sheep; Horizontal Section. 
1, Cortical substance; ^, medullary substance; 5, 
renal crest; 4. renal pelvis; 5, ureter. (From Leisering'a 
Atlas, reduced.) 



toward the right), curves over the lateral aspect of the kidney to its dorsal surface, 
crosses the median plane, and runs backward on the left side. 

The bladder is longer and narrower than that of the horse, and extends further 
forward on the abdominal floor. The peritoneal coat extends backward further 
than in the horse. 



THE ADRENAL BODIES 
The right adrenal lies against the medial part of the anterior pole of the right 
kidney. When hardened in situ, it is pyramidal in form. Its medial surface is 
flattened and is in contact with the right crus of the diaphragm. The lateral sur- 
face is convex and lies in the renal impression of the liver. The ventral surface is 
grooved for the posterior vena cava; on this surface a relatively large vein emerges 
near the apex. The base is concave and rests obliquely against the anterior pole 
of the kidney. The apex fits into the angle between the posterior vena cava and 

1 Wlien the rumen is full, the left kidney (which is attached by a short mesentery) usually 
lies entirely to the right of the median plane, and is ventral to the third, fourth, and fifth lumbar 
transverse processes. The primitive dorsal surface has become ventro-medial, and is somewhat 
flattened by contact with the rumen. 



URINARY ORGANS OF THE PIG 567 

the dorsal border of the hver. The left adrenal hes on the medial face of the 
posterior vena cava, just behind the anterior mesenteric artery, and is therefore 
practically median in position. It is flattened, and irregularly triangular or heart- 
shaped in outline. Its left face is related to the dorsal sac of the rumen. Its right 
face is related to the vena cava, and presents a large emergent vein. The posterior 
border or base is deeply notched. The left adrenal does not migrate with the kid- 
ney, but retains its primitive position; it lies usually two or three inches (ca. 5-8 
cm.) in front of a transverse plane through the anterior pole of the left kidney. 

The adrenals of the sheep are both bean-shaped. The right one lies along 
the anterior part of the medial border of the kidney, at the angle of the junction of 
the right renal vein antl the posterior vena cava. It is a little over an inch (ca. 

Posterior pole 

Groom for vena cava 





Anterior pole 



Anterior pole 



Fig, 509.— Left Adhenal of Ox; Ventral View. Fig. 510.— Right Adrenal of Ox 

Hardened in situ. Hardened in situ. 

3 cm.) long, and about half as wide. The left adrenal is usually longer, and is 
flatter and somewhat bent. It lies across the left renal vein, to which it is at- 
tached; it is not in contact with the kidnej^, from which it may be separated by a 
distance of nearly two inches (ca. 4 cm.). 



URINARY ORGANS OF THE PIG 

The kidneys are smooth and bean-shaped; they are more flattened dorso- 
ventrally, more elongated, and smaller at the extremities than those of the clog. 
The length is about twice the width. They are usually almost symmetrically placed 
ventral to the transverse processes of the first four lumbar vertebrae, but the left 
kidney is often a little further forward than the right one. The lateral border lies 
against the flank parallel with the edge of the longissimus muscle. The posterior 
extremity is usually about midway between the last rib and the tuber coxse. The 
anterior extremity of the right kidney has no contact with the liver. 

Variations in position are not rare, and involve the left kidney oftener than the right; the 
former has been found near the pelvic inlet. When a fifteenth rili is present the anterior end of 
the kidney is usually ventral to it. The right kidney is usually separated from the liver by an 
interval of an inch or more. Absence of the left kidney has beeii recorded. 



568 



URINARY ORGANS OF THE PIG 




Fill. .",11.— KiDNKTS OF Pig in silu; Ventral View 
C.a., Hepatic artery; M,a., gastro-splenic artery. 




Cortical sxihstance 
/ 



Medullary substance 



Papillae 



Calyces minores 



Fig. 512. — Frontal Section of Kidney of Pig. 



URINARY ORGANS OF THE DOG 569 

The weight of the kidney of an adult pig is about seven to nine ounces (200 to 
250 grams). The ratio of their combined weight to that of the body is about 
1 : 150-200. The length in an adult of good size is about five inches (ca. 12.5 cm.) 
and the greatest width about two and a half inches (ca. 6-6.5 cm.). 

Structure. — The hilus is about in the middle of the medial border. The pelvis 
is funnel-shaped, and divides into two calyces majores, which pass in a curve for- 
ward and backward respectively, and give off some eight to twelve short calyces 
minores; each of the latter contains a papilla. Some papillae are narrow and coni- 
cal, and correspond to a single pyramid; others are wide and flattened, and result 
from the fusion of two or more pyramids; some project directly through the wall 
of the renal pelvis without the formation of a calyx. The renal pyramids are dis- 
tinct, but it is apparent that some are compound, i. e., formed by fusion of primi- 
tively separate pyramids. The renal vessels enter the ventral part of the hilus, 
and the ureter leaves it dorsally. 

The adrenals are long and narrow. Each lies along the medial bonier of the 
corresponding kidney from the hilus forward ; they are in contact metlially with the 
crus of the diaphragm and the posterior vena cava. 

The only special features in regard to the ureter are that it is at first relatively 
wide and gradually diminishes in caliter, and that it is slightly flexuous. 

The bladder is relatively very large; when full, it lies chiefly in the abdominal 
cavity. The dorsal surface is almost completely covered with peritoneum, l)ut 
the serous covering does not extend so far back ventrally. 



URINARY ORGANS OF THE DOG 

The kidneys (Fig. 624) are relativel.v large, forming about xttt to -j-^o- of the 
body-weight; the weight of the kidney of a medium-sized dog is about two ounces 
(ca. 50 to 60 grams). They are both bean-shaped, thick dorso-ventrally, with a 
rountled ventral surface and a less convex dorsal surface; the surfaces are smooth. 

The right kidney is not subject to much variation in position; it is situated 
usually opposite to the bodies of the first three lumbar vertebrae, but may be as far 
forward as the last thoracic. Its anterior half or more lies in the deep renal im- 
pression of the liver; its posterior part is related to the sublunibar muscles dorsally, 
and the right branch of the pancreas and duodenum ventrally. 

The left kidney is subject to some variation in position; this is due to the fact 
that it is loosely attached by the peritoneum, and is affected by the degree of ful- 
ness of the stomach. When the stomach is nearly empty, the kidney usually 
corresponds to the bodies of the second, third, and fourth lumbar vertebrae, so that 
its anterior pole is opposite to the hilus of the right kidney; exceptionally the 
anterior pole may be opposite the posterior entl of the first lumbar vertebra. When 
the stomach is full, the left kidney is usually the length of one vertebra further back, 
so that its anterior pole may be opposite the posterior pole of the right kidney. 
The dorsal surface is related to the sublumbar muscles. The ventral surface is in 
contact wth the left part of the colon. The lateral border is related to the spleen 
antl the flank. The anterior extremity touches the stomach and the left extremity 
of the pancreas. 

The lateral border of the left kidney usually has considerable contact with the flank, and 
hence it may be palpated more or less distinctly in the living animal, about half-way between the 
last rill and the crest of the ilium. But in some cases the spleen assumes an almost longitudinal 
direction, thus intervening between the kidney and the flank. 

Structure. — The hilus is in the middle of the medial border and is relatively 



570 URINARY ORGANS OF THE DOG 

wide. Cortex, limiting zone, and medulla are clearly defined. On frontal sections 
it is seen that the medullary substance forms a horizontal renal crest like that of 
the horse, but wdth the important difference that curved ridges proceed dorsally 
and ventrally from the crest somewhat like buttresses. Sections above or below 
the renal crest often cut these ridges in such a manner as to give the appearance 
of conical papillae, and thus tend strongly to produce a false impression. The 
pelvis is adapted to this arrangement of the medullary substance. It encloses a 
central cavity into which the renal crest projects, and is prolonged outward be- 
tween the ridges, forming cavities for the latter, thus simulating the appearance 
of calyces which do not exist. 

The ureters present no special features. 

The bladder, when full, is abdominal in position, the neck lying at the anterior 
border of the pubic bones. It is relatively large, and when distended, the vertex 
may reach to the umbilicus. When empty and contracted, it is usually entirely in 
the pelvic cavity. It has a practically complete peritoneal coat. 



THE ADRENALS 
The right adrenal lies between the anterior part of the medial border of the kid- 
ney and the posterior vena cava. It is somewhat prismatic, and is pointed at 
either end. The left adrenal lies along the posterior aorta, from the renal vein 
forward, but is not in contact with the kidney. It is elongated and flattened dorso- 
ventrally. (There is a furrow on the ventral surface for the phrenico-abdominal 
vein which crosses it; the part in front of this furrow is discoid, and may be taken 
for the entire organ in a fat subject.) The cortex is pale yellow in color, the me- 
dulla dark brown. 



THE MALE GENITAL ORGANS 

The male genital organs (Organa genitalia masculina) are: (1) The two 
testicles, the essential repr(j(luctive glands, with their coverings and appendages; 
(2) the ductus deferentes, the ducts of the testicles; (3) the vesiculae seminales; 
(4) the prostate, a musculo-glandular organ; (5) the two bulbo-urethral (or Cow- 
per's) glands; (6) the male urethra, a canal which transmits the generative and 
urinary secretions; (7) tlie penis, the male copulatory organ. The vesiculse 
seminales, the prostate, and the bulbo-urethral glands discharge their secretions 
into the urethra, where they mix with the fluid secreted by the testicles; hence they 
are often termed the accessorv sexual glands. 



GENITAL ORGANS OF THE STALLION 

THE TESTICLES 

The testicles (Testes) are situated in the inguinal region, enclosed in a divertic- 
ulum of the abdomen termed the scrotum. Their long axes are nearly longitu- 
dinal. ^ They are ovoid in form, but considerably compressed from side to side. 
Each presents two surfaces, two borders, and two extremities. The medial and 
lateral surfaces (Facies medialis, lateralis) are convex and smooth; the former is 
somewhat flattened by contact with the septum scroti. The free border (jSlargo 
liber) is ventral and is convex. The attached or epididymal border (Margo epi- 
didymidis) is dorsal; it is nearly straight, and is the one l)y wliich the gland is 
suspended in the scrotum by the spermatic cord ; the epididymis is attached to this 
border and overlies it laterally. The anterior and posterior extremities (Extremitas 
capitata, caudalis) are rounded. 

At, the anterior extremity there is often a sessile or pedunculated sac which contains a clear 
fluid; this is the appendix testis, from which a thread-like process extends backward toward 
the ductus deferens. It is regarded as a remnant of the Mtillerian duct of the embryo. 

A testicle of average size of an adult stallion is about four or five inches (ca. 
10 to 12 cm.) long, two and a half to three inches (ca. 6 to 7 cm.) high, and two 
inches (ca. 5 cm.) wide; it weighs about eight to ten ounces (ca. 225-300 grams). 
They vary much in size in different subjects, and are commonly of unequal size, 
the left one being more often the larger. 

The epididymis is adherent to the attached border of the testicle, and overlaps 
somewhat the lateral surface. Its anterior enlarged end is termed the head (Caput 
epididymidis) ; and its posterior, slightly enlarged end is the tail (Cauda epididy- 
midis); the intermediate narrow part is the body (Corpus epididymidis). The 
head is closely connected with the testicle by the efferent ducts of the latter, by 
connective tissue, and by the serous membrane. The body is less closely attached 
by the serous covering, which forms laterally a pocket beneath the epiditlymis 
termed the sinus epididymidis. The tail is continued by the ductus deferens ; it is 
attached to the posterior extremity of the testicle by a short ligament (Lig. epididy- 
midis), which is formed by a thick fold of the tunica vaginalis and contains smooth 
muscle-fibers. 

' When the testicle is drawn up or has not completed its descent into the scrotum, its long 
axis is almost vertical. 

571 



Oil GENITAL ORGAN'S OF THE STALLION 

Structure of the Testicle and Epididymis. — The greater part of tlie surface 
of the testicle is covered liy a serous memlsrane, the tunica vaginalis propria, which 
is the visceral layer of the serous envelop of the cord and testicle; this is reflected 
from the attached border of the gland, leaving an uncovered area at which the 
vessels and nerves in the spermatic cord reach the testicle. ^ Beneath this serous 
covering is the tunica albuginea, a strong capsule composed of dense white fibrous 
tissue and unstriped muscle-fibers. When the tunic is cut, the gland substance, 
which is soft and reddish gray in color, protrudes. From the attached border and 
from the deep face of the tunica albuginea trabeculse and septa of connective tissue 




"'^ MUfcy 



Fig. 513. — Inguinal Region of Staluon, with Testicles Exposed. 
a, a'. Testicles: 6, scrotum, opened and reflected: c, tunica vaginalis communis, opened and reflected: d, reflection 
of tunica vaginalis enclosing scrotal ligament: f, tunica vaginalis propria (mesorchium) : /, ductus deferens: g, g', tail 
of epididymis: h^ body of same; i, head of same: k, sinus epididymidis: /, spermatic vessels showing through tunica 
vaginalis propria: m, spermatic artery; ji, prepuce; n', raph^; o, preputial orifice. (After EUenberger-Baum, Top. 
Anat. d. Pferdes.) 



and unstriped muscle (Septula testis) pass into the gland and sulidividc the 
parenchyma into lobules (Lobuli testis). The larger trabeculse radiate from the 
attached border into the central part of the gland. 

A distinct mediastinum testis, such as is present in man and many animals, does not exist in 
the horse. The trabecule and interlobular septa form a network which shows no special conden- 
sation in any part of the gland. In correlation with this is the absence of a rete testis, formed by 
the anastomosis of the semmiferous tubules in the mediastinum. 

The spaces imperfectly marked ofT by the septa contain the parench5rma 
testis, which consists of seminiferous tubules (Tubuli seminiferi), supported 

' In the normal state the surface of the testicle is quite smooth on account of the serous 
covering. Frequently, and especially in old subjects, local inflammation has produced roughen- 
ing of the surface and thread-like proliferations. 



THE TESTICLES 



573 



by loose intralobular connective tissue. The tuljules are at first very tortuous 
(Tubuli contorti); then they unite with other tuljules, forming larger straight 
tubules (Tubuli recti). The latter unite with adjacent tubules and converge to- 
ward the anterior part of the attached Ijoriler of the gland. In this way there are 
formed more than a dozen larger efferent ducts (Ductuli efferentes), which pierce 
the albuginea at a small area (about a centimeter in diameter) at the anterior part 
of the attached liorder and enter the head of the epididymis. 

The epididymis is covered by the tunica vaginalis propria and a thin albugin(>a. 
Its head consists of a dozen or more coiled tubules, which are grouped into lobules 
(Lobuli epididymidis). The tubules of a lobule (foiu' or five in number) unite to 
form a single tube, and by the union of the latter with those of the other lobules 
there is formed a single tube, the duct of the epididymis (Ductus epitlidymidis). 





Fig. 514. — Right Testicle and Spermatic Cord of 
Horse, Enclosed in Tunica Vaginaijs. 
c. Tunica vaginalis communis: o, prominence 
caused by tail of epididymis; p, cremaster externus 
muscle, (.\fter EUenberger-Baum, Top. Anat. d. 
Pferdes.) 



Fig. 515. — Right Testicle and Spermatic Coed of 
Horse, Exposed. 
a', Lateral surface of testicle: c, tunica vagin- 
alis, cut and reflected: d, reflection of tunica vaginalis; 
e, mesorchium; g, tail, h, body, i, head, of epididymis; 
k, sinus epididymidis; I, spermatic vessels showing 
through tunica vaginalis propria; m, end of spermatic 
artery. Dotted line indicates position of ductus 
deferens on other side of mesorchium. (After Ellen- 
berger-Baum, Top. .-Vnat. d. Pferdes.) 



which, by its complex coils, forms the bodj' and tail of the epididymis and termin- 
ates in the ductus deferens. The tubules and the coils of the tluct of the epididymis 
are held together by comiective tissue and unstriped muscle-fibers. The tubules 
and duct are lined with ciliated epithelium, and the duct has a muscular coat which 
consists of longitudinal and circular fibers. 

Several fa?tal remnants in connection with the epididymis and adjacent part of the spermatic 
cord have been described in man. The appendix epididjrmidis is a small, piriform body, 3-4 
nmi. long, which is attached to the head of the (>i>iilidymis. The paradidsrmis consists of a numlier 
of tubules which lie in the lower part of the siicnnatic cord close to the head of the epididymis. 
Most of the tubules are blind and disappear in early life, but one or more may communicate with 
the epididymis or rete testis; the latter may give rise to cysts. The ductuli aberrantes are 
tubules that extend upward from the canal of the epididymis and end blindh-. Similar structures 
have been mentioned as occurring in the domestic animals, but authentic ilata in rcfjard to tliem 
are lacking. 

Vessels and Nerves. — The testicle is richly supplied wdth blood by the sper- 
matic artery, a branch of the posterior aorta. The artery descenils in the anterior 



574 GENITAL ORGANS OF THE STALLION 

part of the spermatic cord, and is very tortuous near the testicle; on reaching the 
attached border of the gland it passes backward in a flexuous manner, giving 
branches to the testicle and epididymis, turns around the posterior extremity, and 
runs forward on the free border to the anterior extremity. It is partially embedded 
in the tunica albuginea, and detaches lateral branches which ascend and descend in 
a tortuous fashion on each surface of the testicle; these give off small branches 
which enter the gland on the trabeculse and septa. The veins on leaving the 
testicle, form a network, the pampiniform plexus, around the artery in the sper- 
matic cord. The spermatic vein, which issues from this plexus, usually joins the 
posterior vena cava on the right side, the left renal vein on the left side. The 
Ijntnph-vessels follow in general the course of the veins and enter the lumbar lymph 
glands. The nerves, derived from the renal and posterior mesenteric plexuses, 
form the spermatic plexus around the vessels, to which they are chiefly distributed. 

THE SCROTUM 

The scrotum, in which the testicles and the adjacent parts of the spermatic 
cords are situated, is somewhat globular in form, but is commonly as.vmmetrical, 
since one testicle — more often the left — is the larger and more dependent. It 
varies in form and appearance in the same subject, according to the condition of its 
subcutaneous muscular tissue. The latter contracts on exposure to cold, so that 
the scrotum is drawn up and becomes thicker and wrinlcled; when relaxed under the 
influence of heat or fatigue, or from debility, it becomes smooth and pendulous, 
with a constriction or neck superiorly. It consists of layers which correspond 
with those of the abdominal wall; considered from without inward, these are: 

(1) The skin, which is thin, elastic, usually dark or l)lack in color, and smooth 
and oily to the touch. It presents scattered short fine hairs, and is abundantly 
supplied with very large sebaceous and sweat glands. It is marked centrally by a 
longitudinal raphe scroti; this is continued forward on the prepuce and behind on 
the perineum. 

(2) The dartos (Tunica dartos) is redtlisli in color and is closely adherent to 
the skin except superiorly. It consists of fibro-elastic tissue and unstriped muscle. 
Along the raphe it forms a median partition, the septum scroti, which divides the 
scrotum into two pouches. Dorsally the septum divides into two layers which 
diverge on either side of the penis to join the abdominal tunic. At the bottom 
of the scrotum fibers connect the dartos closelj^ -with the tunica vaginalis (and thus 
indirectly with the tail of the epididymis), constituting the scrotal ligament.' 
Elsewhere the dartos is loosely comiected with the underlying tunic b.y areolar 
tissue which contains no fat. 

(3) The scrotal fascia, which is apparently derived from the oblique abdom- 
inal muscles. 

It has liccu customary to describe three layers of fascia, in conformity with the accounts 
given in Icxl-liiKiks of human anatomy. These are: (1) The intercolumnar or spermatic fascia, 
derived fnmi i lir margin of the extmiat inguinal ring; (2) the cremasteric fascia, derived from the 
internal ohhciuc muscle; (3) the infundibuUform fascia, derived from the fascia transversalis. 
The first two camiot be distmguished by dissection and the third is (in the scrotum) fused with 
the parietal peritoneum of the tunica vaginalis. 

(4) The parietal layer of the tunica vaginalis. — This is a fibro-serous sac which 
is continuous with the jiarietal jjcM-itoneum of the abdomen at the internal inguinal 
ring. It is thin above, but is thick in its scrotal part, where it is strengthened liy 
fibrous tissue (Lamina fibrosa) derived from the transversalis fascia. It will be 
described further under the caption tunica vaginalis. - 

' This is a remnant of the gubernaculum testis of the foetus. 

^ The tunica vaginalis is not a part of the scrotum in the strict or narrow sense of that term, 
but is included here on practical grounds. 



THE DUCTUS DEFERENS THE SPERMATIC CORD 575 

Vessels and Nerves. — The blood supply is derived from the external pudic 
artery, and the veins go chiefly to the external pudic vein. The nerves are tlerived 
from the ventral l:)ranches of the second and third lumbar nerves. 



THE DUCTUS DEFERENS 
This tube, also commonly termed the vas tleferens, extends from the tail of the 
epididymis to the pelvic part of the urethra. It ascends in the inguinal canal, 
enclosed in a fold detached from the medial surface of the mesorchium, near the 
posterior (attached) border of the latter. At the vaginal ring it separates from the 
other constituents of the spermatic cord, and turns backward and inward into the 
pelvic cavity (Fig. 370). For some distance it lies in the free edge of the genital 
fold, by which it is attached to the inguinal part of the abdominal wall and the 
ventral part of the lateral wall of the pelvis. In its further course (over the dorsal 
surface of the bladder) it leaves the edge of the fold and inclines medially between 
its layers, and comes in contact with the medial face of the vesicula seminalis. Over 
the neck of the bladder the two ducts lie very close together, flanked laterally by the 
necks of the vesiculse seminales, and having the uterus masculinus between them. 
They then disappear inider the isthmus of the prostate, and are continued through 
the wall of the urethra to open in a small diverticulum on the colliculus seminalis 
with the excretory duct of the vesicula seminalis. The common opening is the 
ejaculatory orifice (Orificium ejaculatorium). 

It has been customary to describe a short tube, the ejaculatory duct, as resulting from the 
union of the ductus deferens and the duct of the corresponding vesicula seminalis. Such a duct, 
about 18-20 mm. (ca. ?a in-) long, exists in man a,s the morphological continuation of the ductus 
deferens. lu the domestic animals it is not present, since the ductus deferens and duct of the 
vesicula seminalis open either in common or alongside of each other in a diverticulum or evagina- 
tion of the mucous membrane on the side of the colliculus seminalis. 

From its origin until it reaches the dorsal surface of the bladder the ductus 
deferens has a uniform diameter of about a quarter of an inch (ca. 6 mm.). It then 
forms a fusiform enlargement, the ampulla ductus deferentis (Fig. 517); this part 
is about six to eight inches (ca. 15 to 20 cm.) long, and in its largest part nearly an 
inch (ca. 2 cm.) in diameter in the stallion; in geldings the enlargement is usually 
not very pronounced. Beyond the ampulla the duct abruptly diminishes in size.^ 

Structure. — The wall of the ductus deferens is thick and the lumen very small, 
so that the tube has a firm and cord-like character. It is covered with peritoneum, 
except in the last few inches of its coiu'se. The loose adventitia contains numerous 
vessels and nerves. The thick muscular coat consists of longitudinal and circular 
fibers. The mucous membrane lias an ejiithelium of short columnar cells. In the 
posterior part of the tulie, and especially in the ampulla, there are numerous glands. 

Vessels and Nerves. — The arteries are branches of the spermatic, umbilical, 
and internal pudic arteries, and the nerves come from the pelvic plexus of the 
sympathetic. 

THE SPERMATIC CORD 

The spermatic cord (Funiculus spermaticus) consists of the structures carried 
down by tlie testicle in its migration through the inguinal canal from the abdominal 
cavity to the scrotum. It begins at the abdominal inguinal ring, where its constitu- 
ent parts come together, extends obliquely downward through the inguinal canal, 
passes over the side of the penis, and ends at the attached border of the testicle. 
It consists of the following structures: 

(1) The spermatic artery. 

' The term "ampulla " is not entirely satisfactory, since it is likely to be interpreted to mean a 
dilatation. There is no increase here in the lumen of the tube, and the increase in size is caused 
by a thickening of the wall, due to the presence of numerous branched tubular glands. The term 
"pars glandularis, " suggested by Schmaltz, seems worthy of adoption. 



576 



GENITAL ORGANS OF THE STALLION 



(2) The spermatic veins, which form the pampiniform plexus around the 
artery. 

(3) The lymphatics, which accompany the veins. 

(4) Sympathetic nerves, which run with the artery. 

(5) The ductus deferens. 

(6) The internal cremaster muscle, which consists of bundles of unstriped 
muscular tissue aljout the vessels. 

(7) The visceral layer of the tunica vaginalis. 

The first four of these constituents are gathered into a rounded mass which 
forms the anterior part of the cord; they are united by coimective tissue, inter- 
spersed with which are bundles of the cremaster internus. The ductus deferens is 
situated postero-medially, enclosed in a special fold detached from the medial surface 
of the tunic; hence it is not visible laterallj'. 

The term spermatic cord is to a certain extent misleading as applied to most animals, while 
in man the structure is distinctly cord-like. Li the horse, when the tunica vaginalis is slit open 
and the "cord" stretched out, the latter is seen to have the form of a wide sheet, the mesorchiimi, 
which has a thick, rounded anterior edge, the so-called "vascular part" of the cord. The posterior 
edge of the mesorchium is continuous with the parietal layer of the tunic; its medial surface pre- 
sents posteriorly the deferential fold (Plica ductus deferentis). Between the two layers of the 
mesorchium are bundles of mistriped muscle (cremaster internus) and small vessels. 



THE TUNICA VAGINALIS 

The tunica vaginalis is a flask-like serous sac which extends through the in- 
guinal canal to the iDottom of the scrotum. Like the abdominal peritoneum, of 

which it is an evagination, it con- 



Spermatic -oessels and mrves 



Parid.nl layer 
of tunica 
vaginalis 



sists of two layers — parietal and vis- 
ceral. The parietal layer or tunica 
vaginalis communis lines the scrt)tum 
below; its narrow, tuljular part lies 
in the inguinal canal, and is directly 
continuous with the parietal perito- 
neum of the abdomen at the abdom- 
inal inguinal ring. The cavity of the 
tunica vaginalis (Cavnm vaginale) is 
a diverticulum of the general perito- 
neal cavity, with which it commimi- 
cates through the vaginal ring (An- 
nulus vaginalis) ; it contains nor- 
mallj' a small quantity of serous fluid. 
The parietal layer is reflected from 
the posterior wall of the inguinal 
canal around the structures of the 
cord, forming the mesorchium, a 
fold analogous to the mesentery of 
the intestine. The visceral layer 

or tunica vaginalis propria covers the spermatic cord, testicle, and epididymis. 
The external cremaster muscle (M. cremaster externus) lies on the lateral and 

posterior part of the tunic, to the scrotal part of which it is attached. 

Confusion has arisen from the use of the term abdominal or internal inguinal ring in two 
senses. The term is used to designate the abdominal opening of the inguinal canal, but it is also 
often applied to the opening of the cavity of the tunica vaginalis. It should not be used in the 
latter sense. The peritoneal ring at which the cavity of the tunica vaginalis opens into the 
general peritoneal sac is distinguished by the name vaginal ring. It is four or five inches (ca. 
10 to 12 cm.) from the linea alba, and two or three inches (ca. 6 to 8 cm.) in front of the ilio-pec- 
tineal eminence. In staUions it will usually admit the end of the finger readily, but it may be 




Ductus 
deferens 



Fig. 516. — Diagram of Cross-section op Spermatic Cord 
AND Tunica Vaginalis; Latter Represented as Dis- 



DESCENT OF THE TESTICLES 577 

abnormally large and allow a loop of bowel to enter the cavity of the tunica vaginalis. It is large 
in the young foal. In the gelding it is smaller and sometimes partially occluded. In man the 
ca\'ity is almost always obliterated early, except in its scrotal portion, tlius abolishing the vaginal 
ring and the inguinal part of the cavity. 



DESCENT OF THE TESTICLES 

During early foetal life the testicle is situated against the dorsal wall of the 
abdominal cavity, in contact with the ventral surface of the corresponding kidney. 
As growth proceeds it gradually migrates from this primitive position, and finall.y 
passes down the inguinal canal into the scrotum. Previous to its descent through 
the abdominal wall the testicle is attached to the sulilumbar region by a fold of 
peritoneum, termed the mesorchium. This fold contains the vessels and nerves 
of the testicle in its anterior Ijorder. In its posterior edge is the elongated tail of 
the epididymis, and two cords of fibrous tissue and unstriped muscle. One of these 
cords is short and connects the tail of the epididymis with the testicle; later it 
becomes shorter, and is termed the ligament of the epididymis. The other cord, 
the gubemaculum testis, extends from the tail of the epididymis to the subperi- 
toneal tissue in the vicinity of the future vaginal ring. The deferential fold (Plica 
ductus deferentis) is given off from the medial face of the mesorchiiun, and joins the 
genital fold posteriorly. The body of the epididymis at this time lies in the edge 
of an oblique fold formed by the lateral layer of the mesorchium. After the middle 
of foetal life a pouch of the peritoneum, the processus vaginalis, grows downward 
through the inguinal canal, carrying with it cremaster fibers derived from the 
internal oblique muscle and a layer from the transversalis fascia. It is accom- 
panied by an inguinal extension of the gubemaculum testis. The latter blends 
below with the subcutaneous tissue which later becomes the dartos. The tail of 
the epididymis first enters the processus vaginalis, followed by the testicle with its 
mesorchium, which descends within this diverticulum of the peritoneum until it 
reaches the scrotum. The ductus deferens and its fold descend sjmchronously ^vith 
the epididymis and testicle. In the foal the descent of the testicles is often com- 
plete at birth, but it frequently happens that one testicle or both may be retained 
in the inguinal canal or in the alDdomen for some months. In other cases the 
testicle may return into the canal or abdomen, since in the j'oung foal the vaginal 
ring is large and the testicle small and soft, and not yet closely anchored by the 
scrotal ligament. In rare cases the descent may be completed as late as the fourth 
year. 

The mechanical factors concerned in the migration of the testicle are matters on which 
much uncertainty still exists. That the gubemaculum exerts sufficient traction to guide the 
epididymis and testicle to the inguinal canal seems plausible. The abdominal inguinal ring may 
constitute a locus minoris resistentise in the abdominal wall, especially after the descent of the 
processus vaginalis. Progressive shortening of the gubemaculum was formerly considered to be 
the chief cause of the descent through the abdominal wall. Increase m the intra-abdominal 
pressure is probably an important factor. 

Indefinite retention of one testicle or both in the abdominal cavity or inguinal canal is not 
rare in horses; this condition is termed cryptorchism. Abdominal retention is the more usual 
form of cryptorcliism in adult horses, inguinal retention being usually temporary. The retained 
testicle is usually, but not always, small, thin, soft, and flabby, and is non-spermiogenio. The 
processus vaginalis and the inguinal part of the gubemaculum are usually present, but may be 
rudimentary. The ligament of the epididymis and the corresponding part of the mesorchium 
are often so long that the tail of the epididymis may be several inches distant from the testicle. 
The abdominal part of the gubemaculum may be eight to ten inches (ca. 20 to 2.5 cm.) long, and the 
hgament of the epididjonis much elongated (10 to 15 cm. in length, according to Vennerholm) ; 
thus the testicle may have a wide range. The vaginal ring is sometimes closed. 

In many mammals the testicles normally remain in the abdominal cavity; such animals are 
termed testiconda, and include the elephant, some insectivora, hyrax, sloths, ant-eaters, armadillos, 
and cetacea. In others the testicles descend periodically during the period of oestrum, and then 
return into the abdomen, or they may be extruded and retracted voluntarily; this is true of most 
rodents, many insectivora (moles, shrews, hedgehog), and bats. 
37 



578 



GENITAL ORGANS OF THE STALLION 



Bladder 



THE VESICUL^ SEMINALES 
The vesiculae seminales (Fig. 517) are two elongated and somewhat piriform 
sacs, which lie on each side of the posterior part of the dorsal surface of the blad- 
der. They are partly enclosed in 
^"^^ the genital fold, and are related to 

the rectum dorsally. Their long axes 
are parallel with the ductus def- 
erentes and converge posteriorly. 
Each consists of a rounded blind 
end, the fundus; a middle, slightly 
narrower part, the body ; and a pos- 
terior constricted part, the neck or 
duct. 

In the stallion they are about 
six to eight inches (ca. 15 to 20 cm.) 
long, and their greatest diameter is 
about two inches (ca. 5 cm.); in 
the gelding they are usually much 
smaller.^ 

The vesiculse are chiefly retro- 
peritoneal, but the fundus extends 
forward into the genital fold and 
hence has a serous covering. The 
excretory duct (Ductus excretorius) 
dips under the prostate, and opens 
in common ^vith or alongside of the 
ductus deferens in a pouch of the 
mucous membrane on the side of 
the colliculus seminalis. 

Structiu-e. — The wall, exclusive 
of the partial serous coat, consists 
of a fibrous adventitia, a middle 
muscular coat, and a mucous lining. 
The muscular coat is thickest at the 
fundus, and consists of two planes 
of longitudinal fibers with a circular 
layer between them. The mucous 
membrane is thin, and is arranged 
in numerous folds and projections 
which form a network; the spaces 
so enclosed present the openings of 
tubulo-alveolar glands. The epithe- 
lium is columnar. The blood-supply 
is derived from the internal pudic 
artery. 




3-4- 



Fig. 517. — Internal Genit, 




Staluon; Dorsal 



On left side urethral muscle has been removed over bulbo- 
urethral gland. Cornua of uterus masculinua are indicated in 
genital fold. The posterior limit of the peritoneum is shown 
but not marked. 1, Round ligament of bladder; 2. lateral liga- 
ment of bladder; 3, bulbo-urethral gland. 



THE PROSTATE 
The prostate (Prostata) is a lobulated gland which lies on the neck of the 
bladder and the beginning of the urethra, ventral to the rectum. It consists of 

' Sometimes one or both of the vesiculae are very large in the gelding. The writer has seen 
four cases in the dissecting room, three of which were bilateral, the other unilateral. The vesicula 
resembled the urinary bladder in appearance and contained about a quart of thick, amber-colored 
secretion. 



THE UTERUS MASCULINUS — THE BULBO-URETHRAL GLANDS 579 

two lateral lobes and a connecting isthmus. The lateral lobes, right and left 
(Lobus dexter et sinister), are somewhat prismatic in form, and are directed forward, 
laterally, and somewhat upward. The deep surface of each lobe is concave and 
partly embraces the corresponding vesicula seminalis. The dorsal surface is con- 
cave and is in relation with the rectum. The ventral surface is convex and lies 
on the obturator internus muscle and fat. The apex is pointed and lies near the 
posterior end of the superior ischiatic spine. The isthmus is a thin, transverse 
band, about four-fifths of an inch (ca. 2 cm.) wide. It lies over the junction of the 
bladder with the urethra, the uterus masculinus, the terminal parts of the ductus 
deferentes, and the ducts of the vesiculse seminales. Dorsally it is partlj' covered 
by fibers of the urethral muscle. 

Structure. — The prostate is enclosed in a capsule of fibrous tissue, with an 
admixture of unstriped muscle fibers. The gland substance is divided into sphe- 
roidal or ovoid lobules by trabeculse which consist to a large extent of unstriped 
muscle. Each lol^ule is traversed by an axial duct, which gives off numerous 
tubular branches and these ramify further in the lobule. The tubules are thickly 
beset v/ith saccular diverticula, giving the gland a branched, tubulo-alveolar struc- 
ture. The ducts and tubules are lined with cubical or columnar epithelium. The 
prostatic secretion (Succus prostaticus) is milky in appearance and has a character- 
istic odor. There are fifteen to twenty prostatic ducts (Ductus prostatici) on either 
side, which perforate the urethra and open lateral to the colliculus seminalis (Fig. 
521). The blood-supply is derived from the internal pudic artery. 

The surface of the prostate is commonly tuberculate in old subjects, and amyloid bodies 
and calcareous concretions may be found in it. 

THE UTERUS MASCULINUS 
The uterus masculinus or utriculus prostaticus is a foetal remnant of variable 
size and form, which is situated centrally on the posterior part of the dorsal surface 
of the bladder. When well developed, it consists of a median flattened tube, some 
three or four inches (ca. 7.5 to 10 cm.) long, and about half an inch (ca. 1 to 1.5 cm.) 
wide, the anterior part of which lies in the genital fold and gives off two slender 
processes or cornua; the latter curve forward and outward in the fold a variable 
distance, being sometimes traceable as far as the anterior end of the ampulla of the 
ductus deferens. The posterior extremity of the tube passes under the isthmus of the 
prostate, and opens into the urethra on the summit of the colliculus or joins a duct 
of a vesicula seminalis or has a blind end. It has a muscular coat and a mucous 
lining. In many cases it consists merely of a very small central tuliule with a blind 
anterior end, or a band, not sharply marked off from the adjacent tissue; in other 
cases it cannot be recognized. It is a remnant of the ducts of Miiller and the 
homologue of the uterus and vagina. 



THE BULBO-URETHRAL GLANDS 

The bulbo-urethral glands (GlanduliE bulbourethrales)^ are two in number, 
and are situatetl on eitlier side of the pelvic part of the urethra close to the ischial 
arch (Fig. 577). They are covered by the urethral muscle, from which bundles 
enter the larger trabeculae of the gland. They are ovoid in form, somewhat de- 
pressed dorso-ventrally, and their long axes are directed obliquely forward and 
outward. In the stallion they may measure nearly two inches (ca. 4 cm.) in length, 
and about an inch (ca. 2.5 cm.) in mdth. In the gelding they are about the size of 
an average hazel-nut. 

Structure. — They resemble the prostate in general structure, but the inter- 
' Also termed Cowper's glands. 



580 



GENITAL ORGANS OF THE STALLION 



stitial tissue is much less abundant, and contains much less muscular tissue ; hence 
the loljulation is not very distinct. The parenchyma consists of large collecting 
tubules, into which numerous side branches open; these are lined with cubic 
epitlielium. In the larger septa there are striped muscle-fibers. Each gland has 
six to eight excretory ducts (Ductus excretorii) which open into the urethra on a 
series of small papillae behind the prostatic ducts and close to the median plane 
(Fig. 521). The blood-supply comes from the internal pudic artery which overlies 
the gland. 

THE PENIS 
The penis, the male organ of copulation, is composed essentially of erectile 
tissue, and encloses the extrapelvic part of the urethra. It extends from the ischial 
arch forward between the thighs to the umbilical region of the abdominal wall. 
It is supported by the fascia penis and the skin, and its prescrotal portion is situated 
in a cutaneous pouch, the prepuce or sheath. It is cylindrical in form, but much 
compressed laterally in the greater part of its extent. 

In the quiescent state it is about 20 inches (ca. 50 cm.) long; of tliis, about 6 to S inches 
(ca. 1.5 to 20 cm.) is free in the prepuce. In erection it increases 50 per cerit. or more in length. 

Deep artery {from iiilernal pudic) 



Dorsal artery {from Corona glandis 

external pudic) Collum glandis 

Proc. dorsalis 




Retractor penis muscle 



BODY 



Via. 518. — Penis of Hohse; Lateral View. 



It may be divided into a root, a body, and a terminal enlargement, the glans. 

The root of the penis (Radix penis) is attached to the lateral parts of the ischial 
arch by two crura, which converge and unite below the arch (Fig. 577). The 
urethra passes over the ischial arch between the crura, and curves sharply forward 
to become incorporated with the penis. The body of the penis (Corpus penis) 
begins at the junction of the crura and constitutes the bulk of the organ. At its 
origin it is attached to the symphysis ischii by two strong flat bands, the suspensory 
ligaments of the penis (Ligamenta suspensoria penis), which blend with the tenilon 
of origin of the graciles muscles (Figs. 518, 576). This part of the penis is flattened 
laterally for the most part, but becomes rounded and smaller anteriorly. It pre- 
sents four surfaces. The dorsum penis is narrow and rounded; on it arc the dorsal 
arteries and nerves of the jienis and a rich venous plexus. The urethral surface 
(Facies urethralis) is ventral; it is rounded, and along it runs the urethra, embedded 
in the deep urethral groove of the corpus cavernosum. The lateral surfaces are 
high and flattened, except anteriorly, where they are lower and rounded; thej- are 
covered to a large extent by a plexus of veins. 

The glans penis is the enlarged free end of the organ. Its anterior surface or 
base is surrounded by a prominent, denticulated margin, the corona glandis. The 



THE PENIS 



581 



surface is convex; its lower part slopes backward, and presents a deep depression, 
the fossa glandis, in which the urethra protrudes for about an inch (ca. 2.5 cm.) as a 
free tul)e, tlie urethral process (Processus urethrae), covered by a thin integument. 
The urethra is thus surrounded by a circular fossa, which opens superiorly into the 
urethral sinus, a bilocular tiiverticulum lined by thin skin. This diverticulum is 
filled sometimes with a caseous mass of sebaceous matter and epithelial debris. 
Behind the corona glandis there is a constriction, the collum glandis. It is to be 
noted, however, that this does not indicate the demarcation between the glans and 
corpus penis, since the former extends backward above the corpus cavernosum a 
distance of about four inches (ca. 10 cm.), forming the processus dorsalis glandis 
(Fig. 518). 

Structure. — The penis consists essentially of two erectile bodies, the corpus 
cavernosum penis and the corpus cavernosum urethrae. 

The corpus cavernosum penis forms the greater part of the bulk of the penis 
except at its free extremity. It arises from each side of the ischial arch by a cms 
penis, which is embedded in the ischio-cavernosus muscle. Below the ischial arch 
the crura unite to form the laterally compressed body of the corpus cavernosum; 
this presents ventrally the urethral 



Dorsum penis 



Corpus 
cavi-rnosum 
pe?iis 



Corpus 
cavernosum 
urelhrce 




Trabeculce 



Tunica 

albuginea 



Urethra 

Bulbo- 

cavemosus 
muscle 



Retractor penis muscle 



-Cross-section of Body < 



groove (Sulcus urethralis), which con- 
tains the urethra and corpus caverno- 
sum urethrse. Anteriorly the corpus 
cavernosum penis divides into three 
processes — a long central one, which is 
capped by the glans penis, and two 
short blunt lateral ones. The corpus 
cavernosum is enclosed by the tiuiica 
albuginea, a thick capsule of fibrous 
tissue which contains some elastic 
fibers. Externally the fibers are chiefly 
longitudinal ; internally they are mainly 
circular and are looser in arrangement. 
Numerous trabeculae pass inward from 
the tunic and form a framework in the 
interior of the corpus cavernosum. En- 
closed by this framework is the erectile 
tissue, which is readily distinguished 
from the fibrous trabeculae by its red- 
dish-gray color and softer texture. It is composetl largely of strands of unstriped 
muscle, between which there are cavernous spaces (Cavernae). These spaces may 
be regarded as greatly enlarged capillaries; they contain blood, are lined with flat 
endothelial cells resting upon a layer of delicate connective tissue, and are directly 
continuous with the veins of the penis. Erection is produced by distention of 
-■these spaces with blood ; at other times the spaces are mere slits. 

In man there are two distinct corpora cavernosa, separated by a median septum penis, 
which is complete except in the middle part of the organ, where the septum is composed of vertical 
trabecule, between which are slit-like intervals; through the latter the blood-spaces of the two 
corpora cavernosa communicate. In the horse no distinct septum exists except near the root, but 
in the proximal and distal parts of the corpus cavernosum there are vertical trabecular, which 
form an arrangement like the septum pectiniforme of man. 

The corpus cavernosum urethrae (or corpus spongiosum) forms a tube around 
the urethra, and is continuous at its anterior end with the glans penis. It forms a 
slight enlargement at the root of the penis, which is termed the bulb (Bulbus 
urethrae). In the body of the penis it forms a thinner layer dorsally than on the 
sides and ventrally. The structure of the corpus cavernosum urethrae is somewhat 



582 GENITAL ORGANS OF THE STALLION 

like that of the corpus cavernosum penis, but the trabeculae are much finer; they 
consist of fibrous tissue, much of which is elastic, and of bundles of unstriped muscle 
which are chiefly longitudinal in direction. The spaces are numerous and large. 

Intheglans penis the trabeculae are highly elastic, and the spaces are large and 
very distensible ; the latter are specially wide in the posterior part of the processus 
dorsalis, where they communicate with large veins on the dorsum penis. There is 
a partial septum glandis. The skin covering the glans is thin, destitute of glands, 
and richly supplied with nerves and special nerve-endings. 

Vessels and Nerves. — The penis is supplied with blood by three arteries, viz., 
the internal pudic, obturator, and external pudic. The terminal part of the internal 
pudic artery enters the root as the artery of the bulb and breaks up in the Isulb into 
numerous branches. The obturator artery gives off the large arteria profunda 
penis, which enters the crus penis and ramifies in the corpus cavemosmn. The 
external pudic artery gives off the tlorsal arteries of the penis, branches from which 
pass through the tunica albuginea. The veins form a rich plexus on the dorsum 
and sides of the penis, which is drained by the external pudic and obturator veins; 
from the root the blood is carried by the internal pudic veins.' The IjTnph vessels 
run with the veins and go to the superficial inguinal glands. The nerves are derived 
chiefly from the pudic nerves and the pelvic plexus of the sympathetic. The former 
supply the dorsal nerves of the penis; special nerve-endings, the end-bulbs (of 
Krause), occur in the skin of the glans penis. The sympathetic fibers supply the 
unstriped muscle of the vessels and the erectile tissue. 



MUSCLES OF THE PENIS (Figs. 272, 576, 577, 581) 

1. The ischio-cavemosus- is a short but strong, paired muscle, which arises 
from the tuber ischii and the adjacent part of the sacro-sciatic ligament, and is 
inserted on the crus and adjacent part of the bodj' of the penis. It is somewhat 
fusiform, encloses the crus as in a sheath, and is situated in a deep depression in the 
semimembranosus muscle. It pulls the penis against the pelvis, and assists in 
producing and maintaining erection by compressing the dorsal veins of the penis. 
Its blood-supply is derived from the obturator artery, and the nerve-supply from 
the pudic nerve. 

2. The retractor penis is an unstriped muscle which is a continuation of the sus- 
pensory ligaments of the anus. The latter arise on the ventral surface of the first 
and second coccygeal vertebriE and pass downward over the sides of the rectum to 
meet below the anus. Here there is a decussation of fibers, thus forming a sort of 
suspensory apparatus for the posterior part of the rectum and the anus. From the 
decussation the muscle passes for a short distance between superficial and deep 
layers of the bulbo-cavernosus, and then along the ventral surface of the penis, to 
which it is loosely attached. Near the glans penis it splits up into bundles which 
pass through the bulbo-cavernosus and are attached to the tunica albuginea. Be- 
low the anus the muscle is attached to the sphincter ani externus. On the penis 
the two muscles are intimately united to each other. Their action is to ^vithdraw 
the penis into the sheath after erection or protrusion. 



THE PREPUCE 

The prepuce (Prseputium), popularly called the "sheath," is a double in- 
vagination of the skin which contains and covers the free or prescrotal portion of 

' It. has been shown that the cavernous spaces of the glans penis receive blood exclusively 
from vems which come from the penile layer of the prepuce. This may account for the fact that 
the glans reaches its extreme size during erection later than the corpus cavernosum penis. 

^ Also termed the erector penis. 



THE PREPUCE 



583 



the peiiis when not erect. It consists of two parts, external and internal. The 
external part or sheath extends from the scrotum to within two or three inches of 
the umbilicus, where the external layer is reflected ventrally and laterallj^, forming 
the thick margin of the preputial orifice (Ostium prteputiale) ; dorsally it is directly 
continuous ^vith the integument of the abdominal wall. It is marked by a median 
raphe prseputii, a continuation of the scrotal raphe. At the lower margin of the pre- 
putial orifice there are often in the stallion two papillae, which are regarded as 
rudimentary teats. The internal layer passes backward from the preputial orifice 
a distance of about six to eight inches (ca. 1.5 to 20 cm.), lining the cavity of the ex- 
ternal part of the prepuce, and is then reflected forward until it approaches the 
orifice, where it is again reflected backward. It thus forms within the cavity of the 
sheath a secondary tubular invagination, the prepuce proper, in which the anterior 
part of the penis lies. This tubular cavity is closed behind by the reflection of the 
internal layer on to the jienis to form the iicnile layer of the prepuce. Its orifice is 



^hdofnihal Uja// 




Fig. 520. — Sagittal Section of Prepuce a?jd Part of Penis of Horse. 

P, Internal part of prepuce or prepuce proper; P', external part of prepuce or sheath: C.p., preputial cavity: F.g.t 

fossa glandis: D, diverticulum of fossa glandis; P.ii., processus urethrge. 

surrounded by a thick margin, the preputial ring (Annulus praeputialis), which is 
comiected ventrally with the external part by the preputial frenum (Frenulum 
prseputii). 

The arrangement differs from that found in man in the fact that the inner part of the pre- 
puce as described above is equivalent to the entire human prepuce. This part, the prepuce 
proper, is well seen on sagittal sections, and can be demonstrated by pulling the penis, enclosed 
in this prepuce, out of the cavity of the sheath; the arrangement of the free part of the penis and 
prepuce is then like that in man. (In paraphimosis the penis is strangulated by the preputial 
ring.) The external part might be distinguished as the sheath or vagina penis. 

Structure. — The outer skin of the external part resembles that of the scrotum. 
The internal layers of skin, as far as the preputial ring, are almost hairless, variable 
in color, and often irregularly pigmented ; they form irregular folds, and are supplied 
with numerous large sebaceous glands and coil glands, which reach their greatest 
size at the ring. Beyond this the glands are absent, and the skin resembles a non- 
glandular mucous membrane. The secretion of the preputial glands (Glandulse 
preeputiales), together with desquamated epithelial cells, forms the fatty smegma 
praeputii, which has a strong, unpleasant odor, and often accumulates in consitlerable 



584 



GENITAL ORGANS OF THE STALLION 



amount. Beneath the skin there is a large amount of loose connective tissue, 
except over the glans penis, where the skin is closely attached to the tunic of the 
erectile tissue. The external part of the prepuce is strengthened by a layer of 
elastic tissue, derived from the abdominal tunic, and termed the suspensory liga- 
ment of the prepuce. 

Vessels and Nerves. — The arteries are branches of the external pudic artery, 
and the veins go chiefly to the external pudic vein. The l3miph vessels go to the 
superficial inguinal and lumbar lymph glands. The nerves are derived from the 
pudic, ilio-hypogastric, and ilio-inguinal nerves. 



THE MALE URETHRA 
The male urethra (Urethra masculina) is the long mucous tube which extends 
from the bladder to the glans penis. It passes backward on the floor of the pelvis, 



Lateral lobe of -prostate 



Orifice of uterus wasculinus — 



Ducts of lateral urethral 
glands 




Collicvlus scminalis 



Ducts of bulho-urethral 
glands 



ELVic Urethra and Posterior Part of Bl.\dder of Horse Slit Ventrally apjd Laid Open. 
e.d., openings of ductus doferentes and ducta of vesiculse seminales. 



turns around the ischial arch, forming a sharp bend, and passes forward as a part of 
the penis, enclosed in the corpus cavernosum urethrse. It may, therefore, be divided 
into two parts, pelvic and extrapelvic. 

The pelvic part (Pars pelvina) is four or five inches (ca. 10 to 12 cm.) long. 
At its origin it is not distinguishable from the neck of the bladder in size or structure; 
in fact, no line of demarcation exists between the two. Behind the prostate the 
tube dilates to a potential wdth of two inches or more (ca. 5 to 6 cm.). Near the 



THE MALE URETHRA 585 

ischial arch, Ijetween the bulbo-urethral glands, it contracts again, forming the 
isthmus urethrae. It is related dorsally to the rectum and the prostate, ventrally 
to the internal obturator muscles, and laterally to the bulbo-urethral glands. It 
is enclosed, except at its origin, by the urethral muscle. ^ 

The extrapelvic part (Pars externa) passes between the two crura of the penis 
and runs along the groove on the ventral surface of the corpus cavernosum penis, 
enclosed by the corpus cavernosum urethrae and the bulbo-cavernosus muscle. It 
passes through the glans penis and projects forward about an inch in the fossa 
glandis as a free tube, the processus lu-ethrae; this part is covered by a delicate 
integument, under which there is a thin layer of erectile tissue. 

The lumen of the tube is largely obliterated in the inactive condition of the parts. When 
moderately distended, its dimensions in a horse of medium size are as follows: At its origin the 
diameter is about half an inch (1 to 1.5 cm.). The pelvic dilatation at its widest part measures one 
and a half to two inches (ca. 3.5 to 5 cm.) transversely, and about an inch (2 to 3 cm.) vertically; 
it is elliptical in cross-section when fully distended. The isthmus at the ischial arch is a little 
smaller than the initial part. Beyond this the lumen is about on^half to three-fourths of an 
mch (ca. 1.5 cm.) in diameter, and is fairly uniform to the glans penis. Here there is a slight 
fusiform dilatation (Fossa navicularis), beyond which the tube contracts. 

The opening from the bladder into the urethra is termed the internal urethral 
orifice (Orificium urethrse internum); it is closed except during urination. The 
terminal opening is the external urethral orifice (Orificium urethrse externum) or 
meatus urinarius. The colliculus seminalis is a rounded prominence, situated 
medially on the dorsal wall, about two inches (ca. 5 cm.) behind the internal ure- 
thral orifice. On either side of the colliculus there is a small diverticulum, in which 
the ductus deferens and the duct of the vesicula seminalis open. The small orifice 
of the uterus masculinus is placed centrally on the colliculus; it is inconstant. The 
orifices of the prostatic ducts are on two groups of small papillte, tjlaced lateral to 
the ejaculatory openings. The ducts of the bulbo-urethral glands open on two 
lateral series of small papillse, about an inch (ca. 2.5 cm.) further back and close to 
the median line. The small orifices of the lateral urethral glands are situated 
laterally in the wide pelvic portion. 

Structure. — The mucous membrane contains a large amount of fine elastic 
fibers, and in its pelvic part there are tubulo-alveolar urethral glands (Glandulae 
urethrales).- The epithelium is at first like that of the Ijladder, then becomes 
cylindrical, and in the terminal part is stratified sciuamous. In the dorsal wall the 
membrane forms a median ridge, the urethral crest (Crista urethralis) ; this termi- 
nates about two inches from the internal urethral orifice in the colliculus seminalis. 

At the origin of the urethra there is a layer of circular unstriped muscle-fibers 
outside of the raucous coat. Beyond this the latter is enclosed by a layer of erectUe 
tissue (Stratum cavernosum), which contains plexuses of veins supported by 
tralieculse of elastic and unstriped muscular tissue; in its peripheral part- there are 
numerous small arteries. There is a slight thickening of the erectile tissue at the 
ischial arch, producing an enlargement kno-\vn as the bulb of the lu-ethra (Bulbus 
urethrae). This is continued by the corpus cavernosum urethrse. Outside of the 
erectile tissue there is a continuation of the intrinsic unstriped muscular coat, 
consisting of external and internal longitudinal strata, with a layer of circular 
fibers between them. 

'It has been customary to divide the pelvic part of the urethra into prostatic and mem- 
branous parts. These terms apply well in human anatomy, but have no special value in com- 
parative anatomy. In the horse a prostatic part hardly exists, imless we assume that it and the 
neck of the bladder together are only about an inch in length. There is no membranous part in 
the sense in which that term is used in regard to man, since the tube has a continuous envelop of 
erectile tissue. 

2 Two sets of glands can be distinguished in the pelvic part of the urethra. Two rows of dor- 
sal glands occur close to the median plane; their ducts open into those of the bulbo-urethral glands. 
A series of lateral glands extends on either side from a point near the prostatic ducts to the end of 
the pelvic urethra; their ducts open laterally, as mentioned above. 



586 GENITAL ORGANS OF THE BULL 

Except at its origin and termination the urethra is provided with a continuous 
layer of striped muscle, placed outside of the erectile tissue. This is described as 
consisting of two parts or muscles. 

(1) The urethral muscle (M. urethralis)^ encloses the wide pelvic part of the 
urethra, and covers the bulbo-urethral glands. It consists of longitudinal and 
transverse fibers. It is a compressor of the pelvic part of the urethra and the l^ulbo- 
urethral glands. By its forcible contraction it plays an important role in the ejacula- 
tion of the seminal fluitl, and also in evacuating the last of the urine in micturition. 

(2) The bulbo-cavemosus muscle (M. bulbocavernosus)- is the continuation 
of the urethral muscle on the extrapelvic part of the urethra; it extends from the 
ischial arch to the glans penis. At the root of the penis it is the thickest, and 
forms a complete layer of circular fibers which enclose the corpus cavernosum 
urethrse. Beyond this it diminishes very gradually in thickness, and consists of 
fibers which arise on a median ventral raphe and curve around the corpus cavernosum 
urethrffi to end on the tunica albuginea of the corpus cavernosum. Its action is to 
empty the extrapelvic part of the urethra. 

The ischio-urethral muscles (Fig. 577) are small bands which arise on the 
ischial arch and crura of the penis and pass forward to become lost on the ventral 
layer of the urethral muscle. They may assist in erection of the penis by exerting 
pressure on the dorsal veins. 



GENITAL ORGANS OF THE BULL 

The scrotum is situated somewhat further forward than in the horse. It is 
ovoid, but compressed from before backward, is long and pendulous, and has a well- 
marked neck when not contracted. The skin here is usually flesh-colored, but in 
some breeds it is more or less pigmented; it is sparsely covered with short hairs. 
Just in front of it are four (sometimes only two) rudimentary teats. 

The testicles are relatively larger than those of the horse, and have an elon- 
gated, oval outline. The long axis is vertical, the attached border being posterior. 
The medial surface is somewhat flattened. A testicle of an adult bull measures on 
the average about four or five inches (10 to 12 cm.) in length, exclusive of the epi- 
didymis; with the latter the length is about six inches (15 cm.). The width is 
about two and a half to three inches (ca. 6 to 8 cm.), and the anterior-posterior 
diameter about the same. The weight is about ten to twelve ounces (ca. 300 grams). 
The tunica albuginea is thin; it contains many elastic fibers, but no unstriped 
muscle. The parenchyma is yellowish in color. The mediastinum testis is an 
axial strand of connective tissue (about 5 mm. in thickness), which descends from 
the upper part of the attached border deeply into the gland. From it the chief 
trabeculsB radiate, but distinct interlobular septa are not present. The seminif- 
erous tubules form in the mediastinum a network, the rate testis. The efferent 
ducts from the rete, a dozen in number, leave at the upper end of the mediastinum. 

The epididymis is verj^ closely attached to the testicle along the posterior 
border of the latter. The head is long; it curves over the upper extremity and 
about a third of the way clonal the anterior border of the testicle; it is covered by 
an extension of the tunica albuginea. The body is very narrow, and lies along the 
lateral part of the posterior border of the testicle, to which it is attached by a narrow 
peritoneal fold. The tail is large and is closely attached at the lower extremity of 
the testicle. 

The spermatic cord and the tunica vaginalis are much longer than in the horse; 

' Formerly termed Wilson's muscle. ^ Formerly called the accelerator uriiiae. 



GENITAL ORGANS OF THE BULL 



587 



the extra-inguinal part of the cord is about eight to ten inches (20 to 25 cm.) in 
length. The cremaster extemus is well developed, and almost completely encloses 
the tunic to the neck of the scrotum; it is inserted about at the level of the upper 
pole of the testicle. The vaginal ring is relatively very small, and is about four 
inches (ca. 10 cm.) from the linea alba. The cremaster internus is feeble. 

The spermatic cords emerge through the lateral angles of the subcutaneous inguinal rings, and 
curve downward and inward to the neck of the scrotum. The rings are about four inches (ca. 
10 cm.) long, and are two and a half to three inches (6 to 8 cm.) apart. In animals in good condi- 
tion there is a large mass of fat above the neck of the scrotum, between the spermatic cords. The 
niesorchium extends to the bottom of the tunica vaginalis, forming a narrow fold (ca. 1 cm. wide) 
which attaches the epididymis to the posterior part of the tunic. 

Vesicula seminalis 
Body 0/ prostate ^-vC^, '^ 




Fig. 522. — General View of Genit.^l 0rq.\ns of Bul 



The inguinal canal presents several specia:! features in the bull. The abdominal ring is very- 
long. Its anterior border, formed by the edge of the internal oblique, is decidedly concave and 
is tendinous in its medial part. The long axis of the subcutaneous ring is directed outward, for- 
ward, and downiward. The spermatic cord lies in its lateral part, the external pudic vessels in its 
middle. A. muscular band about an inch wide, detached from the internal obhque muscle, crosses 
the lateral side of the vaginal ring. 

The ductus deferens is small in cahber and has a much thinner wall than that 
of the horse. At first it pursues a flexuous course upward along the posterior 
border of the testicle, then becomes straight and lies in the posterior part of the 
spermatic cord. The genital fold is narrow, so that the ducts are closer together 
in it than in the horse. On reaching the posterior part of the bladder they are in 
apposition for a chstance of about four inches (10 cm.), flanked and overlapped by 
the vesiculae seminales. They form ampullee about four or five inches (10 to 12 cm.) 
long and half an inch (1.2 to 1.5 cm.) wide, the mucous lining of which is plicated. 
They then pass under the body of the prostate and end, just medial to the ducts of 
the vesiculae seminales, as slit-like openings on either side of the colliculus seminalis. 

The vesiculae seminales are not bladder-like sacs, as in the horse, but are 
compact glandular organs wth a lobulated surface. In the adult they measure 
about four or five inches (ca. 10 to 12 cm.) in length, two inches (5 cm.) in width in 



588 



GENITAL ORGANS OF THE BULL 



their largest part, and an inch or more (ca. 3 cm.) in thickness. The dorsal surface 
of each faces upward and medially and is partially covered with peritoneum. The 
ventral surface faces in the opposite direction and is non-peritoneal. Each may be 
regarded as consisting of a very thick-walled, sacculated tube, bent on itself in a 
tortuous manner. This tube, if straightened out, would be-about ten inches (25 




Fig. 523. — Internal Genital Organs of Bull; 
Dorsal View. 
The right vesicula is sectioned frontally. The 
dotted Hne indicates the bacicward extension of the 
peritoneum. 1, Ureter; 2, body of prostate; 3, vesicula 
seminaUs; 4, urethral muscle; 5, bulbo-urethral gland. 



Fig. 52.5. — Cross-section of Pelvic Urethra of Bull. 
1, Prostate gland (pars disseminata); 2y urethra; S, 
urethral muscle; 4, aponeurosis. The lumen of the urethra 
is black and the shaded area around the urethral lumen ic 
the stratum cavernosum. 



cm.) in length. They are commonly unsymmetrical in size and shape. Short 
branches are often given off from the chief tube. The excretory duct opens at the 
colliculus seminalis, just lateral to the ductus deferens. 

The structure of the vesic-ula is masked by a thick capsule of fibrous tissue and luistriped 
muscle, which maintains it in its bcnl rondilidn and also sends trabecule betwci'ii llir alveoli. 
There is a central canal into whicli I he .sciict inn fornied in the alveoli passes. The ia\ il iis (central 
canal and alveoli) are lined with ciiluninar epithelium. On account of this structure the term 
glandular vesiculares is preferred by some anatomists. 



GENITAL ORGANS OF THE BULL 589 

The prostate is pale yellow in color, and consists of two parts, which are, how- 
ever, continuous with each other. The body (Corpus prostatas) is a small mass 
which stretches across the dorsal surface of the neck of the bladder and the origin 
of the urethra. It measures about an inch and a half (ca. 3.5 to 4 cm.) transversely, 
and about half an inch (ca. 1 to 1.5 cm.) in width and thickness. The pars dis- 
seminata surrounds the pelvic part of the urethra; dorsally it forms a layer about 
half an inch (ca. 10 to 12 mm.) thick, but ventrallj' it is cjuite thin (ca. 2 mm.). 
It is concealed by the urethral muscle and its aponeurosis; hence it often escapes 
notice, but is very evident on cross-section (Fig. 525). It has a branched tuliular 
structure, and the interlobular tissue contains a large amount of unstriped muscle. 
The prostatic ducts open into the urethra in rows, two of which are between two 
folds of the mucous membrane that proceed backward from the colliculus seminalis; 
two other series occur on either side, lateral to the folds. 

The uterus masculinus appears to be absent usually. Ellenberger states that 
it opens between the ejaculatory orifices, while Martin says that it usually has two 
orifices at the colliculus, liut that it often unites with the ductus deferens. 

The bulbo-urethral glands are somewhat smaller than in the stallion. They 
are liable to escape notice, since they are covered by a thick laj^er of dense fibrous 
tissue and also partially by the bulbo-cavernosus muscle. Each has a single duct 
which opens into the urethra under cover of a fold of the mucous membrane. 

The penis is cylindrical, and is longer and of very much smaller diameter than 
in the horse. Just l^ehind the scrotum it forms an S-shaped ciu've, the sigmoid 
flexure; thus about one foot of the penis is folded up when it is fully retracted. 
The flexure is effaced during erection. The glans penis is about three inches (ca. 
8 cm.) in length. It is flattened dorso-ventrally, and its extremity is pointed and 
twisted. The external urethral orifice is situated at the end of a groove formed 
by this twist; it is only large enough to admit a probe of medium size. Even in 
the non-erect state the penis is remarkaljly dense and firm. The tunica albuginea 
is very thick, and encloses the urethra; it is composed of dense white fibrous tissue. 
In the first part, as far as the first curve, there is a thick median septum penis. 
Beyond this there is a central axial band of dense fibrous tissue from which numerous 
strong trabeculse radiate. The erectile tissue is small in amount, except in the root, 
so that the organ undergoes very little enlargement in erection, the chief effect 
being increased rigidity. The walls of the cavernous spaces are fibro-elastic, not 
muscular. 

The length of the penis in the adult is about three feet (ca. 90 cm.). The crura are flattened 
laterally; they contain a well-developed corpus cavernosum and numerous helicine arteries, some 
of which open directly into the cavernous spaces. The suspensory ligaments are attached to the 
ventral ridge on the symphysis pelvis. The body is somewhat flattened dorso-ventrally beyond 
the first curve. The extremity of the glans is unsymmetrical, the urethral orifice being situated 
ventro-laterally. The glans contains only a thin superficial stratum of erectile tissue, and hence 
undergoes little enlargement in erection. In the body of the penis there is a longitudinal vein on 
either side in the ventral part of the corpus cavernosum. 

The bulbo-cavernosus muscle presents several remarkable features. It is for 
the greater part an inch or more (ca. 3 cm.) in thickness, but its length is only 
six to eight inches (15 to 20 cm.). It is covered by a strong aponeurosis, and is 
divided by a median raphe into two lateral halves, except at its origin. It 
diminishes in size from behind forward, and its anterior extremity is pointed.' 

The ischio-cavemosus muscle resembles in general that of the horse, but is 
flattened laterally. It is covered by a tight aponeurosis. 

The retractor penis muscle resembles that of the horse in origin. Its two parts 

■ In the sheep and sometimes in the ox there is a m. ischio-bulbosus which consists of fibers 
that extend across the initial part of the bulbo-cavernosus. Fibers which extend from the iscliial 
arch over the bulbourethral gland form the m. ischio-glandularis. A urethro-cavernosus muscle 
is sometimes present; it consists of fibers which arise on the urethra near the origin of the bulbo- 
cavernosus and end on the latter and the ischio-cavemosus. 



590 



GENITAL ORGANS OF THE BULL 



are about an inch (ca. 2 to 5 cm.) apart on the root of the penis, where they He 
in a groove on either side of the bulbo-cavernosus. They then come close together 
and pass on either side of the ventral curve of the sigmoid flexure. Further for- 
ward they are on the ventral surface of the penis, and end about five or six inches 
(ca. 12 to 15 cm.) behind the glans. 

The prepuce is very long and narrow. Its orifice is about two inches (ca. 
5 cm.) Ijehind the umbilicus; it is only large enough to admit a finger readily, and 
is surrounded by long hairs. The preputial cavity is about fifteen inches (35 to 40 
cm.) long and a little over an inch (ca. 3 cm.) in diameter. The lining membrane 
forms longitudinal folds; it is covered with squamous stratified epithelium, and 
has coiled tubular glands. The penile layer is glandless, and is reddish in color. 
It presents lymph nodules in its posterior part. 

There are two pairs of preputial muscles which are derivatives of the cutaneus 
muscle. The anterior preputial muscles or protractors of the prepuce (Mm. 
prisputiales craniales) are two flat banils, two inches or more (5 to 6 cm.) in width, 
which arise close together in the xiphoid region, about eight inches (20 cm.) in 



Process^is urethra. 

Galea glandis 

Corona glandis 
Collum glandis 

Prepace 




Processus urethrce 
Galea glandis 
Corona glandis 

Tuhcrculum 
Collum glandis 

Prepuce 
Raphe prcepulii 



Fio. 526. — Antebioh Pabt of Penis op Ram. 
A. Right side; B. left side. (After Bohm.) 



front of the preputial orifice. Traced backwaril they diverge, leaving the umbilicus 
and an area about one and a half inches wide free, and then unite Ijehind the pre- 
putial orifice. They draw the prepuce forward. The posterior preputial muscles 
or retractors of the prepuce (Mm. prseputiales caudales) arise in the inguinal region 
and converge on the anterior part of the prepuce. They draw the prepuce back- 
ward.' 

The urethra in its pelvic part is about five inches (12 cm.) long, and is of 
relatively small and uniform caliber. The urethral muscle encloses the tube 
ventrally and laterally; it is very thick, crescentic in cross-section, and is covered 
by an aponeurosis. Dorsally the aponeurosis is thick and the muscle absent. 
Inside of these the pars disseminata of the prostate surrounds the urethra as far 
back as the bulbo-urethral glands. The colliculus seminalis is a rounded promi- 
nence about an inch (ca. 2.5 cm.) in length. On it there are two slit-like openings, 
situated close together. These are the ejaculatory orifices, at which the ductus 
deferens and the excretory duct of the vesicula seminalis open. The urethral 

' These muscles are subject to a good deal of variation. The retractor may be absent. Many 
fibers come in from the cutaneus on either side, dip under the protractor, and are inserted into 
the skin just behind the preputial opening. The homologue of the protractor is present in the 
cow. 



GENITAL ORGANS OF THE BOAR 591 

crest extends forward from the colliculus, and two mucous folds pass backward 
from it and diverge. The mucous membrane behind the coUiculus is red in color. 
The extrapelvic part has an enlargement, the bulb, at its origin; it then gradually 
diminishes in diameter, and is relatively very small at its termination. Other 
features have been mentioned in preceding paragraphs. 

The bulb of the urethra has a thick tunica albuginea, enclosing a highly developed erectile 
tissue. The cavernous spaces are wide; their walls are relatively thin and consist of fibrous tis- 
sue and unstriped muscle. On cross-section many arteries are visible laterally. Further forward 
the uretlira is siu-rounded by a well-developed corpus cavemosum, which is thickest vent rally; 
here an artery of considerable size occurs on each side. 

In the ram the genital organs resemble in general those of the bull. But the 
testicles are relatively much larger; a testicle of an adult ram may be four inches 
(ca. 10 cm.) long and weigh about nine to ten ounces (ca. 2.50-300 gm.). They are 
broader in proportion to their length. The prostate is entirely disseminate. The 
bulbo-urethral glands are relatively very large. The peculiar character of the 
terminal part of the penis is shown in the annexed figure. The urethra lies in a 
groove on the ventral surface of the corpus cavernosum. Its terminal part pro- 
jects commonly about an inch and a half (ca. 3-4 cm.) beyond the glans penis, 
forming a twisted processus urethrse. 



GENITAL ORGANS OF THE BOAR 

The scrotum is situated a short distance from the anus, and is not so sharply 
defined from the surrounding parts as in the other animals. 

The testicles are very large and are regularly elliptical in contour. They are 
placed so that the long axis is directed upward and backward, the free border being 
superficial and the tail of the epididj-mis highest. They are comparatively soft in 
texture. The tunica albuginea contains much elastic tissue, but no muscular fibers. 
The mediastinum testis is an axial strand of fibro-elastic tissue, from which inter- 
lobular septa radiate. Other septa are given off from the deep face of the tunica 
albuginea. The interlobular tissue is abundant, and the lobulation correspond- 
ingly distinct. The parenchyma is gray and often dark in fat animals. There is a 
rete testis from which seven or eight efferent ducts proceed to the epididymis. 
The epididymis is closely attached to the testicle; its tail is very large and forms a 
blunt conical projection at the posterior end of the testicle. 

The spermatic cord is necessarily very long (20 to 25 cm. in a boar of medium 
size). The ductus deferens in its testicular part is flexuous, and is closelj' attached 
by the tunica vaginalis; it forms no distinct ampulla. The cremaster extemus is 
well developed, and extends to about the middle of the scrotal part of the tunic. 

The vesiculae seminales are exceedingly large, and extend into the abdominal 
cavity. They are three-sided pyramidal masses, are in apposition with each other 
medially, and cover the posterior part of the bladder and the ureters, the ductus 
deferentes, the body of the prostate, and the anterior part of the urethra and bulbo- 
urethral glands. They are pale pink in color, distinctly lobate and glandular in 
structure, and are enclosed in a thin fibrous capsule. Half a dozen or more large, 
thin-walled ducts emerge from the medial surface of each and converge to a much 
smaller excretory duct. The latter passes back lateral to the ductus deferens, and 
terminates at a slit-like opening on the colliculus seminalis. The two ducts may 
unite. 

In the adult boar the vesiculse are about five to six inches (ca. 12 to 15 cm.) long, two to 
thi'ee inches (ca. 5 to 8 cm.) wide, and one and a half to two inches (ca. 4 to 5 cm.) thick; they 
weigh about 6 to 8 ounces each. They have a branched tubular structure and are distinctly di- 



592 



GENITAL ORGANS OF THE BOAR 



vided into lobules. Many of the tubules are extremely wide (as much as 2 mm. in diameter), and 
are beset with bay-like extensions and short, wide branches. These axial spaces of the lobules are 
succeeded by the efferent ducts. The cavities are lined by a single layer of columnar cells. The 
secretion is thick and turbid, and has an acid reaction. 

The prostate consists of two parts, as in the ox. The body is about an inch 
(2.5 cm.) wide, and overhes the neck of the bladder and tlio urethra at their junc- 
tion. It is concealed by the vesiculae seminales. The pars disseminata forms a 
layer which surrounds the pelvic part of the urethra, and is covered by the urethral 
muscle, except dorsally. 

The uterus masculinus is small, and appears to be inconstant. 
The bulbo-urethral glands are very large and dense. They are somewhat 

cylindrical, and lie on either 
side of and upon the posterior 
two-thirds of the pelvic ure- 
thra.i In a large boar they 
are about five inches (ca. 12 
cm.) in length and an inch or 
more (ca. 2.5 to 3 cm.) in 
width. They are partially 
covered with a layer of stri- 
ated muscle (M. bulbo-glan- 
dularis), and have a lobulated 
surface. Each gland has a 
large excretory duct which 
leaves at the deep face of the 
posterior part, perforates the 
dorsal wall of the urethra at 
the ischial arch, and opens in 
a cul-de-sac covered bj^ a fold 
of mucous membrane. 

It is to be noted that these 
accessory glands are very small in 
animals which have been castrated 
early; the bulbo-urethral glands may 
be only al^out an inch long in such 
subjects. 

The penis resembles in 
general that of the ox. The 
sigmoid flexure is, however, 
prescrotal. The anterior part 
has no glans, and is spirally 
twisted, especially in erection. 
The external urethral orifice is 
slit-like antl is situated ventro- 
laterall.y, close to the pointed 
extremity. The penis in the 
adult boar measures about 18 
to 20 inches (ca. 45 to 50 cm.) in length. Its muscles resemble those of the bull. 
The bulbo-cavernosus is very strong but short. The retractor penis arises from 
the third and fourth sacral segments; its two parts run backward and a little 
ventrally on each side of the rectum to the perineum, where they reach the urethral 
surface of the penis; they end on the ventral curve of the sigmoid flexure of the penis. 

1 When hardened- in situ, they are in great part three sided, with rounded edges. They are in 
contact with each other to a considerable extent and cover the urethra dorsally and laterally. The 
urethral muscle partly covers their lateral surfaces. 




Fig. 527. — Genital Organs of Boar. 
a, Testicle; 6, epididymis; c, ductus deferens; d, spermatic artery; 
€, vesicula seminalis ; e', excretory ducts of vesiculEB ; /, body of prostate ; 
g, bulbo-urethral gland; h, urinary bladder: i, urethral muscle; k, 
bulbo-cavernosus muscle; /, penis; /', sigmoid flexure of penis; /", 
spiral anterior part of penis, exposed by slitting open prepuce; m, ori- 
fice of preputial pouch; n, retractor penis muscle. The vesiculse sem- 
inales are drawn outward to show the structures which, in the natural 
position, are covered by them. (Ellenberger-Baum, Anat. d. Haustiere.) 



MALE GENITAL ORGANS OF THE DOG 593 

The prepuce has a narrow orifice, around which there are stiff hairs. The 
cavity is very long, and is partially divided by a circular fold into a posterior narrow 
part and a much wider anterior part. The lining membrane of the posterior part is 
papillated, and is in close contact with the penis; it contains numerous lymph 
nodules, the largest of which occur in the fundus. In the dorsal wall of the wide 
part there is a circular opening which leads into a cul-de-sac, the preputial diver- 
ticulum. This pouch is ovoid in form (when distended), and varies greatly in size 
in different subjects. It extends for the most part backward over the narrow part 
of the prepuce. Its cavity is partially divided by a narrow septum. It contains 
usually decomposing urine and macerated epithelium, which have a characteristic 
and very unpleasant odor. Concrements have been found in it. 

Oehmke found that a cast of the pouch in a Yorkshire boar weighing about 500 poimds 
measured 9 cm. in length, 12} 2 cm. in breadth, and 6 cm. in height. The opening into the pre- 
puce will admit two fingers in the adult, but is ordinarily closed by folds of the lining membrane. 
The sac is much smaller in animals which were castrated young, and the opening is vertical and 
further back; in them it is often empty or contains only a little clear urme. The pouch is gland- 
less, but contains many small lymph nodules; it is covered by a layer of striped muscle which is 
mamly derived from the homologue of the protractor of the prepuce of ruminants. 

The urethra has a very long pelvic part (ca. 15 to 20 cm long in the adult); 
it is covered (with the pars disseminata. of the prostate) by a thick urethral muscle, 
except dorsally, where there is a dense fibrous layer. Surrounding the mucous 
membrane there is a rich venous plexus, which is regarded as a stratum cavernosum. 
Outside of this the pars disseminata of the prostate is easily distinguished on cross- 
section by its j'ellow color. The prostatic ducts are numerous and small. The 
ductus deferentes and the excretory ducts of the vesiculse seminales have slit-like 
openings close together in small diverticula on either side of the colliculus seminalis. 
The latter has the form of a round prominence. A small uterus mascuUnus may 
occur in the colliculus between the ducts, but it is often absent. There is a distinct 
bulb at the root of the penis. It has a dense covering, which in part resembles 
fibro-cartilage. The erectile tissue here is highlj' developed. The cavernous 
spaces are large, and the trabeculse contain much unstriped muscle; between the 
spaces there are numerous arteries. The penile part is of small caliber, and is 
surrounded by erectile tissue which, however, does not extentl to the extremity of 
the penis. 



MALE GENITAL ORGANS OF THE DOG 

The scrottun is situated about half way between the inguinal region and the 
anus. The skin covering it is pigmented and is covered sparsely with fine hairs. 
The raphe is not very distinct. 

The testicles are relatively small, and have a roimd-oval form. The long 
axis is oblique, and is directed upward and backward. The mediastintim testis 
is central and is well developed. The epididymis is large, and is closely attached 
along the dorsal part of the lateral surface of the testicle. 

The spermatic cord and the tunica vaginalis are long; they cross the side of 
the penis very obliquely. The ujjijer end of the tunic is sometimes closed, so that 
there is then no vaginal ring. The ductus deferentes have narrow ampullae. 

The vesiculse seminales are absent. 

The prostate is relatively large; it is yellowish in color, dense in structure, 
and lies at or near the anterior border of the pubis. It is globular, and surrounds 
the neck of the bladder and the urethra at their junction. A median furrow indi- 
cates a division into two lateral lobes. The capsule and stroma contain a large 
amount of unstriped muscle. The ducts are numerous. Lobules of prostatic 
38 



694 



MALE GENITAL ORGANS OF THE DOG 



tissue (pars disseminata) are also found in the wall of the urethra for a short distance 
further back. The gland is subject to much variation in size, and is often enlarged, 
especially in old subjects. 

The position of the prostate varies. When the bladder is empty and contracted, the gland 
is entirely in the pelvic cavity and may be an inch or more behind the anterior border of the 
pubis. When the bladder is full, the prostate is often largely or entirely prepubic. 

The uterus masculinus is a small compressed saccule in the colliculus seminalis- 

The bulbo-urethral glands are absent. ^ 

The penis presents several special features. In its posterior part there are two 
distinct corpora cavernosa, separated by a median septum penis. In its anterior 
part there is a l^one, the os penis, which in large dogs reaches a length of four inches 
(ca. 10 cm.) or more. It is regarded as a part of the corpus cavernosum which has 





Fig. 528. — External Gephtal Organs of Male Dog; Ventro- 
lateral View op Preparation. 
1, Scrotum; t\ tunica vaginalis: £, epididymis: 3, vascular 
part of spermatic cord: 4> ductus deferens: 5, prepuce; 6,fpa.Ts longa 
glandis; 6', corpus cavernosum penis; 7, bulbus glandis; 7', con- 
tour of bulbus in erection: S, ischio-cavernosus muscle; a, acetab- 
ulum; b, obturator foramen, (.\fter Ellenberger, in Leisering'a 
Atlas.) 



Fig. 529. — Internal Genital Organs of 
Male Dog; Dorsal View. 
I, Urinary bladder; S, ureter: 3, ductus 
deferens; 4' prostate; 5, urethral muscle; 6, 
bulb of urethra; a, abdominal wall; b, ilium; 
c, ischium. (After Ellenberger, in Leisering's 
Atlas.) 



ossified. Ventrally it is grooved for the urethra; dorsally it is convex, and an- 
teriorly it becomes smaller and has a curved fibrous prolongation.^ The glans 
penis is very long, extending over the entire length of the os penis; its anterior 
part, the pars longa glandis, is cylindrical, with a pointed free end; behind this 
there is a rounded enlargement, the bulbus glandis. Both are composed of erectile 
tissue. The two dorsal veins arise from the bullius glandis, pass backward on the 
dorsum penis, and unite at the ischial arch. A small muscle (M. compressor venae 
dorsalis penis) arises from the tuber ischii on either side; the two converge on the 
dorsum penis near the bulbus glandis. They compress the dorsal veins, and may 
also tend to elevate the penis and thus assist in copulation. The other muscles 
offer no features worthy of special description. 

^ They are present in the cat, and are the size of a pea. 

* In the young subject it has a prolongation composed of hyaline cartilage, which becomes 
fibrous later. 



MALE GENITAL ORGANS OF THE DOG 595 

The cavernous spaces of the glans penis are venous in character. Von Frey has showTi that 
the spaces of the pars longa are continuous with veins which come from the penile layer of the pre- 
puce, and have no arterial blood supply. The erectile tissue of the bulbus glandis receives its 
blood by veins which come from the pars longa. This arrangement is considered to accoiuit for 
the erection of the bulbus during copulation, and the slowness with which erection subsides. 

The prepuce forms a complete sheath around the anterior part of the penis. 
The outer layer is ordinary integument. The inner layers are thin, reddish in 
color, and glandless. The penile layer is closely attached to the pars longa glandis, 
more loosely to the bulbus glandis. There are many lymph nodules in these layers, 
which are specially large and often prominent in the fimdus of the preputial cavity. 
The protractor muscles arise in the xiphoid region and decussate posteriorly around 
the extremity of the prepuce. 

The pelvic part of the urethra is relatively long. Its first part is enclosed in 
the prostate.' At the ischial arch the urethra has a well-developed bulb, formed 
by an enlargement here of the corpus cavernosiun urethrae. It is divided by a 
median furrow and septum (Septum bulbi urethrte) into two lateral lobes or hemis- 
pheres (Hemispheria bulbi urethrse), and is covered by the strong but short bulbo- 
cavemosus muscle. The other erectile bodies have been described. The urethral 
muscle is very strong; it encircles the urethra from the prostate backward and has 
a median raphe dorsally. The ischio-urethral muscle arises from the tuber ischii 
and ends on a fibrous ring at the symphysis ischii which encircles the dorsal veins 
of the penis. 

' This is clinically important, since enlargement of the prostate may interfere with mic- 
tm"ition. 



THE FEMALE GENITAL ORGANS 

The female genital organs (Organa genitalia feminina) are: (1) The two 
ovaries, the essential reproductive glands, in which the ova are produced; (2) 
the uterine or Fallopian tubes, which convey the ova to the uterus ; (3) the uterus, 
in which the ovum develops ; (4) the vagina, a dilatable passage through which the 
foetus is expelled from the uterus; (5) the vulva, the terminal segment of the genital 
tract, which serves also for the expulsion of the urine; (6) the mammary glands, 
which are in reality glands of the skin, but are so closely associated functionally 
with the generative organs proper that they are usually described with them. 



GENITAL ORGANS OF THE MARE 

THE OVARIES 

Tlie ovaries (Ovaria) of the mare are hean-shapcd, and are much smaller 
than the testicles. Their size varies much in different subjects, and they are 




Fig. 530. — Lateral View of Genital Organs and Adjacent Structures of Mare. 
It is to be noted that the removal of the other abdominal viscera has allowed the ovaries and uterus to sink down; 
this has, however, the advantage of showing the broad ligaments of the uterus. 1, Left ovary; 2, uterine or Fallopian 
tube; S, left cornu uteri; 4. right cornu uteri; 5, corpus uteri; 5', portio vaginalis uteri, and 5" , os uteri, seen through 
window cut in vagina : 6, broad ligament of uterus; 6'", round ligament of uterus; 7, vagina; 5, labia vulvae; 5, rima 
vulvae; 9\ dorsal commissure, and 9", ventral commissure, of vulva; 10, constrictor vulvae; 11, position of vestibular 
bulb; IS, ventral wall of abdomen; IS, left kidney; H, left ureter; IB, urinary bladder; 16, urethra; 17, rectum; 
18, anus; 19, 19', unpaired and paired parts of sphincter ani externus; 20, retractor ani cut at disappearance under 
sphincter ani externus; 21, suspensory ligament of anus; 22, longitudinal muscular layer of rectum; 22\ recto-coccygeus; 
23, constrictor vaginae; a, utero-ovarian artery, with ovarian {a') and uterine {a") branches; b, uterine artery; c, um- 
bilical artery; d, ischium; e, pubis; /, ilium, (.\fter Elleuberger, in Leisering's Atlas.) 



normally larger in young than in old animals; one ovary is often larger than the 
other. They are about three inches (ca. 7 to 8 cm.) long and an inch to an inch 

596 



THE OVARIES 



597 



^^ 



and a half (ca. 3-4 cm.) thick. The weight is about two and a half to three 
ounces (ca. 70-80 grams). 

Each presents for description two surfaces, two borders, and two extremities. 
The surfaces are termed medial and lateral (Facies medialis, lateralis); they are 
both smooth and rounded.^ The attached or mesovarial border (Margo mes- 
ovaricus) is convex. It is enclosed in a part of the broad ligament termed the mes- 
ovarium; the vessels and nerves reach the gland at this border. The free border 
(Margo liber) is marked by a notch which leads into a narrow depression, the 
ovulation fossa. The tubal or anterior extremity (Extremitas tubaria) is rounded, 
and is related to the fimbriated end of the uterine 
tube. The uterine or posterior extremity (Extremitas 
uterina) is also round, and is comiected with the horn 
of the uterus by the ovarian ligament. 

The ovaries are situated in the sublumbar region, 
and are usually ventral to the fourth or fifth lumbar 
vertebra. They are usually in contact with the lum- 
bar wall of the abdomen. The average distance from 
the ovaries to the vulvar orifice is about twenty to 
twenty-two inches (ca. 50-55 cm.). in a mare of 
medium size. 

The position of the ovaries is very inconstant, as might 
be expected from their mode of attachment. Either ovary or 
both may be deflected transversely in either direction to the 
full limit allowed by the mesovarium. The so-called medial 
and lateral surfaces are usually dorsal and ventral, or vice 
versa, according to the direction of the deflection. The range 
of variation in the longitudinal direction is greater than was 
formerly thought to be the case. The right ovary is often 
about six inches (ca. 15 cm.) beliind the correspondmg kid- 
ney, but the distance between them may be nearly twice as 
great or may be only about two inches (ca. 5 cm.). The left 
ovary is usually a little (ca. 2-3 cm.) further back than the right 
one, but is usually nearer the corresponding kidney, the average 
distance between them being about four inches (ca. 10 cm.). 
They may be about two inches (ca. 5 cm.) from the extremity 
of the corresponding cornu of the uterus or in contact with it. 
Except during pregnancy, they are almost always in contact 
with the lumbar abdominal wall, and do not hang down among 
the adjacent viscera. 




Fig. 5.31. — Right Ovabt of Make, 
WITH .\djacent Structures. 
The extremity of the cornu is 
opened. 1, Ovary; 1', corpus luteum; 
2, uterine or Fallopian tube, with its 
ostium abdominale (^'). fimbriae {2"), 
and ostium uterinum {2'") ; 3, cornu 
uteri with its mucous lining (5') ex- 
posed: 4t ligament of ovarj'; 4'. meso- 
salpinx. (After Ellenberger, in Leiser- 
ing's Atlas, reduced.) 



The ovary is attached to the .sublumbar region 
by the anterior part of the broad ligament of the 
uterus; this part of the ligament, the mesovarium, 
is about three or four inches (ca. 8 to 10 cm.) wide, 
measured from the ovary directly to the parietal at- 
tachment. The uterine ex-tremity of the ovary is 
connected with the extremity of the cornu of the 
uterus by the ligament of the ovary (Lig. ovarii pro- 

prium) ; this is a band of unstriped muscle enclosed between the layers of the broad 
ligament. 

Structure. — The greater part of the surface of the ovary has a covering of 
peritoneum. The peritoneal investment is absent at the attached border where 
the vessels and nerves enter; this area is termed the hilus of the ovary (Hilus 
ovarii), although there is no depression here. The ovulation fossa is covered by 
a layer of short polygonal cells, a remnant of the primitive germinal epithelium. 

' These terms apply properly only when the adjacent viscera are removed and the ovaries 
are actually "suspended" by the broad ligaments. When the ovary is in its natural position, 
the surfaces are usually dorsal and ventral, the former corresponding to the "lateral" surface if the 
free border is directed outward, to the "medial" if the free edge is medial. 



598 



GENITAL ORGANS OF THE MARE 



The stroma of the ovary (Stroma ovarii) is a network of connective tissue. In the 
meshes of the stroma there are (in young subjects) numerous ovisacs or folliculi 
oophori, containing ova (Ovula) in various stages of development. The immature 
ovum is surrounded by folhcle cells; those more advanced in development are 
enclosed by several (5-8) layers of follicle cells, forming the stratum granulosimi, and 
by a condensation of the stroma termed the theca folliculi; within the theca is a 
quantity of fluid, the liquor folliculi. At one point the follicle cells are heaped up as 
a sort of mound (Cumulus oophorus), in which the ovum is enclosed. Such sacs 
are termed folliculi oophori vesiculosi;' they enlarge as they mature, becoming 
visible to the naked eye as vesicles with a diameter of a centimeter or more. When 
fully developed, the follicles are superficially situated, and often project slightly 
from the surface of the ovary. At intervals follicles rupture and their contents 
escape. This process, which sets free the ovum, is termed ovulation; it 

takes place in the mare only 
at the ovulation fossa, and 
occurs during the periods of 
oestrum. 

The structure of the ovary of 
the mare is pecuHar and differs from 
that of other animals in the fact 
that it does not consist of a cortex 
(zona parenchymatosa), in which 
the foUicles are situated, and a me- 
dulla (zona vasculosa), which con- 
tains the vessels and nerves. This 
arrangement is present in the fcctute, 
but later the follicles become dis- 
tributed tliroughout the interior of 
the gland, and the vascular zone is 
superficial. 

After rupture of a follicle, its 
cavity is partly occupied by a blood- 
clot, constituting what may be 
termed a corpus rubnmi. By prohf- 
eration and enlargement and fatty 
changes, the follicle cells are trans- 
formed into lutein cells, forming a 
yellow mass known as a corpus lu- 
teum. If impregnation takes place, 
the accompanying increase in vas- 
cularity of the organs may cause 
the corpus luteum to reach a large 
size; if impregnation does not oc- 
cur, it is much smaller, and is 
sooner replaced by scar tissue, form- 
ing the corpus albicans s. fibrosum. 
In the new-boni foal the ovaries are large and oval in form. The free border is convex and 
is covered by germinal epithelium, which extends over a large part of the surfaces also. This area 
is distinguishable by its duU gray appearance from the peritoneal surface, which has the usual 
smooth ghstenuig character. The limit of the peritoneal epithelium is a distinct line, termed l)y 
Waldeyer the margo limitans peritona^i. As growth proceeds the ovary gradually becomes bent 
until It assumes its definitive curved shape. The germinal epithelium is then limited to the ovu- 
lation fossa. The ovaiy migrates somewhat during development from its primitive position, 
wliich is the same as that of the testicle. 




OVAEY OF 



I.) 

figure) and 



Fig. 532. — .Schematic Representation of Changes 
Mare from Fcetal to Adult State. (After B 
The changes affect chiefly the free border (upper i 
the extent and form of the area covered by germinal epithelium (4). 
1, Peritoneum (broad ligament); g, ligament of ovary; 3, fimbria of 
uterine tube; 4. germinal epithelium; 5, vessels, which reach the 
ovary at the attached border (fi). The latter represents the hilus, 
while the deep depression at the free border is the ovulation fossa. 
(Ellenberger, in Leisering's Atlas.) 



In old animals the ovaries commonly consist largely of fibrous tissue, in which 
there are often cysts of various sizes. The ova, present in enormous number at 
birth, have then been extruded, or destroyed by phagocytic action or degeneration. 

Vessels and Nerves. — The arteries of the ovary are derived from the ovarian 
artery. The artery is relatively large and is flexuous; it reaches the attached 
border of the ovary by passing between the layers of the mesovarium. The veins 
are large and nmnerous. They form a plexus somewhat like that of the spermatic 

1 Also known as Graafian follicles. 



THE UTERINE TUBES THE UTERUS 599 

cord. The lymph vessels pass to the himbar glands. The nerves are derived from 
the sympathetic system through the renal and aortic plexuses. They accompany 
the arterial branches. 

THE UTERINE TUBES 

The uterine or Fallopian tubes (Tulate uterinse) act as excretory ducts of the 
ovaries, since they convey the ova from the reproductive glands to the uterus. 
They are not, however, in direct continuity with the glantls, but rather partly in 
contiguity ^vith, and partly attached to, them.' They are two flexuous tubes, 
eight to twelve inches (ca. 30 to 20 cm.) long, which extend from the extremities 
of the uterine cornua to the ovaries. The tubfe is very small at its uterine end 
(ca. 2-3 mm. in diameter), but toward the ovary it widens considerably (4-8 mm. 
in diameter), forming the ampulla tubae. Each is enclosed in a peritoneal fold, 
derived from the lateral layer of the broad ligament, and termed the mesosalpinx. 
This largely covers the lateral aspect of the ovary, and forms with it and the broad 
ligament a pouch called the bursa ovarica. The uterine extremity (Extremitas 
uterina) of the tul)e communicates with the cavity of the cornu by a minute orifice, 
the ostium uterinum tubae. The ovarian extremity is expanded and somewhat 
funnel shaped, and is therefore termed the infimdibulum tubae uterinae. The 
margin of the latter is slit into irregular processes, the fimbriae, some of which, the 
fimbriae ovaricae, are attached in the ovulation fossa. About the middle of the 
infundilDulum is a small opening, the ostiiun abdominale tubae, by which the tube 
communicates with the peritoneal cavitj'. The ovarian extremity of the tube 
appears normally to be applied to the ovary, so that the extruded ova pass into it 
and are conveyed to the uterus. - 

Pedunculated cysts, the hydatides tenninales,' are often found on one or more of the 
fimbriae. In the mesosalpinx are bUntl flexuous tuljules, which constitute the paroophoron, a 
remnant of the Wolffian body. They are most evident in the young adult, and tend to disappear 
with increasing age. Not uncommonly they give rise to cysts. 

Structure. — The tube is covered ex-ternally by a serous coat formed by the 
mesosalpinx. The serous membrane is continuetl on the fimbriae, and meets the 
mucous lining on them. The fibrous adventitia is |continuous vnth the fibrous 
lamina of the broad ligament. The muscular coat consists chiefly of circular 
fibers, outside of which there are longitudinal fibers derived from the broad liga- 
ment; the thickness of the muscular coat diminishes toward the ovarian extremity. 
The mucous coat is thin and is much plicated. The folds (Plicae tubarite) are 
chiefly longitudinal, but in the wide part of the tube (Ampullae tubae) they are very 
complex, so that on cross-sections the spaces between the folds maj' be mistaken for 
branched tubular glands. The folds are continued on to the fimbriae. The epithe- 
lium is a single layer of columnar ciliated cells, the cilia producing a current directed 
toward the uterus. At the ovarian extremity this epithelium passes gradually into 
the squamous type of the serous coat. 

Vessels and Nerves. — The arteries are derived from the utero-ovarian artery. 
The veins are satellites of the arteries. The lymph vessels pass with the ovarian 
vessels to the lumbar glands. The nerves have a similar origin to those of the 
ovary. 

THE UTERUS 

The uterus is a hollow muscular organ, which is continuous with the uterine 
tubes anteriorly and opens into the vagina posteriorly. It is situated chiefly in the 

' The tubes may be regarded, both in origin and structure, as prolongations of the uterus. 

- The arrangement is the only exception to the general rule that the serous cavities are 
closed. In this case the mucous membrane of the infundibulum is continuous with the adjacent 
peritoneum, a persistence of the embryonic relations of the Miillerian duct. 

^ Also known as hydatids of Morgagni. 



600 



GENITAL ORGANS OF THE MARE 



abdominal cavity, but extends a short distance into the pelvic cavity. It is at- 
tached to the sublumbar region and the lateral walls of the pelvic cavity by two 
folds of peritoneum termed the broad ligaments. It consists of two horns, the body, 
and the neck. 

The horns or comua of the uterus (Cornua uteri) are situated entirely in 
the abdomen. They appear to vary considerably in position; commonly they 
are pressed up against the sublumbar muscles by the intestine (ceecum, left parts of 




Fig. 533. — Genital Organs of Mare; Dorsal View 
The left horn and adjacent part of the body of the uterus and the vagina and vulva are opened up. /, Ovary; 3^ 
uterine tube, with;?', its ovarian end; 3, cavity of body of uterus: 4, cavity of left horn; o, right horn, with J', its com- 
munication with the body ; ^, portio vaginalis uteri; t*', external orifice of uterus: 7, broad ligament of uterus; <9, liga- 
ment of ovary: 9, vagina; 10, vulva; iO', orifices of ducts of glandulae vestibularcs majores; iO", orifices of ducts of 
glandulse vestibularcs minores; II, transverse fold; 12, external urethral opening; 13, 13', labia vuIveb; 14, glans 
clitoridis: 14', junction of crura to form corpus clitoridis indicated by dotted lines; IS, urinary bladder; a, utero- 
ovarian artery with ovarian (a') and uterine (a") branches; b, middle uterine artery. (After Ellenberger, in Leisering's 
Atlas.) 



large colon, small colon, and small intestine). They are cylindrical when moder- 
ately distended, and are about ten inches (ca. 25 cm.) in length. The anterior 
extremity of each forms a blunt point which receives the uterine tube. Posteriorly 
they increase somewhat in caliber, converge, and unite Avith the body. The dorsal 
border (Margo mesometricus) is slightly concave and is attached to the sul)lunibar 
region by the broad ligament. The ventral border (Margo liber) is convex and free. 

Wlien a soft uterus is distended, its horns are strongly curved, but this does not represent 
the natural form. When fixed in situ, the liorns are either shghtly curved or nearly straight. 



THE UTERUS 601 

The two horns are commonly unsymmctrical in length and diameter in mares which have borne 
young. 

The body of the uterus (Corpus uteri) is situated partly in the abdominal, 
partly in the pelvic, cavity. It is cylindrical, but considerably flattened dorso- 
ventrally, so that in cross-section it is elliptical. Its average length is seven or 
eight inches (ca. 18-20 cm.), and its diameter, when moderately distended, about 
four inches (10 cm.). Its dorsal surface (Facies dorsalis) is related to the rectum 
and other parts of the intestine. Its ventral surface (Facies ventralis) is in contact 
with the bladder, and has inconstant relations with various parts of the intestine. 
The term fundus uteri is applied to the wide anterior part from which the cornua 
diverge. 

The position of the body of the uterus is variable, especially in regard to its anterior part. 
It is often pressed up against tlie rectum, and may be deflected to either side — most frequently 
to the left — by the pelvic flexure of the great colon or coils of the small colon. 

The neck or cervix of the uterus (Cervix uteri) is the constricted posterior 
part which joins the vagina. It is about two to three inches (5-7.5 cm.) in length, 
and an inch and a half (3.5-4 cm.) in diameter. Part of it (Portio vaginalis uteri) 
projects into the cavity of the vagina; it is therefore not visible externally, but 
may be felt through the vaginal wall. 

Attachments. — The body and horns are attached to the abdominal and pelvic 
walls by two extensive peritoneal folds, the broad ligaments of the uterus (Liga- 
menta lata uteri). These extend on either side from the sulilumbar region and the 
lateral pelvic walls to the dorsal border of the cornua and the lateral margins of the 
body of the uterus. They contain the vessels and nerves of the uterus and ovaries, 
connective tissue, and a large amount of unstriped muscular fibers which arc con- 
tinuous with those of the uterus. The ureters are situated along their parietal 
margins. The lateral layer of each gives off a fold, the round ligament of the uterus 
(Ligamentum teres uteri), which blentls with the parietal peritonetmi over the 
abdominal inguinal ring; its anterior extremity is situated above the extremitj' of 
the cornu and forms a long round appendix. It contains muscular tissue, vessels, 
and nerves, and is the homologue of the gubernaculum testis. The anterior part of 
the neck is continuous wnth the vagina, and thus has a more fixed position than the 
rest of the organ. 

The cavity of the uterus (Cavum uteri) is largely obliterated in the non- 
pregnant state by the contraction of the wall and by folds of the mucous lining. 
At the extremity of each cornu it communicates wilh the uterine tube by a minute 
opening on a small papilla. The cavity of the neck is termed the cervical canal 
(Canalis ccrvicis); it is closed ordinarily by mucous folds and a plug of mucus. 
It opens into tlie vagina by the orificium externum uteri,' and into the body Ijy the 
orificiiun internum uteri. 

Structure. — The wall of the uterus consists of three coats. The serous coat 
(Perimetrium) is, for the most part, closely adherent to the muscular coat. It is 
continuous with the broad ligaments. The muscular coat consists essentially of 
two layers, a thin external stratum of longitudinal fibers, and a thick internal layer 
of circular fibers. Between these is a very vascular layer (Stratum vasculare) of 
connective tissue with circular and oblique muscular fibers in it. The circular coat 
is very thick in the neck, where it forms a sphincter half an inch or more (ca. 1.5 cm.) 
in thickness. The mucous membrane rests directly on the muscular coat, and is 
brownish-retl in color, except in the neck, where it is pale. It is covered by a single 
layer of high columnar cells, and contains nimierous long, branched tubular uterine 
glands (Glanduhe uterinte) ; these are absent in the cervix. 

Vessels and Nerves. — The chief arteries are the uterine and the uterine 
branch of tlie utero-ovarian, which have a flexuous course in the broad ligaments; 
1 This is frequently designated the os uteri. 



602 GENITAL ORGANS OF THE MARE 

there is also a branch from the internal pudic artery. The veins form pampini- 
form plexuses and accompanj^ the arteries. The l3rmph vessels are numerous and 
go to the internal iliac and lumbar glands. The nerves are derived from the 
sympathetic through the uterine and pelvic plexuses. 

The foregoing statements refer to the non-gravid uterus. In the pregnant state it under- 
goes important changes in size, position, and structure. The increase in size affects chiefly the 
gravid horn (except in the case of twins) and the body. The horn attains a length of aljout 
two and a half to three feet (ca. SO to 90 cm.), and a corresponding diameter; in this process it 
extends much beyond the ovary and the broad Ugament. The gravid uterus is entirely abdominal 
in position, and extends along the ventral wall, chiefly to the left of the median plane. It weighs 
about nnie pounds (ca. 4 kg.), according to EUenberger. The broad ligaments increase greatly 
in size and contain more muscular tissue. The vessels are greatly enlarged and form new branches. 
The muscular coat, in spite of the increase in size and number of the fibers, is somewhat thinner, 
except in the neck. The mucous membrane is tliicker and more vascular. 

THE VAGINA 

The vagina is the passage which extends horizontally through the pelvic 
cavity from the neck of the uterus to the vulva. It is tubular, is about six to eight 
inches (ca. 15-20 cm.) in length, and, when slightly distended, about four or five 
inches (ca. 10-12 cm.) in diameter. Its dilatabilitj' appears to be limited only by 
the pelvic wall. There is no external line of demarcation between the vagina 
and the uterus or the vulva. 

It is related dorsalh' to the rectum, ventralh' to the bladder and urethra, and 
laterally to the pelvic wall. The recto-genital pouch of the peritoneum commonly 
extends between the vagina and rectum for a distance of about two inches (5 cm.), 
and ventrally the vesico-genital pouch passes backward somewhat further between 
the vagina and bladder. Thus most of the vagina is retroperitoneal and is sur- 
roundetl by a quantity of loose comiective tissue, a venous plexus, and a variable 
amount of fat.' 

Structure. — With the exception of the short peritoneal part, as indicated above, 
the proper wall of the vagina is composed of muscular and mucous coats. The 
muscular coat is composed of a thin layer of longitudinal fibers, and a thicker layer 
of circular fibers; it is covered externally by a fibrous adventitia, and there is a 
large amount of intermuscular comiective tissue. The mucous coat is highly 
elastic, and is covered Tvith a stratified — but not squamous — epithelium. It has 
no glands. 

Under usual conditions the cavity is practically obliterated bj' apposition of 
the walls, so that the linnen is a transverse slit; this condition is pronounced when 
the rectum is full. The anterior end of the vagina is largely occupied by the intra- 
vaginal part of the neck of the uterus, so that the cavit}^ is here reduced to an an- 
nular recess termed the fornix vaginae. The posterior part is directly continuous 
with the vulva without any line of demarcation except the transverse fold which 
covers the external urethral orifice; in very young subjects this fold is continued 
on either side, forming the hymen, which narrows the entrance to the vagina (In- 
troitus vaginse).^ 

Vessels and Nerves. — The arteries are branches of the internal pudic arteries. 
The veins form a rich plexus which is drained by the internal pudic veins. The 
Ijmiph vessels go to the internal iliac lymph glands. The nerves are derived from 
the sympathetic through the pelvic plexus; numerous ganglia are present in the 
adventitia. 

'The amount of the vagina which is covered by peritoneum varies, depending apparently 
on the degree of fullness of the rectum and bladder. When these organs are empty, the peritoneum 
may cover the vagina for a distance of three or four inches (ca. 8-10 cm.); when they are full, the 
vagina may be completely retroperitoneal or nearly so. 

2 In formalin-hardened subjects there is frequently a pronounced ring-like constriction at the 
junction of the vulva and vagina. 



THE VtTLVA 603 

THE VULVA 

The vulva or urogenital sinus (Vcstibulum vaginte) is the terminal part of the 
genital tract. ^ It is continuous in front with the vagina, and opens externally at 
the vulvar cleft below the anus. There is no external line of demarcation between 
the vagina and vulva. The tube is four or five inches (ca. 10-12 cm.) in length, 
measured from the external urethral orifice to the ventral commissure; dorsally 
(from a point vertically opposite to the external urethral orifice) it is considerably 
shorter. It is related dorsally to the rectum and anus, ventrally to the pelvic floor, 
and laterally to the sacro-sciatic ligament, the semimembranosus muscle, and the 
internal pudic artery. The external orifice, the vulvar cleft (Rima vulvae), has the 
form of a vertical slit, four or five inches (ca. 10-12 cm.) high, and is margined 
by two prominent rountled lijjs, the labia vulvae. The labia meet above at an acute 
angle, forming the dorsal commissure (Commissura dorsalis), which is about two 
inches (ca. 5 cm.) below the anus. They unite below to form the thick, rounded 
ventral commissure (Commissura ventralis), which lies about two inches (ca. 5 cm.) 
behind and below the ischial arch. When the labia are drawn apart, a rounded 
body, about an inch (ca. 2.5 cm.) wide, is seen occupying a cavity in the ventral 
commissure; this is the glans cUtoridis, the homologue of the glans penis, and the 
cavity in which it lies is the fossa clitoridis. The roof of the fossa is formed by a 
thin fold, which overlies the glans clitoridis and is attached centrally to it. At 
the anterior extremity of the ventral wall of the vulva, i. e., four or five inches (ca. 
10-12 cm.) from the ventral commissure, is the external urethral orifice (Ori- 
ficium urethrte externum).' It readily admits the finger and is very dilatable. It 
is covered by a fold of mucous membrane, the free edge of which is directed back- 
ward (Fig. 533). 

Structure. — The labia are covered by thin, pigmented, smooth skin, which is 
richly supplied with sebaceous and sweat glands. This is continuous at a distance 
of about half an inch (ca. 1-1.5 cm.) from the free edge with a thin, glandless 
mucous membrane. Under the skin there is a layer of striped muscle, the con- 
strictor vulvae; this fuses above with the sphincter ani, and embraces the clitoris 
below, spreading out laterally at the ventral commissure. It constricts the vulvar 
orifice and elevates the clitoris. The constrictor vestibuU muscle embraces the 
vulva in front of the preceding; it is deficient dorsallj' and is joined on either side 
by a band of unstriped muscle, the suspensory ligament of the anus. It constricts 
the vulva. Within this there is an unstriped muscular coat, most of the bundles 
of which are circular. Chiefly between this coat and the mucous membrane there 
is in the lateral wall, just in front of the labia, a flattened, oval body, the bulbus 
vestibuli (Fig. 578); this is an erectile structure, homologous with the corpus 
cavernosum urethrsB of the male. It is about two and a half to three inches (ca. 
6-8 cm.) long, and an inch or more (ca. 3 cm.) wide. It is similar in structure to 
the bulb of the corpus cavernosum urethrse of the male, and is supplied with l)lood 
by a large branch of the internal pudic artery. The mucous membrane of the 
vulva is reddish in color, and forms longitudinal and transverse folds. It presents 
ventrally two linear series of small papillae which converge toward the ventral 
commissure; these mark the orifices of the ducts of the glandulae vestibulares 
minores. On either side of the dorsal wall is a group of eight to ten larger promi- 
nences on which the ducts of the glandulae vestibulares majores open (Fig. 533). 

Quite exceptionally there may be found on either side of the urethral orifice the openings of 
the canals of Gartner (Ductus epoophori longitudinales). 

^ The term vulva is used here in the sense in which it is understood generally by English 
and French veterinarians. In the German works it is applied only to the labia and other struc- 
tures around the external orifice of the urogenital sinus, while the sinus itself is termed the vestibule 
of the vagina (Vestibulum vagins). 

^ Also termed the meatus urinarius. 



604 GENITAL ORGANS OF THE MARE 

The clitoris is the homologue of the penis and consists of similar parts (minus 
the urethra and its muscle). The corpus clitoridis is about two inches (ca. 5 cm.) 
long, and its diameter about that of one's little finger. It is attached to the ischial 
arch by two crura (Crura clitoridis). The glans clitoridis is the rounded and en- 
larged free end of the organ which was noted above as occupying the fossa clitoridis 
in the ventral commissure of the vulva. It is covered by a thin pigmented integu- 
ment, similar to and continuous with that which lines the fossa; these constitute 
the prepuce of the clitoris (Praeputium clitoridis) . The organ is composed of erectile 
tissue similar to the corpus cavernosum penis. The ischio-cavemosus is the 
homologue of the muscle of the same name of the male ; it is a very feeble muscle. 
The veins of the clitoris communicate by an intermediate plexus on either side with 
the bulbus vestibxili. 

THE FEMALE URETHRA 

The female urethra (Urethra feminina) represents only that part of the canal 
of the male which lies between the internal urethral orifice and the colliculus semi- 
nalis. Its length is two to three inches (5-7.5 cm.), and its lumen is sufficient to 
allow easily the introduction of the finger; it is, however, capable of remarkable 
dilatation if sufficient care and patience are exercised in the process. It lies centrally 
on the pelvic floor, and is related dorsally to the vagina, to which it is in part at- 
tached. The external orifice is at the anterior end of the vulva, as described above. 

Structure. — The intrinsic muscular coat consists of external longitudinal and 
internal circular fibers; it is absent where the urethra is attached to the vagina. 
The mucous membrane is thro^vn into longitudinal folds when the canal is closed ; 
it is highly elastic, and is covered with stratified epithelium. There is a rich sub- 
mucous network of veins, forming a sort of corpus cavernosum. 

The urethral muscle (M. compressor urethra) embraces the urethra and is 
continuous with the constrictor vestibuli. It is covered by a fibro-elastic membrane. 



THE MAMMARY GLANDS 

The mammary glands (Glandulse lactiferse) are modified cutaneous glands 
which are so closely associated functionally with the genital organs as to be con- 
sidered accessory to them. 

In the mare they are two in number, and are placed on either side of the median 
plane in the inguinal region. Each gland has the form of a very short, flattened 
cone, much compressed transversely, and having a flat medial surface. It consists 
of the glandular mass or body of the gland (Corpus mammte) and the papUla or 
teat (Papilla mammae). The base is related to the abdominal wall, to wliich it is 
attached by areolar tissue, which contains a venous plexus, the superficial inguinal 
Ijinph glands, and a variable amount of fat. The apex is constituted by the teat, 
which is also flattened transversely and varies in length from one to two inches 
(ca. 2.5 to 5 cm.). Between the bases of the teats is the intermammary groove. 
On the apex of each teat there are usually two small oriflces placed close together; 
these are the openings of the lactiferous ducts. 

Structure. — The skin covering the glands is thin, pigmented, chiefly hairless, 
and supplied with numerous large sebaceous and sweat glands. Under this are two 
layers of fascia, except on the teats. The superficial fascia presents no special 
features. The ileep fascia consists of elastic tissue; centrally two laminae detached 
from the abdominal tunic descend on either side of the median plane, forming a 
septum between the two glands, and constituting their ligamentum suspensorium.' 

The gland substance or parench5rma is pinkish gray in color, and of firmer 

' These laminte are separated almost completely by a layer of areolar tLssue, so that it is pos- 
sible to remove a'diseased gland by careful dissection between the layers of the septum. 



GENITAL ORGANS OF THE COW 



605 



consistence than the fat which is found around and within the giand. It is enclosed 
by a fibro-elastic capsule which sends inward numerous trabeculae; these form the 
interstitial tissue, and divide the gland into lobes and lobules. In the latter are 
the secretory tubules and alveoli, which unite to form the larger ducts. Each lobe 
has a duct, which opens at the base of the teat into a space called the lactiferous 
sinus (Sinus lactiferus), and from this two (or three) lactiferous ducts (Ductus 
lactiferi) pass through the extremity of the teat. These ducts are lined with a non- 
glandular mucous membrane, which is covered with stratified squamous epithelium. 
They are surrounded by unstriped muscular tissue, the bulk of the fibers being ar- 
ranged in a circular manner to form a sphincter. 

The size and form of the mammary glands are subject to much variation. In the young 
subject, before pregnancy, they are small and contain little gland tissue. During the latter part 
of gestation, and especially during lactation, they increase greatly in size, and the gland tissue is 
highly developed. After lactation the secretory structures undergo marked involution, and the 
gland is much reduced in size. The relative amounts of gland substance and interstitial tissue 
vary greatly; in some cases a gland of considerable size contains little parenchyma and is con- 
sequently functionally deficient. 

Vessels and Nerves. — The arteries are derived from the external pudic artery, 
which enters the gland at the posterior part of its base. The veins form a plexus 
on either side of the base of the gland, which is drained by the external pudic vein 
chiefly. The lymph vessels are numerous and pass to the superficial inguinal and 
lumbar lymph glands. The nerves are derived from the inguinal nerves and the 
posterior mesenteric plexus of the sympathetic system. 



GENITAL ORGANS OF THE COW 

The ovaries of the cow are much smaller than those of the mare; they measure 
usually about one and a half inches (ca. 3.5-4 cm.) in length, and an inch 





Fig. 534. — Ovary of Cow. 
1, Broad ligament of uterus; 2, ligament of 
ovary; 3, fimbria ovarica; 4. attachment of broad 
ligament; 5, surface of ovary covered witli ger- 
minal epitlielium; 6, corpora lutea; 7, Graafian 
follicle. (From Leisering'a Atlas.) 



Fig. 535. — Uterus of Cow, Contr.icted; Dorsal View. 
a, Body of uterus; b, b', horn of uterus; c, ovary; d, d, 
triangular folds connecting horns of uterus (Ligg. intercornu- 
alia). (After Zieger.) 



(ca. 2.5 cm.) in thickness in their largest part; the weight is half an ounce 
or more (ca. 15-20 gm.).' They are oval in form, pointed at the uterine 

' Hess gives the following average measurements of the ovaries of 95 cows: Length of right, 
4.3 cm.; of left, 3.71 cm.; width of right, 2.S cm.; of left, 2.36 cm. Zieger found that the right 
one was larger than the left m 65 out of 75 cases. 



606 



GENITAL ORGANS OF THE COW 



end, and have no ovulation fossa. They are situated usually a little above 

the middle of the lateral margin of the pelvic inlet in the non-pregnant subject, but 

may be a little further forward. They are thus about 16 to 18 inches (ca. 40-45 

cm.) from the vulvar opening in a cow of medium size. The greater part of the 

surface of the gland is covered with germinal epithelium, the peritoneal epithelium 

being limited to a narrow zone along the 

attached border. Follicles of various sizes :"■ 

are often seen projecting from the surface, 

as well as corpora lutea; a corpus luteum 

verum has a pronounced yellow color, and 

may reach a width of half an inch or more 

(ca. 1-1.5 cm.). 

The uterine or Fallopian tubes are long 
(ca. 20-25 cm.) and less flexuous than in the 
mare. The junction with the cornu of the 
uterus is not so abrupt as in the mare, since 
the extremities of the horns are pointed. 
The uterine orifice of the tube is rather large 
and funnel-shaped. The fimbriae are not so 
extensive as in the mare. 

The uterus lies almost entirely within 
the abdominal cavity in the adult. The 
body is only about an inch and a half (ca. 
3-4 cm.) in length, although externally it 






Fig. 536. — Cotyledon OF Gbavid Uterus or Cow. Fig. 537. — Genital Organs of Cow; Dorsal 

The photograph is about three-fourths natural size of a speci- View. 

men of medium size. The right uterine cornu and the vagina and 

vulva are opened up: /, Labium vulvae; ^.ventral 
commissure; S, glans clitoridis; ^, glandula vestib- 

appears to be about five or six inches long. "'''"^ '"^'°'- ''^'^"'"^J'l '"* T TTl "''"" 

^' ... 1 r 1 brane; a, pouch in which the ducts of the pre- 

This false impression is due to the fact that ceding open; e. suburethral diverticulum; 7, ex- 
the posterior parts of the COrnUa are united ternal urethral opening; S, openings of canals of 

by comiective and muscular tissue and have ^H' .l^Z:; I^.Z^! ^'S^ 

a common peritoneal covering. The COmUa tube; 14, ostium abdomlnale tuba; is, ovary. 

are, therefore, really more extensive than (From Leisering's Atlas, reduced.) 

they appear externally and have an average 

length of about fifteen inches (ca. 35-40 cm.) . They taper gradually toward the free 

end, so that the junction with the uterine tubes is not abrupt, as in the mare. The 

free part of the horn curves at first downward, forward, and outward, and then turns 

backward and upward, forming a spiral coil. The cervix is about four inches (ca. 

10 cm.) long; its wall is remarkably dense, and may be more than an inch (ca. 3 cm.) 



GENITAL ORGANS OF THE COW 607 

in thickness. Its lumen, the cervical canal, is spiral, and is ordinarily tightly closed 
and very difficult to dilate. The vaginal part of the uterus is fused ventrally with 
the vagina, so that the fornix vaginte is dorsal, and not an aiuiular space as in the 
mare. The muscular coat of the uterus is thicker than in the mare. It consists 
of an external .longitudinal layer and two circular strata. The imier circular layer 
is about a fourth of an inch (ca. 6 mm.) thick in the cervix. The other layers are 
continued in the vagina. The mucous membrane of the horns and body presents 
as a characteristic feature the uterine cotyledons (Cotyledones uterinae).^ These 
are oval prominences, about a hundred in number, which are either irregularly 
scattered over the surface or arranged in rows of about a dozen. 

In the non-gravid uterus they average about half an inch or more (ca. 1.5 mm.) in length, 
and a Uttle less in width and thickness. During pregnancy they become greatly enlarged and 
pedunculated. The larger ones then measure about four or five inches (10 to 12 cm.) in length, 
an inch and a half (.3 to 4 cm.) in width, and an inch (2 to 2. .5 cm.) in thickness. The deep face has 
a hilus at which the vessels enter. The rest of the surface has a spongy appearance, due to numer- 
ous crypts wliich receive the villi of the chorion. 

The uterine glands are long and branched. The mucous membrane of the 
cervix is pale, glandlcss, and forms numerous folds. The latter are arranged in 
several series which obliterate the lumen. 
At the external uterine orifice the folds 
(Plicse palmatte) form roimded prominences 
arranged circularly, which project into the 
cavity of the vagina. There are no glands 
in the cervix, but a thick mucus is secreted 
by goblet cells. 

The broad ligaments are not attached 
in the sublumbar region as in the mare, but 

to the upper part of the flanks, about a Fig. 538.— diagrammatic Sagittal Section op 

handbreadth below the level of the tuber P^^Rt ot Urogenital Tract of Cow, 

coxffi. They contain a conspicuous amount ®"°"™° SnBnHETHR..L Diverticdlcm. 

of unstriped muscle. The round ligaments 

are well developed, and can be traced distinctly to the vicinity of the abdominal 
inguinal ring. 

The vagina is somewhat longer and more roomy than that of the mare; its 
wall is also thicker. Its length in the non-pregnant animal is about eight to ten 
inches (ca. 20-2,5 cm.); but in the pregnant cow the length increases to twelve 
inches (30 cm.) or more. The recto-genital pouch of peritoneum extends backward 
about five inches (ca. 12 cm.) on the dorsal surface, while ventrally the serous coat 
only extends backward about two inches (ca. 5 cm.). In the ventral wall of the 
vagina, between the muscular and mucous coats, there are common!}' present the 
two canals of Gartner (Ductus epoophori longitudinales). When well developed, 
they may attain the tliameter of a goose ciuill, and may be traced forward to the 
anterior part of the vagina or even further. They open posteriorly near the ex- 
ternal urethral orifice. - 

The vulva has thick, wrinkled labia, and both commissures are acute; the 
ventral one is pointed, and has on it a number of long hairs ; it lies about two inches 
(5 cm.) bchintl, and about the same distance below the level of, the ischial arch. 
The external urethral orifice is four or five inches (10 to 12 cm.) from the ventral 
commissure. Beneath it is a blind pouch, the suburethral diverticulimi, which is 

^ Also known as carunculae uterinae. 

- These tubes are remnants of the Wolffian ducts, and, like other fcctal vestiges, are very 
variable. Roder states that the right canal was absent in over 52 per cent., the left in only 22 per 
cent., of the cows examined by him. In some cases they may be traced in the broad ligaments for 
a variable distance toward the ovary. They are of clinical mterest in that cysts frequently form 
along their course. 




60S 



GENITAL ORGANS OF THE COW 



about an inch fca. 3 cm.) long, and readily admits the end of a finger.' The two 
glandulae vestibulares majores- are situated in the lateral walls of the vulva, under 
the constrictor vulvae. They are little over an inch (ca. 3 cm.) long and about half 
an inch (ca. 1.5 cm.) in width. Each has two or three ducts which open into a 
small pouch of the mucous membrane; this cul-de-sac opens on the floor of the 
vulva, about an inch and a half (ca. 3^ cm.) lateral to and behind the external 




Fig. 539. — Cross-section of Mamm. 
, Body of gland; 6, lactiferoua 



' Glani)S of Cow. 



■, cavity of teat; d, lactiferous duct; e, intermammary groove 
tween glands; g, supramammary fat. 



urethral orifice. The gland consists of lobules separated by relatively thick trabec- 
ulae of connective tissue and unstriped muscle. The glandulae vestibulares 
minores occur along the median ventral groove. Numerous lymph nodules are 
present in the mucous membrane, especially in the ventral part; they may be 
large enough to cause visible prominences. 

The clitoris has very short crura, but the body is four or five inches (ca. 10-12 

■ The form and position of this pouch should be carefully noted on account of the difficulty 
it causes in catheterizing the bladder. If the catheter is passed along the ventral wall of the 
vulva (as in the mare), it will always enter the pouch instead of the urethra. 

^ Also known as the glands of Bartholin. 



GENITAL ORGANS OF THE EWE 609 

cm.) long and is flexiious. Only the pointed end of the glans is visible in the ventral 
commissure of the vulva. 

The urethra is about four inches (10 cm.) in length; it is narrower and much 
less dilatable than that of the mare. It is fused dorsally ^vith the wall of the 
vagina, while laterally anil ventrally it is covered by the constrictor vaginae muscle. 

The mammary glands, normally two in number, are popularly termed the 
udder. They are very nmch larger than in the mare, and the body of each is 
somewhat ellipsoidal in form, but flattened transversely. The base of each gland 
is slightly concave and slopes obliciuel.v downward and forward in adaptation to 
the abdominal wall, to which it is adherent; it is in relation posteriorly to the large 
supramammary lymiDh-glands and a cjuantity of fat. The medial surface is flat, 
and is sejjarated from the other gland by a well-developed double septum. The 
lateral surface is convex. Four well-developed teats are present; they average 
about three inches (ca. 7-8 cm.) in length. It is customary to consider the udder 
to consist of four "quarters"; there is no septum nor visible division between the 
two quarters of the same side, but, on the other hand, injections of fluids of different 
colors into the two teats of the gland demonstrate that the cavities drained by them 
do not communicate. 

The size and form of the glands vary "greatly; in the highly specialized dairy breeds (e. g., 
Holsteins) they often attain enormous dimensions. The size of the udder is not a certain index 
of its productivity, since some so-called "fleshy" udders contain a very large amount of inter- 
stitial tissue and relatively little parenchyma. Small accessory teats often occur posteriorly; 
commonly these are rudimentary and imperforate (polythelia), but sometimes they drain a small 
amount of gland substance (polymastia). Sanson described a case in which there were seven 
teats, aU giving milk. 

Each teat has a single duct which widens superiorly and opens freely into a 
roomy lactiferous sinus (Sinus lactiferus), popularly known as the milk cistern. 
The lactiferous duct (Ductus lactiferus) or teat canal is lined by a glandless mucous 
membrane wliich is covered with stratified squamous epithelium; the lower part 
(ca. 1 cm.) of the canal is narrow, and is closed by a sphincter of unstriped muscle. 
The mucous membrane of the sinus forms numerous folds which render the cavity 
multilocular. 

Vessels and Nerves. — The arteries are derived from the external pudic arteries. 
The veins form a circle at the base of the udder, from which the blood is drained by 
three trunks, viz., the very large subcutaneous abdominal, the external pudic, and 
the perineal vein. The lymph vessels are numerous, and pass to the supramammary 
glands chiefly. The nerves are derived from the inguinal nerves and the posterior 
mesenteric plexus of the sympathetic. 



GENITAL ORGANS OF THE EWE 

The genital organs of the ewe resemble in general those of the cow, but a few 
special features may be noted. 

The ovaries are almond shaped and are half an inch or more (ca. 1.5 cm.) in 
length. 

There is no demarcation between the uterine tube and the horn of the uterus; 
the tube is verj^ flexuous near the infundibulum. 

The uterus resembles that of the cow. The horns are four or five inches (ca. 
10-12 cm.) long and taper in such a maniier to their junction ^ath the uterine tubes 
that no clear distinction between the two exists. They are coiled in a close spiral, 
and an inch or more of their posterior parts are united. The body is less than an 
inch (ca. 2 cm.) long. The cotyledons are much smaller than those of the cow and 
39 



610 GENITAL ORGANS OF THE SOW 

have a depression on the free surface. The neck is about an inch and a half (ca. 
4 cm.) in length; its lumen is closed by reciprocal prominences and depressions of 
the mucous membrane. The external uterine orifice is in the ventral part of the 
vagina. 

The vagina is three or four inches (ca. 8 cm.) long. Its ventral part contains 
numerous lymph follicles. 

The vulva is an inch or more (ca. 2.5-3 cm.) in length. There is a very small 
diverticulum behind the urethral orifice. The glandulte vestibulares majores are 
inconstant; when present, they may be about the size of a small bean. The labia 
are thick and the ventral commissure is pointed and projects downward. 

The clitoris is short, and the glans is concealed in the fossa clitoridis. 

The mammary glands, two in number, are relatively large, and are approxi- 
mately globular, but flattened on the septal side. 



GENITAL ORGANS OF THE SOW 

The ovaries are concealed in the bursa ovarii, owing to the large extent of the 
mesosalpinx. They are more rounded than in the bitch, and have a distinct hilus. 
They may be situated at or near the lateral margin of the pelvic inlet, as in the cow; 
but their position is quite variable in animals which have borne young and they may 
be only an inch or two behind the kidney. The surface commonly presents rounded 
prominences, so that the gland usually has an irregular lobulated appearance; 
the projections are large follicles and corpora lutea. Mature follicles may have a 
diameter of about a third of an inch (ca. 7-8 mm.), and corpora lutea may be found 
which measure half an inch or more (ca. 12-15 mm.). 

The uterine or Fallopian tubes are long (ca. 15-30 cm.), and less flexuous than 
in the mare. The fimbriated extremity forms an ampulla and has a large abdominal 
opening. The uterine end shades insensibly into the small extremity of the cornu 
of the uterus. 

The uterus presents several striking features. The body is only about two 
inches (ca. 5 cm.) long. The horns are extremely long and flexuous, and are freely 
movable, on account of the large extent of the broad ligaments. In the non- 
pregnant animal they are arranged in numerous coils and appear somewhat like 
thick-walled small intestine. They may be four or five feet (1.2-1.5 m.) in length. 
The extremities of the horns taper to about the diameter of the uterine tubes. The 
neck is remarkable for its length (ca. 10 cm.) and the fact that it is directly con- 
tinued by the vagina without forming any intravaginal projection. When slit open, 
peculiar rounded prominences are seen on its interior; some of these dovetail and 
occlude the cervical canal. They are continuous behind with folds of the mucous 
membrane of the vagina. The broad ligaments contain a large amount of unstriped 
muscle; they also contain a large lymph gland near the ovary.' In the upper part 
of the ligament the muscular tissue forms a rounded band termed the round liga- 
ment. In an adult sow of full size it is about six inches (ca. 15 cm.) long; its 
anterior end forms a blunt projection and posteriorly it ends in the subserous 
tissue at the internal inguinal ring. The medial layer of the broad ligament is 
continuous with the lateral ligament of the bladder. 

The vagina is about four or five inches (ca. 10-12 cm.) long in a sow of medium 
size. It is small in caliber, and has a thick muscular coat which consists of circular 

' The changes in form and position of the uterus during pregnancy are similar to those men- 
tioned later in the case of the bitch (p. 613). 



GENITAL ORGANS OF THE SOW 



611 



fibers between two layers of longitudinal fibers. The mucous membrane is plicated, 
and is intimately united with the muscular coat. 

The vulva is about three inches (7. .5 cm.) in length. The labia are thick and 
are covered with a wrinkled integument. The dorsal commissure is rounded, but 
the ventral one is produced to form a long pointed projection. The fossa clitoridis 
is nearly an inch (ca. 2 cm.) anterior to the ventral commissure. Above it the 
glans clitoridis forms a pointed projection, from which a mucous fold extends 
laterally and backward on each side. There is a deep central depression about 
half way between the fossa clitoridis and the external urethral orifice. The latter 
is bounded on each side by a thick fold which extends backward for a variable 




Fig. 540.^<Jeottal Organs or Sow; Dorsal View. The Vulva, Vagina, and Cervix Uteri abe Slit Open. 
1, Labium vulvae; 2, glans clitoridis; 3, vulva; 4^ external urethral orifice; 5, vagina: 5', cervix uteri; 6, corpus 
uteri; 7, cornua uteri, one of which is opened at 7' to show folds of mucous membrane; 8, uterine tube; S', abdominal 
opening of tube ; 9,9, ovaries; 10, ovarian bursa; 11, 11, broad ligaments of uterus; 12, urinary bladder. (From 
Leisering's Atlas.) 



distance. Lateral to this fold is a depression in which the ducts of vestibular glands 
open. 

On either side of the anterior part of the floor of the vulva there is a cul-de-sac and a deep 
groove leading back from it; these are bounded medially by a longitudinal fold. Ductus epo- 
ophori (canals of Gartner) may be found opening anterior to the external urethral orifice. 

The clitoris is long and flexuous; its glans forms a pointed projection over the 
fossa clitoridis. 

The urethra is about three inches (ca. 7-8 cm.) long. Its posterior part is fused 
with the vagina and produces a corresponding elevation of the floor of the latter. 

The mammary glands are usually ten or twelve in number, and are arranged 
in two rows, as in the bitch. Each teat has commonly two ducts. 



612 



GENITAL ORGANS OF THE BITCH 



GENITAL ORGANS OF THE BITCH 
The ovaries (Fig. 4-42) are small, elongated-oval in outline, and flattened. 
The average length is a little less than an inch (ca. 2 cm.). Each ovary is commonly 
situated a short distance (ca. 1-2 cm.) behind, or in contact with, the posterior pole 
of the corresponding kidney, and thus lies opposite to the third or fourth lumbar 
vertebra, or about half way between the last rib and the crest of the ilium. The 

right one lies between the right part of the 
duodenum and the lateral abdominal wall. 
The left one is related laterally to the spleen. 
Each is concealed in a peritoneal pouch, the 
bursa ovarii, which has a slit-like opening 
ventrally. The two layers which form this 
pouch contain a quantitj' of fat and unstriped 
muscle. They are continued to the cornu of 
the uterus, constituting the mesosalpinx and 
the ligament of the ovary. The surface of 
the ovarj' presents prominences caused by 
projecting follicles. Many follicles contain 
several ova. There is no distinct hilus. 

The uterine or Fallopian tubes arc small 
and average two or three inches (ca. 5-8 
cm.) in length. Each passes at first forward 
in the lateral part of the bursa ovarii, and 
then runs backward in the medial part of 
the pouch ; it is only slightly flexuous. The 
pouch is thus a part of the mesosalpinx. The 
fimbriated extremity lies chiefly in the bursa 
ovarii, but part of it often protrudes through 
the slit-like opening of the bursa ovarii; it 
has a rather large abdominal opening. The 
uterine orifice is very small. 

The uterus has a very short body and 
extremely long narrow horns. In a bitch of 
medium size the body is about an inch (ca. 
2-3 cm.) and the cornua five or six inches 
(ca. 12-15 cm.) long. The horns are of 
uniform diameter, are nearly straight, and lie 
entirely within the abdomen. They diverge 
from the body in the form of a V toward each 
Iddney. Their posterior parts are united by 
the peritonemn. The neck is very short and 
has a thick muscular coat. Dorsally there 
is no line of demarcation between uterus and 
vagina, but the cervix uteri is much thicker 
than the vagina. Ventrally the cervix forms 
a cylindrical projection which lies in a depression of the vaginal wall. The mucous 
membrane of the uterus has long uterine glands and also short tubular crypts. 

The broad ligaments contain much fat and some unstriped muscle. They are 
much wider in the middle than at cither end. The posterior part is attached to the 
anterior part of the vagina. The round ligaments are contained in the free edge of 
folds given off from the lateral face of the broad ligaments. They are bands of 
unstriped muscle and fat. Each passes through the inguinal canal, enveloped by a 
peritoneal pouch (processus vaginalis). A ligamentous fold extends forward from 




Fig. 541. — Genital Organs of Bitch. 
Vulva, vagina, and uterus (in part) are slit 
open, a. Ovarian bursa: 6, same opened to sliow 
the riglit ovary, c; d, d, horns of uterus; e, e', body 
of uterus; /, neck of uterus: /', external uterine 
orifice; g, vagina; h, hymen; i, vulva; k, external 
urethral orifice; I, urinary bladder; m, urethra; 
n, n, labia vulvae; o, fossa clitoridis; p, central 
projection of fold of mucous membrane which con- 
ceals the cUtoria. (After EUenberger, in Leisering's 
Atlas.) 



GENITAL ORGANS OF THE BITCH 613 

the bursa ovarii lateral to the kidney and is attached to the abdominal wall at the 
middle of the last rib. 

The horns of the gravid uterus present dilatations, the ampullae, which contain the 
foetuses, and are separated by constrictions. The gravid uterus lies on the ventral abdominal wall, 
and toward the end of gestation extends forward to the stomach and liver. 

The vagina is relatively long. It is narrow anteriorly, antl has no distinct 
fornix. The muscular coat is thick and consists chiefly of circular fibers. The 
mucous membrane forms longitudinal folds. The canals of Gartner are usually 
absent. 

The vulva has thick labia which form a pointed inferior commissure. The 
mucous lining is smooth and red. It frequently presents small prominences caused 
by lymph follicles. On either side of the urethral orifice there is a small depression. 
The glanduliB vestibulares majores are absent, but the smaller glands are often 
present, and their ducts open ventrally on either side of a median ridge. The 
vestibular bulbs are relatively large and are commonly united ventrally by a sort 
of isthmus. The constrictor muscle is strong and divides into two layers which 
enclose the vestibular bulb. The body of the clitoris is broad and flat, and is about 
an inch and a half (ca. 3^ cm.) long in a subject of medium size. It is not erectile 
in structure, but is infiltrated with fat. It is enclosed by a fibrous albuginea and 
contains large arteries and numerous nerves in its ventral part. The glans clitoridis 
is composed of erectile tissue and is situated in a large fossa clitoridis. A fold of 
mucous membrane extends backward over the glans and fossa; a central projection 
of this fold may be mistaken for the glans clitoridis. 

The mammary glands are usually ten in number, and are arranged in two series, 
extending from the posterior part of the pectoral region to the inguinal region; they 
are, therefore, designated according to location as pectoral, abdominal, and inguinal. 
The teats are short, and present on their apices six to twelve small orifices of the 
excretory ducts. 



ANGIOLOGY 

Angiology is the description of the organs of circulation of the blood and lymph 
—the heart and vessels. The heart is the central hollow muscular organ which 
functions as a suction and force pump; the differences in pressure caused by its 
contraction and relaxation determine the circulation of the blood and lymph, 
It is situated in the middle mediastinal space of the thorax and isenclosed in a fibro- 
serous sac — the pericardium. The vessels are tubular and run through almost all 
parts of the body. They are designated according to their contents as blood- and 
lymph-vessels. 

THE BLOOD-VASCULAR SYSTEM 

The blood-vascular system consists of: (1) The arteries, which convey blood 
from the heart to the tissues; (2) the capillaries, microscopic tubes in the tissues, 
which permit of the necessary interchange between the blood and the tissues; 
(3) the veins, which convey the blood back to the heart. 

The blood-vessels are divided into the pulmonary and the systemic. The 
pulmonary artery conveys the blood from the right ventricle of the heart to the 
lungs, where it is arterialized, and is returned by the pulmonary veins to the left 
atrium of the heart, and passes into the left ventricle. The systemic arteries 
convey the blood from the left ventricle all over the body, whence it is returned by 
the venas cav£e to the right atrium, and passes into the right ventricle.^ 

The term portal system is often applied to the portal vein and its tributaries 
which come from the stomach, intestine, pancreas, and spleen. The vein enters 
the liver, where it branches like an artery, so that the blood in this subsidiary 
system passes through a second set of capillaries before being conveyed to the heart 
by the hepatic veins and the posterior vena cava. 

The arteries (Arterite), as a rule, divide at an acute angle, giving off finer 
and finer branches. In some cases branches come off at a right angle, and others 
are recurrent, i. e., run in a direction opposite to that of the parent stem. The 
intercommunication of branches of adjacent arteries is termed anastomosis. Most 
commonly the connections are made by a network of numerous fine In-anches which 
constitute a vascular plexus (Plexus vasculosus). Relatively large communicating 
branches (Rami communicantes) occur in certain places; they may be transverse 
or in the form of arches. Wide-meshed networks of vessels are termed retia vas- 
culosa. Terminal or end arteries are such as form isolated networks, i. e., do not 
anastomose with adjacent arteries. A rete mirabile is a network intercalated in 
the course of an artery. A collateral vessel (Vas collaterale) is one which pursues 
a course near and similar to that of a larger vessel. 

The veins (Venae) are in general arranged like the arteries, but are usually of 
greater caliber. When a vein accompanies an artery, it is termed a vena comitans 
or satellite vein and is usually homonymous; in many places two veins accompany 
a single artery. The primitive venous trunks do not run with the arteries, and most 
of the superficial veins (Vense cutanese) pursue independent courses. They anas- 
tomose even more freely than the arteries, and large communicating branches 
are very common. Venous plexuses (Plexus venosi) occur in many places. Some 
veins which are enclosed by dense membranes and run usually in bony grooves are 

' It should be noted, however, that the limgs also receive arterial blood through the systemic 
bronchial arteries. This blood is returned in part by the bronchial veins to the right atrium (in- 
directly), in part by the pulmonary veins to the left atrium. 

614 



ANGIOLOGY — THE LYMPHATIC SYSTEM 615 

termed (venous) sinuses; their wall consists of endothelium only; examples of 
this are the sinuses of the dura mater of the brain. A vein which connects one of 
these sinuses with veins outside of the cranium is termed an emissarium. 

A corpus cavemosum is an erectile structure which consists essentially of 
intercommunicating blood-spaces enclosed by unstriped muscle and fibro-elastic 
tissue. These spaces (Cavernse) are lined with endothelium and contain blood. 
Some are to be regarded as greatly enlarged capillaries, since minute arteries open 
into them and they are drained by veins; others are intercalated in the course of 
veins. Distention of the cavernae with blood produces the enlargement and harden- 
ing of the corpus cavemosum which is termed erection. 

Structiu-e of Arteries. — The wall consists of three coats. The external coat 
or adventitia (Tunica externa) consists chiefly of fibrous connective tissue. In the 
deeper part are some elastic fibers, and in some arteries there are also longitudinal 
unstriped muscle-fibers. The middle coat (Tunica media) is composed of unstriped 
muscle and elastic tissue in medium-sized arteries. In small vessels there is chiefly 
muscular tissue, and in the largest trunks almost exclusively elastic tissue. The 
internal coat or intima (Tunica intima) consists of a laj'er of endothelial cells, resting 
on an elastic membrane. The sheath of the vessel (Vagina vasis) is a condensation 
of the surrounding connective tissue,- and is attached more or less closely to the 
external coat. 

Structxire of Veins. — The walls of veins are similar in structure to those of 
the arteries, but are very much thinner, so that veins collapse more or less com- 
pletely when empty, while arteries do not. The middle coat is very thin and con- 
sists to a large extent of ordinary fibrous tissue. The internal coat is also less 
elastic than in the arteries. In many veins this coat forms semilunar valves, the 
free edges of which are directed toward the heart. They are most numerous in the 
veins of the skin and of the extremities (except the foot), while in most vems of the 
body cavities and viscera they are absent or occur only where the veins open into 
larger ones or where two veins join. 

The walls of the vessels are supplied vfiib. blood by numerous small arteries, 
called vasa vasorum. These arise from branches of the artery which they supply 
or from adjacent arteries, ramify in the external coat, and enter the middle coat 
also. The nerves of the vessels (Nervi vasorum) consist of both medullated and 
non-medullated fibers. They form plexuses around the vessels, from which fibers 
pass mainly to the muscular tissue of the middle coat. 



The Lymphatic System 

The l3rmphatic system (Systema lymphaticum) is subsidiary to the venous 
part of the circulatory system, from v/hich it arises in the embryo. It consists of 
the lymph vessels and glands. t'! i ''% '1 

The Ijrmph vessels (Vasa lymphatica) contain a colorless fluid, the lymph, 
which contains numerous lymphocj^tes.' They resemble the veins in structure 
but have thinner walls and are provided with more numerous valves. The vessels 
are sacculated opposite the segments of the valves and have a characteristic beaded 
appearance when distended. The collecting lymph vessels do not usually form rich 
plexuses, as veins often do, their branching is more limited and less tree-like than 
that of the blood-vessels, and their caliber therefore increases less from the periphery 
toward their termination. All of the lymph is ultimately carried into the venous 
system by two trunks, the thoracic duct and the right lymphatic duct. Almost all 

* The term chyle is often applied to the lymph carried by the efferent vessels of the intestine 
when it contains products of digestion, and these vessels may be designated accordingly as lacteals 
or chyle vessels. 



616 ANGIOLOGY 

of the lymph passes through at least one group of lymph glands before entering the 
blood-vascular system. 

The lymph glands or nodes (Lymphoglandulae) are intercalated in the course 
of the lymph vessels. They vary widely in size, some being microscopic, others 
several inches in length. In form they may be globular, ovoid and flattened, 
elongated, or irregular. In certain situations they are aggregated into groups, 
and a knowledge of the position of these and the territory drained into them is im- 
portant. It is convenient, when possible, to indicate their position with regard to 
arteries on the course of which they are placed. In color they are usually gray or 
yellowish-brown in the dead subject, pink or reddish-brown during life, but this 
varies according to their position and functional state. The bronchial glands 
are often blackened by infiltration with carbon. The mesenteric glands are creamy 
or white while the chyle is passing through, but pink at other times. Vessels 
which carry lymph to a gland are called afferent; the efferent vessels which convey 
it away are larger and fewer. Each glanil has a depression, the hilus, at which the 
blood-vessels enter and the efferent lymph vessels emerge. 

Lymph nodules or follicles (Noduli lymphatici) are minute masses of lymphoid 
tissue which occur in certain mucous membranes. They may be solitary, as in the 
solitary nodules or glands of the intestine, or aggregated into masses or patches, as 
in the tonsils and the aggregate glands or so-called Peyer's patches. 

The lymph nodiUe or follicle is the unit of structure of the lymph gland. It consists 
essentially of an artery surrounded by a reticulum of connective tissue, the meshes of which 
contain numerous lymphocytes. Surrounding this is a rich plexus of lymph vessels, forming the 
so-called sinus, enclosed in some cases by a fibrous capsule. The gland consists of a mass of 
follicles, enclosed in a fibrous capsule, from which trabeculse pass in and unite the follicles. Be- 
neath the capsule is the peripheral sinus, which consists of a very rich plexus of lymph vessels; 
to this the afferent vessels pass at various points of the surface. In the cortical substance the 
cells are in rounded masses, the cortical norlules, while in the medullary substance they lie 
around the arteries, forming the so-called medullary cords. The medulla is redder than the cor- 
tex, since it is more vascular; it contams the central lymph sinuses, which have a similar struc- 
ture to the peripheral sinus. 

The haemolymph glands differ from the lymph glands in color and structure. 
They are of a deep red color or even black, which is due to the high vascularity of 
the cortical substance. The peripheral sinuses especially are greatly developed 
and contain numerous red blood-cells. There is no clear division into cortical and 
medullary substance, and the trabeculae contain smooth muscle-cells. Some have 
afferent and efferent lymph vessels and others do not. They resemble the spleen in 
some respects, but their significance is not yet clear. They are numerous in the ox 
and sheep, much fewer in the dog, and apparently are absent in the horse. They 
occur along the course of the aorta, in the perineal fat, at the portal fissure, and with 
the gastric and mesenteric lymph glands. In the ox they are also found under the 
trapezius muscle, under the skin of the upper part of the flank, and in other places 
less constantly. 

The tissue or lymph spaces are interstices of varying size between cells or in 
the meshes of connective tissue. They contain a fluid derived from the blood- 
plasma, which is usually called lymph. They are drained by the veins and lymph 
vessels. The large serous sacs are often included in this category. 

The exact relationship between the lymphatic capillaries and the tissue spaces is still a niatter 
of controversy. It is held by some that the lymph vessels are in direct communication with the 
tissue spaces, while others maintain that the lymphatics are complete closed tubes. Communi- 
cation between the spaces and vessels is in general very free. Mall has showTi that granules in- 
jected into the hepatic artery are returned by the lymphatics as well as by the veins, and intra- 
muscular injections will enter the lymph vessels of the tendon in spite of the absence of lymphatics 
in muscle. 



BLOOD-VASCULAR SYSTEM OF THE HORSE THE HEART 617 

BLOOD-VASCULAR SYSTEM OF THE HORSE 

THE PERICARDroM' 

The pericardium is the filjro-serous sac which surrounds the heart, and also 
the great vessels in connection with it to a greater or less extent. Its form is in 
general similar to that of the heart. The fibrous layer is relatively thin, but 
strong and inelastic. It is attached dorsally to the large vessels at the base of the 
heart, and is continued in jjart up to the longus colli muscle. It is firmly attached 
ventrally to the middle of the posterior half of the thoracic surface of the sternum. 
The serous layer is a closed sac, surrounded by the fibrous pericardium, and invag- 
inated by the heart. It is smooth and glistening, and contains a small amount of 
clear serous fluid, the liquor pericardii. Like other serous membranes, it may be 
regarded as consisting of two parts, parietal and visceral. The parietal part lines 
the fibrous layer, to which it is closely attached. The visceral layer covers thfe 
heart and parts of the great vessels, and is therefore also termed the epicardium. 
The serous pericardium is composed of a connective-tissue membrane, rich in 
elastic fibers, and covered on its free surface by a laj^er of flat mesothelial cells. 

The pericardium is covered by the pericardiac part of the mediastinal pleura 
(Pleura pericardia), and is crossed laterally by the phrenic nerves. Its lateral 
surfaces are related chiefly to the lungs, but the lower part is in partial contact with 
the chest-wall. On the left side the area of contact is from the third rib to the 
sixth rib and intercostal space. On the right side the contact is smaller and is 
chiefly opposite the ventral part of the third and fourth intercostal spaces and inter- 
vening rib. The anterior end of its base is opposite to the second intercostal space 
or third rib, and the posterior bortler is opposite to the sixth rib and space. The 
base is related to the great vessels, the trachea and its bifurcation, the bronchial 
lymph glands, the oesophagus, and the vagus, left recurrent, and cardiac nerves. 

The extent of contact of the pericardium with the lateral wall of the thorax is determined by 
the cardiac notch of the lung. On the left side the anterior margin of the notch is at the third 
rib and the posterior margin is at the sLxth rib dorsally and sixth intercostal space ventrally. The 
greatest height of the notch is at the fourth rib and intercostal space, where it is a handbreadth 
or more (ca. 10-12 cm.) above the sternal end of the rib. The notch is quadrilateral, but much 
narrower above than below. On the right side the notch is usually triangular and is much smaller. 
Its anterior margin begins at the third intercostal space, about three inches (ca. 7-8 cm.) above the 
sternal ends of the third and fourth ribs and runs obUquely to the sternal end of the third rib. The 
posterior marghi begins at the same point and extends to the ventral end of the fourth intercostal 
space or of the anterior border of the fifth rib. 

The two parts of the serous pericardium are, of course, continuous with each other at the 
line of reflection on to the great vessels. The latter are covered in varying degree by the visceral 
layer. The aorta anil pulmonary artery are enclosed in a complete common sheath as far as the 
liifurr-ation of tlic latter. The membrane passes inward between the pulmonary artery and the 
left auricle, and is cdiitinued between the right auricle and the aorta, thus forming the transverse 
sinus of the pericardium (Sinus transversus pericardii). The posterior vena cava is covered 
on the right and ventrally for a di.stance of an inch or a little more (ca. 3 cm.). The pulmonary 
veins have practically no serous coveruig. The epicardium is closely adherent to the muscular 
tissue of the heart, but is attached to the vessels by areolar tissue and fat, and hence is easily dis- 
sected off them. 

THE HEART 
The heart (Cor) occupies the greater part of the middle mediastinal space. 
Its shape is that of an irregular and somewhat flattened cone. It is attached at 
its base by the great vessels, but is otherwise entirely free in the pericardium. It 
is decidedly asymmetrical in position, about two-fifths being to the right of the 
median plane and three-fifths to the left. The long axis (from the middle of the 
base to the apex) is directed ventrally and backward. The base of the heart (Basis 
cordis) is directed dorsally and its highest part lies about at the junction of the 

^ The pericardium is described before the heart, since it must be examined first in the labor- 
atory. 



618 



BLOOD-VASCULAR SYSTEM OF THE HORSE 



dorsal and middle thirds of the dorso-ventral diameter of the thorax. It is opposite 
to the lateral wall of the thorax, from the second intercostal space or third ril) to the 
sixth rib or intercostal space.' The apex (Apex cordis) lies centrally above the last 
segment of the sternum; it is half an inch or less (ca. 1 cm.) above the sternum and 
about an inch (ca. 2-3 cm.) from the sternal part of the diaphragm. The anterior 
border (Margo cranialis) is strongly convex and curves ventrally and backward; 
the greater part is parallel with the sternum. The posterior border (Margo cau- 
dalis) is much shorter, is nearly vertical, and is opposite to the sixth rib and inter- 
costal space. The surfaces, right and left (Facies dextra, sinistra), are convex and 



Lig. arltrioswn Pulmonary veins 



Brachiocephalic trunk 



Coronary 
groove 



Left auricle 




Left longitudinal groove 
Fig. 542. — Heart of Horse; Left View. Hardened in situ. 
The dotted line indicates the Une of reflection of the serous pericardium. The epicardium and subepicardial fat have 



■J 



not been removed. 



are marked by grooves which indicate the division of the heart into four chambers, 
the two atria above and two ventricles below. The left surface (covered by the 
pericardium) is related to the lower third of the chest-wall from the third to the 
sixth rib. On the right side the cardiac notch of the lung is smaller, so that the 
area of relation to the chest-wall extends from the third to the fourth intercostal 
space. - 

' The size and form of the heart vary according to the degree of its contraction and relaxa- 
tion (systole and diastole). In subjects which have been bled and preserved by intravas&ular 
injection of formalin solution the right side is usually fixed in diastole while the left is more or less 
strongly contracted. The base may extend back to the seventh rib. 

^ The arrangement in this regard has been stated at greater length in the descriptions of the 
lungs and the pericardium. 



THE HEART 



619 



The coronary groove (Sulcus coronarius) indicates the division between the atria 
and the ventricles. It almost completely encircles the heart, but is interrupted at 
the origin of the pulmonary artery. The longitudinal grooves,- right and left, 
correspond to the septum between the ventricles. The left longitudinal groove 
(Sulcus longitudinalis sinister) is left-anterior in position. It begins at the coronary 
groove, behind the origin of the pulmonary artery, and clescends almost parallel to 
the posterior border. The right longitudinal groove (Sulcus longitudinalis dexter) 
is right-posterior in position. It begins at the coronary groove, below the termina- 



Pulmonary veins 



Pulmonary artery 



Vena azygns 




Line of reflection of s 



? pericardium dotted. Epieardium and subepicardial fat have not been f 
Left ventricle is considerably contracted. 



ved from heart. 



tion of the posterior vena cava and passes toward the apex, but ends about an inch 
and a half (ca. 3-4 cm.) above the latter. Thus the two grooves do not meet. 
The grooves are occupied by the coronary vessels and a variable quantity of fat. 

The left groove is opposite to the fourth rib, and the right one is opposite to the fifth inter- 
costal space above and the sixth rib below. 

Size and Weight. — The average weight of the heart is about nine pounds 
(ca. 4 kg.) and is about 0.7 per cent, of the body-weight. There is, however, 
great range of variation in apparently normal specimens. 

' Also termed the atrio-ventricular or auriculo-ventricular groove. 
^ Also termed the interventricular grooves. 



620 



BLOOD-VASCULAR SYSTEM OF THE HORSE 



As might be expected, race horses have hearts which are larger than the average, both abso- 
kitely and relatively. In fat subjects the ratio to the body-weight may be about 0.4 per cent., and, 
on the other hand, it is commonly 1 per cent, or more in light horses which are not fat. 

The following average measurements were olitained in medium-sized hearts: 

Sagittal diameter of base'. 25 cm. 

Greatest width of base 18 to 20 cm. 

Circumference at coronary groove 65 to 70 cm. 

Distance between origin of pulnmnary nrtery and apex 25 cm. 

Distance between termination nl ]in-trriiii \('na i:iva and apex 18 to 20 cm. 




J/ Pulmonary veins 



fe=. — 
Pulmonary 



Posterior vena cava 
Left atrium 



Horse with Large Vessels; Dorsal View. Specimen Hardened i 



The Right Atrium 

The right atrivun (Atrium dextrum)' forms the right-anterior part of the liase 
of the heart, and lies alcove the right ventricle. It consists of a sinus venanim, 
into which the veins open, and an auricle- (Auricula dexter). The latter is a conical 
diverticulum which curves around the right and anterior surfaces of the aorta, its 
blind end appearing on the left side in front of the origin of the pulmonary artery- ; it 
is the most anterior part of the heart. 

There are five chief openings in the right atrium. The opening of the anterior 
vena cava (Ostium venae cavse cranialis) is in the dorsal part, and is chiefly opposite 
to the fourth rib. The opening of the posterior vena cava (Ostium venge cavse 

1 Also termed the right auricle. " j^igo termed the auricular appendix. 



THE RIGHT ATRIUM 



621 



caudalis) is at the posterior part, opposite to tiie fifth intercostal space. Between 
the two the wall pouches upward somewhat, and here the vena azygos opens. The 
coronary sinus opens ventral to the posterior vena cava; the orifice is provided with 
a small semilunar valve (Vaivula sinus coronarii). The small coronary vein has a 
separate oldening in some cases close to that of the coronary sinus. The right 
atrio-ventricular orifice (Ostium atrio-ventriculare dcxtrum) is in the ventral part, 



Orifice of vena azyyt 



Anterior vena cava 




Cimus 
iirdrinsus 



liight ventricle 
y'' (septal wall) 



Fig. 545. — Right Side of H: 



Greater Part of Right W.i 



Orga 



\. ' 1|*i:n-ed up by Remov.a 

Hardened in nitu. 

The right ventricle was in diastole, r, Intervenous crest; V, V, tricuspid valve: P, P, papillary muscles; m, z 

moderator bands. Arrow points into origin of pulmonary artery. The crista supraventricularis, which separates tl 

atrio-ventricular orifice from the conus arteriosus, is shown but not marked. The crista terminalis (unmarked) 

nearly directly dorsal to the preceding. 



and leads into the right ventricle. In addition to the foregoing there are several 
small orifices of the vense cordis parvse; these are concealed in the depressions 
between the musculi pectinati. 

The atrium is lined with a glistening membrane, the endocardium. Its walls 
are smooth except on the right and in the auricle, where it is crossed in various 
directions by muscular ridges, the musculi pectinati. Small bands extend across 
some of the spaces enclosed by the musculi pectinati. The latter terminate above 



622 



BLOOD-VASCULAR SYSTEM OF THE HORSE 



on a curved crest, the crista terminalis, which indicates the junction of the primi- 
tive sinus reuniens of the embryo with the atrium proper, and corresponds with the 
sulcus terminahs externally.^ The openings of the venae cavse are valveless. A 
ridge, the intervenous crest (Crista intervenosa) ,- projects downward and forward 
from the dorsal wall just in front of the opening of the posterior vena cava; it 
tends to direct the flow of blood from the anterior vena cava to the atrio-ventricular 




Aorta 

Left pulmonary artery 
pulmonary artery 

Pulmonary vein 
Posterior vena cava 



Fig. 546. — Left Side of Heart of Horse, Opened tp by Removal of Part of Wall. 
A.S., Left atrium; Au. s., left auricle; V, V. 1', bicuspid valve; V. s., left ventricle; M, M, moderator band 
P, papillary muscles; /. ;3, great cardiac vein and circumflex branches of coronary arteries; 3. position of foramen ( 
of foetus; 4< 4> openings of pulmonary veins (chiefly cut av 
aortic orifice. 



atrio-ventricxdar orifice; 6, arrow points toward 



opening. The fossa ovalis is a diverticulum in the septal wall, at the point of 
entrance of the po.sterior vena cava, bounded laterally by a concave margin (Limbus 
fossee ovalis). The fossa is the remnant of an opening in the septmn, the foramen 
ovale, through which the two atria communicate in the fcetus. 

' The crista terminalis is shown, but not marked, in Fig. 545; it is almost opposite (anterior) 
to the intervenous crest. The sulcus terminalis is commonly indistinct e.xcept near the vens& 
caviE. 

^ Also termed the tubercle of Lower. 



THE RIGHT VENTRICLE 



623 



Although called a fossa, it is usually a deep but narrow diverticulum in the horse. The 
interatrial septum is very thin here, and in some cases the foramen ovale fails to close entirely. 

The Right Ventricle 

The right ventricle (Ventriculus dexter) constitutes the right-anterior part of 
the ventricular mass. It forms ahnost all of the anterior border of the heart, but 
does not reach the apex, which is formed entirely by the left ventricle. It extends 
from the third rib to the fourth intercostal space on the left side, to the fifth inter- 
costal space on the right side. It is somewhat triangular in outline, and is crescentic 
in cross-section. Its base is connected largely with the right atrium, with which it 



Pulmonary veiTis 



Pulmonary 



/A, 
lonary artery /fi iv>^ 




Tricuspid vol. 
Chordm ten 



Great coronary 
vein 
Left coronary 

_, artery {circum- 
flex branch) 

— Bicuspid valve 

. Chordw tendinece 

Musculus 
papillaris 

Moderator band 



Left ventricle 



ronary artery ■ 
Fig. 547. — Section of He.\rt of Horse. 
ed in situ and cut nearly at right angles to the ventricular septum. The left ventricle is contracted, 



but not ad 



Segment of aortic valv 



communicates through the right atrio-ventricular orifice; but its left part projects 
higher and forms the conus arteriosus, from which the pulmonary artery arises. 
Its apex is two inches or more (ca. 5-6 cm.) above the apex of the heart. On 
opening the cavity it is seen that the atrio-ventricular orifice and the cavity of the 
conus arteriosus are separated by a thick rounded ridge (Crista supraventricularis). 
The axis of the cavity, taken from this ridge to the apex, forms a spiral curve down- 
ward and to the right. The septal wall is convex and faces obliquely forward and 
to the right. 

The right atrio-ventricular orifice (Ostium atrio-ventriculare dextrum) is oval 
and is chiefly opposite to the fourth and fifth ribs and the intervening space.' The 
plane of the opening is oblique, much lower in front than behind. 

' The extent of the atrio-ventricular orifices, of course, varies with the phase in which the heart 
is fixed. In subjects which are preserved by intravascular injection of formalin solution the right 
side of the heart is usually in diastole, while the left side is more or less contracted. 



624 



BLOOD-VASCULAR SYSTEM OF THE HORSE 



1 he anterior part of the orifice is usually only about an inch or two (ca. 3-5 cm.) above the 
level of the ventral end of the first rib, while the posterior part is four or five inches (ca. 10-12 cm). 
higher than the sternal end of the fifth rib. 

It is guarded by the tricuspid valve (Valvula tricuspidalis) ; of the three large 
cusps of this valve, one is between the atrio-ventricular opening and the conus 
arteriosus, one is septal, and the third is on the right margin. Small intermediate 
cusps intervene between the large ones. The peripheral edges of the cusps are at- 
tached to the fibrous ring at the atrio-ventricular opening. The central edges are 
irregular and hang down into the ventricle; they give attachment to chordae ten- 
dinese. The auricular surfaces are smooth. The ventricular surfaces are rough and 
furnish attachment to interlacing branches of the chordfe tendinese. The valves 
are folds of the endocardium, strengthened by fibrous tissue and at the periphery 



Musculi peclinati 



Pulmonary artery ^ 



Musculi peclinati 



Aortic valve. ^ 

1 

Great coronary ^ j 

vein "/j^ 

Left coronary _ W 

artery . \ 

Bicuspid valve '»"' 

Chorda- tendiiiva; .- - 

Papillary muscle 




^ Right coronary 
artery 



*-^ Trabecula: carnece 



Fig. 5-lS. — Section of Heart of Horse. Specimen Hardened in situ. 
The section is cut nearly at right angles to the ventricular septum, and is viewed from the right and posteriorly. 



by muscular fillers also. The chordae tendineae are attached below to the three 
musculi papillares, which project from the ventricular wall; superiorly they 
divide into branches which are inserted into the ventricular surfaces and the free 
edges of the valves. Each cusp of the valve receives chordae tendineae from 
two papillary muscles. Of the latter, two are on the septum and the third and 
largest springs from the anterior wall. 

The pulmonary orifice (Ostium pulmonale) is circular and is situated at the 
summit of the conus arteriosus, opposite to the third rib and intercostal space. 

The position of the orifice is somewhat variable. Its anterior margin may not be quite so 
far forward as the posterior border of the third rib, and the posterior margin is often opposite to 



THE LEFT ATRIUM THE LEFT VENTRICLE 625 

the fourth rib. It is commonly about three or four inches (ca. 6-9 cm.) above the sternal ends 
of the ribs. 

It is guarded by the pulmonary valve, composed of three semilunar cusps 
(ValvuljB semilunares arteriae puhnonalis) ; of these, one is medial, one lateral, 
and the third posterior.^ The convex peripheral border of each cusp is attached 
to the fibrous ring at the junction of the pulmonary artery and the conus arteriosus. 
The central border is free and concave. Each cusp consists of a layer of endo- 
cardium on its ventricular surface, a continuation of the inner coat of the artery on 
its arterial surface, and an intermediate layer of fibrous tissue. The edge of the 
conus arteriosus forms three arches with intermediate projecting angles or horns, 
to all of which the cusps are attached; and the artery forms opposite each cusp a 
pouch, the sinus of the pulmonary artery .- 

The walls of the ventricle (except in the conus arteriosus) bear muscular ridges 
and bands, termed trabeculse cameae. These are of three kinds, viz., (1) ridges or 
columns in relief; (2) musculi papillares, somewhat conical flattened projections, 
continuous at the base witli the \\all and giving off the chordse tendineae to the 
tricuspid valve; (3) moderator bands (Musculi transversi cordis) which extend 
from the septum to the opposite wall. The latter are partly muscular, partly 
tendinous, and vary in different subjects. The strongest one is usually about 
midway between the base and apex and extends from the septum to the base of 
the lateral musculus papillaris (Fig. 547). It is considered that they tend to prevent 
overdistention. 

The Left Atrium 
The left atrium (Atrium sinistrum)' forms the posterior part of the base of the 
heart. It lies behind the pulmonary artery and the aorta and above the left 
ventricle. The auricle (Auricula sinistra) ''extends outward and forward on the left 
side, and its pointed, blind end is behind the origin of the pulmonary artery. The 
pulmonary veins, usually seven or eight in number, open into the atrium behind 
and on the right side. The cavity of the atrium is smooth, with the exception of 
the auricle, in which the musculi pectinati are present. In some cases there is a 
depression on the septal wall opposite the fossa ovalis, bounded above by a fold 
which is the remnant of the valve of the foramen ovale of the foetus. The left 
atrio-ventricular opening (Ostium atrio-ventriculare sinistrum) is situated below 
and in front; it usually appears smaller than the right one on account of the con- 
traction of the left ventricle in the dead subject. The apertures of small veins of 
the heart are founcj in the spaces enclosed by the musculi pectinati. 

The number and the arrangement of the pulmonary veins are variable. They may be 
five to nine in number. The largest vein is posterior; it is formed by the union of veins from both 
lungs. Usually three veins of considerable size, which lie above the posterior vena cava, enter 
close together on the right, and three or four open close to the ridge which projects from the roof 
at the base of the auricle. 

The Left Ventricle 

The left ventricle (Ventriculus sinister) forms the left posterior part of the 
ventricular mass. It is more regularly conical than the right ventricle, and its 
wall is much thicker except at the apex. It forms all of the posterior contour of 
the ventricular part and the apex of the heart. Its base is largely continuous with 
the left atrium, with which it communicates through the left atrio-ventricular 
opening, but its anterior part opens into the aorta. The cavity usually appears 
smaller than that of the right ventricle in the dead subject, on account of the greater 
contraction of its wall. It is almost circular in cross-section. 

'■ In some cases there are four cusps, and very rarely only two. 
- These are also known as the smuses of Valsalva . 

' Also termed the left auricle. * Also termed the auricular appendix. 

40 



626 



BLOOD-VASCULAR SYSTEM OF THE HORSE 



The left atrio-ventricular orifice (Ostium atrio-ventriculare sinistrum) is 
chiefly opposite to the fifth rib and intercostal space. 

The orifice frequently extends back opposite to the sixth rib, and its anterior margin may 
be opposite to the posterior border of the fifth rib. It is about four inches (ca. 10 cm.) above the 
sternal end of the fifth rib. The plane of the opening is somewhat oblique, and is higher behind 
than in front. 

It is almost circular and is guarded by the bicuspid valve ( Valvula bicuspidalis) .^ 
The two cusps of this valve are larger and thicker than those of the right side of the 




Fig. 549. — Cross-section of Ventricttlah Part of Heart of Horse. 
The section is cut about 5 cm. from the coronary groove. The ventricles are moderately distended. V. d., Right 
ventricle: V. s., left ventricle; 5. v., ventricular septum; 1, 1', papillary muscles of right ventricle: 2, large moderator 
band of right ventricle; 3, 3, 3', papillary muscles of left ventricle; 4, 4', moderator bands of left ventricle; 5, descend- 
ing branch of left coronary artery and great cardiac vein; 6, right coronary artery and small cardiac vein. The anterior 
septal papillary muscle of the right ventricle is not visible, and the right one of the left ventricle is double. 



heart. One is placed in front and separates the atrio-ventricular and aortic open- 
ings. The other is placed behind and laterally and is usually divided into two or 
three parts. 

The aortic orifice (Ostium aortioum) is directed upward and slightly forward. 
It is chiefly situated opposite to the fourth rib and intercostal space, but may extend 
forward to the third space or backward to the fifth rib. It is about five inches (ca. 
12-13 cm.) above the sternal end of the fourth rib.^ It is guarded by the aortic 
valve, composed of three semilunar cusps (Valvulse semilunares aortje); one cusp is 

' Also termed the mitral valve. 

^ It may be noted that the aortic opening is partly overlapped laterally, so to speak, by the 
orifice of the pulmonary artery. 



STRUCTURE OF THE HEART 



627 



anterior, the others right and left posterior. They are similar to those of the pul- 
monary valve, but are much stronger. The free edge of each contains a central 
nodule of fibrous tissue (Nodulus valvulae semilunaris).^ 

The chordae tendinese are fewer but larger than those of the right ventricle. 
There are two large musculi papillares, one on each side; they are usually com- 
pound. The moderator bands are variable. Commonly two larger ones (which are 
often branched) extend from the musculi papillares to the septum. Smaller ones 
may be found in various places, especially at the apex. The other trabeculse are 
fewer and less prominent than in the right ventricle. 

The interventricular septum (Septum ventriculorum) is the musculo-membran- 
ous partition which separates the cavities of the two ventricles. It is placed ob- 
liquely, so that one surface, which is convex, faces forward and to the right, and 
bulges into the right ventricle ; the other surface, which faces into the left ventricle, 



Origin of right coronary artery 



Conus arteriosus 



Pulmonary orifice 



Origin of left coronary 
artery 




Kight atrio-ven- 
Iricular orifice 



Fig. 550. — The Bases of th 

■emoved and the aorta and pul: 

left ventricle is contracted. 



Aortic orifice 



Left atrio-ventricular 
orifice 



THE Heart of the Horse. 
artery cut off short. The right ventricle is dilated and the 
, Pulmonary valve; a.v., aortic valve. 



is concave and looks backward and to the left. The greater part of the septum is 
thick and muscular (Septum musculare), but the upper part is thin and membranous 
(Septum membranaceum). The latter intervenes between the left ventricle, on 
the one hand, and the right ventricle and atrium, on the other. 



Structure of the Heart 
The heart-wall consists mainlj^ of peculiar striped muscle, the myocardium, 
which is covered externally by the visceral part of the serous pericardium or epi- 
cardium, and is lined by the endocardium. 

The epicardixun is in general closely attached to the muscular wall, but is 
loosely attached over the coronary vessels and the associated subepicardial fat. 
' These nodules are also termed the corpora Arantii. 



628 BLOOD-VASCULAR SYSTEM OF THE HORSE 

It consists of a layer of fiat polygonal cells, resting on a membrane of white and 
elastic fibers. 

The myocardiiun consists of planes of fibers arranged in a somewhat compli- 
cated manner. The muscular tissue of the atria is almost completely separated 
from that of the ventricles by the fibrous rings around the atrio-ventricular orifices. 

The connection between the musculature of the atria and that of the ventricles is established 
by the atrio-ventrictilar bundle (Fasciculus atrio-ventricularis). This beguis as a network of 
fibers about the opening of the coronary sinus and the adjacent atrial waU. The fibers con- 
verge to a flat, irregular mass at the upper border of the ventricular septum. From this two chief 
divisions proceed. One of these descends on the right side of the ventricular septum and pa.sses 
by the moderator band to the lateral papillarj' muscle. The other branch descends on the left 
side of the septum and ramifies on the wall of the ventricle. The left branch is somewhat diffi- 
cult to follow, since it is thin and reticulate and is co\-ered in great part by a layer of ventricular 
muscle fibers. The right branch is subendocardial. The bundle and its divisions are enclosed 
in a fibrous sheath. The functional importance of the bvmdle in mediating the contraction 
wave was shown by Erlanger, who fomid that clamping the bmidle caused heart-block. 

In the atria the muscle bands fall naturally into two groups — superficial and 
deep. The former are common to both atria, the latter special to each. The 
superficial or common fibers for the most part begin and end at the atrio-ventricular 
rings, but some enter the interatrial septum. The deep or special bundles also 
form two sets. Looped fibers pass over the atria from ring to ring, while annular 
or spiral fibers surround the ends of the veins which open into the atria, the auricles, 
and the fossa ovalis. 

The muscular wall of the ventricles is much stronger than that of the atria. 
That of the left ventricle is in general about three times as thick as that of the right 
one, but is thin at the apex. The superficial fibers are attached above to the atrio- 
ventricular fibrous rings and pass in a spiral toward the apex. Here they bend 
upon themselves and pass deeply upward to terminate in a papillary^ muscle of the 
ventricle opposite to that in which they arose. The loops so formed at the apex 
constitute a whorl, the vortex cordis. The deep fibers, although they appear to 
be proper to each ventricle, have been shown by MacCallum to be in reality almost 
all common to both. Their arrangement is scroll-like. They begin on one side, 
curve around in the wall of that ventricle, then pass in the septum to the opposite 
side, and curve arountl the other ventricle. There is a laj^er of deep fibers which is 
confined to the basal part of the left ventricle; it is attached to the left atrio- 
ventricular ring. 

Four fibrous rings (Annuli filjrosi) surroimd the orifices at the bases of the 
ventricles. The atrio-ventricular rings separate the musculature of the atria from 
that of the ventricles. Those which surround the origins of the pulmonary artery 
and aorta are festooned in conformity with the attached borders of the valves. 
The aortic ring contains on the right side a plate of cartilage (Cartilago cordis), 
which frequently becomes more or less calcified in old animals. Sometimes a 
smaller plate is present on the left side. 

The endocardium lines the cavities of the heart and is continuous with the 
internal coat of the vessels which enter and leave the organ. Its free surface is 
smooth and glistening and is formed by a layer of endothelial cells. The latter 
rest on a thin laj^er of fibro-elastic tissue, which is connected with the myocardium 
by a subendocardial elastic tissue containing vessels and nerves. 

Vessels and Nerves. — The heart receives a large blood-supply through the two 
coronary arteries which arise from the aorta opposite to the anterior and left cusps 
of the aortic valve. Mo.st of the blood is returned by the coronary veins, which 
open into the right atrium by the coronary sinus. ' A few small veins open directly 
into the right atrium, and others are said to open into the left atrium and the 
ventricles. The lymph-vessels form a subepicardial network which communicates 

' These vessels will be described later in their systematic order. 



THE ARTERIES THE PULMONARY ARTERY THE SYSTEMIC ARTERIES 629 

through stomata with the cavity of the pericardium. There is a less distinct 
subendocardial network. The vessels converge usually to two trunks, which ac- 
company the blood-vessels in the grooves and enter the glands at the Ijifurcation 
of the trachea. The nerves are derived from the vagus and sympathetic through 
the cardiac plexus. 



The Arteries 
the pulmonary artery 
The pulmonary artery (A. puhnonalis) springs from the conus arteriosus at the 
left side of the base of the right ventricle. It curves upward, backward, and medi- 
ally, and divides behind the arch of the aorta into right and left branches. It is 
related in front to the right auricle, behind to the left auricle, and medially to the 
aorta. It is enveloped with the latter in a common sheath of the visceral layer of 
the serous pericardium. Near the bifurcation it is connected with the arch of the 
aorta by a fibrous band about half an inch (ca. 1.2 cm.) in i\aclth; this is the liga- 
mentiun arteriosum (Fig. 542), a remnant of the large ductus arteriosus, which 
conducts most of the blood from the pulmonary artery to the aorta in tlie foetus.^ 
The artery is bulbous at its origin, and forms three pouches, the sinuses of the 
pulmonary artery, which correspond to the cusps of the pulmonary valve. Beyond 
this it gradually diminishes in caliber. 

In a horse of medium size the artery is about seven inches (ca. 17-18 cm.) long. At the 
origm it is about two and a half inches (ca. 6-6.5 cm.) in width; at the bifurcation its caUber 
is about one and a half inches (ca. .3.5-4 cm.). The wall is relatively thin, especially at the 
origin. 

The right branch (Ramus dexter) of the pulmonary artery is longer and a little 
wider than the left one. It passes over the forepart of the left atrium and 
under the bifurcation of the trachea to the hilus of the right lung, and enters the 
latter below the right bronchus. In the lung it passes to the ventro-lateral side of 
the stem-bronchus and accompanies it to the base of the organ. The branches 
correspond to the ramification of the bronchi. The left branch (Ramus sinister) 
is very short. It passes backward and enters the lung below the left bronchus. Its 
branches Avithin the lung are arranged like that of the right one 



THE SYSTEMIC ARTERIES 
The aorta is the main systemic arterial trunk. It begins at the base of the left 
ventricle and is almost median at its origin. Its first part, the ascending aorta 
(Aorta ascendens), passes upward and forward between the pulmonary artery on 
the left and right atrium on the right. It then curves sharply backward and dor- 
sally, inclines somewhat to the left, forming the arch of the aorta (Areas aortae), 
and reaches the ventral surface of the spine at the eighth or ninth thoracic vertebra. 
After passing backward along the ventral aspect of the bodies of the vertebree and 
between the lungs, it traverses the hiatus aorticus and enters the abdominal cavity, 
where it lies ventral to the vertebral bodies and the psoas minor, just to the left of 
the median plane. It divides under the fifth luml^ar vertebra into the two internal 
iliac arteries. 

From the bifurcation a small vessel, the middle sacral artery (A. sacralis media), sometimes 
passes backward on the pelvic surface of the sacrum. It becomes lost in the periosteum or joins 
the coccygeal artery, or in exceptional cases is traceable to the sphincter ani extemus. 

The caliber of the aorta is greatest at its origin, which is termed the bulbus 

' There is a depression in the interior of the artery which corresponds to the attachment of 
the Ug. arteriosum, and in some cases the latter has a very small lumen. 



630 



BLOOD-VASCULAR SYSTEM OF THE HORSE 



aortae. Here is forms three pouch-like dilatations, the sinuses of the aorta. These 
correspond to the cusps of the aortic valve, and the coronary arteries arise from the 
left posterior and anterior sinuses. At the arch the diameter is about two inches 
(ca. 5 cm.), and beyond this it diminishes rather rapidly in width. 

It is convenient to divide the aorta into thoracic and abdominal parts. The 
thoracic aorta (Aorta thoracica) (Figs. 553, 554) lies within the pericardium to the 
point of attachment of the ligamentum arteriosum, and is enclosed with the pulmon- 
ary artery in a prolongation of the epicardium. Beyond this it is between the two 
pleural sacs. It is crossed on the right by the oesophagus and trachea, on the left 
by the left vagus nerve. The left recurrent nerve winds around the concavity of the 



Pulmonary reins 



Rigid braiicli (if 
pulnKiiKinj 



Vena azygos 



Great coronary vein 



Small coronary vein 




Veins are black, arteries white 



Rigid coronary artery 



Fig. ,551. — Cardiac Vessels of Horse; Right Side. 

The circumflex branch of the coronary artery is largely concealed by the great coronary 



arch from the lateral to the medial side, and the vena azygos and thoracic duct lie 
along the dorsal part of its right face. The trachea causes it to deviate to the left, 
but beyond this it becomes median. The abdominal aorta (Aorta abdominalis) 
(Fig. 575) is related dorsally to the lumbar verteljrte, the ventral longitudinal 
ligament, and the left psoas minor muscle; in the hiatus aorticus it is related to the 
cisterna chyli. On its right is the posterior vena cava, and on its left the left kidney 
and ureter. 



BRANCHES OF THE THORACIC AORTA 
I. CORONARY ARTERIES 
The two coronary arteries, right and left, are distributed almost entirely to 
the heart, but send some small twigs to the origins of the great vessels. 

The right coronary artery (A. coronaria dextra) arises from the anterior sinus 
of the aorta. It passes forward between the conus arteriosus and the right auricle 



COMMON BRACHIOCEPHALIC TRUNK 



631 



to the coronary groove, in which it curves around to the right and backward. It 
then descends in the right longitudinal groove ahnost to the apex of the heart. It 
usually gives off a circumflex branch as it turns downward; this branch (Ramus 
circumflexus) passes back in the coronary groove, and anastomoses with the cor- 
responding branch of the left artery. 

The left coronary artery (A. coronaria sinistra) arises from the left posterior 
sinus of the aorta, emerges behind the origin of the pulmonary artery, and divides 
into two branches. The descending branch (Ramus descendens) passes down the 



Pulmonary veins 




Great coronary vein 

Left coronary artery, 
circumflex branch 



Left coronary artery. 
descending branch 

Great coronary vein 



The ligamentum 



left longitudinal groove toward the apex. The circumflex branch ( Ramus circum- 
flexus) runs backward in the coronary groove, in which it winds around to the right 
side. 



2. COMMON BRACraOCEPHALIC TRUNK 

The common brachiocephalic tnmk (Truncus t)rachiocephalicus communis)' 
is a very large vessel which arises from the convexity of the arch of the aorta wthin 
the pericardium. It is directed forward and upward. Its length in horses of 
medium size is usually about two inches (ca. 5 cm.), but it is sometimes only half 
an inch or less (ca. 1 cm.). It is crosised on the left by the left vagus and cardiac 
nerves, and the left recurrent nerve runs between it and the trachea. It divides 
opposite to the second intercostal space or third rib into the brachiocephalic and 
left brachial arteries. 

The brachiocephalic artery (A. brachiocephalica) is directed forward and some- 
what dorsally in the anterior mediastinum, beneath the trachea. Opposite the 
first rib it gives off the bicarotid trunk and is continued as the right brachial artery. 
The latter (A. subclavia dexter) turns ventrally and bends around the anterior 
'■ Also known as the anterior aorta. 



632 



BLOOD-VASCULAR SYSTEM OF THE HORSE 



border of the first rib and the insertion of the scalenus muscle above the brachial 
vein. Its course and branches beyond this point will be described with the vessels 
of the thoracic limb. 

The left brachial artery (A. subclavia sinistra) is longer than the right one and 
rises to a higher level. It forms an almost semicircular curve, the concavity being 
ventral. It is related medially to the oesophagus, trachea, and thoracic duct; 
and the left vagus, phrenic, and cardiac nerves cross under its origin.' It emerges 
from the thorax like the artery of the right side. There is thus a difference at first 




Fig. 553.^Topogbapht of Thor.^x of Hobse, Left Side, afteb Removal of Likg, Pericaedicm, and Greater 
Part of Mediastinal Pleura. 
1, Right ventricle; 1', left ventricle; 2, right auricle; 2', left auricle; 3, pulmonary artery; 3', left branch of 3; 
4, aorta; 5, brachiocephalic trunk; 6, left brachial vessels; 7, dorsal artery; 7', subcostal artery; 8, deep cervical 
artery; 9, vertebral artery; 10, internal thoracic artery; 11, musculo-phrenic artery; 12, inferior cervical artery; 13, in- 
tercostal artery; 14, bicarotid trunk; 15, common carotid arteries; 16, anterior vena cava; 17, thoracic duct; IS, left 
vagus; IS', cesophageal continuations of vagi; 19, left recurrent nerve; 20, left phrenic nerve (part which crosses peri- 
canlium indicated by dotted line) ; 21, cardiac nerve; 22, sympathetic trunk; 23, great splanchnic nerve; 24, oesophagus; 
25, trachea; 26, left bronchus; 27, pulmonary veins; 2,S, apical lobe of right lung; 29, basal border of left lung indicated 
by dotted line; 30, diaphragm; 30', diaphragmatic line of pleural reflection; 31, 32, external and internal intercostal 
muscles; 33, longus colli ; 34, levator costfe; 35, multifidus dorsi. 



between the trunks of opposite sides, but beyontl this their course and distribution 
are similar. 

The left brachial and brachiocephalic arteries give off within the thorax the 
dorsal, deep cervical, vertebral, and internal thoracic arteries. At the first rib each 
gives off the external thoracic and inferior cervical arteries. 

1. The dorsal or costo-cervical artery (A. costo-cervicalis) of the left side 
passes dorsally across tlie left face of the trachea and oesophagus toward the ■second 
intercostal space. The right artery arises usually by a common trunk with the 
deep cervical, crosses the right face of the trachea, and has no contact with the 
oesophagus. Both detach small branches to the trachea, mediastinal lymph glands, 
and pleura, and on reaching the longus colli divide into two branches. Of these, the 

' In .some cases the artery is too low to touch the oesophagus. 



COMMON BRACHIOCKPHALIC TRUNK 



633 



subcostal artery (A. intercostalis suprema) is the smaller. It passes backward 
along the lateral liorder of the longus colli with the sympathetic trunk. It gives 
off the second, third, and fourth intercostal arteries, and ends at the fifth space, 
where it anastomoses with the first aortic intercostal artery, or constitutes the fifth 
intercostal artery, or dips into the longissimus muscle. It also gives off spinal 
branches and twigs to the longus colli and the pleura. The other branch (A. 
transversa colli) is the direct continuation of the trunk. It emerges through the 




Fig. 554. — Topogr.\phv of Thorax of Horse, Right Side, after Removal of Lung, Pericardium, and Greater 

Part of Mediastinal Pleura. 

1, Right ventricle; 1', left ventricle; 2, right atrium; 2', left atrium: 3, anterior vena cava; 4, posterior vena cava 

5, vona azygos; 6, phrenic vein; 7, aorta; 8, right coronary artery; 9, bronchial artery; 9', oesophageal artery and vein 

10, first aortic intercostal arter.v and vein; 11, right pulmonary artery; 12, puImonar>' veins; 13, right brachial vessels 

14, dorsal vessels; 14', subcostal vessels; 15, deep cervical vessels; 16, vertebral vessels; 17, inferior cervical artery 

15, internal thoracic vessels: IS', musculo-phrenic artery; 19, bicarotid trunk; 20, common carotid arteries: 21, jugu- 
lar vein; 22, thoracic duct: 23, right vagus; 23', oesophageal continuations of vagi; 24, right recurrent nerve ; 25, right 
phrenic n^rve (part which crosses pericardium indicated by dotted line); 26, sympathetic trunk; 27, great splanchnic 
nerve; 28, oesophagus: 29, trachea: 30, right bronchus; 31, left lung; 32, basal border of right lung indicated by dotted 
line; 33, mediastinal pleura; 34, diaphragm; 35, diaphragmatic line of pleural reflection; 36, intercostal muscle; 37, 
longus colli; 38, psoas; 39, interspinous ligament: 40, supraspinous ligament; 41, funicular part, 41', lamellar part, of 
ligamentum nuchse. 



dorsal end of the second intercostal space, passes across the longissimus costarum and 
longissimus dorsi toward the withers, and divides into several diverging branches. 
An anterior branch passes upward and forward between the splenius and complexus 
and anastomoses with branches of the deep cervical artery; the others ascend on 
the dorso-scapular ligament under cover of the serratus ventralis and rhomboideus 
to the withers, supplying the muscles and skin of this region. 

The left dorsal artery sometime.s arises with the deep cervical by a common trunk; this 
arrangement is usual on tlie right side, and there may be a common stem for the dorsal, deep cervi- 
cal and vertebral arteries. Occasionally the artery arises from the brachiocephalic tnmk. Some- 
times it emerges through the third space. The subcostal may arise mdependently behind the 
dorsal or from the deep cervical artery. 

2. The deep or superior cervical artery (A. cervicalis profunda) arises in front 
of the dorsal or by a common trunk with it. It crosses the oesophagus (left side), 



634 BLOOD-VASCULAR SYSTEM OF THE HORSE 

the trachea (right side), and the longus colU, and emerges from the thoracic cavity 
by passing through the space behind the first costo-transverse articulation.^ In 
the tlaorax it gives off a small mediastinal branch (A. mediastini cranialis) to the 
mediastinmn and the pericardium ; also the first intercostal artery (A. intercostalis 
prima), a very small vessel which passes dowii in the first intercostal space. After 
leaving the thorax the arterj' passes upward and forward on the spinalis muscle 
and the lamellar part of the ligamentum nuchse, covered by the complexus. Its 
terminal branches anastomose with branches of the occipital and vertebral arteries 
in the region of the axis. Numerous collateral branches are detached to the lateral 
muscles of the neck, the ligamentum nuchse, and the skin, and anastomoses occur 
with the dorsal artery also. 

3. The vertebral artery (A. vertebralis) arises from the brachial on the left 
side, the brachiocephalic on the right; it begins opposite the first intercostal space 
and passes upward and forward. On the left side it crosses the oesophagus, on the 
right, the trachea. Emerging from the thorax it passes between the longus colli 
mediall.v and the scalenus laterally, under the transverse process of the seventh 
cervical vertebra, and continues along the neck through the series of foramina trans- 
versaria, between which it is covered by the intertransversales colli.- Emerging 

Branches of 
occipital artery Vertebral artery 




Fig. 555. — Vertebral .\rtert of Horse. ("After Schmaltz, Atlas d. Anat. d. Pferdes.) 

from the foramen of the axis, it crosses the capsule of the atlanto-axial joint, and 
joins the recurrent branch of the occipital artery under cover of the obliquus 
capitis posterior. At each intervertebral foramen a spinal branch (Ramus spinalis) 
is given off which enters the vertebral canal and reinforces the ventral spinal artery. 
It also gives off series of dorsal and ventral muscular branches (Rami musculares). 
The dorsal branches are the larger; they supply the deep extensor muscles of the 
head and neck, and anastomose with the deep cervical and occipital arteries. The 
ventral branches supply chiefly the scalenus, longus colli, intertransversales, and 
rectus capitis ventralis major. The artery is accompanied by the vertebral vein 
and a sympathetic nerve trunk (Nervus transversarius). 

4. The internal thoracic artery (A. thoracica interna) is a large vessel which 
arises from the ventral side of the brachial opposite the first rib. It curves down- 
ward and backward, being at first on the medial surface of the rib, and then crosses 
the ventral part of the first intercostal space and passes under the transversus 
thoracis muscle. It runs backward under cover of that muscle over the chondro- 
sternal joints to the eighth costal cartilage, where it divides into musculo-phrenic 
and anterior abdominal branches. At each intercostal space two collateral branches 
are detached. The intercostal branches (Rami intercostales) ascend in the inter- 
costal spaces and anastomose with homonymous descending arteries. The ventral 

' The artery sometimes emerges through the second intercostal space. 

- In some cases the last cervical transverse process has a foramen transversarium, through 
which the artery passes. 



THE COMMON CAROTID ARTERY 635 

branches detach small twigs to the transversus thoracis, pleura, and pericardium, 
and pass out between the costal cartilages as perforating branches (Rami perfor- 
antes) to supply the pectoral muscles and skin, anastomosing with the external tho- 
racic artery. A very small pericardiaco-phrenic artery (A. pericardiaco-phrenica) 
ascends in the mediastinum on the left side, in the caval fold of pleura on the right 
side; it supplies fine twigs to the pericardium and pleura and a^ccompanies the 
phrenic nerve to the diaphragm. In the young subject it gives small iDranches, 
the thymic arteries (Aa. thymicte), to the thymus gland. The musculo-phrenic 
or asternal artery (A. musculophrenica) passes along the groove between the eighth 
and ninth costal cartilages and continues along the costal attachment of the trans- 
versus abdominis (Fig. 275). It gives off intercostal branches which anastomose 
with those descending from the thoracic aorta, and tmgs to the diaphragm and 
transversus abdominis. The anterior abdominal artery (A. epigastrica cranialis) 
is the direct continuation of the internal thoracic. It passes between the ninth 
costal cartilage and the xiphoid cartilage, runs backward on the abdominal surface 
of the rectus abdominis, and then becomes embedded in the muscle (Fig. 590). 
It supplies the ventral wall of the abdomen and anastomoses with the posterior 
abdominal artery. 

5. The external thoracic artery (A. thoracica externa) is given oH from the 
ventral aspect of the brachial, usually at the medial surface or anterior border of 
the first rib. It turns around the first rib ventral to the brachial vein (when given 
off within the thorax), and passes backward under cover of the deep pectoral muscle; 
it is continued as a small vessel in the cutaneous muscle, where it accompanies the 
external thoracic vein. It gives branches to the pectoral muscles and the axillary 
lymph glands and terminates in the cutaneous muscle and the skin of the ventral 
wall of the abdomen. 

This artery varies in origin and size. Not rarely it arises from the internal thoracic or 
from the brachial outside of the thorax. In other cases it arises by a common trunk with the 
inferior cervical. It may be very small or even aljsent, in which case the perforating branches 
of the internal thoracic compensate. 

6. The inferior cervical artery (Truncus omo-cervicalis) arises usually from 
the dorsal surface of the brachial artery opposite the first rib or where that vessel 
winds around the rib. It is directed dowTiward and a little forward across the 
lateral surface of the terminal part of the jugular vein and the deep face of the 
scalenus among the posterior cervical lymph glands, and divides into ascending and 
descending branches. The ascending branch (A. cervicalis ascendens) passes 
upward and forward along the lateral siu'face of the jugular vein, then turns sharply 
backward and runs upward along the anterior border of the anterior deep pectoral 
muscle, between the omo-hyoideus and brachiocephalicus and in relation to the 
prescapular lymph glands; it gives branches to these muscles and the posterior 
cervical and prescapular lymph glands. The descending branch (A. transversa 
scapulae) passes ventro-laterally across the surface of the anterior deep pectoral and 
then runs in the groove between the anterior superficial pectoral muscle and the 
brachiocephalicus in company with the cephalic vein. It supphes branches to these 
muscles and the skin of the breast.' 



THE COMMON CAROTID ARTERY 

The two common carotid arteries arise from the brachiocephalic artery by a 
common trunk. This stem, the truncus bicaroticus, is detached from the medial 
face of the brachiocephalic opposite the first rib and passes forward medially on the 
ventral face of the trachea. It is related ventrally to the posterior cervical lymph 
glands, the terminal parts of the jugular veins, and the anterior vena cava, and 
' In rare cases the two branches arise separately. 



636 



BLOOD-VASCULAR SYSTEM OF THE HORSE 



laterally to the vagus and recurrent nerves. It is commonly two or three inches 
(ca. 5-7 cm.) in length, but it may vary between one and eight inches (ca. 2.5- 
20 cm.).' 

The right common carotid artery (A. carotis communis dextra) passes obliquely 
from the ventral face of the trachea to its right side and continues in this position, 
but inclines toward the dorsal surface of the trachea near its termination. It 




Fig. 556. — Vessels and Nerves of Neck of Horse. 
a, Brachiocephalicus; 6, sterno-cephaiicus; c, omo-hyoideus; (/, sterno-thyro-hyoideus ; c, trachea; /, position of 
cariniform cartilage: g, anterior superficial pectoral muscle; h, scalenus; i, intertransversales; k, insertion of serratua 
cervicis: /. remnant of trapezius; m, rhomboideus; n. splenius; o, complexus; p, g, longissimus capitis et atlantis; p\q\ 
tendons of same; r, longissimus; s, obliquus capitis posterior; /, wing of atlas; u, parotid gland; v, supraspinatus; w, 
anterior deep pectoral; x, spine of scapula; y, prescapular lymph glands; 1, external maxillary vein; .g, 3, jugular vein; 
4, carotid artery, exposed by drawing jugular vein aside; 5, 6, ascending and descending branches of inferior cervical 
artery; 7, cephalic vein; S, branches of deep cervical artery; 9-14, ventral branches of second to seventh cervical nerves; 
15, branches of dorsal divisions of cervical nerves. (EUenberger-Baum, Top. .\nat. d. Pferdes.) 



divides at the crico-pharyngeus muscle and under cover of the mandibular gland 
into external carotid, internal carotid, and occipital arteries.- It is enclosed in a 
fibrous sheath, and is accompanied dorsally by the vagus and sympathetic nerves, 
ventrally by the recurrent nerve. In the posterior part of the neck it is in contact 

' In very rare cases there is no truncus bicaroticus. The two carotid arteries then arise 
separately from the brachiocephahc, the left one first, and the right one an inch or more further 
forward. 

^ A small nodule is present in the angle of division. This is the carotid body or glomus caro- 



THE COMMON CAROTID ARTERY 



637 



superficially with the jugular vein, l)ut further forward the omo-hyoideus muscle 
intervenes between the artery and vein. Near its termination the artery becomes 
more deeply placed and is related laterally 
to the mandibular and parotid glands, medi- 
ally to the esophagus. In some cases it is in 
contact ventrally with the lateral lobe of the 
thyroid gland, especially when the latter is 
more dorsally situated or larger than usual. 
The left common carotid artery (A. 
carotis communis sinistra) differs from the ,,, , , , 

right one in that it is related deeply to the III I .\i \ \M 

oesophagus also, which usually separates it 
from the trachea in part of its course. 

The left carotid is commonly in contact with 
the trachea for a short distance (ca. 8-10 cm.) at the 
root of the neck, but this contact may be even less 
when the a?,sophagus is more ventral than usual and 
the bicarotid trunk long. On the other hand, the re- 
lation to the trachea may be more extensive. 

The collateral branches of the common 
carotids are in the main small. They com- 
monly comprise the following: 

1. Muscular branches (Rami muscu- 
lares) of varial)le size go to the ventral 
muscles of the neck and the skin. 

2. CEsophageal and tracheal branches 
(Rami cesophagei et tracheales). Small 
twigs go to the cervical lymph glands also. 

3. The parotid artery (A. parotidea) 
comes off near the termination and enters 
the ventral part of the parotid gland. It 
also sends twigs to the adjacent lymph 
glands, and sometimes detaches a branch to 
the mamlibular gland. It is inconstant. 

4. The anterior thjrroid or thyro-laryn- 
geal artery (A. thyreoidea cranialis), the 
largest collateral branch of the carotid, 
arises from the latter two or three inches 
before it divides. It curves over the anterior 
end of the thyroid gland, into which it sends 
several branches. It gives off the lar3mgeal 
artery (A. laryngea), which sends branches 
to the external muscles of the larynx and the 
con.strictors of the pharynx, passes between 
the cricoid and thyroid cartilages, and sup- 
plies the internal muscles and the mucous 
membrane of the larynx. A small pharyn- 
geal branch (A. pharyngea ascendens) runs 
upward and forward to the crico-pharyn- 
geus, and supplies twigs to the posterior 
part of the pharynx and the origin of the 
cesophagus. Small innominate twigs are 
given off to the trachea, the cesophagus, and 
hyoideus muscles. 




Fig, 557. — Cross-section of Neck of Horse, 
Passing through Fifth Cehvicai. Ver- 
tebra; Anterior View. 

o, Branches of cervical nerves; a', nuchal fat; 
b, intertransversalis muscle; c, longissimus mus- 
cle; d, vertebral artery; e, vertebral vein; /, ner- 
vus transversarius; g, spinal accessory nerve (dor- 
sal division); h, recurrent nerve; i, vago-sympa- 
thetic trunk; A-, tracheal lymph duct; I, body of 
fifth cervical vertebra; /', transverse process of 
same; m, common carotid artery: n, jugular vein; 
o, deep cervical artery; o', satellite vein of o; 
p, spinal cord; q, dura mater; r, spinal vein; s, 
ligamentum nuchce; t, rhomboideus muscle; u, 
splenius; r, complexus; w, inultifidus; x, serratus 
cervicis; i/, brachiocephalicus; r, sterno-cephalicus; 
7, rectus capitis ventralis major; 3, omo-hyoideus; 
3, cutaneus; 4. sterno-thyro-hyoideus; 5, longus 
colli; G, 7, longissimus capitis et atlantis; 5, trape- 
zius; 9, spinalis; 10, oesophagus; 11, trachea, with 
cartilaginous ring (,11'), mucous membrane (11"), 
and muscular layer (11'"). (.Uter EUenberger, 
in Leisering's Atlas.) 

the sterno-thyro-hyoideus and omo- 



638 



BLOOD-VASCULAR SYSTEM OF THE HORSE 



In some cases the thyroid and laryngeal arteries arise from the carotid separately or by a 
short common stem. A laryngeal branch is often detached from the carotid in front of the thyro- 
laryngeal and enters the larynx wdth the anterior laryngeal nerve. The pharyngeal branch fre- 
quently comes directly from the carotid. 




Fig. 558. — Deep Dissection of Neck of Horse 



a, a, Endsof sterno-cephalicus; 6, anterior part of omo-hyoideus; c, sterno-thyro-hyoideus; rf, trachea; c, oesopha- 
gus; /. cariniforin cartilage; g, rectus cap. ventralis major; h, stump of longissimua atlantis; i, intertransversales; A;, 
multifidus; I, m, scalenus; n, serratus cervicis; o, o, stumps of splenius; p, longissimus cervicis; q, complexus (most of 
which is removed) ; r, rhoinboideus; 5, trapezius; ^ spinalis et semispinalis; u, lamellar part of lig. nuchae; v, brachio- 
cephalicus; uj, anterior deep pectoral; x, supraspinatus; j/, anterior superficial pectoral; z, tuber scapulae; i , i , articular 
processes of cervical vertebrae; 2, 2, transverse processes of same; 3, atlas; 3\ axis; 4- 4. jugular vein (remainder re- 
moved) ; 6, common carotid artery, from which a piece is removed to show the accompanying nerves and the oesophagus; 
6, vago-sympathetic trunk; 7, 7, tracheal and muscular branches of carotid artery; 8, recurrent nerve; 10, left tracheal 
lymph-duct; 11, 12, ascending and descending branches of inferior cervical artery {13) ; 1^, cephalic vein; 15-20, ven- 
tral branches of second to seventh cervical nerves; 21, roots of phrenic nerve; 22, pectoral nerves; 22', nerve to ser- 
ratus ventralis; ^3, musculo-cutaneousnerve; ;24, median nerve; 55, ulnar nerve; ;g(?, radial nerve; ^7, axillary nerve; 
28, dorsal branches of cervical nerves; 28', accessory nerve (cut) ; 29, deep cervical artery; 30, muscular branch of ver- 
tebral artery; 31, posterior branch of occipital artery; 32, vertebral artery; 33, muscular branches of occipital artery; 
54 , obliquus capitis post. ; 35, obi. cap. ant. ; 36, twig from dorsal branch of third cervical nerve. (After Ellenberger- 
Baum, Top. Anat. dea Pferdes.) 



5. The posterior thyroid artery (A. thyreoidea caudalis) is a small and incon- 
stant vessel which arises from the carotid at a variable distance behind the anterior 
thyroid or from the latter or the parotid artery. It sends branches into the pos- 
terior part of the thyroid gland, and detaches small tracheal and muscular twigs. 
In some cases it is distributed chiefly or entirely to the adjacent muscles. 



THE OCCIPITAL ARTERY 



639 



THE OCCIPITAL ARTERY 

The occipital artery (A. occipitalis) is usually the second in size of the terminals 
of the carotid. It arises commonly just in front of the internal carotid, but in some 
cases with that artery by a common trunk of variable length. It pursues a some- 
what flexuous course to the fossa atlantis, where it divides into anterior and posterior 
branches. It is related superficially to the mandiliular gland and the brachio- 
cephalicus, and deeply to the guttural pouch and the rectus capitis ventralis major.i 
The internal carotid artery, the 
ventral cerebral vein, and the ac- 
cessory, vagus, and sympathetic 
nerves cross its deep face. It 
gives off twigs to the mandibular 
gland, the ventral straight mus- 
cles of the head, the guttural 
pouch and the adjacent lymph 
glands, and two named collateral 
branches.2 The condyloid artery 
(A. condyloidca) is a small vessel 
which passes upward and forward 
on the guttural pouch, and divides 
into muscular and meningeal 
branches. The latter enter the 
cranium through the foramen 
lacerum and hypoglossal foramen 
and are distributed to the dura 
mater. This artery is very vari- 
able in its origin.' The posterior 
meningeal artery (A. meningea 
aboralis)-* is a much larger vessel 
which runs upward and forward 
between the obliquus capitis an- 
terior and the paramastoid proc- 
ess, passes through the mas- 
toid foramen into the temporal 
canal, enters the cranial cav- 
ity, and is distributed to the 
dura mater. It gives collateral 
branches to the atlanto-occipital 
articulation and the adjacent 
muscles. 

The posterior or recurrent 

1 The relation to the guttural 
pouch is not constant. In some cases — 
especially when the head and neck are 
extended — the artery lies behind the 
pouch. The backward extension of the 
latter is variable. • 

= The branch to the mandibular 
gland (A. glandulje mandibularis dor- 
salis) may come from the external caro- 
tid or the posterior meningeal artery. 

' It is also known as the preverte- 
bral; it of ten comes from the posterior 
meningeal artery. 

* Also termed the mastoid artery. 




Fig. 5.59. — Vessels and Nerves of Base of Brain of Horse. 
ii, Cerebro-spinal artery; /4. ventral spinal artery; i.5, basilar 
artery; 16, posterior cerebellar artery; 17, anterior cerebellar ar- 
tery; 18, internal auditory artery; 19, posterior cerebral artery; 
SO, deep cerebral artery; ^1, stump of internal carotid artery; 22, 
anterior chorioid artery; S3, anterior meningeal artery; 24, middle 
cerebral arterj-; 2,5, artery of corpus callosum; 26, anterior com- 
municating artery; 1, 1\ 1" , olfactory striae; 1'" , olfactory 
tract; 2-12, cranial nerves; a, olfactory bulb; h, trigonum olfac- 
torium; c, lamina perforata anterior; d, fossa lateralis; e, piri- 
form lobe; /, cerebral peduncle; g, tractus transversus; h, corpus 
i, lateral fissure (of Sylvius); 
, p>Tamid; p, facial eminence; 
i; s, middle peduncle of cerebel- 
, Top. .\nat. d. Pferdes.) 



mammillare; i, tuber 
I, presylvian fissure; ra, pons; 
g, corpus restiformo; r, cerebellu 
lum. (After Ellenbcrger-Ba 



640 ■ BLOOD-VASCULAR SYSTEM OF THE HORSE 

branch (Ramus recurrens)' of the occipital passes up tlirough the foramen trans- 
versarium of the atlas and joins the vertebral artery. It gives branches to the 
obliquus capitis posterior, which covers it. 

The anterior or occipital branch (Ramus occipitalis)- passes through the alar 
foramen of the atlas anil supj^lies the muscles and skin of the poll, anastomosing 
with the deep cervical art(>ry and its fellow of the opposite side. In the alar furrow 
it gives off the cerebrospinal artery (A. cerebrospinalis), which enters the spinal 
canal through the intervertebral foramen of the atlas, perforates the dura mater, 
and divides into cerebral and spinal Ijranches. The cerebral branch (Ramus 
ceretiralis) unites with that of the opposite side to form the basilar artery, and the 
spinal branch (Ramus spinalis) similarly forms by union with its fellow the ventral 
spinal artery. 

The basilar artery (A. basilaris cerebri) passes forward in the median groove 
on the ventral surface of the medulla oblongata and pons and divides into the two 
posterior cerebral arteries. The collateral branches of the basilar are: 

1. Medullary branches (Rami medullares), ten or twelve in numl^er, dis- 
tributed to the medulla olilongata. 

2. Posterior cerebellar arteries (Aa. ccrebelli aboralcs), which pass outward 
around the medulla behind the pons to the cerebellum, to which they are distributed 
after giving twigs to the medulla and pons. 

3. The small auditory artery (A. auditiva interna) accompanies the eighth 
nerve to the internal ear. It often arises from the posterior cerebellar. 

4. Anterior cerebellar arteries (Aa. cerebelli orales) . These are very variable 
in number and origin. There are often two or three on either side, and they fre- 
quently arise from the posterior cerebral. Thej- pass outward in front of the pons 
and supply the anterior part of the cerebellum. 

The posterior cerebral arteries (Aa. cerebri aborales) diverge at an acute angle 
and join the posterior communicating branches of the internal carotid arteries on 
the ventral surface of the cerebral peduncles. They are connected by a transverse 
branch and liy a network of fine twigs which form often a rete mirabile. 

The ventral spinal artery (A. spinalis ventralis) runs along the ventral median 
fissure of the spinal cord, which it supplies. It is reinforced along its course by- 
branches from the vertebral, intercostal, lumbar, and lateral sacral arteries, which 
enter the vertebral canal through the intervertebral foramina. 



THE INTERNAL CAROTID ARTERY (Figs. 559, 561, 562) 

This artery (A. carotis interna) is usually somewhat smaller than the occipital. 
It usually arises just behind that artery, crosses its deep face, and runs upward and 
forward on the guttural pouch to the foramen lacerum.^ It is closely related to 
the vagus nerve and the anterior cervical ganglion of the sympathetic nerve, fibers 
from which accompany it. It is crossed laterally by the ninth and twelfth cranial 
nerves and the pharyngeal branch of the vagus. It passes through the ventral 
petrosal sinus and enters the cavernous sinus, within which it forms an S-shaped 
curve. It is connected with the opposite artery by a transverse branch, the inter- 
carotid artery (A- intercarotica), which lies in the intercavernous sinus behind the 
pituitary body. A branch (A. caroticobasilaris) often connects it with the basilar 
artery. It then perforates the dura mater, gives off the posterior communicating 
artery, and passes forward and divides at the side of the optic chiasma into anterior 
and middle cerebral arteries. 

The posterior commimicating artery (A. communicans aboralis) turns back- 

1 Also termed the retrograde or anastomotic branch. 

"^ Also termed the musculo-occipital. 

' Not rarely it arises with the occipital artery from a common trunk of variable length. 



THE EXTERNAL CAROTID ARTERY 641 

ward and joins the posterior cerebral branch of the basilar. It gives off the deep 
cerebral artery (A. cerebri profunda), which winds around the cerebral peduncle 
and is distributed chiefly to the mid-brain; it is often double. A smaller collateral 
branch is the anterior chorioid artery (A. chorioidea oralis), which passes along the 
optic tract and is ilistriliutccl in the chorioid plexus of the lateral ventricle. 

The anterior cerebral artery (A. cerebri oralis) unites with the corresponding 
branch of the (ijiiJosite arter,\- above the optic chiasma. From this junction pro- 
ceeds the artery of the corpus callosum (A. corporis callosi), which turns around the 
genu of the corpus cuUostun, enters the great longitudinal fissure, divides into two 
branches, and is distributed to the medial aspect of the cerebral hemispheres. The 
anterior cerebral gives off the small internal ophthalmic artery (A. ophthalmica 
interna), which passes forward at first lateral to the optic nerve; then, crossing over 
the latter to its medial side, it joins a branch of the external ophthalmic. A small 
anterior meningeal branch (A. meningea oralis) of the anterior cerebral is distributed 
to the anterior part of the dura, and assists in forming a network in the ethmoidal 
fossa (Rete ethmoidale), anastomosing with the ethmoidal branch of the external 
ophthalmic arter\- and the artery of the corpus callosum. 

The middle cerebral artery (A. cerebri media) passes outward in the fossa 
lateralis in front of the piriform lobe, reaches the lateral fissure, and divitles into 
branches on the lateral surface of the hemisphere. 

The circulus arteriosus (Fig. 559)^ is formed at the interpeduncular space of 
the base of the brain l)y tlie union of the anterior cerebral arteries in front, by the 
diverging posterior cerebral arteries behind, anrl is completed laterally by the junc- 
tion of the latter with the posterior communicating arteries and by the internal 
carotid. It is irregularly polygonal in outline, and surrounds the optic chiasma 
and pituitary body.- 



THE EXTERNAL CAROTID ARTERY (.Figs. 56J, 562) 
This artery (A. carotis externa), by its si?e and direction, constitutes the con- 
tinuation of the common carotid. It passes forward on the lateral wall of the 
pharynx at the lower border of the guttural pouch, covered by the mandibular 
gland and the occipito-mandibularis, digastricus, and stylo-hyoideus muscles, and 
in relation to the parapharyngeal lymph glands. It then emerges between the stylo- 
hyoideus and the great cornu of the hyoid bone, ascends on the latter parallel with 
the posterior border of the lower jaw, and terminates about two inches (ca. 5 cm.) 
below the temporo-mandibular articulation by dividing into superficial temporal 
and internal maxillary branches. It is crossed deeply near its origin by the anterior 
laryngeal and pharyngeal branches of the vagus nerve. Just before its emergence 
its superficial face is crossed by the hj'poglossal nerve, and the glosso-pharyngeal 
nerve passes over its medial surface at the ventral border of the great cornu. The 
chief collateral branches are the masseteric, external maxillarj', and posterior^ 
auricular. It also furnishes variable branches to the mandibular and parotid 
glands, the guttural pouch, and the pharyngeal lymph glands, as well as twigs to 
some adjacent muscles. 

1. The masseteric artery (A. masseterica)^ is given off from the external 
carotid at its emergence from beneath the stylo-hyoideus. It passes downward 
and slightly fonvard under cover of the parotid gland and over the tendon of in- 
sertion of the sterno-cephalicus to the posterior border of the mandible and appears 
on the masseter muscle, which it enters after a short course on its surface. It gives 

1 Also termed the circle of Willis. 

^ The cerebral arteries are very variable in arrangement, and the foregomg account is a brief 
statement cf the more usual disposition of the larger vessels. 
^■AIso termed the maxillo-muscular. 
41 



642 BLOOD-VASCULAR SYSTEM OF THE HORSE 

branches also to the medial pterygoid and occipito-niandibularis muscles and the 
parotid gland. 

2; The external maxillary artery (A. maxillaris externa)' arises from the ex- 
ternal carotid on the deep surface of the posterior belly of the digastricus (Fig. 561). 
It runs downward and forward on the lateral wall of the pharynx across the deep face 
of the stylo-hyoideus toward the great cornu of the hyoid bone, accompanied by 
the glosso-pharyngeal nerve in front and the hypoglossal nerve behind. After 
giving off the lingual artery at the posterior border of the great cornu, it inclines 
more ventrally on the medial surface of the medial pterygoid muscle, crosses over 
the hyo-glossus muscle, the hypoglossal nerve, the mandibular duct, and the inter- 
mediate tendon of the digastricus, and turns forward in the mandibular space. 
Here it lies on the lower part of the medial pterygoid muscle, and is related medially 
to the mandibular lymph glands, above to the anterior belly of the digastricus, and 
below to the homonymous vein. At the anterior border of the masseter it turns 
around the ventral border of the jaw and ascends on the face in front of that 
muscle. At the turn the artery is in front, the vein in the middle, and the parotid 
duct posterior.- The artery is conveniently placed at its inflection for taking the 
pulse, since it is superficial and lies directly on the bone. Beyond this point it is 
commonly termed the facial artery (A. facialis). The artery and vein pass upward 
along the anterior border of the masseter, under cover of the facial cutaneus and 
the zygomaticus, and are crossed superficially by branches of the facial nerve and 
deeply by the parotid duct. The artery terminates over the levator labii super- 
ioris proprius l)y dividing into the dorsal nasal and the angular artery of the eye. 
The chief branches of the external maxillary are as follows: 

(1) The pharyngeal artery (A. palatina ascendens) arises usually behind the 
stjio-pharyngeus, passes between that muscle and the great cornu, and runs for- 
ward on the lateral wall of the pharynx under the elastic pharyngeal fascia. It is 
distributed to tlu' pharynx, soft palate, and tonsil. 

(2) The lingual artery (A. lingualis) is a large branch which diverges from the 
parent trunk at an acute angle, runs along the ventral border of the great cornu 
of the hyoid bone, antl dips under the hyo-glossus muscle. It then passes across 
the kerato-hyoideus, turns inward untler the intercornual joint of the hyoid bone, 
and runs forward in the tongue between the hyo-glossus and genio-glossus. This 
part (A. profunda linguip) is flexuous and is accompanied liy branches of the hypo- 
glossal and lingual nerves. It is the chief artery of the tongue, and anastomoses 
with the opposite artery and the sublingual.^ 

(3) The sublingual artery (A. sublingualis) is a smaller vessel which arises at 
the anterior extremity of the mandibular gland (Fig. 561). It passes forward on the 
anterior belly of the digastricus, between the ramus of the mandible and the mylo- 
hyoideus, perforates the latter, runs along the lower border of the sulilingual gland, 
and ramifies in the mucous membrane of the anterior part of the floor of the mouth. 
It detaches branches to the muscles and skin in the mandibular space, the mantlib- 
ular Ij'mph glands, and the suljlingual gland. It also gives off the small submental 
artery (A. submentalis), which runs forward superficially toward the lower lip, 
supplying twigs to the skin and the mylo-hyoideus. ' 

In some cases the sublingual artery arises from the lingual and the submental from the 
external maxillary. Sometimes the sublingual remains on the superficial face of the mylo-hyoideus 
— thus resembling the submental of man — and the sublingual gland is supplied by a special 
branch of the lingual. 

' Also termed the submaxillary or facial artery. The term facial may be applied to the artery 
after it reaches the lateral surface of the face. 

- In exceptional cases the vein is in front of the artery. 

' In some cases the lingual trimk runs on the superficial face of the hypoglossus insteail of 
passing beneath it; in such specimens a small branch extends forward a variable distance under 
the muscle. 



THE EXTERNAL CAROTID ARTERY 



643 



A considerable branch may be given off in the mandibular space, which turns around the 
lower border of the jaw and enters the middle of the lower part of the masseter muscle. In some 
cases this artery is of large size and its pulsation can be felt. It is accompanied by a vein. 

(4) The inferior labial artery (A. labialis inferior) arises from the external 
maxillary a little before it reaches the depressor laljii inferioris (Fig. 560). It 
passes forward, dips under the depressor muscle, and continues to the lower lip. 
It supplies branches to the muscles and skin in this region, to the inferior buccal 
glands, the mucous membrane of the cheek, and the lower lip, anastomosing with 
the mental artery and the corresponding vessels of the opposite side. It detaches 




Fig. 560. — Supehficial Dissection op Head of Horse. Most of the Cutaneus is Removed. 
a, Lateralis nasi; b, levator labii superioris proprius: c, levator naso-labialis: d, dilatator naris lateralis; e, buc- 
cinator; /, zygomaticus. posterior part of which is removed: g, depressor labii inferioris; h, stump of retractor anguU 
oris- i, masseter; k, k, scutularis; I, scutulo-auriculares superficialea ; m, zygomatico-auricularis; n, parotido-auricu- 
laris; o, occipito-mandibularis; p, sterno-cephalicus; p', tendon of p; g, omo-hyoideus; r, splenius; s, tendon of sple- 
nius and longissimus capitis; t, corrugator supercilii; u, orbicularis oris; v, parotid gland; w, zygomatic arch; x, scuti- 
form cartilage: y, upper commissure of nostril; 1, facial nerve; S, superior buccal nerve; 3, inferior buccal nerve; ^, 
transverse facial nerve; 5, cervical branch of facial nerve; (?, posterior auricular branch of second cervical nerve; 7, 
cutaneous cervical branch of same: 5, infratrochlear nerve; P, frontal nerve; 70, lacrimal nerve; JO', end of auriculo- 
palpebral nerve; 11, masseteric artery and vein; 13, transverse facial artery and vein; 13, facial artery; 14, inferior 
labial artery; 15, superior labial artery; 16. lateral nasal artery; 17, dorsal nasal artery; IS, angular artery of the eye; 
J5, posterior auricular artery; ^0, i?/, jugular vein; ^5, external maxillary vein: ^3, great auricular vein; j34, parotid 
duct; ^4', origin of same; 25, superior buccal glands; 26, facial vein. (After Ellenberger-Baum. Top. Anat. d. Pferdes.) 



a branch (A. anguli oris) to the angle of the moutli, wliich anastomoses with the 
superior labial. 

(5) The superior labial artery (A. labialis superior) arises from the facial in 
front of the facial crest (Fig. 560). It passes forward under the dilatator naris lat- 
eralis and levator nasolabialis to the upper lip, gives twigs to the upper part of the 
cheek and the lateral nasal region, antl ramifies in the upper lip, anastomosing with 
the opposite artery and the palato-labial. 

(6) The lateral nasal artery (A. lateralis nasi) arises usually a little above the 
preceding one, and runs forward parallel with it and under the levator nasolabialis 
to the nostril (Fig. 560). It supplies branches to the lateral nasal region and the 
nostril. 



644 



BLOOD-VASCULAR SYSTEM OF THE HORSE 



The vessel is often double. It may arise from the superior labial at the point of bifurcation 
of the facial or with the dorsal nasal from the infraorbital artery (as in the ox). In some cases 
it gives off a dorsal nasal branch. 

(7) The dorsal nasal artery (A. dorsalis nasi) arises on the levator labii superi- 
oris proprius and passes forward under the levator nasolabialis to the dorsum nasi 
(Fig. 560). 

(8) The angular artery of the eye (A. angularis oculi) runs toward the medial 




Fig. 561. — Pahotid, Masseteric, and Lingual Regio.vs of Horse; Deep Dls 
a, Mylo-hyoideus, anterior part, reflected; b, genio-hyoideus; c, genio-glossus; d, sublitigual gland; e. ramu.s of man- 
dible, greater part removed: f', stump of masseter; /, maxillary tuberosity; (;, great cornu of hyoid bone; h, wing of atlas; 
i, intermediate tendon of digastricus; i', anterior belly, i", posterior belly, of digastricus; k, posterior part of mylo- 
hyoideus; /, hyo-glossus; m, pterygoideus medialis (cut); n, stj'lo-hy oideus ; o, occipito-mandibularis; p, crico- 
pharyngeus; g, obliquus capitis ant. ; r, tendon of longissimus atlantis; s, rectus cap. ventralis; t, brachiocephalicus 
(cut) ; u, sterno-cephalicus (cut); v, sterno-thyroideus (cut) ; w, sterno-hyoideus (cut); x, omo-hyoideus; y. obliquus 
cap. post.; 2, splenius (cut) ; i-4, upper cheek teeth ; 4', last cheek tooth; 5, stump of facial nerve; 6, stump of bucci- 
nator nerve; 7, lingual nerve; 7\ superficial branch, 7", deep branch, of lingual nerve; 5, stumps of inferior alveolar 
artery, vein and nerve; 9, mylo-hyoid nerve (cut); 10, glosso-pharyngeal nerve; U, hypoglossal nerve ; 13, anterior laryn- 
geal nerve; 13, ventral branch of first cervical nerve; 14, vagus and sympathetic; 15, dorsal branch of spinal accessory 
nerve; ^ (J, ventral branch of same; i 7, ventral cerebral vein; J5, mandibular duct; ii?, common carotid artery; 20, 
parotid branch; SI, thyro-laryngeal artery; 22, pharyiigeal artery; 33, laryngeal artery: 24, internal carotid arterj^: 
^5, occipital artery: 26, external carotid artery; 27, 31, external maxillary arterj-; 2S, pharyngeal artery; 2ft, lingual 
artery; 30, sublingual artery; 32, external carotid artery after emergence; 33, internal maxillary vein (origin): 34, 
remnant of parotid gland: 35, thyroid gland; 36, jugular vein; 37, parapharyngeal lymph glands. (After EUen- 
berger-Baum. Top. Anat. d. Pferdes.) 



canthus of the eye, where it anastomoses with the orl^ital branch (Ramus malaris) 
of the infraorbital artery (Fig. 560). 

In addition to the preceding, unnamed branches are supplied to the mandibu- 
lar salivary gland and lymph glands. There is commonly a branch of considerable 
size which is given off as the external maxillary artery passes the anterior end of the 
mandibular gland ; it rims upward and backward along the dorsal border of the 
gland, which it supjjlies. 

3. The posterior auricular artery (A. auricularis posterior) arises at an acute 
angle from the external carotid jast above the origin of the masseteric. It passes 



THE EXTERNAL CAROTID ARTERY 645 

upward under cover of the parotid gland, to which it gives branches, and divides 
into several branches which suppl}^ the skin and muscles of the external ear (Fig. 
560). The posterior branch passes to the posterior part of the base of the ear, 
where it divides into two branches; of these, one (Ramus intermedius) passes up the 
convex surface of the external ear to the apex, while the other (Ramus medialis) 
winds around to the anterior (medial) border, and forms an arch with the inter- 




FiG. 5G2. — Deep Dissection of Head of Horse. 
The left ramus of the mandible and structures connected with it have been removed, a, a, Stunips of styloglossus; 
6, genio-glossus ; c, genio-hyoidcus; d, omo-hyoideus; e, kerato-hyoideus; /, thyro-hyoideus; g, thyro-pharyngeus; 
h, crico-thyroideus; (', sterno-thyroideus; k, thyroid gland: m, crico-pharyngcus; n, palatinus and palato-pharyngeus; 
o, pterygoideus lateralis; p, tensor palati; g, levator palati; r, temporalis; s, rectus cap. ventralis major; t, obhquus 
cap. ant. ; u, guttural pouch; i', great cornu of hyoid bone, extremity of which is removed and indicated by dotted line; 
uf, position of small cornu, dotted line; x, thyroid cornu; ^.tongue; 2, anterior pillar of soft palate; i, superficial tem- 
poral nerve; 2, chorda tympani; ^, stump of inferior alveolar nerve; ^, 4. Ungual nerve, intermediate part removed; 5, 
deep temporal nerve; 6, masseteric nerve; 7, buccinator nerve; 8, great palatine nerve; 9, infraorbital nerve; 10^ 
sphenopalatine and posterior nasal nerves; 11, spinal accessory nerve; 12, vagus; 13, pharyngeal branch of vagus; 
14, anterior laryngeal nerve; 13, vago-sympathetic trunk; IG, sympathetic, with anterior cervical ganglion a little fur- 
ther back; 17, glosso-pharyngeal nerve; IS, pharyngeal and 19, lingual, branches of glosso-pharyngeal ; 20, hypoglossal 
nerve; ;?/, left recurrent nerve; ;?^, common carotid artery; ;33, parotid branch; ;24. anterior thyroid or thjTO-Iaryngeal 
artery; ^.j', laryngeal artery; ^o, occipital artery; 5^, internal carotid artery; 57, external carotid artery-; 2S,30,ex- 
ternal maxillary artery-; ^5, pharyngeal arterj-; 5/, lingual artery; 35, internal maxillary artery; 53, stump of inferior 
alveolar artery; 3^, middle meningeal artery; 35, deep temporal artery; 36, buccinator arterj'; 37, palatine arterj'; 
38, end of internal maxillary artery; 39, right external maxillary artery; JfO, satellite vein of 39; 41 > right parotid duct; 
42, mandibular lymph glands; 43. parapharyngeal lymph glands; 44' trachea; 4o, wing of atlas; 4^. dotted line indi- 
cating outUne of mandibular gland; ^7, lacrimal gland. (After Ellenberger-Baum, Top. Anat. d. Pferdes.) 

mediate branch. The lateral branch (Ramus lateralis) passes up the posterior 
(lateral) border' of the ear and forms an arch with the intermediate branch. The 
deep branch (A. auricularis profunda) enters the interval between the external 
acoustic process and mastoid process, and passes through an opening into the 
interior of the external ear and ramifies in the skin which lines it. It gives off the 
stylomastoid artery, which passes through the stylomastoid foramen into the tym- 



646 



BLOOD-VASCULAR SYSTEM OF THE HORSE 



panum, forms an arch arountl the membrana tympani, and supplies the middle ear 
and its muscles. 



THE SUPERFICIAL TEMPORAL ARTERY 

This artery (A. temporalis superficialis) is much the smaller of the two terminal 
branches of the external carotid, and is usually less than an inch (ca. 2 cm.) in length. 

It passes upward behind the posterior 
border of the ramus of the mandible, 
under cover of the parotid gland, and 
divides below the level of the condyle 
into the anterior auricular and trans- 
verse facial arteries. It is crossed super- 
ficially by the facial nerve. 

The anterior auricular artery (A. 
auricularis anterior) ascends behind the 
temporo-mandibular articulation under 
cover of the parotid gland and reaches 
the temporalis muscle. It is crossed 
deeply at its origin by the superficial 
temporal nerve and is accompanied by 
a satellite vein and the auriculo-palpe- 
bral branch of the facial nerve. It is 
distributed to the skin and the temporal 
and anterior auricular muscles, and sends 
a branch through the conchal cartilage 
to the skin which lines it. Collateral 
twigs are detached to the parotid gland, 
and an anterior branch anastomoses with 
the supraorbital artery. A branch some- 
times passes into the temporal canal and 
anastomoses with the posterior meningeal 
artery. 

The transverse facial artery (A. 
transversa faciei) is larger than the pre- 
ceding. It turns around the neck of 
the mandible and emerges from beneath 
the parotid gland (Fig. 560). It then 
passes forward a short distance on the 
masseter about half an inch below the 
zygomatic arch, and enters the muscle, 
in which it commonly divides into two 
chief branches. It is accompanied by a 
vein and a branch of the superficial tem- 
poral nerve. It supplies the masseter and the skin of this region, and anastomoses 
with the external maxillary and posterior deep temporal arteries. 




Fig. 563. — Right Ete of Horse. 
a, Remnants of periorbita; 6, levator palpebrse 
auperioris; c, obliquus oculi inferior: d, rectus oculi 
inferior; c, rectus oculi lateralis; /, rectus oculi superior; 
17, sclera; g', cornea; h, lacrimal gland; i, frontal nerve; 
i', trochlear nerve; k, supraorbital artery; Z, branches of 
lacrimal nerve to gland; m, lacrimal artery; n, zygo- 
matic nerve; o, branch of ophthalmic artery; p, branch of 
oculomotor nerve to obliquus oculi inferior; g. maxil- 
lary nerve; r, infraorbital nerve; s, posterior nasal 
nerve; t, great palatine nerve; u, small palatine nerve: 
t), internal maxillary artery; w, buccinator artery (cut); 
X, infraorbital artery; x\ malar artery; y, spheno- 
palatine artery; z, great palatine artery; z', small 
palatine (or staphyline) artery; 1, posterior deep 
temporal arterj-; £, stump of zygomatic arch (sawn 
off) ; 3, stump of supraorbital process (sawn off) ; 4, fa- 
cial crest; 5, temporal fossa; G, foramen orbitale; 7, 
foramen rotundum and anterior end of alar canal; 
S, posterior opening of alar canal. (After EUenberger, 
in Leisering's Atlas.) 



THE INTERNAL MAXILLARY ARTERY (Figs. 562, 563, 564) 

This artery (A. maxillaris interna) is much the larger of the two terminal 

branches of the external carotid. It begins at the medial side of the posterior border 

of the mandible, about two inches (ca. 5 cm.) below the articulation of the jaw, 

and ends in the anterior part of the pterygo-palatine fossa. On account of its 



THE INTERNAL MAXILLARY ARTERY 647 

complex course and the large number of branches given off it is convenient to divide 
it into three parts. 

I. The first part is much the longest, forms an S-shaped curve, and is in great 
part in contact with the guttural pouch. It passes upward and forward on the 
medial surface of the mandible a distance of about an inch (ca. 2-3 cm.), and is 
related here to the vein, which is ventral. It then turns inward on the ventral 
surface of the lateral pterygoid muscle and the mandibular nerve, passes between 
that muscle and the tensor palati, and runs forward to enter the alar foramen. 
This part gives off the following branches: 

1. The inferior alveolar artery (A. alveolaris mandibulse s. inferior)' passes 
downward and forwartl with the homonymous vein and nerve, being at first between 




Fig. 564. — Left Ete of Horse, Deeper Dissection. 
The outer plate of bone has been removed behind the pterygoid crest to expose the vessels and nerves, a, a. Rem- 
nants of periorbita; 6, 6, stumps of rectus ocuU superior; c, obliquus oculi inferior; rf, rectus oculi inferior ; e, rectua 
ocuh lateralis; e', retractor oculi; /, rectus oculi medialis; fl, ff, obhquus oculi superior; ft, eyeball; i, trochlear nerve; 
A, ophthalmic nerve; ^', nasal nerve; ^■'^ infratrochlear nerve; A-'", ethmoidal nerve; /, optic nerve; m, frontal nerve; 
71, lacrimal nerve; o, zygomatic nerve; p, nerve to obliquus inferior (from oculomotor); g, maxillary nerve; r, infra- 
orbital nerve; s, sphenopalatine nerve; t, great palatine nerve; u, small palatine nerve; jj, internal maxillary artery; 
w, buccinator artery (cut off); x, infraorbital artery; x', malar artery; y, spheno-palatine artery; 2, great palatine 
artery; ?', small palatine artery; 1, S, stumps of zygomatic arch; S, stump of supraorbital process; 4, facial crest; 
J, temporal fossa; 5, external ophthalmic artery; 7, muscular branch of 6; 5, lacrimal artery (cut) ; 5, supraorbital 
artery; 10, anterior deep temporal artery ; i i , ethmoidal artery . (After Ellenberger-Baum, Top. Anat. d. Pferdes.) 

the lateral and medial pterygoid muscles, then between the latter and the ramus of 
the mandible. It enters the mandibular foramen, passes downward and forward 
in the mandibular canal, and terminates at the mental foramen by dividing into 
mental and incisor branches. The mental branch (A. mentalis) emerges through 
the mental foramen and anastomoses in the lower lip with the opposite arterj' and 
the inferior labial. The incisor branch (Ramus incisivus) continues forward in the 
bone, supplies twigs to the canine and incisor teeth, and anastomoses with its fellow 
of the opposite side. Collateral branches are detached to the pterygoid and mylo- 
hyoid muscles, and within the bone to the teeth, alveolar periosteum, the gums, 
and the spongy substance of the mandible. 

2. The pterygoid arteries, two or three in number, are distributed to the ptery- 
goid and tensor and levator palati muscles. 

1 Also kiiown as tlie inferior dental artery. 



648 



BLOOD-VASCULAR SYSTEM OF THE HORSE 



3. The tympanic artery is a very small vessel which passes along the Eusta- 
chian tube to the i:)ctro-tynipanic fissure and enters the middle ear. 

4. The middle meningeal artery (A. meningea media) arises beneath the buc- 
cinator nerve, where the internal maxillary turns forward. It passes backward 
across the temporal wing of the sphenoid to the antero-lateral part (foramen spino- 
sum) of the foramen lacerum. Entering the cranium, it divides into branches which 
course in the grooves on the temporal and parietal bones and supply the dura 
mater. It anastomoses with the posterior meningeal. 

The size of this artery is variable, and is in inverse ratio to that of the posterior meningeal. 




Fig. 565. — Sagittal Section of Head of Horse, Cut a Little to the Right of the Median Plane. 
i.Skin; 5, nasal bone; 3, frontal bone; 4, parietal bone; 4'. tentorium osseum; J, occipital bone; 5, sphenoid bone; 
7, hard palate: S, premaxilla; 9, mandible; 10, hyoid bone; 11, septum between frontal sinuses; 12, alar cartilage; 
13, transversus nasi; 1^, septum nasi with venous plexuses; 15, palato-labiai artery; 16, 16', upper and lower 
septal branches of /5; i 7, septal branch of sphenopalatine artery and satellite vein; IS, septal branch of ethmoidal 
artery; 19, sphenoidal sinus: iO, guttural pouch; £1, pharynx; 23, pharyngeal orifice of Eustachian tube; 23, posterior 
naris; 24, soft palate; 25, palatinus muscle; 26, pharyngeal muscles; 27, cesophagus; 3S, dotted line indicating posi- 
tion of posterior pillar of soft palate: 29, lamina, 29', arch of cricoid cartilage: SO, arytenoideus transversus muscle; 
31, epiglottis: 32, body of thyroid cartilage; 33, vocal process and cord; 34, arytenoid cartilage; 35, lateral ventricle 
of larynx; 36, trachea; S?, ventral straight muscles of head; 3S, longus colH; 39, atlas; 40, axis; ^-f. lig- nuchse; 42, 
dorsal spinal muscles; 4^, muscles of external ear; 44' omo- and sterno-hyoideus; 45, tongue: 46, mylo-hyoideus; .J7, 
genio-hyoideus; 4^, genio-glossus; 49, longitudinalis inferior; 50, longitud. superior; 51, hypo-epiglotticus; 62, chin 
and mentalis muscle; 53, venous plexus of hard palate; 54, corpus callosum; 55, septum pellucidum; 56, fornix: 57, 
thalamus: 58, pineal body; 59, corpora quadrigemina; 60, cerebral peduncle; 61, corpus mammillare; 62, pituitary 
body; 63, chiasma opticum; 64, intercarotid artery; 65, medulla oblongata: 66, interventricular foramen; 67, infun- 
dibulum; SS. third ventricle; 69, cerebral aqueduct; 70, anterior medullary velum; 7/, fourth ventricle; 72, posterior 
medullary velum; 73, basilar artery; 74, spinal cord; 75, ethmoidal nerve; 76, septal branch of posteriornasal nerve; 
76', branch of same to vomero-nasal organ ; 77, olfactory nerve to vomero-nasal organ; 7S, naaal branches of palatine 
artery, (.\fter Ellenberger, in Leisering's Atlas.) 



5. The posterior deep temporal artery (A. temporalis profunda aboralis) 
arises from the internal maxillary just before the latter enters the alar canal. It 
passes upward and backward in the temporal fossa on the deep face of the temporalis 
muscle, in which it ramifies. It sends a branch outward to the masseter, and 
anastomoses with the superficial temporal and middle meningeal arteries. 

In some cases the tympanic and middle meningeal arise from this artery. 

II. The second part lies in the alar canal, and is about an inch (ca. 2-3 cm.) in 
length. It gives off two branches — the anterior deep temporal and the external 
ophthalmic. 

1. The anterior deep temporal artery (A. temporalis profunda oralis) emerges 
from the canal through the small alar or temporal foramen, and asccnils in the 



THE INTERNAL MAXILLARY ARTERY 649 

anterior part of the temporal fossa on the deep face of the temporalis muscle, in 
which it is chiefly distributed. It gives twigs to the orbital fat and the skin of the 
frontal region. 

2. The external ophthalmic artery (A. ophthalmica externa) emerges from the 
anterior opening of the alar canal, and enters the apex of the periorbita. Within 
this it forms a semicircular bend under the rectus oculi superior, and is continued 
by the ethmoidal artery. Its branches are as follows: 

(a) The supraorbital artery (A. supraorbitalis) is a small vessel which often 
arises from the anterior deep temporal or the internal maxillary. It passes along 
the inner wall of the orbit in company with the nerve of the same name to the supra- 
orbital foramen, through which it emerges. It is distributed to the orbicularis 
oculi, the corrugator supercilii, and the skin of the supraorbital region. 

(b) The laorimal artery (A. lacrimalis) runs upward and forward within the 
periorbita along the lateral edge of the levator palpebrse superioris to the lacrimal 
glantl, in which it is chiefly distributed. It also sends twigs to the upper eyelid. 

(c) Muscular branches (Rami musculares) supply the orbital muscles, the 
periorbita, the third eyelid, and the conjunctiva. 

(d) Ciliary branches (Aa. ciliares), two sets of very slender arteries, arise 
from the ophthalmic direct and from the muscular branches. The anterior ciliary 
arteries (Aa. ciliares anteriores) pierce the sclera in front of the equator and ramify 
chiefly in the ciliary body and the iris. The posterior cihary arteries (Aa. ciliares 
posteriores) pierce the posterior part of the sclera; most of them ramify in the 
chorioid coat as the short ciliary arteries, but two of larger size, the long ciliary 
arteries, run forward, one on each side, between the sclera and chorioid to the 
periphery of the iris. Here the.y divide into branches which anastomose and form 
a circle (Circulus iridis major). From this secondary branches are detached which 
form a second circle around the pupil (Circulus iridis minor). 

(e) The central artery of the retina (A. centralis retince) is a small vessel which 
arises from the ophthalmic or from a posterior ciliary artery. It pierces the optic 
nerve a short distance behind the sclera, and runs in its center to the lamina cribrosa, 
where it breaks up in thirty to forty fine branches. These appear in the fundus of 
the eye at the margin of the optic papilla and radiate in the posterior part of the 
retina. 

(/) The ethmoidal artery (A. ethmoidalis) is the continuation of the oph- 
thalmic. It enters the cranial cavity through the ethmoidal foramen, passes 
inward on the cribriform plate, and divides into meningeal and nasal branches. 
The former ramify in the anterior part of the dura mater and anastomose with 
branches of the artery of the corpus callosum. The nasal branch passes through the 
cribriform plate, gives branches to the mucous membrane of the lateral mass of the 
ethmoid and the adjacent part of the septum nasi, and runs forward on the dorsal 
turbinate. 

III. The third part passes forward in the pterygo-palatine fossa, accompanied 
by branches of the maxillary nerve. On reaching the posterior palatine foramen it 
is continued by the greater palatine artery. Its branches are as follows: 

(1) The buccinator artery (A. buccinatoria) arises from the ventral aspect of 
the internal maxillary shortly after its emergence (Fig. 562). It turns around the 
maxillary tuberosity, accompanied by the buccinator nerve, and under the masseter 
muscle, enters the cheek, and runs forward in it. It supplies branches to the 
cheek, the superior buccal glands, antl the masseter and pterygoid muscles. Near 
its origin it gives off a branch to the orbital fat behind the periorbita. 

(2) The infraorbital artery (A. infraorbitalis)' arises from the upper aspect of 
the internal maxillary a little in front of the preceding vessel. It passes upward 
and forward to the maxillary foramen, runs in the infraorbital canal in company with 

' Also termed the superior dental artery. 



650 BLOOD-VASCULAR SYSTEM OF THE HORSE 

the nerve of the same name, and is continued forward within the jaw to the incisor 
teeth. It gives branches to the teeth and gums, and detaches a branch through the 
infraorbital foramen which anastomoses with the lateral nasal and superior labial.^ 
Al^out midway between its origin and the maxillary foramen it gives off the malar 
branch (Ramus malaris), which passes along tlie floor of the orbit to end in the lower 
lid and anastomose with the angularis oculi. It gives twigs to the inferior ol^lique 
muscle and the lacrimal sac. 

(3) The lesser palatine artery (A. palatina minor) is a small vessel which 
passes forward in the groove at the medial side of the maxillary tuberosity to the 
soft palate. In the groove it is accompanied by the nerve of the same name and the 
palatine vein. 

(4) The sphenopalatine artery (A. sphenopalatina) arises in the anterior 
part of the pterygo-palatine fossa, passes through the sphenopalatine foramen into 
the nasal cavity, and divides into two branches. The medial branch is distributed 
to the mucous membrane of the septum nasi ; the lateral one goes to the ventral 
turbinate, the ventral meatus, the posterior nares, and the maxillary and frontal 
sinuses. It may arise from the infraorbital. 

(5) The greater palatine artery (A. palatina major) is the direct continuation 
of the internal maxillary. It passes through the palatine canal to the roof of the 
mouth, accompanied by the palatine nerve, and runs forward in the palatine 
groove, where it is joined by the vein. A little behind the plane of the corner 
incisor teeth it curves medially over a bar of cartilage to the foramen incisivum, 
where it unites with its fellow of the opposite side. The single artery thus formed 
(A. palato-labialis) passes up through the foramen and divides under the transversus 
nasi into two branches. These ramify in the upper lip and anastomose with the 
lateral nasal and superior labial arteries. In its course in the palate the artery gives 
off branches to the hard and soft palate and the gums, and others which pass through 
the accessory palatine foramina to be distril:)uted in the mucous membrane of the 
lower part of the nasal cavity. Commonly two branches, right and left, are de- 
tached from the convexity of the arch formed Ijy the union of the two arteries; 
these run forward in the anterior part of the hard palate. 



Arteries of the Thoracic Limb 

THE brachial ARTERY 

The brachial artery, after crossing the ventral border of the scalenus at the 
first rib, passes backward and downward across the origin of the coraco-brachialis 
and the insertion of the subscapularis muscle at the medial side of the shoulder 
joint." At the posterior border of the subscapularis it gives off the subscapular 
artery, and turns distally on the medial surface of the arm. In its course in the 
arm it inclines a little forward, crosses the humerus very obliciuely, and is continued 
by the median artery. 

In its course over the chest-wall the artery is related medially to the ventral 
border of the serratus thoracis and the rectus thoracis. Opposite the ventral end 
of the first rib it is crossed medially by the median nerve and laterally by the mus- 
culo-cutaneous nerve; the two nerves unite below the artery, which is thus sus- 
pended in a sort of loop. In the arm it is related medially to the posterior deep 
pectoral muscle and is covered by the deep brachial fascia. Laterally it lies on the 
subscapularis, the brachialis, the insertion of the teres major and latissimus dorsi, 

^ The infraorbital artery is usually small at its emergence upon the face, but in some cases it 
is rather large and may partially replace the superior labial and lateral nasal arteries. 

- The term axillary is often applied to the artery from the first rib to the point of origin of 
the subscapular artery, and the name brachial is given to the artery beyond this. 



THE BRACHIAL ARTERY 651 

and the medial head of the triceps. The coraco-l^rachialis muscle lies along the 
front of the artery, which, however, overlaps the muscle distally. The vein crosses 
the medial face of the artery and runs down behind it, accompanied part way by the 
ulnar and radial nerves. The chief branches are as follows: 

1. The suprascapular artery (A. thoraco-acromialis) is a small and somewhat 
flexuous vessel, which arises near the anterior border of the subscapularis, runs 
dorsally, and dips in between that muscle and the supraspinatus. It gives branches 
to these muscles, the anterior deep pectoral, and the brachiocephalicus. A branch 
passes in front of the coraco-brachialis to the shoulder joint and the proximal end 
of the humerus.' 

2. The subscapular artery (A. subscapularis) is a very large vessel which arises 
at the posterior border of the suljscapularis muscle. It ascends in the interstice 
between that muscle and the teres major, on the medial surface of the long head 
of the triceps, turns around the posterior border of the scapula below the dorsal 
angle, and ends in the infraspinatus and deltoid. Besides collateral muscular 
branches (Rami musculares) to the subscapularis, teres major, triceps, and tensor 
fasciae antibrachii, it gives off the following named branches: 

(a) The thoraco-dorsal (A. thoracodorsalis) is a long artery which is usually 
given off about an incli from the origin of the subscapular, crosses the medial face 
of the teres major, and runs upward and backward on the latissimus dorsi. It gives 
branches to these muscles, the abdominal cutancus and the axillary lymph glands. 

{b) The posterior circumflex artery of the humerus (A. circumfiexa humeri 
posterior) arises a little above the preceding vessel, and passes outward behind the 
shoulder joint between the long and lateral heads of the triceps with the axillary 
nerve. It gives branches to these muscles, the joint capsule, and the muscles and 
skin of the lateral side of the shoulder, anastomosing with the anterior circumflex 
artery. 

(c) The circiunflex artery of the scapula (A. circumfiexa scapulae) arises about 
two or three inches (ca. 5-7.5 cm.) above the shoulder joint, passes forward to 
the posterior border of the scapula, and divides into two branches. The lateral one 
runs forward on the lateral surface of the scapula below the spine, and gives branches 
to the supraspinatus, infraspinatus, and teres minor. The medial branch passes 
forward in a similar fashion on the costal surface of the scapula and supplies branches 
to the subscapularis. 

3. The anterior circumflex artery of the humerus (A. circumfiexa humeri 
anterior)- arises usually at the anterior border of the teres major. It passes forward 
between the two parts of the coraco-brachialis or between the latter and the humerus. 
It gives branches to the coraco-brachialis and deep pectoral and ends in the upper 
part of the biceps and in the brachiocephalicus. It anastomoses with the posterior 
circumflex artery. 

Not rarely it is replaced largely by an artery which arises from the brachial at the distal end 
of the coraco-brachialis, and ascends on the front of the humerus, hi these cases a small branch 
for the coraco-brachialis is usually given off at the usual point of origin of the anterior circumflex. 

4. The deep brachial artery (A. profunda brachii) is a large but short trunk 
which arises usually about the middle of the humerus. It passes backward to the 
interval between the tendon of the teres major and latissimus dorsi, and the long and 
medial heads of the triceps, where it divides into several branches which supply the 
triceps, tensor fascia antibrachii, anconeus, and brachialis. A branch runs in the 
musculo-spiral groove with the radial nerve to the front of the elbow joint and 
anastomoses with the anterior radial. A slender branch descends along the lateral 

' This vessel may be double, or be represented by one or more branches of the inferior cer\-ical 
artery. 

' Also termed the prehumeral artery. 



652 



BLOOD-VASCULAR SYSTEM OF THE HORSE 



A nterior deep 

pectoral 7n.uscle 

Suprascapular 

artery 




Posterior deep pecto- '" 

ral muscle 

Tendon of cutantus 

Nerve to biceps 

Anterior drcumfltx 

artiry 

Anterior superficial 

pectoral muscle 



Extensor carpi radiahs 

Radius 
Accessory cephalic vein 



Elbow joint 
flexor carpi 
ulnar is 
Fk xor carpi 
rudialis 
Midinl liga- 
mi nt of elbow 
joint 



Fig. 566.— Dissection of Shoolder and Asm of House; Medial Suhface. 
A, Brachial artery, the stump of which has been turned backward; B, subscapular artery; C, thoraco-dorsal 
artery; D, deep brachial artery; E. ulnar artery; F, anterior radial artery; C, median artery; H, stump of brachial yein; 
J, external thoracic yem; J, brachial vein, part of which has been removed to expose deep brachial artery A' A" A", 
median veins; L. cephalic vein; L'. communicating vein; M. brachialis muscle; N. medial epicondyle of hu- 
merus U. prescapular lymph glands; P. indicating position of axillary lymph glands, should be dorsal to vein; Q, posi- 
tion 01 cubital lymph glands; 1, suprascapular nerve; i, subscapular nerves; S. thoraco-dorsal nerve; 4. musculo- 
cutaneous nerve ; r, cutaneous branch of musculo-cutaneous nerve; 5, median nerve; ff, axillary nerve- 7 ulnar nerve- 
7 . cutaneous branch of ulnar nerve; S. radial nerve; 9. thoracic nerves. The vein at the elbow which lies in front of the 
meoian artery should be shown crossing over the median nerve and the median and ulnar arteries, as in the next figure 
(After Schmaltz, Atlas d. Anat. d. Pferdes.) . 



THE BRACHIAL ARTERY 



653 



border of the extensor carpi and supplies cutaneous twigs. Anastomoses occur 
with the ulnar and recurrent interosseous arteries. 

The point of origin is inconstant and it is not uncommon to find two arteries instead of one. 
Often a large liranch for the posterior deep pectoral muscle is detached close to the origin or arises 
from the brachial directly. 



Ulnar nerve 



BrdcJiial i'es. 
Median ner 
Coraco-brachialis 



Biceps brachii 

Cephalic vein 

Vena communicans 

Cuianeoxis branch of 
musculo-culaneous nerve 

Extensor carpi radialis 



Accessory cephalic vein 

Cephalic vein 

Rad'us 

Flexor carpi radialis 

Artery of rete carpi 
dorsale 



Medial ligament of 
carpus 

Tendon of cxlensor 
carpi obliquus 

Common digital vein 

Branch to deep volar 
arch 



Dorsal metacarpal artery 




Long head of triceps 

^ Medial head of triceps 



Tensor fascia" antibrachii 



Ulnar head of flexor 
carpi ulnaris 
II mill ral head of flexor 
ciiijii ulnaris 

Uliiiir head of deep flexor 
Flexor air pi radialis 



Common interosseous 
artery 

Median artery 

Ulnar vessels and nerve 

Deep fascia 



Lateral branch of median 

nerve 

Medial branch of median 

ncrre 

Flexor carpi radialis 

Lateral volar nerve 

Lateral volar met. artery 
and vein 

Medial volar nerve 

Common digital artery 

Medial volar met. artery 

Flexor tendons 



Fig. 567. — Dissection of Right Forearm and Carpus of Horse; Medial View. 
1, Ulnar vessels; 2, cutaneous branch of musculo-cutaneous nerve; 3, 3. satellite veins of median artery; 4, posi- 
tion of cubital lymph glands; 5, anastomosis of ulnar and lateral volar metacarpal arteries; 6. brachialis muscle; 7, 
superficial digital flexor; 8. deep digital flexor. Dotted lines indicate contour of flexor carpi radialis, most of which has 
been removed. (,\fter Schmaltz, .\tlas der Anatomic des Pferdes.) 



654 BLOOD-VASCULAR SYSTEM OF THE HORSE 

5. Musciilar branches (Rami musculares) are distributed to the teres major, 
deep pectoral, eoraco-brachialis, and biceps. The largest and least variable of 
these supplies the distal part of the biceps. 

6. The ulnar artery (A. collateralis ulnaris proximalis) arises at the distal 
end of the eoraco-brachialis and passes downward and backward along the ventral 
edge of the medial head of the triceps under cover of the brachial vein and the 
tensor fascise antibrachii. It gives branches to these muscles, the posterior super- 
ficial pectoral, the cubital lymph glands, cutaneus, and skin. At the elbow it lies 
on the posterior part of the medial epicondyle, in relation in front to the ulnar 
nerve, and largely covered by the satellite vein; it then turns do^vnward under the 
ulnar head of the flexor carpi ulnaris. It continues its descent with the vein and 
nerve under the deep fascia of the forearm between the ulnar and humeral heads of 
the deep flexor of the digit, and in the distal half of the region between the lateral 
and middle flexors of the carpus. It unites just above the carpus (under cover of 
the flexor carpi ulnaris) with a branch of the median artery, with which it forms the 
supracarpal arch. It detaches small collaterals to the muscles along which it passes 
and terminal twigs to the lateral surface of the carpus. 

7. The nutrient artery of the humerus (A. nutritia humeri) is a short vessel 
which enters the nutrient foramen of the humerus. It often arises from the ulnar. 

8. The anterior radial artery (A. collateralis radialis distalis)' passes do^\^lward 
and a little outward on the anterior face of the humerus under cover of the biceps 
and brachialis to the front of the ell)OW joint, where it is in contact with the radial 
nerve. It then descends on the anterior surface of the radius, under cover of the 
common digital extensor, to the carpus, where it concurs in the formation of the rete 
carpi dorsale, anastomosing with the median and dorsal interosseous arteries. It 
supplies branches to the elbow joint, the biceps, brachialis, and the extensors of 
the carpus and digit. A cutaneous branch emerges between the distal end of the 
biceps and the brachialis. 

THE MEDIAN ARTERY 

The median or posterior radial artery (A. mediana)- is the direct continuation 
of the brachial. It descends, inclining slightly backward, at first on the medial 
surface of the humerus, and then over the capsule and medial ligament of the elbow 
joint, under cover of the posterior superficial pectoral muscle.^ At the proximal 
third of the forearm it dips under the flexor carpi radialis and passes down the medial 
part of the posterior surface of the radius. In the distal part of the forearm it 
inclines Imckward and is separated from the radius by the reinforcing band (Caput 
tendineum) of the superficial flexor of the digit and is continued by the conmion 
digital or large metacarpal artery. 

It is accompanied by the median nerve, which lies in front of the artery at its 
origin, then usually crosses over it obliquely at the elbow joint and becomes posterior. 
At the distal end of the arm the artery is crossed by the large anastomotic vein 
which connects the cephalic and brachial veins, and a radicle of the brachial vein lies 
behind and partly upon the artery ; lower down there are usually two satellite 
veins, anterior and posterior. The chief collateral branches are as follows: 

1. Articular branches are supplied to the elbow joint. 

2. Muscular branches go to the flexors of the carpus and digit; the largest of 
these arise at the proximal third of the forearm. 

3. The common interosseous artery (A. interossea communis) is a vessel of 

1 This vessel is apparently the A. transversa cubiti of comparative anatomy. 

' Although the homology of some arteries in this region are still unsettled, it seems clear that 
this vessel should be termed the median artery. 

^ The pulse can be taken where the artery lies on the ligament, since the pectoral muscle is 
thin here. 



THE MEDIAN ARTERY 



655 



considerable size which arises at the level of the interosseous space, through which 
it passes outward. Before entering the space it gives off a small branch, the volar 



Deltuid 

Brachiocephalicits 

Lateral head of 

triceps (cut) 



Cutaneous brnnrli nf 

axillary iicrri' 

Anterior radial art< ry 

Common digital extensor 

Brachialis 



Extensor carpi radialis 




Extensor carjd obliquus 

Tendon of extensor carpi 
radialis 
Lateral Kg. of carpus 

Rete carpi dorsale 

Te ndon of common extensor 

Branch to lateral extensor 



Tensor fascia: antibrachii 
Long head of triceps 

Branch of radial nerve to 
heads of triceps and anconeus 
Deep brachial artery 

Radial nerve 

Long head of triceps 

Medial head of triceps 

Anconeus 

Lateral head of triceps (cut off) 

Olecranon 

Ulnar head of deep flexor 
Cutaneous branch of ulnar 

nerve 
Lateral lig. of elbow 
Vlnaris lateralis (cut 
and reflected) 



Common interosseous artery 

Ulna 

I'hiar hi ad of common 

digital extensor 
Deep digital flexor 

Lateral digital extensor 
Ulnar nerve and vein 

Vlnaris lateralis (stump) 

Dorsal interosseous artery 

Superficial branch of ulnar 
nerve 

Carpal sheath (opened) 
Lateral tendon of ulnaris 

lateralis 
Accessoiy carpal bone 

A ccessorio-metacarpal 
ligaments 

Band from accessory carped 
to lateral extensor tendon 
Lateral extensor tendon 



Fig. 568. — Dissection of Left Forearm of Horse; Lateral Surface. 
The radial and ulnar heads of the anterior digital extensor are shown in front of the lateral extensor, but are not 
marked. The muscular branches of the radial nerve are shown, but not designated individually. Dotted lines indi- 
cate contour of parts of muscles which have been removed (lateral head of triceps, extensor carpi radialis, lateral flexor 
of carpus), (.\fter Schmaltz, .\tlas d. .\nat d. Pferdes.) 



interosseous artery (A. interossea volaris), which descends to the radial head of the 
deep flexor. In the .space it supplies the nutrient arteries of the radius and ulna. 



656 



BLOOD-VASCULAR SYSTEM OF THE HORSE 



Emerging from the space it gives off branches to tlie uhiaris lateralis, and the small 
recurrent interosseous artery (A. interossea recurrens) , which ascends on the lateral 



Artery of rcte carpi volare 



Oblique ligamcnl 

Medial lig. 
First carpal bone 

Deep volar metacarpal arteries 
Medial metacarpal banc 




Acccssorio-radial lig. 
Accessorio-ulnar lig. 

Lateral lig. 
Check ligament 

A ccessorio-m eta car pa I Ug. 

Deep volar areii 

Siis/ieiisory ligti inent 
Lateral metacarpal bone 



Fig. 569. — Deep Dissection of Right Carpus of Horse; Posterior View. 
/, Radial carpal bone; 2, accessory carpal bone; 3, second carpal bone. (After Schmaltz, Atlas d. .\nat. d. Pferdes.) 



Joint capsule 



Tendon of lateral 

crtensor 

Lateral ligament 



Long tendon of, 
ulnaris lateralis 

Superficial branch 
of ulnar nerve 



Fig. 570. — CROss-SErTio 

Cr, a, Cii, Ca, radial, intermediate, ulna 

tendon; 3 (on volar carpal ligament), carpal c 

common exten.sor; G, medial volar nerve; 7, 1 




Tnidon of extensor 
( (; pi radialis 



1 1 ndoii of extensor 
I II iii obliquus 



Mi^dial ligament 



Ti ndon of flexor 
cm pi radialis 
Common digital vein 
Ml dial volar meta- 
ta) pal artery 
Common digital arteiy 

L ittral metacarpal lein 

■ Lateral volar metacarpal artery 
OF Proximal Part of Left Carpus of Horse. 
, and accessory carpal bones; 1, superficial flexor tendon; 2, deep flexor 
mal; 4, oblique ligament from radius to radial carpal bone; 5, tendon of 
teral volar nerve. Synovial cavities are black. 



surface of the ulna and anastomoses with the deep brachial and ulnar arteries. 
Under cover of the common digital extensor it connects with the anterior radial 
artery and gives off the dorsal interosseous artery (Fig. 568). This vessel (A. 



THE MEDIAN ARTERY 



657 



interossea dorsalis) descends between the common and lateral extensors of the digit 
and concurs with the anterior radial in forming a network on the dorsal surface of 
tlie carpus, the rete carpi dorsale. From the latter arise two small vessels, the 
medial and lateral dorsal metacarpal arteries (A. metacarpea dorsalis medialis, 
lateralis), which run distalh' in the gnxjvcs l>etween the large and small metacarpal 
bones and anastomose with the volar metacarpal arteries. 

4. The artery of the rete carpi volare (A. retis carpi volaris) is a small vessel 
which arises at the distal third of the forearm and descends on the radius to the 
posterior surface of the carpus, where it concurs with branches of the volar meta- 
carpal arteries in forming tlie rete carpi volare. 

5. The lateral volar metacarpal artery (A. metacarpea volaris lateralis)^ is a 
small vessel which arises just above the carpus under cover of the flexor carpi 
ulnaris and anastomoses with the ulnar artery, forming the supracarpal arch. 
From the latter a branch descends with the lateral Ijranch of the median nerve, 



Skin 



Mc. Ill 



Mr. II 




Common digital vein 
Common digital artery 
Medial volar nerve 
Superficial flexor tendon ' 

Fig. 371. — Cross-section of Right Metacarpus of Horse. 
Section is cut a little above middle of region. 
Dorsal metacarpal arteries; 2, 2', deep volar metacarpal arteries; 3, deep volar metacarpal ' 
carpal sheath. 



Tendon of common eJiensor 



un of lateral extensor 



Mc. IV 

Suspensory ligamciU 

Lateral volar metacarpal 

vessel 

Lateral volar nerve 

Check ligament 
Deep flexor tendon 
Deep fascia 



4, distal part of 



inclines outward toward the posterior border of the accessory carpal bone, and 
arrives at the head of the lateral metacarpal bone. Here it is connected with the 
medial volar metacarpal artery, usually by two transverse branches, thus forming 
the deep volar or subcarpal arch (Arcus volaris profundus proximalis). One of 
these branches lies between the subcarpal check ligament and the suspensory 
ligament ; the other (not always present) lies beneath the latter on the large meta- 
carpal bone. A small branch descends to the fetlock with the lateral volar nerve. 
Below the arch the artery pursues a flexuous course downward on the volar face of 
the large metacarpal bone alongside of the lateral small metacarpal and under 
cover of the suspensory ligament. At the distal third of the metacarpus it com- 
monly unites with the corresponding vessel of the other side to form a short trunk 
which passes backward through the angle of divergence of the branches of the sus- 
pensory ligament and joins the lateral digital or the common digital artery. This 
junction forms the distal volar arch (Arcus volaris distalis). 

6. The medial volar metacarpal artery (A. metacarpea volaris medialis)- is 
' Also termed tlie external metaearpal artery. 
2 Also called the internal or small metacarpal artery. 
42 



658 



BLOOD-VASCULAK SYSTEM OF THE HORSE 



given off from the median at an acute angle, usually a little above the lateral 
one or by a common trunk with it. It passes down the medial side of the carpus 
behind the tendon of the flexor carpi radialis and embedded in the posterior annular 
ligament. Arriving at the proximal end of the medial metacarpal bone it becomes 
more deeply placed and is connected with the lateral volar artery by one or two 
transverse branches, as stated above. It then pursues a flexuous course downward 



Medial ligament of carpus 

Tendon of extensor carpi radialis 
Tendon of extensor carpi ohliquus 



Medial ligament of fetlock joint 
Comtnon extensor tendon 

Extensor branch of suspensory 
ligament 

Dorsal artery of first pitalanx 



Medial ligament of pastern joint 



Coronary corium 
Laminar corium 



Fig. 572. — Dissection of Right CARpns 




Lateral metacarpal vein 
Medial metacarpal vein 

Posterior annular ligament of 
carpus 



Superficial flexor tendon 
Medial volar nerve 

Communicating branch 
Common digital artery 
Medial metacarpal vein 
Suspensory ligament 
Lumhricalis muscle 
Dorsal digital nerve 
Volar digital nerve 
Digital artery 
Digital vein 
Ldgament of ergot 
Deep flexor tendon 
Cartilage of third phalanx 

Coronary plexus 



.(. AHi'is, AND Digit of Horse; Medial View. (After Schmaltz, Atlas 
d. Anat. d. Pferdes.) 



alongside of the medial small metacarpal bone, like the corresponding lateral 
artery, with which it commonly unites as described above. It is larger than the 
lateral artery, and supplies the nutrient artery to the large metacarpal bone. 

The foregoing account describes the most common arrangement of the dorsal and volar 
metacarpal arteries. Variations in their origin and connections are common, but have no great 
surgical importance. Collateral branches are omitted for the same reason. In some cases the 
medial volar metacarpal is connected with the common digital artery a little below the carpus by 
a branch passing obliquely across the medial border of the deep flexor tendon; this forms a super- 
ficial volar arch. 



THE COMMON DIGITAL ARTERY THE DIGITAL ARTERIES 659 



THE COMMON DIGITAL ARTERY 
The common digital artery (A. digitalis communis s. metacarpea volaris 
superficialis) ' is tiie direct continuation of tlie median. It descends in the 
carpal canal along the medial side of the flexor tendons in company with the 
medial volar nerve. Continuing down the limb it preserves this relation to the 
tendons to the distal third of the metacarpus, where it inclines toward the middle 
line of the limb behind the suspensory ligament, and divides into the medial and 
lateral digital arteries. In the metacarpus the artery is related to the vein in front 
and the nerve behind, and is covered by the fascia and skin. It furnishes collateral 
branches to the suspensory ligament, the flexor tendons, and the skin. 



THE DIGITAL ARTERIES 
The digital arteries, medial and lateral (A. digitalis volaris propria medialis, 
lateralis), are formed by the bifurcation of the common digital at the distal third 
of the metacarpus. They diverge, pass down over the abaxial surface of the cor- 
responding sesamoid at the fetlock, and descend parallel with the borders of the deep 
flexor tendon to the volar grooves and foramina of the third phalanx. Entering the 
latter the two arteries unite in the semilunar canal and form the terminal arch 
(Arcus terminalis), from which numerous branches pass through the bone to the 
dorsal surface and ramify in the corium of the wall and sole of the hoof.- A num- 
ber of branches emerge through the foramina at the distal border, where they anas- 
tomose with each other in arciform fashion. 

These branches were named by Spooner the inferior communicating arteries, and the anas- 
tomotic arch formed by them is termed the circumflex artery of the third phalanx (Chauveau) 
or the artery of the distal border of the third phalanx (Leisering). 

Each artery is accompanied by a vein and by the digital nerves. Above the 
fetlock the artery is most deeply placed and is covered by the vein; the nerve is 
beh nd the vein. At the fetlock the arter.v has become superficial and is related 
to the vein in front and the posterior branch of the nerve behind. The anterior 
branch of the nerve crosses over the artery obliquely to the side of the first phalanx. 
The artery and nerves are crossed oblicjuely by a small band, the tendon or ligament 
of the ergot {vide digital fascia). 

In addition to branches to the joints, tendons and synovial sheath, ergot, and 
skin, the digital arteries give off the following named branches: 

1. The artery of the first phalanx (A. phalangis primse)' is a short trunk which 
arises at a right angle about the middle of the first phalanx, and divides into 
dorsal and volar branches. The dorsal branch (Ramus dorsalis) passes between 
the first phalanx and the extensor tendon and ramifies on the front of the digit, 
anastomosing with its fellow. The volar branch (Ramus volaris) dips in between 
the flexor tendons and the first phalanx and anastomoses with the opposite artery 
between the superficial and middle tlistal sesamoidean ligaments. 

2. The artery of the digital cushion (A. toricte phalangis tertise) arises at the 
proximal border of the cartilage of the third phalanx and passes backward and 
downward to ramify in the digital cushion and the corium of the heels and frog. 

3. The dorsal artery of the second phalanx (Ramus dorsalis phalangis secundse) 
arises a little above the level of the distal sesamoid bone, and passes forward under 
cover of the cartilage of the third phalanx and the extensor tendon to the front of 
the second phalanx, where it anastomoses with the opposite vessel. It gives 

1 This vessel is also termed the large or palmar metacarpal artery. 

2 The terminal part of the digital artery has been termed the plantar artery. 
^ Also termed the perpendicular artery. 



660 BLOOD-VASCULAR SYSTEM OF THE HORSE 

liranches to the skin, the tendon, the coffin joint, and the coronary coriuni of the 
hoof. 

4. The volar artery of the second phalanx (Ramus volaris phalangis secundse) 
is smaller than the preceding, opposite to which it arises. It passes alcove the 
proximal border of the distal sesamoid and unites with the opposite artery. 

The arteries of the second phalanx form what is termed by Chauveau the coronary circle. 
The dorsal (anterior) part of the circle gives off commonly an artery (A. coronalis phalangis tertia-) 
near either side of the extensor tendon, which divides into two branches. The central branch 
unites with that of the opposite side, while the other joins a branch of the artery of the digital 
cushion. In this way is formed the circumflex artery of the coronary cushion, an anastomotic 
arch which lies on the extensor tendon at the coronet. In .some cases descending branches of the 
arteries of the first phalanx concur in the formation of the arch. 

5. The dorsal artery of the third phalanx (A. dorsalis phalangis tertise)^ arises 
at the deep face of the angle of the third phalanx, passes through the notch or fora- 
men there, antl runs forward in the groove on the dorsal surface. It gives off 
ascending and descending branches, which ramify in the corium of the wall of the 
hoof, anastomosing above with the circumflex artery of the coronary cushion and 
distally with the circumflex artery of the third phalanx. Before passing through 
the wing it detaches a retrograde branch to the digital cushion, and after emerging, 
one which ramifies on the convex surface of the cartilage of the third phalanx. 

BRANCHES OF THE THORACIC AORTA 
In atldition to the coronary arteries and the common Ijrachiocephalic trunk 
(which have been describetl), the thoracic part of the aorta gives off branches to the 
thoracic walls and viscera and to the spinal cord and its membranes. The visceral 
branches (Rami viscerales) are the broncliial and cesophageal, which arise by a 
broncho-a\sophageal trunk. The parietal branches (Rami parietales) are the 
intercostal and phrenic arteries. 

1. The broncho-cesophageal artery (Truncus broncho-oesophageus) is a short, 
usually bulbous, trunk which arises at the sixth thoracic vertebra from the aorta or in 
common wth the first aortic intercostal arteries. It descends (under cover of the 
vena azygos) over the right face of the aorta toward the bifurcation of the trachea 
and divides into bronchial and cesophageal branches. The bronchial artery (A. 
bronchialis) crosses the left face of the cesophagus to the bifurcation of the trachea, 
where it divides into right and left branches. Each enters the hilus of the cor- 
responding lung above the bronchus, wliich it accompanies in its ramification. It 
supplies the lung tissue antl also dct.;iches twigs to the bronchial lymph glands and 
the mediastinum. The oesophageal artery (A. oesophagea) (Fig. 554) is a small 
vessel which passes backward dorsal to the oesophagus in the posterior mediastinum 
and anastomoses with the oesophageal branch of the gastric artery. It detaches 
twigs to the oesophagus and the mediastinal Ij'mph glands and pleura, and gives off 
two branches which pass between the layers of the ligaments of the lungs and ramify 
in the subpleural tissue. Very commonly there is another artery which runs back- 
ward ventral to the oesophagus.^ 

2. The intercostal arteries (Aa. intercostales) (Figs. 553, 554) number eighteen 
pairs. The first arises from the deep cervical artery, the next three from the 
subcostal Ijranch of the dorsal artery, and the remainder from the aorta. The 
aortic intercostal arteries arise from the dorsal face of the aorta in pairs close to- 
gether; the fifth and sixth usually spring from a common stem. Each passes across 
the body of a vertebra to the corresponding intercostal space, detaches twigs to the 
vertebrae and the pleura, and divides into dorsal and ventral branches. The dorsal 

>■ Also termed the preplantar artery. 

- In some cases there is no broncho-a'sophageal trimk, the bronchial and a'sophagoal arising 
separately. In other cases the second aortic intercostal arises in common with them also. 



BRANCHES OF THE ABDOMINAL AORTA 



661 



branch (Ramus dorsalis) gives off a spinal branch (Ramus spinalis) which passes 
tlu-ough the intervertebral foramen, gives twigs to the membranes of the spinal 
cord, perforates the dura, and reinforces the ventral spinal artery. A muscular 
branch passes to the muscles and skin of the back. The ventral branch (Ramus 
ventralis) is much the larger. It descends, at first almost in the middle of the 
intercostal space between the intercostal muscles, then gains the posterior border 
of the rib, and is subpleural. Each is accompanied by a vein and nerve, the artery 
being in the middle and the vein in front. At the ventral part of the space it unites 
with a ventral intercostal branch of the internal thoracic or the musculo-phrenic 
artery. It supplies the intercostal muscles, the ribs and the pleura, and gives off 
perforating branches which pass out to the serratus ventralis, the abdominal 
muscles, and the skin. 

3. The phrenic arteries (Aa. phrenicse) are two or three small vessels which 
arise at the hiatus aorticus from the ventral aspect of the aorta, often by a common 
trunk. They supply the crura of the diaphragm. In some cases they arise in 
common with an intercostal artery. 



BRANCHES OF THE ABDOMINAL AORTA 

The collateral branches of the abdominal part of the aorta are distributed 
chiefly to the walls and contents of the abdominal cavity, but some branches are 




Fig. 57.3. — Plan of Branches of C(Eliac .\nTERY of Horse. 
1, Coeliac artery; 2, gastric artery; 3, hepatic artery; 4. splenic artery; 5, posterior gastric artery; 6, anterior 
gastric artery; 7, oesophageal branch; S, gastro-duodenal artery; 9, pancreatico-duodenal artery; 10, right gastro- 
epiploic artery; 11, pyloric artery; 12, left gastro-epiploic artery; IS, short gastric branches of splenic. 



supplied to the spinal cord and its membranes, and others extend into the pelvis 
and to the scrotum. The visceral branches are the coeliac, anterior mesenteric, 



662 BLOOD-VASCULAR SYSTEM OF THE HORSE 

renal, posterior mesenteric, and internal spermatic or utero-ovarian. The parietal 
branches are the lumbar arteries. 

I. The coeliac artery (A. coeliaca) is an unpaired vessel, usually half an inch 
or less (ca. 1 cm.) in length, which arises from the ventral aspect of the aorta at its 
emergence from the hiatus aorticus. It divides on the dorsal surface of the pan- 
creas into three branches — the gastric, hepatic, and splenic. 

1. The gastric artery (A. gastrica sinistra) passes downward and forward in 
the gastro-phrenic ligament, gives off oesophageal and pancreatic branches, 
and divides above and behind the cardia into anterior and posterior branches. 
The anterior branch (Ramus cranialis) crosses the lesser curvature just to the right 
of the cardia and ramifies on the parietal surface of the stomach. The branches 
pursue a flexuous course toward the greater curvature and anastomose with the 
short gastric arteries and the gastric branch of the hepatic artery. The pos- 
terior branch (Ramus caudalis) is distributed in a similar fashion on the visceral 
surface. The oesophageal branch (Ramus oesophageus) passes through the hia- 
tus opsophageus into the thoracic cavity above the oesophagus antl anastomoses 
with the (Esophageal branch of the broncho-cesophageal artery. 

The gastric artery often arises by a common trunk with the splenic. The two terminal 
branches may arise separately, or the anterior from the splenic and the posterior from the hepatic. 
The oesophageal branch often arises from the splenic or the posterior gastric. 

2. The hepatic artery (A. hepatica) is larger than the gastric. It passes for- 
ward and to the right and ventrally on the dorsal surface of the pancreas, covered by 
the gastro-pancreatic fold, crosses obliquely under the vena cava, and reaches the 
medial border of the portal vein. It divides into three or four branches which enter 
the portal fissure of the liver and ramify within the gland with the portal vein and 
the hepatic duct. It gives off the following collateral branches: (1) Pancreatic 
branches (Aa. pancreaticse) are given off as the artery crosses the pancreas, in 
which it is partly embedded. (2) The pyloric artery (A. gastrica dextra) arises 
above the first curve of the duodenum. It descends to the pylorus, sending branches 
to the pylorus and the first part of the duodenum, and anastomoses with the gastric 
and right gastro-epiploic arteries. It may arise from the gastro-duodenal. (3) 
The gastro-duodenal artery (A. gastroduodenalis) passes to the second curve of the 
duodenum and divides into the right gastro-epiploic and the pancreatico-duodenal. 
The right gastro-epiploic artery (A. gastroepiploica dextra) crosses over the posterior 
surface of the duodenum and enters the greater omentum, in which it runs to the 
left, parallel with the greater curvature of the stomach. It gives branches to the 
latter and to the omentum and forms an anastomotic arch with the left gastro- 
epiploic artery. The pancreatico-duodenal artery (A. pancreaticoduodenalis) 
divides into pancreatic and tluodenal branches. The former (Ramus pancreaticus) 
supplies the middle part of the jiancreas and is often replaced by a number of 
variable twigs. The duodenal branch (Ramus tluodenalis) passes to the right along 
the lesser curvature of the duodenum and anastomoses with the first branch of the 
anterior mesenteric artery. 

Variations in the branching of the hepatic artery are not uncommon. The pancreatico- 
duodenal may arise directly from the trunk, and there may be a common trunk for the pyloric and 
right gastro-epiploic which runs along the dorsal surface of the first curve of the duodenum to the 
pylorus; here it gives ofJ the small pyloric branch and is continued across the parietal surface 
of the pylorus as the right gastro-epiploic. No gastro-duodenal trunk is present. 

3. The splenic artery (A. lienalis) is the largest branch of the coeliac. It passes 
to the left (with the large satellite vein) on the left extremity of the pancreas and 
across the saccus csecus of the stomach. Entering the suspensory ligament of the 
spleen, it runs in the hilus of the spleen to the apex, beyond which it is continued 
as the left gastro-epiploic. It gives off the following branches: (1) Pancreatic 
branches (Rami pancreatici), which supply the left extremitj^ of the pancreas. 



BRANCHES OF THE ABDOMINAL AORTA 



663 



(2) Splenic branches (Rami lienales), which plunge into the substance of the spleen. 

(3) Short gastric branches (Aa. gastricae breves), which pass in the gastro-splenic 
omentum to the greater curvature of the stomach, where they bifurcate and anas- 
tomose with the branches of the gastric arteries. (4) The left gastro-epiploic 




Fig. 574. — Plan of Chief Branches of Anterior Mesenteric Artery of Hobse. 
/, Stump of anterior mesenteric artery; 2, stumps of arteries of small intestine; 3, lateral cffical artery; 4» 
medial eaecal artery; 5, ileal artery; (?, ventral colic artery; 7, dorsal colic artery; S, middle colic or first artery of 
small colon. By an oversight the left ventral colon is erroneously labeled right dorsal (upper left part of figure). 



artery (A. gastroepiploica sinistra) is the continuation of the splenic artery. It 
passes to the right in the greater omentum, parallel with the greater curvature of the 
stomach, and anastomoses with the right gastro-epiploic. It gives off branches 
to the greater curvature of the stomach and twigs to the omentum. 



BLOOD-VASCULAR SYSTEM OF THE HORSE 




1 J3 " 0. j 



■3 ..-at) 

III s- 
I -s iC -^ ■ 



BRANCHES OF THE ABDOMINAL AORTA 665 

S ej I s II. The anterior or great mesenteric artery 

i S ^. « (A. mescnterica cranialis) arises from the ventral 

^' ^ ^. I face of the aorta at the first lumbar vertebra. It 

i I I -9 is a large unpaired trunk, about an inch (ca. 2-3 

i i S § cm.) in length, which passes ventrally between the 

e" J ■= -S vena cava and the left adrenal into the root of 

the great mesentery, when it divides into three 
branches — left, right, and anterior.^ 

1. The left branch gives off at once about 
fifteen to twenty arteries of the small intestine 
(Aa. intestinales).- These come off close together 
and pass in divergent fashion between the layers 
of the great mesentery, each dividing into two 
branches which anastomose with adj acent branches 
to form a series of arches. In the anterior part of 
the series secondary arches are formed by the union 
of branches given off from the primary set of 
arches. From the convex side of these arches 
terminal branches pass to the wall of the small 
intestine, in which they ramify and form a vascu- 
lar network. They are accompanied by satellite 
veins and by nerves and Ijonph vessels. The first 
artery anastomoses with the pancreatico-duodenal, 
and the last ^vith the ileal branch of the great 
mesenteric artery. Branches are supplied to the 
mesenteric lymph glands. 

2. The right branch (A. ileo-cseco-colica) 
might be regarded as the continuation of the 

^ s I '^- :?" "s f trunk. It runs downward and a little forward 

I -3 I i .2 I I and to the right, and gives off the ileal, the two 

a il S l"^'! cffical, and the ventral colic arteries. (1) The 

I ~. I 5 ° .2 'Z ileal or ileo-csecal artery (A. ilea) passes in retro- 

I ^. i ^ I ■S S. grade fashion along the terminal part of the ileum 

and unites with the last branch of the left division. 
(2) The lateral caecal artery (Ramus ctecalis later- 
alis) passes between the caecum and the origin of 
the colon and runs on the lateral band of the caecum 
I -I '^. ! i I € " I 5 I || I to the apex, where it anastomoses with the medial 

Q &|«| ilfcg". I'Sl'a artery. Besides numerous collaterals to the ccecum, 

I. Si i'l- i -c " 1 '!'. i I g^ it gives off the artery of the arch, which passes 

fe g I & «- I 11 1 1 1 I 'S . along the lesser curvature of the base of the caecum 

-s".li IeIIII"^!" and runs on the lateral face of the origin of the 
^ i '^^ 1 1 1 .2 I o- 1 1 I i 1 1 great colon. (3) The medial caecal artery (Ramus 
•s 'li S i I i ^-s I 1= 1 1 csecaHs medialis) passes along the medial band to 
11-"^ iS°'w"|ls»-^°-a the apex of the caecum, where it anastomoses with 
a I I 5 2 I 71 ^ M !<■ I g ^ the lateral caecal artery. (4) The ventral colic 






S 1 ■§ s fe : 
i > g p. 4 I . 



S-S.S 



: ^ 2 .^- -3 .2 



I '^' ~ "^ 1 In the great majority of subjects this vessel and some 

S .2 ^ -3 of its branches are the seat of more or less extensive vermin- 
i I 2 "* ous aneurysm, produced by the Sclerostomum bidentatum. 
i "S S i In the author's experience an entirely normal specimen is 
I I o I quite unlikely to be encountered except in very young foals. 
". -s ! -fi - The left branch is a descriptive convention rather 

than a realitv, smce the arteries of the small iiitestine spring 
from the me'senteric trunk either directly or by short com- 
mon stems with an adjacent vessel. 



666 BLOOD-VASCULAR SYSTEM OF THE HORSE 

artery (A. colica ventralis)'^ runs along the dorso-medial bands of the opposed 
surfaces of the ventral parts of the great colon to the pelvic flexure, where it unites 
with the dorsal colic artery. It supplies the ventral parts of the great colon and 
sends a branch to the base of the csecum. 

3. The anterior branch divides after a very short course into the dorsal and 
middle colic arteries. (1) The dorsal colic artery (A. cohca dorsalis)- is a large 
vessel which passes along the dorsal parts of the great colon to the pelvic flexure, 
where it joins the ventral colic artery. (2) The middle colic artery or first artery 
of the small colon (A. colica media) is a much smaller vessel which passes to the 
origin of the small colon, enters the colic mesentery, and forms an arch by joining 
the first branch of the posterior mesenteric artery close to the lesser curvature of 
the bowel. It sends an anastomotic branch to the dorsal colic artery. 

III. The renal arteries (Aa. rcnalcs), right and left, are relatively large vessels 
which arise from the aorta near the anterior mesenteric. The right artery is the 
longer of the two. It crosses over the dorsal surface of the vena cava to the right 
and somewhat forward. At the hilus it divides into several (five to eight) branches; 
some of these enter the gland at the hilus, while others pass to the ventral surface 
and enter there. The left artery is short and usually arises a little further back; 
it passes directly outward to the kidney and is then disposed like the right one. 
Small collateral branches are supplied to the ureters, the perirenal fat, the renal 
lymph glands, and the adrenals. The latter also receive small adrenal arteries 
directly from the aorta. The distribution within the kidney has been described. 

Variations in the renal arteries are frequent. Two or more arteries may occur on one side or 
both. Accessory arteries are more common on the left side and usually enter the posterior part 
of the gland. They may arise from the aorta, the external iliac, or the circumflex iliac artery. 

IV. The posterior or small mesenteric artery (A. mesenterica caudalis) is an 
unpaired vessel which arises from the ventral face of the aorta at the fourth lumbar 
vertebra, i. e., about five or six inches (ca. 12-15 cm.) behind the origin of the 
anterior mesenteric artery. It is much smaller than the latter and supplies the 
greater part of the small colon and rectum. It descends in the colic mesentery 
and, after a short course, divides into two branches. The anterior branch (A. colica 
sinistra) gives off three or four arteries which divide and form anastomotic arches 
close to the bowel. The first arch is formed by union with the middle colic branch of 
the anterior mesenteric. The posterior branch or anterior haemorrhoidal artery 
(A. hEemorrhoidalis cranialis) passes backward in the upper part of the mesentery 
and the mesorectum and terminates near the anus by anastomosing with the 
internal pudic artery. Three or four of its anterior collateral branches form 
arches. 

V. The internal spermatic arteries (Aa. spermaticse internee), right and left, 
are long slender arteries which arise from the aorta near the posterior mesenteric 
and supply the testicle and epididymis.^ Each passes backward in a narrow fold 
of peritoneum (Plica vasculosa) to the internal inguinal ring and descends through 
the inguinal canal to the scrotum. In its course in the anterior border of the 
spermatic cord it forms numerous coils, surrounded by the pampiniform plexus 
of veins, and associated closely with the spermatic nerves and lymphatics and 
unstriped muscle-fibers. It passes between the epididymis and testicle, runs in 
flexuous fashion along the attached border of the latter, turns around the posterior 
pole, and runs forward on the free border to the anterior pole. The largest branches 
arise from its ventral part, pass tortuously up either side of the gland, embedded 
in the tunica albuginea, and give off fine branches to the gland substance. Small 

' Also termed the right or direct colic artery. 
- Also termed the left or retrograde colic artery. 

' Variations in the origin of the internal spermatic artery are common. It may arise from 
the posterior mesenteric, or from the renal, or the two may arise by a short common trunk. 



BRANCHES OF THE ABDOMINAL AORTA 



667 



Internal iliac lymph i 

Circumflex iliac vessels 
External iliac lymph gla 

Remnant of inguinal 
ligament 
Posterior branch of circum- 
flex iliac artery 
Lateral cutaneous nerve 
of thigh 
External spermatic nerrc 

Tensor fascia: lata: 

Femoral nerve and ante- 
rior femoral vessels 
Femoral artery 
Prefemoral lymph glands 

Deep inguinal lymph 
glands 

Fascia lata 



Saphenous nerves 
Saphenous vessels 



Medial patellar ligament 
Middle patellar ligament 




Fig. 576. — Dissection of Pelvis, Thigh, .\nd Phoxlm.^l P.\rt of Leg of Horse; Medul View. 
L, Lumbar vessels; V.c, posterior vena cava; A, aorta (termination); C, sympathetic trunk; /, internal iliac 
arterj*: 2, lateral sacral artery; 3, middle coccygeal artery; A, lateral coccygeal artery; -5. umbilical artery (cut off); 
6, internal pudic artery; 6'. vesico-prostatic artery; 7, obturator artery; S, a. profunda penis (from left obturator); 
9, posterior gluteal vessels; iO, external iliac artery; ;i, ii', deep femoral artery; J^, prepubic artery; l,J, branch of 
deep femoral artery; /4, great sciatic nerve; 15, posterior gluteal nerve; 16 (above), pudic nerve; 16 (below, near 
pehdc outlet), suburethral venous plexus; ^7, saero-coccygeus ventralis; JS, coccygeus; 79, recto-coccygeus; «0, re- 
tractor ani; 3/, iJ/', two heads of obturator internus; 22, symphysis pelvis; 23, prepubio tendon; 2.} suspensory liga- 
ment of penis; 2S. retractor penis muscle; 26. bulbo-cavernosus muscle; 27, urethra (cross-section); 28, crus penis 
(cross-section); 29, suspensory ligaments of anus; dO, anal lymph glands; 37, tibial nerve. (After Schmaltz, Atlas d. 
Anat. d. Pferdes.) 



668 



BLOOD-VASCULAB SYSTEM OF THE HOBSE 



collateral branches are detached to the ureter, the epididymis, and the spermatic 
cord. 

V a. The utero-ovarian arteries in the female correspond to the preceding ves- 
sels, but are much larger and shorter. Each is placed in the anterior part of the 
broad ligament of the uterus and divides into ovarian and uterine branches. The 
ovarian artery (A. ovarica) pursues a flexuous course to the ovary, which it supplies. 
The anterior uterine artery (A. uterina cranialis) passes to the concave border of the 
cornu of the uterus, which it supplies, anastomosing with the middle uterine artery. 

VI. The lumbar arteries (Aa. lumbales) are in series with the intercostal 



'^ncro-coccygeus venlralis 
■ Recto-coccygeus 

Sphincter am externus 

Retractor am 




I, Bulbo-urethr.il gland; 



Fig. 577. — Dissectio 
transversus perinei mu 



uscle I?); i 
C.\fter Schn 



^ Horse (MAle). 

i-urethral muscle; 4* retractor penis muscle; 

tias d. Anat. d. Pferdes.) 



arteries and have a similar origin and distribution. There are usually six pairs of 
lumbar arteries, of which five arise from the aorta and the sixth from the internal 
iliac or the lateral sacral at the junction of the last lumbar vertebra and the sacrum. 
Each passes across the body of a lumbar vertebra to the intertransverse space, 
gives branches to the sublumbar muscles, and divides into dorsal and ventral 
branches. The dorsal branch (Ramus dorsalis), the larger of the two, passes 
upward to ramify in the extensor muscles of the spine and the skin of the loins; 
it gives off a spinal branch (Ramus spinalis) which comports itself like the corre- 
sponding brancli of an aortic intercostal artery. The ventral branch (Ramus 
ventralis) runs outward in the intertransverse space, passes between the transversus 



THE INTERNAL ILIAC ARTERY 



669 



and obliquus internus abdominis, gives branches to these muscles, and ends in the 
obliquus externus, the cutaneus, and the skin of the flank. 

THE INTERNAL ILIAC ARTERY 
The internal iliac or hypogastric arteries (Aa. hypogastricse) result from the 
bifurcation of the aorta under the fifth or sixth lumbar vertebra. They diverge 
at an angle of about 60 degrees, and each passes backward under the wing of the 
sacrum, then inclines downward on the pelvic surface of the shaft of the ilium, 
along the ventral border of the iliac head of the obturator internus, and divides a 




Coccygeut muscle 
Anal lymph glands 
Branch of posterior gluteal 
artery 

Po'^terinr hoemorrhoidal 
nene 

\ ulvar branch of 
pudi( nerve 
iilirnal pudic 
<nk>y 

lit a II ch of pu- 
dii iicnr to 
ihtoris 



Oblurntor artery 

. Fig. S78. — Dissection of Perineum op Mahe. 
J. Sacro-coccygeus dorsalis; 2, sacro-coccygeus lateralis; J, intertransversales; 
recto-coccygeus; 6, sphincter ani externus: 6', branch connecting sphincter ani with 
bulb; 5, tuber ischii; 9, 



sacro-coccygeus ventralis; 6 
nstrictor vulvae; 7, vestibula 



i-sciatic ligament. (After Schmaltz, Atlas d. Anat. d. Pferdes.) 



little (ca. 2 cm.) above the psoas tubercle into iliaco-femoral and obturator arteries. 
The chief branches are as follows: 

1. The last pair of lumbar arteries pass up through the foramina at the junc- 
tion of the last lumbar vertebra antl the sacrum and are distributed as already 
described. 

2. The intemalpudic artery (A. pudenda interna) arises near the origin of the 
internal iliac. It passes backward and somewhat downward, at first along the 
ventral border of the iliac head of the obturator internus, then above the superior 
ischiatic spine on the deep surface of the sacro-sciatic ligament, perforates the latter 
and runs for a variable distance in its substance or on its lateral face. It then re- 
enters the pelvic cavity, passes backward on the retractor ani to the ischial arch, 
and divides into the perineal artery and the artery of the bulb in the male, perineal 
and artery of the clitoris in the female. It is accompanied posteriorly by the 
pudic nerve. Its chief branches are as follows: 



670 



BLOOD-VASCULAR SYSTEM OF THE HORSE 



(1) The umbilical artery is given off from tiie internal pudic about an inch 
(ca. 2-3 cm.) from the origin of tliat vessel. It is a very large artery in the 
foetus, in which it curves downward and forward at the side of the bladder in the 
edge of the lateral umbilical fold of peritoneum, passes through the umbilical open- 
ing, becomes a component of the umbilical cord, and ramifies in the fcetal placenta. 
After birth it extends only to the vertex of the bladder and is much reduced. Its 
lumen is almost oljliterated and its wall is very thick, giving the vessel a cord-like 
character, hence it is commonly termed the round ligament of the bladder.' It 
gives off small vesical branches (Aa. vesicales craniales) to the bladder, and twigs 
to the prostate and ductus deferens in the male. In the mare a small branch runs 
forward along the ureter into the broad ligament of the uterus. 

(2) The middle haBmorrhoidal or vesico-prostatic artery (A. hsemorrhoidalis 
media) in the male arises usually near the prostate and runs backward lateral to 
the rectum. It supplies branches to the rectum, bladder, urethra, and accessory 
genital glands. In the female the homologous vessel is much larger and gives off 

the posterior uterine artery (A. 
uterina caudalis). This runs for- 
ward on the side of the vagina, to 
which it gives branches, and rami- 
fies on the body of the uterus, anas- 
tomosing with the anterior and 
middle uterine arteries. (In some 
cases this artery arises from the 
internal iliac or the umbilical.) 

(3) The perineal artery (A. 
perinei) is relatively small in the 
male. It ascends at the side of the 
anus, which it supplies, and gives 
twigs to the bulbocavernosus mus- 
cle and the skin of the perineum. 
In the female it is large and is dis- 
tributed to the anus and vulva, and 
gives a large branch to the vestibu- 
lar bulb. 

(4) The artery of the bulb (A. 
bulbi urethris) may be regarded as 
the direct continuation of the in- 
ternal pudic in the male. It lies 

at the side of the urethra above the ischial arch, dips under the bulbo-cavernosus 
muscle, and ramifies in the corpus cavernosum urethrse. Before doing so it gives 
off a small branch which turns around the ischial arch to reach the dorsum penis, 
and anastomoses wth the deep branch of the obturator. 

(4 a) The artery of the clitoris (A. clitoridis) is the homologue in the female 
of the precetling vessel, but is much smaller. It passes to the ventral surface of 
the vulva with a branch of the putlic nerve, supplies the clitoris, and gives twigs to 
the vulva. 

3. The lateral sacral artery (A. sacralis lateralis) arises at the lumbo-sacral 
articulation (Fig. 576). It passes backward under the wing of the sacrum, then 
along the pelvic surface of the bone below the ventral sacral foramina and the 
nerves emerging from them, and is continued by the lateral coccygeal artery. The 
branches are as follows: 

(1) Spinal branches (Rami spinales) enter the vertebral canal through the 

' The oliliteration in the adult extends a variable distance from the vesical end toward the 
origin, but usually involves completely only a small part. 




Fig. 579. — Cross-section of Tail of Hohse. 
1 , Dorso-lateral coccygeal vessels and nerve; 2, ventro-lateral 
coccygeal artery and nerve; 5, middle coccygeal artery; 4> sacro- 
coccygeus dorsalis; 4'> sacro-coccygeus lateralis; o, d\ intertrana- 
versales; 6, sacro-coccygeus ventralis; 7, recto-coccygeus; 5, 
coccygeal fascia; 9, fibro-cartilage between fourth and fifth 
coccygeal vertebrae. The veins are black. 



THE INTERNAL ILIAC ARTERY 



671 




l)i II) k moral 

tcssels 
PLronenl nerve 

Ti!n;il iicrrc 
l'n\li riiir j'ciiiuriil 

nrU ni 
\ rii/iineus 

I'nplilad lymph 

gin lids 
Castrocnentius 
Recurrent tarsal 



Superficial peroneal nerve ■ 
Deep peroneal nerve ■ 



Tarsal or acces- 
sory Icndoii of 
biceps femoris 

Deep flexor of 
f/ir/d 

(I'lishitnieinius 
li inliin 

Supcijicial flexor 
tendon 

Tuber calcis 



Middle annular ligament ■ 
External lateral ligament ■ 

Distal annular ligament 

Fig. 580. — Dissection of Pelvis, Thigh, and Leg of Horse; Lateral View. 
1, Dorsal branches of last thoracic and first three lumbar nerves; 2, cutaneous branch of fourth lumbar nerve; 5, 
ventral branches of last thoracic nerve; 4, branches of ilio-hypogastric nerve; S, superficial branch of ilio-inguinal ner\'e; 
6, great sciatic nerve; 7, 8, nerves to biceps femoris (from posterior gluteal nerve); 3, nerve to semitendinosus (from 
same); /O, posterior cutaneous nerve of thigh; iJ, pudic nerve; 12, anterior gluteal vessels and nerves; ;d, posterior 
gluteal vessels; 14, branches of obturator vessels; 13, proximal muscular branches of great sciatic nerve to biceps fem- 
oris, semitendinosus, and semimembranosus; 16, nerve to tensor fasciae latK (from anterior gluteal nerve); 17, gluteus 
profundus; 7S, stump, of gluteus medius; iS, gemellus; ;80, stump of quadratus femoris; .2i, stump of biceps femoris; 
BB, saoro-coccygeus dorsahs; «a', sacro-coccygeus lateraUs; 2S, coccygeus; S4, sacro-coccygeus ventralia; So, line of 
fusion of aponeuroses of internal and external obUque muscles of abdomen; 25', aponeurosis of external oblique muscle 
(lamina iliaca); 26, branches of iliaco-femoral vessels; 27, ilio-lumbar vessels; 2S, ilio-lumbar ligament or deep layer 
of lumbo-dorsal fascia; 29, tuber coxae; SO, tuber sacrale; 31, lateral sacro-iliac Ugament; 32, sacro-sciatic ligament. 
The ventral part of a nineteenth rib is shown in front of 3. (.\fter Schmaltz, Atlas d. Anat. d. Pferdes.) 



G72 



BLOOD-VASCULAR SYSTEM OF THE HORSE 



ventral sacral foramina. They give off branches to the spinal cord and its mem- 
branes, which reinforce the ventral spinal artery, and others which emerge through 
the dorsal sacral foramina and supply the muscles and skin of the croup. 

(2) The middle coccygeal artery (A. coccygea) is an unpaired vessel which 
arises from the right or left lateral sacral or from a lateral coccygeal artery. It 
passes backward on the pelvic surface of the sacrum to the median line and con- 
tinues in that position along the tail between the ventral muscles, supplying 
these and the skin. 

(3) The posterior gluteal artery (A. glutea caudalis)^ emerges through the 
upper part of the sacro-sciatic ligament and runs on the latter toward the tuber 
ischii, under cover of the biceps femoris (Fig. 580). It gives branches to that 



Common 
iliac viins 



Internal iliac arhri) 

External iliac aricrii 
Circumflex iliac arte 
Tuber coxae 



Rcmiinnt of 

inguinal hqumtnt 

Sartoiius 

Ftmiiral nerve 



Deep fimoi 

ics\th 
Trnthnnti) tiitiu 




Obturator i 



hiapii femons 
^ — Si mitcndinosus 

Snnimembranoseis 



Fig. 581. — Deep Dissection op Ventral Wall of Pelvis op Horse (Male). 
1, External pudio artery and small satellite vein; S, anastomosis between external pudic and deep femoral veins; 
S, accessory ligament: -J, round ligament; 5, transverse ligament; 5, head of femur; 7, obturator externus (stumps) ; 
S, medial margin of obturator foramen; 9, origin of gracilis; ;0, origin of adductor; j;, bulbocavernosus; /S, retractor 
penis; 13, suspensory ligament of penis. (After Schmaltz, Atlas d. Anat. d. Pferdes.) 



muscle, the semitendinosus, semimembranosus, superficial gluteus, and coccygeus, 
and anastomoses with the ol)turator, deep femoral, and posterior femoral arteries. 
(4) The lateral coccygeal artery (A. caudalis lateralis ventralis) continues the 
direction of the lateral sacral, but is much smaller than the preceding vessel. It 
passes back between the ventral and intertransversales muscles of the tail and 
divides into dorsal and ventral branches which supply twigs to the muscles and 
skin. 

4. The ilio-lumbar artery (A. iliolumbalis) arises at a right angle from the 
internal iliac and runs outward behind the sacro-iliac joint, crossing the ventral 
surface of the ilium under cover of the iliacus muscle. It gives branches to the ilio- 
psoas and longissimus, turns around the lateral border of the ilium a little behind 
the tuber coxae, and ends in the gluteus medius and tensor fascise latse (Fig. 580). 

5. The anterior gluteal artery (A. glutea cranialis) is the largest branch of the 
internal iliac. It arises usually opposite to the preceding vessel, and passes outward 

' Also termed the ischiatic artery. 



ARTERIES OF THE PELVIC LIMB 673 

through the greater sciatic foramen, dividing into several branches as it emerges; 
these enter the gluteal muscles (Fig. 580). 

6. The iliaco-femoral or lateral circumflex artery of the thigh (A. circumflexa 
femoris lateralis) passes vcntro-latcrally across and Ijeneath the shaft of the iliuin, 
under cover of the iliacus muscle, and dips in between the rectus femoris and vastus 
lateralis. It is accompanied by two satellite veins. It gives collateral branches to 
the iliopsoas, the glutei, and the tensor fasciae latse, supplies the nutrient arteiy of 
the ilium, and terminates in the quadriceps femoris (Fig. 580). 

7. The obturator artery (A. obturatoria), the medial terminal branch of the 
internal iliac, passes downward and backward on the pelvic surface of the shaft of 
the ilium, along the ventral border of the iliac head of the obturator internus, ac- 
companied by the satellite vein and nerve, which lie ventral to the artery (Fig. 576). 
On reaching the olDturator foramen it dips under the obturator internus and passes 
obliquely through the lateral part of the foramen. In this part of its course it 
gives ofif a vesical branch and twigs to the obturator internus and the hip-joint. 
It emerges from the obturator foramen behind the obturator externus, passes be- 
tween the quadratus femoris and the adductor, runs backward on the ventral face 
of the ischium, and, in the male, enters the crus penis, forming the arteria profunda 
penis. It anastomoses with the internal pudic, and usually with the external 
pudic by a branch (A. dorsalis penis caudalis) which runs forward on the dorsum 
penis. Collateral branches are detached to the obturator muscles, the adductors 
of the thigh, the semimembranosus, biceps femoris, and semitendinosus, and anas- 
tomoses are formed with the deep femoral and posterior femoral arteries. In the 
female the terminal part is small and enters the root of the clitoris. 



ARTERIES OF THE PELVIC LIMB 
The main arterial trunk of each pelvic limb descends to the proximal part of 
the posterior surface of the tibia, where it divides under cover of the popliteus 
muscle into the anterior and posterior tibial arteries. The different parts of the 
trunk receive names which correspond to the several regions through which it 
passes. In the abdomen it is termed the external iliac artery, in the proximal two- 
thirds of the thigh it is called the femoral artery, antl tlistal to this it is termed the 
popliteal artery. 

The External Iliac Artery (Figs. 575, 576) 
The external iliac artery (A. iliaca externa) arises from the aorta under the 
fifth lumbar vertebra, and usually just in front of the origin of the internal iliac. 
It descends at the side of the pelvic inlet along the tendon of the psoas minor, 
crosses the insertion of that muscle, and reaches the level of the anterior border of 
the pubis, beyond which it is continued by the femoral artery. It is covered by the 
peritoneum and fascia, and is related behind to the corresponding vein. Its chief 
branches are as follows: 

1. The .circumflex iliac artery (A. circumflexa ilium profunda) arises from the 
external iliac at its origin or from the aorta directly. It passes across the iliac 
fascia toward the tuber coxa;, anil divides into two branches at or near the lateral 
border of the psoas minor. The artery lies lietween the fascia and the peritoneum 
and is accompanied by two veins. It fflrnishes small branches to the psoas muscles 
and the external iliac lymph glands. The anterior branch gives twigs to the iliacus 
and psoas muscles, and passes downward and forward in the flank on the trans- 
versus abdominis, along, or under cover of, the ujipcr margin of the obliquus ab- 
dominis internus. It gives branches to these muscles, the obliquus abdominis 
externus, and the skin of the flank. The posterior branch perforates the al^dominal 
wall close to the tuber coxae, and runs downward on the medial face of the tensor 
43 



674 



BLOOD-VASCULAR SYSTEM OF THE HORSE 



fasciffi latse to the fold of the flank, supplying branches to that muscle, the cutaneus, 
the prefemoral lymph glands, and the skin. 

2. The external spermatic or cremasteric artery (A. spermatica externa) is a 
very small vessel which arises in a variable manner. It springs most often from the 
external iliac near the origin of the latter, but may come from the circumflex iliac, 
the aorta between the external and internal iliac, or the latter vessel. It accom- 
panies the cremaster muscle to the inguinal canal, supplies twigs to that muscle, 
the tunica vaginalis, and other constituents of the spermatic cord (Fig. 575). 

2a. The middle uterine artery (A. uterina media) of the female is regarded as 
the homologue of the preceding vessel ; it has a similar origin, but is a much larger 
artery. It enters the broad ligament of the uterus, in which it pursues a flexuous 
course to the posterior part of the horn of the uterus. Its branches are distributed 
to the uterus and anastomose with those of the other uterine arteries. 

The Femoral Artery (Figs. 575, 576) 
The femoral artery is the main arterial trunk of the thigh. It begins at the 
level of the anterior border of the pubis, from which it is separated by the femoral 




Fig. 582. — Dissection of Inguinal Region and Medial Surface of Thigh of Horse. 
1, External pudic artery; S, anterior branches of 1; 3, posterior branches of /; 4, transverse anastomosis between 
external pudic veins; 4'> venous plexus of dorsum penis; 5, femora! artery; 6, saphenous nerve; 7, anterior border of 
external inguinal ring; S, obliquus abdominis internus; 9, posterior border of external inguinal ring; 10, tunica vag- 
inalis; 11. ductus deferens: ./^', cremaster muscle: /3, prepuce; i4. glans penis; 7.5, external ure..hral orifice; 10, pos- 
terior branches of circumflex iliac vessels; 7 7, saphenous vessels; /5, fold of flank; iS, penis (cut) ; A, superficial ingui- 
nal lymph glands; B, prefemoral lymph glands; C, deep inguinal lymph glands. The testicle (on the right side) has 
been rotated somewhat to show the cremaster muscle, (.\fter Schmaltz, Atlas d. Anat. d. Pferdes.) 



vein. It descends almost vertically in the femoral canal behind the sartorius 
muscle, covered at first by the medial femoral fascia and lower down by the gracilis. 
After passing over the insertion of the pectineus, it perforates the adductor muscle, 
crosses in the vascular groove of the posterior surface of the femur, and is continued 



THE FEMORAL ARTERY 675 

between the two heads of the gastrocnemius as the popHtcal artery. It is related 
at its origin to the sartorius in front, the femoral vein behind (which separates it 
from the pcctineus), and the iliacus laterally. Lower dow^i it is related super- 
ficially to the deep inguinal lymph glands, and deeply to the vastus medialis, while 
the saphenous nerve is in front of it, and the vein passes to its lateral face. The 
chief branches are as follows; 

1. The prepubic artery (Truncus pudendo-abdominalis) arises usually by a 
common trunk \vith the deep femoral, a little lielow the level of the pubis. It 
passes forward across the edge of the inguinal ligament, inclining ventro-medially, 
and then runs on the abdominal surface of the ligament to the medial part of the 
internal inguinal ring, where it divides into the posterior abdominal and external 
pudic arteries. (1) The posterior abdominal artery (A. abdominalis caudalis) 
(Fig. 370) passes along the lateral border of the rectus abdominis and anastomoses 
in the umbilical region ■\\ith the anterior abdominal artery. It supplies branches 
chiefly to the rectus and obliquus internus muscles. (2) The external pudic 
artery (A. pudenda externa) descends on the inguinal ligament through the 
medial part of the inguinal canal, and emerges at the mechal angle of the ex- 
ternal ring. In the male it divides into the subcutaneous abdominal artery 
and the anterior dorsal artery of the penis. The former (A. abdominalis sub- 
cutanea) runs forward on the abdominal timic a short distance from the linea alba, 
and gives branches to the superficial inguinal lymph glands, the sheath, and the 
scrotum. The latter (A. dorsalis penis cranialis) passes to the dorsmn penis and 
ends at the glans as the arteria glandis. It gives off collateral branches (Rami 
profundi penis) to the corpus cavernosum, one of which usually passes backward 
and anastomoses ^v^th a branch of the obturator artery. Branches are also supplied 
to the superficial inguinal lymph glands, the prepuce, and the scrotum. In the 
female the manunary artery (A. mammaria) takes the place of the anterior dorsal 
artery of the penis ; it enters the base of the mammary gland, in which it ramifies. 

2. The deep femoral artery (A. profunda femoris) (Fig. 581) arises either by a 
common trunk with the prepubic or a little distal to it. The point of origin is 
usually at the level of the anterior border of the pubis, but may be as much as an 
inch lower. It passes backward and downward across the medial face of the 
femoral vein, then below the pubis in the space between the hip joint and the pec- 
tineus muscle. On reaching the obturator externus it inclines more ventrally and 
laterally, passes out between the posterior surface of the femur and the quadratus 
femoris, and ramifies in the biceps femoris and semitendinosus. It supplies large 
collateral branches to the medial femoral muscles and twigs to the deep inguinal 
lymph glands and the hip joint, and anastomoses with the obturator artery.^ 

3. The anterior femoral artery (A. femoris cranialis) (Fig. 575) arises a little 
distal to the preceding vessel, from the opposite side of the femoral trunk. It 
passes forward, outward, and a little downward across the deep face of the sartorius, 
dips in between the rectus femoris and vastus medialis, and ramifies in these muscles 
and the vastus intermedins. It is related laterally to the ilio-psoas and to the 
femoral nerve. 

In some cases this artery is replaced by a large branch of the iliaco-femoral or external cir- 
cumflex, which passes between the ilio-psoas and rectus femoris and enters the interstice between 
the latter muscle and the vastus mediahs. 

4. Innominate muscular branches (Rami musculares) of variable size and 
arrangement are given off to the muscles of this vicinity. 

5. The saphenous artery (A. saphena) (Figs. 576, 582) is a small vessel which 
arises from the femoral about its middle, or from a muscular branch, and emerges 
between the sartorius and gracilis or through the latter to the medial surface of the 

' In the new nomenclature the term A. circumflexa femoris medialis is applied to the part 
■which turns outward, while the part which rmis backward is regarded as the continumg trunk. 



676 BLOOD-VASCULAR SYSTEM OF THE HORSE 

thigh. In company with the large saphenous vein and the saphenous nerve it 
desceiads superficially on the anterior part of the gracilis, continues on the deep 
fascia of the leg, and divides above the hock into two branches, which accompany 
the radicles of the vein. It gives off cutaneous twigs and anastomoses with the 
recurrent tibial arterj'. 

In some cases this anastomosis does not occur. The artery may be larger and directly con- 
tinuous with the medial tarsal artery. 

6. The articular branch (A. genu suprema) is a slender artery which arises 
from the femoral just before it passes through the adductor. It descends along the 
posterior border of the vastus medialis to the medial surface of the stifle joint, 
where it ramifies. 

7. The nutrient artery of the femtu- (A. nutritia femoris) is given off at the 
middle of the femur and enters the nutrient foramen. 

8. The posterior femoral artery (A. femoris caudalis)' is a large vessel which 
arises from the posterior face of the femoral just before or as the trimk passes be- 
tween the two heads of the gastrocnemius (Fig. 584). It is very short and divides 
into two branches. The ascending branch passes upward and outward between 
the adductor (in front) and the semimembranosus (behind), and ramifies in the 
biceps femoris, vastus lateralis, adductor, and semitendinosus. The descending 
branch passes downward and backward on the lateral head of the gastrocnemius, 
then curves upward between the biceps femoris and semitendinosus (crossed 
laterally by the tibial nerve) and divides into branches to these muscles. A branch 
descends between the heads of the gastrocnemius, gives branches to that muscle 
and the superficial digital flexor, and is continued by a slender artery which ac- 
companies the tibial nerve and unites with the recurrent tibial artery. A small 
branch often ascends alongside of the sciatic nerve, between the biceps and semi- 
tendinosus and anastomoses with a descending branch of the obturator. 

This branch is frequently absent, but the large vein which it accompanies when present, is 
constant and comiects the obturator and posterior femoral veins. 

The Popliteal Artery 
This artery (A. poplitea) is the direct continuation of the femoral. It lies 
between the two heads of the gastrocnemius, at first on the posterior face of the 
femur, then on the femoro-tibial joint capsule. It descends through the popliteal 
notch under cover of the popliteus, inclines outward, and divides near the proximal 
part of the interosseous space into anterior and posterior tibial arteries. The 
satellite vein lies along its medial side at the stifle joint. Collateral branches are 
supplied to the stifle joint and the gastrocnemius and popliteus. 

One of the articular branches (A. genu media) runs directly forward, passes through the 
posterior part of the capsule of the femoro-tibial joint, and supplies the cruciate ligaments, syno- 
vial membrane, etc. Another branch (A. genu lateralis distalis) passes outward under the lateral 
head of the gastrocnemius, and concurs with the articular branch of the femoral artery in forming 
a plexus on the stifle. 

POSTERIOR TIBIAL ARTERY 

The posterior tibial artery (A. tibialis posterior) is much the smaller of the two 
terminals of the popliteal. It lies at first between the tibia and the popliteus, 
then between that muscle and the deep and medial heads of the deep digital flexor. 
Lower down it descends along the tendon of the flexor longus, becomes superficial 
in the distal third of the leg, and divides into lateral and medial tarsal branches. - 
The collateral branches include the nutrient artery of the tibia (A. nutritia tibiae) 
and muscular branches (Rami musculares) to the muscles on the posterior surface 
of the tibia. 

' Also termed the femoro-popliteal artery. 

- Instead of dividing thus, the posterior tibial may be continued by the lateral tarsal. The 
medial tarsal may be a continuation of the saphenous artery. 



POSTERIOR TIBIAL ARTERY 



677 



The lateral tarsal artery (A. tarsea lateralif?) passes outward between the tibia 
and the deep flexor of the digit, and is distributeil to the outer surface of the hock. 



Tibial inseilion < I 
semilendmosii 
Saphenout, vtiii 

Pophtiw, ^ - ' 

Flexor dig lungiii> 



Posterior tibial ussih 
Long I itiitboi 



Medial ligament of hock 
Peroneus tcrtius 



Medial tendon of 

tibialis anterior 

Outline of bursa of above 



Medial or great 
metatarsal vein 



Fig. oS3. — Dissection of Right Leg and Hoi 




Tendon of semitendinosus 

Gastroenemius (medial 
head) 



Tendon of gastrocnemius 

Tendon of supcrjieial 

flexor 
Tor.-<nl ti iiiliin of semi- 

t, inlniusils 
Tibial nerrr 



Recurrent tibied : 
Deep flexor tendon 
Medial tarsal artery 



T( ndon of flexor dig. longus 
Latcial plantar vein 
Medicd plantar artery 

Medial plantar nerve 
Deep flexor tendon 



Medial superficial plantar 
metatarsal vessels 

\ftcr Schmaltz, Atlas d. Auat. d. Pferdes.) 



It gives off the small recurrent tarsal artery (A. tarsea recurrens), which ascends 
along the lateral margin of the gastrocnemius tendon with a satellite vein and nerve 



678 BLOOD-VASCULAR SYSTEM OF THE HORSE 

and anastomoses with a branch of the posterior femoral artery. In some cases an 
arch is formed by junction with the peroneal artery on the lateral surface of the deep 
flexor at the distal fourth of the leg. 

The medial tarsal artery (A. tarsea medialis) usually forms a double curve in 
front of the tuber calcis, then descends on the deep flexor tendon with the plantar 
nerves, and divides into the two plantar arteries. From the second part of the 
curve there arises a small branch, the recurrent tibial artery (A. tibialis recurrens). 
This ascends along the medial border of the superficial digital flexor in company 
with a satellite vein and the tibial nerve, and anastomoses with a descending branch 
of the posterior femoral artery and with the saphenous artery.' 

6. The plantar arteries, medial and lateral (A. plantaris medialis, lateralis), 
are the small terminals of the medial tarsal. They descend along the sides of the 
tarsal sheath of the deep flexor tendon with the plantar nerves to the proximal part 
of the metatarsus, where they unite with the perforating tarsal artery to form the 
proximal plantar arch (Arcus plantaris proximalis). Four plantar metatarsal 
arteries proceed from this arch. The two slender superficial plantar metatarsal 
arteries (A. metatarsea plantaris superficialis medialis, lateralis) may be regarded 
as the continuations of the plantar arteries; they descend on either side of the deep 
flexor tendon with the plantar nerves, and unite with the corresponding digital 
artery. The medial one is the smaller; it may give off or connect with the cor- 
responding dorsal artery. The lateral, larger one usually unites with the lateral 
digital artery. Both may unite at the distal part of the metatarsus to form a short 
trunk which joins one of the digital arteries. They supply twigs to the flexor 
tendons and the skin. The two deep plantar metatarsal arteries (A. metatarsea 
plantaris profundus medialis, lateralis) descend on the plantar surface of the large 
metatarsal bone alongside of the corresponding small metatarsal bone and unite 
near the fetlock with the great metatarsal. The medial artery is the larger of the 
two and usually appears to be the continuation of the perforating tarsal. It 
supplies the nutrient artery of the large metatarsal bone. In other cases it is 
the direct continuation of the medial plantar artery, the lateral artery only uniting 
with the perforating tarsal. The connection of these vessels with the great meta- 
tarsal artery forms the distal plantar arch (Arcus plantaris distalis). 

ANTERIOR TIBIAL ARTERY 

The anterior tibial artery (A. tiljialis anterior) is much the larger of the two 
terminal branches of the popliteal. It passes forward through the proximal part of 
the interosseous space and descends with two satellite veins on the lateral part of 
the front of the tibia, under cover of the tibialis anterior. At the distal part of the 
leg it deviates to the lateral border of the tendon of this muscle, passes on to the 
capsule of the hock joint, gives off the large perforating tarsal artery, and is con- 
tinued as the great metatarsal artery.- It gives off muscular branches to the dorso- 
lateral group of muscles of the leg and articular branches to the hock. The per- 
oneal artery (A. peronea) is a variable vessel which descends along the fibula under 
cover of the lateral extensor; it gives off muscular branches and one which per- 
forates the fascia and divides into ascending and descending cutaneous twigs.' 

The perforating tarsal artery (A. tarsea perforans) arises under cover of the 
lateral tendon of the peroneus tertius. It passes backward through the vascular 
canal of the tarsus with a satellite vein and nerve and unites on the upper part of 

1 The artery may be double in part or throughout. It may join the popliteal artery. The 
S-shaped curve may be absent and the medial tarsal be the direct contmuation of the recurrent 
tibial artery. 

2 The part of the arterial trunk which is on the dorsal surface of tlie tarsus may be distinguished 
by the term A. dorsalis pedis. 

' In some cases the peroneal artery is larger than usual and forms an anastomotic arch with 
the lateral tarsal in the distal part of the leg. 



ANTERIOR TIBIAL ARTERY 



679 



the suspensory ligament with the plantar arteries (or only with the lateral plantai') 
to form the proximal plantar arch (Arcus plantaris proximalis). 



Vastus lateralis 

Biceps femoris 

Gastrocnemius, lateral head 

Superficial digital flexor 

Lateral articular vessels 

Joint capsule 

Lateral condyle of femur 

Popliteus 
Pouch of joint capsule, 

nprni'll 

Lateral ligament of frninrn- 

tiblal joint 

Recurrent tibial vessels 



Soleus 
Tibialis posterior 



Lateral extensor tendon 
Recurrent tarsal vein 
Lateral plantar vein 

Lateral tarsal vein 
Lateral tarsal arteri/ 

Trochlea of tibial tarsal bom 
Lateral ligament of hock join! 

Fibular tarsal ban 




^=^ Femoral vessels 

Posterior femoral artery 
Popliteal artery 
Adductor 
Gastrocnemius, medial head 
Tibial nerve 



Flexor dig. longus 
Flexor hallucis longus 

Posterior tibial artery 



Lateral tarsal artery 
Medial tarsal artery 
Proximal end of tarsal sheath 
Deep flexor tendon 
Long flexor tendon 
Plantar nerves 
Plantar arteries 
Joint capsule 



Fig. 584. — Deep Dissection of Left Stifle, Leg, a.vd Hock of Horse; Posterior View. 
The hock is flexed at a right angle, aod the tuber calcis is sawn off. The tibial nerve' is drawn aside to show its 
muscular branches. The capsules of the stifle and hock joints are partially removed. Branches of tibial nerve. 1, «, 
to gastrocnemius; 3, 4, to superficial flesor; S, to popliteus; 0. to flexor longus; 7, to deep flexor. (After Schmaltz, 
Atlas d. Anat. d. Pferdes.) 



680 



BLOOD-VASCULAR SYSTEM OF THE HORSE 



In well-injected specimens it is seen that there is a fine arterial network (Rete 
tarsi dorsale) on the dorsal surface of the hock, which is formed by twigs from the 



Patella — 9 -°*~ 



Tendon of biceps femoris 

Lateral patellar ligament 
Gastrocnemius, lateral head 

Lateral condyle of tibia 

Lateral ligament of femoro- 
tibial joint 
Common peroneal nerve 



Superficial peroneal nerve 

Lateral extensor 

Long extensor 



Peroneus tertiu. 



Loop of lateral tendon 
of peroneus tertius 

Perforating tarsal artery 

Stump of exteaisor 

dig. brevis 

Great metatarsal artery 

Lateral extensor tendon 

Long extensor tendon 




Vastus medialis 

Accessory cartilage of patella 

Gracilis 

Sartorius 

Trochlea of femur 

{medial ridge) 

Medial patellar ligament 

Middle patellar ligament 

Medial condyle of tibia 
Medial ligament of femoro- 
tibial joint 

Gastrocnemius, medial head 

Crest of tibia 
Tibial tendon of 



Tibialis anterior 
Saphenous vein 
Deep fascia {reflected) 



Anterior tendon of pero- 
neus tertius 

Medial tendon of tibialis 
anterior 



■Distal annular ligament 
.Great metatarsal vein 
■Deep peroneal nerve 



Fig. 585. — Superficial Dissection of Right Stifle, Leg, .\xd Hock of Horse; Front View. (After Schmaltz 
Athis d. Anat. d. Pferdes.) 



anterior tibial and lateral tarsal arteries. From it jDroceed two very slender dorsal 
metatarsal arteries (A. metatarsea dorsalis medialis, lateralis). The medial one 



THE VEINS PULMONARY VEINS — CARDIAC VEINS 681 

descends in the furrow between the medial small and large metatarsal bones, and 
anastomoses usually in the proximal part of the metatarsus with the medial super- 
ficial plantar metatarsal, uniting sometimes with the medial deep plantar meta- 
tarsal. The lateral vessel passes down under the periosteum on the dorsal face of 
the large metatarsal bone and becomes lost or joins the great metatarsal artery. 

In rare cases the anterior tibial artery passes undivided through the tarsus, gives off the 
medial deep plantar metatarsal, and is continued as a very large medial superiicial plantar meta- 
tarsal along the deep flexor tendon, thus resembling the arrangement in the forelimb. 

In a few cases the perforating tarsal is a large vessel, directly continuing the anterior tibial, 
and is continued by a large medial deep plantar metatarsal. The great metatarsal is then small. 
Other variations are common. 

THE GREAT METATARSAL ARTERY 

This arterj' (A. metatarsea dorsalis lateralis) is the direct continuation of the 
anterior tibial. It descends, inclining outward, under cover of the extensor brevis 
and the tendon of the lateral extensor, at first on the joint capsule and then in the 
oblique vascular groove on the proximal part of the large metatarsal bone. It then 
descends superficially in the groove formed by the apposition of the large and lateral 
small metatarsal bones, passes between the two, and divides on the distal part of 
the plantar surface of the large metatarsal bone into the medial and lateral digital 
arteries. It is not usually accompanied by a vein. It is joined near its termination 
by two or more of the plantar arteries, and beyond this the term common digital 
artery (A. digitalis communis) may be applied to it. In the digital region the 
arterial arrangement is the same as in the thoracic limb; it is only necessary in 
reading the description to substitute the word "plantar" for "volar." 



THE VEINS' 
PULMONARY VEINS 
The pulmonary veins (Vv. pulmonales), usually seven or eight in number, 
return the aerated blood from the lungs and open into the left atrium of the heart. 
Thej^ are destitute of valves. Their tributaries arise in the capillary plexuses in 
the lobules of the lungs, and unite to form larger and larger trunks which accompany 
the branches of the bronchi and pulmonary arteries. A very large vein is formed 
by the union at an acute angle of a trunk from each lung, where the latter are ad- 
herent to each other. 

CARDIAC VEINS 
The coronary sinus (Sinus coronarius) is a very short, bulbous trunk which 
receives most of the Ijlood from the wall of the heart. It is situated just below the 
termination of the posterior vena cava, and is covered in part by a thin layer of 
atrial muscle fibers. It opens into the right atrium just below the posterior vena 
cava. It is formed by the union of two tributaries. The great cardiac or left 
coronary vein (V. cordis magna) ascends in the left longitudinal groove and turns 
backward in the coronary groove, in which it winds around the posterior border of 
the heart to the right side and joins the coronary sinus. The middle cardiac or 
right coronary vein (V. cordis media) ascends in the right longitudinal groove and 
joins the coronary sinus, or opens separately into the atrium just in front of the 

1 Most of the veins are depicted in the illustrations of the section on the arteries, to which 
reference is to be made. Many satellite veins which are homonymous with the arteries which 
they accompany, and present no important special features, are not described here. 



682 BLOOD-VASCULAR SYSTEM OF THE HORSE 

orifice of the great cardiac vein, so that a common trunk (coronary sinus) does not 
then exist. 

The small cardiac veins (Vv. cordis minores), three to five in number, are 
small vessels which return some blood from the right ventricle and atrium; they 
open into the latter near the coronary groove in spaces between the musculi pec- 
tinati. 

THE ANTERIOR VENA CAVA (Fig. 554) 

The anterior vena cava (V. eavii cranialis) returns to the heart the blood from 
the head, neck, thoracic limbs, and the greater part of the thoracic wall. It is 
formed at the ventral part of the thoracic inlet by the confluence of the two jugu- 
lar and two brachial veins. It passes backward in the anterior mediastinum, at 
first median and ventral to the common carotid trunk, then deviates to the right 
of the common brachiocephalic trunk, and opens into the right atrium opposite 
to the fourth rib. It is partly enclosed by the pericardium. The demarcation be- 
tween vein and atrium is not very distinct. It contains no valves except at the 
mouths of its radicles. Its length is about five to six inches (ca. 12-15 cm.) and 
its caliber about two inches (ca. 5 cm.) in a subject of medium size. It is related, 
dorsally to the trachea, the right vagus and cardiac nerves, and anterior medias- 
tinal lymph glands. Its right face is crossed by the right phrenic nerve, and on the 
left it is related to the brachiocephalic trunk and artery. The thoracic duct opens 
through the dorsal wall of the origin of the vena cava. It receives, in addition to 
small pericardial and mediastinal veins, the foUowdng tributaries: 

1. The internal thoracic vein (V. thoracica interna) is a satellite of the artery 
of that name. It opens into the anterior vena cava at the first rib. The ventral 
intercostal veins (Vv. intercostales ventrales) open into the internal thoracic and 
musculo-phrenic veins. 

2. The vertebral vein (V. vertebralis) corresponds to the homonymous artery. 
On the right side it terminates either in front of the deep cervical vein or by a short 
common trunk with it. On the left side it usually unites with the deep cervical 
and dorsal veins to form a common trunk. 

3. The deep cervical vein (V. cervicalis profunda) corresponds to the artery. 
On the right side it passes downward and backward across the right face of the 
trachea and opens into the vena cava; it may form a common trunk with the dorsal 
or vertebral. On the left side there is usually a common trunk for all three. It 
receives the first intercostal vein. 

4. The dorsal vein (V. costocervicalis) corresponds to the artery. On the 
right side it leaves the artery on entering the thorax, crosses the right face of the 
trachea, and opens into the vena cava behind the deep cervical or by a common 
trunk with it. On the left sideit usually joins the deep cervical and vertebral to 
form a short common trunk which crosses the left face of the intrathoracic part of 
the brachial artery opposite the second rib and opens into the anterior vena cava. 
It receives the third, fourth, and fifth intercostal veins by means of the subcostal 
vein on the right side. 

The Vena Azygos 

The vena azygos (Fig. 554) is an unpaired vessel which arises at the level of 
the first lumbar vertebra by radicles from the spinal and psoas muscles and the 
crura of the diaphragm. It passes forward along the right side of the bodies of the 
thoracic vei'tebrae, in contact usually with the thoracic duct, which separates the 
vein from the aorta. At the seventh vertebra it leaves the spine, curves downward 
and forward over the right side of the thoracic duct, trachea, and cBsophagus, and 
opens into the right atrium opposite the fourth intercostal space. Its tributaries 
are: 



VEINS OF THE HEAD AND NECK JUGULAR VEINS 683 

1. The last fourteen dorsal intercostal veins {Xv. intercostales dorsales) of the 
right side go directly to the vena azygos; but on the left side a variable number 
(four to seven usually) at the end of the series go to the vena hemiazygos when that 
vessel is present. 

2. The vena hemiazygos arises from a branch of the left first lumbar vein and 
twigs from the crura of the diaphragm. It passes forward through the hiatus 
aorticus and continues along the left dorsal face of the aorta, and about the mid- 
dle of the back joins the vena azygos. It receives the last four to seven dorsal 
intercostal veins of the left side. It is inconstant and variable. In its absence 
its tributaries join the vena azygos. 

3. The oesophageal vein (V. cesophagea), satellite of the oesophageal artery, 
joins the vena azygos as it inclines downward. 

4. The bronchial vein (V. bronchialis) unites with the preceding to form a 
short common trunk, or, according to Chauveau, empties into the great coronary 
vein. The author is unable to find in the horse any distinct bronchial vein 
emerging at the root of the lung.^ 



VEINS OF THE HEAD AND NECK 
Jugular Veins 

The jugular veins (Vv. jugulares), right and left (Fig. 556), arise behind the 
ramus of the mandible, about two and a half inches (ca. 6-7 cm.) below the tem- 
poro-mandibular articulation by the union of the superficial temporal and internal 
maxillary veins. Each passes downward and backward, at first embedded more 
or less in the parotid gland, and continues in the jugular furrow to the thoracic 
inlet, where it unites with its fellow and the two brachial veins to form the anterior 
vena cava. In the neck it is covered by the skin, fascia, and cutaneus muscle, and is 
superficial to the carotid artery, from which it is separated in the anterior half of 
the region by the omo-hyoideus muscle.- It contains valves at the mouths of its 
tributaries, and has several pairs of semilunar valves variably disposed along its 
course. Its tributaries are as follows: 

1. The internal maxillary vein (V. maxillaris interna) is larger than the external 
maxillary. It maj^ be considered to begin as the continuation backward of the 
buccinator vein where that vessel crosses the alveolar border of the mandible, 
about two inches (ca. 5 cm.) behind the last molar tooth. It runs backward on 
the medial surface of the ramus ventral to the lateral pterygoid muscle, and covered 
by the medial pterygoid muscle for a distance of about three inches (ca. 7-8 cm.), 
then inclines a little downward and runs ventral to the arterj^ for about an inch 
(ca. 2-3 cm.). It crosses the lateral face of the artery at the posterior border of 
the jaw, and is joined by the superficial temporal vein to form the jugular. Its 
principal radicles are the following: 

(1) The dorsal lingual vein (V. dorsalis lingua;) is not a satellite on any artery, 

1 In Chauveau- Arloing-Lesbre the statement is made that "the bronchial veins, which ramify 
on the bronchi like the arteries of which they are satelhtes, open into the great coronary vein very 
near its mouth, after having imited to form a single vessel, which sometimes opens directly into 
the atrium. " The arrangement is not illustrated. EUenberger and Baum .state that the bronchial 
and oesophageal veins open into the vena azygos separately or by a common tnmk. Martin de- 
scribes a short broncho-oesophageal trunk, but the vein which he figures as the bronchial does not 
come from the lungs, but is a small mediastinal vessel. The author finds such a vessel usually 
entermg the terminal part of the oesophageal vein, but no distinct bronchial vem m the horse. 
The statement and figure in Bossi's recent work agree substantially with those of the German 
authors. 

- There is usually only one jugular vein on each side in the horse, but in some cases there is an 
internal or deep jugular vein which accompanies the carotid artery and ends at the confluence of 
the external jugulars. M'Fadyean records a case in which the vein lay on the deep face of the 
omo-hyoideus with the carotid artery. This would appear to be an instance of remarkable de- 
velopment of the internal jugular in place of the usual external jugular vein. 



b84 BLOOD-VASCULAB SYSTEM OF THE HORSE 

but is in company with the lingual nerve. It receives tributaries from the tongue 
and soft palate. 

(2) The inferior alveolar or dental vein (V. alveolaris mandibulae) is a satellite 
of the corresponding artery. It often unites with the preceding. 

(3) The middle meningeal vein (V. mcningea media) emerges through the 
foramen laceruni anterius. 

(4) Pterygoid veins (Rami pterygoidei). 

(5) The posterior deep temporal vein (V. temporalis profunda aborahs) is a 




Fig. 586. — Veins op Head of Hokse. 

Parts of the superficial muscles and the ramus of the mandible, and all of the masseter muscle except 
its ventral margin, have been removed. Veins: i, S, Jugular; 2, thyroid; 3, internal maxillary: 4> cranio- 
occipital trunk; 5, ventral cerebral; 6, occipital; 6\ muscular branch of 6; 6", cerebrospinal branch of 6; 6"\ vein 
which emerges through foramen of lateral mass of atlas; 6'"\ vein which emerges through intervertebral foramen of 
axis: 7, great auricular : 7'-7"", radicles of 7; 5, posterior auricular; 5, masseterico-pterygoid; iO, superficial temporal; 
i/, deep auricular; 12, dorsal cerebral; 13, transverse facial and its anastomosis with internal maxillary; 13", pal- 
pebral radicle of 13; 14, pterygoid; 15, mandibular alveolar; 16, dorsal lingual; 17, deep temporal; IS, buccinator; 
19, anastomosis between buccinator and masseteric; 20, anastomosis between buccinator and common labial (21); 22, 
^3. inferior and superior labial ; ^4. angular of mouth; ;g5, 5.5', external maxillary; ;gff, facial; 57. lateral nasal; 5,S, dor- 
sal nasal; 5P, angular of eye; 50, reflexa; 5?, trunk of infraorbital and sphenopalatine. Muscles, etc.; n. Orbicularis oris; 
6, levator nasolabialis; c, dilatator naris lateralis; d, buccalis; e, zygomaticus; /, levator labii superioris proprius; g, 
molaris and depressor Labii inferioris; i, labial glands; k, m. temporalis; I, m, masseter; m, m. pterygoideus medialis; 
n, m. parotido-auriciilaris; o, m. pterygoideus lateralis; p, m. sterno-cephalicus; q, m. rectus capitis ventralis major; 
T, m. omo-hyoideus and sterno-hyoideus; s, parotid gland (dissected away from veins); t, dorsal buccal glands, (.\fter 
Meckel, ) 



large vessel which receives tributaries from the temporalis muscle and emissaries 
from the temporal canal. It is connected with the dorsal cerebral vein antl usually 
with the meningeal veins by its frontal branch. The latter drains chiefly the 
lacrimal gland and passes laehind the supraorbital process. 

2. The superficial temporal vein (V. temporalis superficialis) is the large 
satellite of the corresiioiKhng artery. It is formed by the confluence of the anterior 
auricular and transverse facial veins. The former is much larger than the cor- 



JUGULAR VEINS 685 

responding artery. Its radicles come from ttie posterior part of the temporalis 
muscle and from the external ear. It receives the dorsal cerebral vein (V. cere- 
bralis dorsalis), which is the emissary of the transverse sinus of the dura mater, and 
emerges from the temporal canal behind the postglenoid process. The trans- 
verse facial vein (V. transversa faciei) runs at first above the artery of like name, 
then plunges deeply into the masseter and unites in front with the facial vein. It 
is connected with the vena reflexa and with the posterior deep temporal vein by a 
branch which emerges from the temporal fossa through the mandibular notch. 

3. The masseteric vein (V. masseterica) joins the jugular at the upper border 
of the sterno-cephalicus tendon. It is a short but large trunk which is formed 
bj' the confluence at the posterior border of the jaw of masseteric and pterygoid 
veins. The former is commonl.y connected by an anastomotic branch -(nth the 
buccinator vein. 

4. The great auricular vein (V. auricularis magna) is a satellite of the posterior 
auricular artery above, but joins the jugular a variable distance below and behind 
the point of origin of the artery. 

5. The occipital vein (V. occipitalis) arises in the fossa atlantis by the union of 
two radicles. It passes downward and backward on the rectus capitis ventralis 
major and joins the jugular vein a variable distance in front of the termination of the 
external maxillary vein. The anterior radicle is the ventral cerebral vein (V. 
cerebralis ventralis). This is an emissary of the cavernous sinus of the dura mater; 
it emerges through the foramen lacerum posterius and is connected with a venous 
plexus in the infratemporal fossa. It receives the condyloid vein (V. condyloidea), 
which is an emissary of the basilar plexus and the petrosal sinus, and emerges 
through the hypoglossal foramen.' The posterior radicle is formed by the con- 
fluence of muscular and cerebro-spinal branches. The former (Ramus muscularis) 
comes through the foramen transversarium of the atlas from the muscles of the 
poll; it anastomoses with the vertebral and deep cervical veins. The latter (Ramus 
cerebrospinalis) receives emissary veins from the meningeal plexus in the atlas, 
which emerge through the intervertebral and alar foramina and the foramen of the 
lateral mass of the atlas. 

6. The external maxillary vein (V. maxillaris externa) arises by radicles which 
correspond in general to the branches of the artery of like name. It passes down 
over the cheek along the anterior border of the masseter muscle behind the artery, 
crossing over the parotid duct, which lies behind the vein lower down. Thus on 
the ramus and as they turn around its ventral border the artery is in front, the vein 
in the middle, and the duct posterior. In the mandibular space the vein is ventral 
to the artery for some distance, then parts company with the artery, runs straight 
backward along the ventral border of the parotid gland, and opens into the jugular 
vein at the posterior angle of the gland.- The chief differences in the tributaries 
of the vein as compared with the branches of the corresponding artery are as follows : 

The labial veins (Vv. labiales), superior and inferior, are in the substance of the 
orbicularis oris near the free edges of the lips. The upper one is the larger. They 
anastomose with the opposite veins. They drain into a venous plexus which is 
situated in the submucous tissue of the cheek and the buccinator muscle, and from 
this plexus two veins emerge. The upper one passes back and joins the buccinator 
vein. The lower one, the common labial vein (V. labialis communis), receives a 
submental vein from the chin antl joins the external maxillary vein. 

Three veins connect with the external maxillary at the anterior border of the 
masseter. 

' On account of the existence of this cranial affluent the term cranio-occipital has been pro- 
posed for the venous trunk. 

2 The venous angle formed by this junction indicates the position of the thyroid ghmd. 



686 



BLOOD-VASCULAR SYSTEM OF THE HORSE 



The upper one is the transverse facial vein, which unites close to the end of 
the facial crest. 

A little lower is the large valveless vena refiexa, or alveolar vein. This passes 
back under the upper part of the masseter on the maxilla, turns around the tuber 
maxillare, perforates the periorbita, and joins the ophthalmic vein. It is relatively 
small at each end, but presents one or two large fusiform dilatations. Its posterior 

part is embedded in a mass of fat. It 
receives the following tributaries: (a) 
The great palatine vein (V. palatina 
major), separates from the palatine 
artery at the anterior palatine fora- 
men, and passes in the groove between 
the tuber maxillare and the palate 
bone. The palatine veins form a very 
rich plexus of valveless vessels in the 
submucosa of the hard palate, which 
consists of several layers anteriorly. 
(6) The sphenopalatine vein (V. 
sphenopalatina) is the satellite of the 
artery; it forms a rich plexus of valve- 
less vessels on the turbinate bones 
and the septum nasi. The venous 
plexuses are remarkably developed in 
certain parts of the nasal mucosa. 
On the septum a little below its 
middle and on the turbinates the 
veins are in several layers. The ol- 
factory region does not share in this 
arrangement, and the veins here are 
small and join the ethmoidal vein. 
(c) The infraorbital vein (V. infra- 
orbitalis) is also a satellite of the ar- 
tery ; it usually unites with the s pheno- 
palatine to form a short common 
trunk, (d) The ophthalmic vein (V. 
ophthalmica) is a short trunk, which 
is connected in front with the vena 
refiexa and behind with the cavernous 
sinus through the foramen orbitale. 
It receives veins which correspond to 
the arterial branches. 

The buccinator vein (V. buccin- 
atoria) extends backward from the ex- 
ternal maxillary along the ventral bor- 
der of the depressor labii inferioris and 
buccinator under cover of the mas- 
seter, turns medially over the ramus 
of the mandible about two inches (ca. 
5 cm.) behind the last molar tooth, and is continued as the internal maxillary vein. 
It has a large fusiform dilatation and is valveless. It receives a large vein from 
the buccal plexus, and is usually connected with the masseteric vein. 

The lingual vein (V. lingualis) is formed at the side of the lingual process of the 
hyoid bone by the confluence of several veins which come from the substance of the 
tongue. One or two considerable vessels run partly in the substance of the hyo- 




FiG. 587. — Dissection of Mandibular Space and Ad- 
jacent Part of Neck of Horse. 
a, Ramus of mandible; b, sterno-cephalicus muscle; 
c, c', omo-hyoidei and sterno-hyoidei (portion removed on 
right aide); d, hyoid bone; e, anterior belly of digastricus; 
/, ff, mylo-hyoideus; h, mandibular lymph glands (portion 
removed on right side); t, parotid gland; k, mandibular 
salivary gland; I, chin; m, oceipito-raandibularis; 1, parotid 
duct; 2, facial vein; 3, facial artery; 4> external maxil- 
lary vein; 5, sublingual vein; 6, sublingual artery; 7, ven- 
tral branch of first cervical nerve; S, mylo-hyoid nerve. 
(After Ellenberger, in Leisering's Atlas.) 



THE SINUSES OF THE DURA MATER 687 

glossus, and another in the genio-hyoideus. The vein is at first covered by the 
mylo-hyoideus, perforates that muscle, runs back along the omo-hyoideus in rela- 
tion to the niandibuhir lymph glands, and joins the external maxillary near the 
posterior border of the jaw. 

The sublingual vein (V. sulalingualis) is smaller than the preceding. It re- 
ceives veins from the skin and muscles of the mandibular space, the sublingual 
gland, and the gums. It opens into the external maxillary vein near the lingual or 
joins the latter. 

7. The thyroid vein (V. thyreoidea) is a large vessel which joins the jugular 
near the external maxillary vein. It receives anterior thyroid, laryngeal, and 
pharyngeal radicles, and sometimes a posterior thyroid vein. 

8. Muscular, tracheal, oesophageal, and parotid veins. 

9. The cephalic vein (V. cephalica) enters the jugular near its termination. 
It will be descriljed with the veins of the thoracic limb. 

10. The inferior cervical vein (V. cervicalis ascendens) accompanies the as- 
cending branch of the artery. It may open into the brachial vein. 

The Sinuses of the Dura Mater 
These (Sinus durss matris) are blood-spaces between the meningeal and peri- 
osteal layers of the dura mater and are lined with endothelium. In many places 




Fig. 588. — Median Section of Head of Horse, Upper Part with Septum Nasi Removed. 
o, Lateral mass of ethmoid bone; 6, dorsal turbinate; c, ventral turbinate; d, d', turbinate folds; e, frontal sinus; 
/, falx cerebri; g, tentorium cerebelli; h, medial surface of hemisphere; i, cerebellum; k, occipital bone; k\ occipital 
condyle; fc", paramastoid process; I, external acoustic meatus; ni, temporal condyle; n, temporal canal; I, branches 
of ethmoidal artery; 2, 2' , branches of sphenopalatine artery; 5, 3' , branches of sphenopalatine vein; 4. branches of 
ethmoidal nerve; .5, 6', branches of sphenopalatine nerve; 6, artery of corpus callosum; 7, dorsal longitudinal sinus; 8, 
straight sinus; 0, vena magna cerebri; 10, ventral longitudinal sinus; 11, II', transverse sinuses; /i, dorsal petrosal sinus; 
13, occipital sinus; 14, dorsal cerebral vein; lo, corpus callosum; 16, fornix. (After Ellenberger, in Leisering's .\tlas.) 

the lumen is crossed by fibrous strands. They receive the cerebral veins (Vv. 
cerebri), meningeal veins (Vv. meningese), diploic veins (Vv. diploicse), and com- 
municate with veins outside of the cranium; their connections with the latter 
are by means of emissary veins (Emissaria). They convey the blood directly or 
indirectly to the jugular veins. Some are paired, others unpaired. They maj' be 
divided into dorsal and basilar systems. 

The dorsal system comprises the following: 

The dorsal longitudinal or sagittal sinus (S. sagittalis dorsalis) is situated in 
the convex border of tlie falx cereljri along the internal parietal crest. It begins 
at the crista galli and ends near the tentorium osseum at the confluence of the 
sinuses (Confluens sinuum) formed by the junction with the straight sinus. It 
receives most of the ascending cerebral veins. Along each side are small pouches 
(Lacunae laterales) into which the veins open. The lumen of the sinus is very 
irregular; it is traversed by fibrous bands and is partially divided by a longitu- 
dinal septum. 



688 BLOOD-VASCULAR SYSTEM OF THE HORSE 

The ventral longitudinal or sagittal sinus (S. sagittalis ventralis) is much 
smaller than the dorsal sinus.' It runs l^ackward on the corpus callosum in the 
concave edge of the falx cerebri, and joins the great cerebral vein to form the straight 
sinus. It receives veins from the medial surface of the cerebral hemispheres and 
from the corpus callosum. 

The straight sinus (S. rectus) proceeds from the junction of the ventral longi- 
tudinal sinus with the great cerebral vein behind the corpus callosum. It ascends 
in the falx cerebri, inclining backward, and joins the dorsal longitudinal sinus at 
the conflucns sinuum. 

The transverse sinuses (Ss. transversi), right and left, proceed laterally from 
the confluens sinuum; they pass outward in the transverse grooves of the parietal 
bones, enter the temporal canals, and are continued by the dorsal cerebral veins 
to the superficial temporal veins. They receive the dorsal petrosal sinuses, veins 
from the posterior part of the cerebrum and from the corpora quadrigemina, and 
the posterior meningeal vein. The two sinuses are connected by the sinus com- 
municans, which extends across the cranial vault in a channel in the l^ase of the 
internal occipital protuberance. 

The dorsal petrosal sinuses (Ss. petrosi dorsales) ascend in the tentorium 
cerebelli and join the transverse sinuses near the internal opening of the temporal 
canal. Each is the direct continuation of the vena rhinalis posterior and receives 
the vena basilaris cerebri. There is sometimes an accessory petrosal sinus along- 
side of the chief sinus, which is formed by the confluence of veins from the pons 
and medulla oblongata. 

The occipital sinuses (Ss. occipitales) are situated in the dura mater on each 
side of the vermis cerebelli. They communicate in front with the sinus communi- 
cans, and one of them is continued posteriorly by the dorsal spinal vein. Each 
sinus is connected by a communicating branch with the transverse sinus and with 
the ventral petrosal sinus. The right and left sinuses are connected by anasto- 
motic branches, so that the arrangement is more or less plexiform. Thej^ re- 
ceive veins from the cerebellum, medulla oblongata, and diploe. 

The basilar system consists of the following: 

Tlie cavernous sinuses (Ss. cavernosi) lie in the medial grooves of the root of the 
temporal wings of the splienoid bone at either side of the jjituitary fossa. The two 
are connected by a wide transverse branch, the intercavernous sinus (Sinus inter- 
cavernosus), behind and below the posterior part of the pituitary body.- Each is 
continuous in front with the ophthalmic vein and below with the ventral petrosal 
sinuses; it communicates also by small anastomotic veins with the basilar plexus. 
The third, sixth, and the ophthalmic and maxillary divisions of the fifth nerve lie 
along the lateral wall of the sinus. The internal carotid artery traverses the sinus 
and is connected with its fellow by a transverse branch which lies in the inter- 
cavernous sinus. An oval opening in the floor communicates with the ventral 
petrosal sinus and transmits the internal carotid artery. 

The sinus is not subdivided by strands of fibrous tissue as in man, but a few delicate bands 
attach the artery to its wall. 

The ventral petrosal sinuses (Ss. petrosi ventrales)' lie along the borders of 
the basilar part of the occipital bone, enclosed in the thick dura which closes the 
foramen lacerum. The anterior part extends about half an inch (ca. 12 mm.) 
under the temporal wing of the sphenoid. Here communications exist with veins 
in the pterygopalatine fossa. The posterior end is bulbous and lies in the condy- 

' It is also termed the vena corporis callosi major. 

- A small anterior intercavernous sinus may connect the two cavernous sinuses in front of the 
pituitary gland. Mobilio states that he has seen the cavernous sinus having a blind anterior end, 
the ophthalmic vein passing laterally to the ventral petrosal sinus. 

' These are termed the subsphenoidal confluents by Chauveau and M'Fadyean. 



THE VEINS OF THE CRANIUM — VERTEBRAL AND SPINAL VEINS 689 

loid fossa; it communicates with the condyloid vein issuing from the hypoglossal 
foramen and is drained by the ventral cerebral vein; it also receives an emissary 
vein from the temporal canal. The sinus communicates with the cavernous sinus 
by an oval opening at the carotid notch which transmits the internal carotid artery; 
the latter forms the first bend of its S-shaped curve in the petrosal and the second 
in the cavernous sinus. 

The basilar plexus (Plexus basilaris) is situated on the cerebral surface of the 
basilar part of the occipital bone, and is directly continuous behind with the venous 
plexus in the atlas. Its chief emissary is the condjdoid vein, which brings it into 
communication with the ventral petrosal sinus. It is cormected with the cav- 
ernous and intercavernous sinuses by small veins. 

The Veins of the Cranium 

The cerebral veins (Vena? ceret^ri) tlo not in general accompany the cerebral 
arteries. They have very thin walls, no muscular coat, and no valves. They are 
arranged in two sets, superficial or cortical and deep or central. The superficial 
veins are more numerous and larger than the arteries. They lie on the surface of 
the brain in the pia mater and the subarachnoid space. 

The ascending cerebral veins drain most of the convex surface and the medial 
surface of the cerel^ral hemispheres. Most of them open into the dorsal longitudi- 
nal sinus, but some enter the confluens sinuum or the transverse sinuses. Near the 
termination they become IduIIdous, ami ojdcu into the sinus obliquely and in such a 
manner as to tend to prevent reflux of blood into them.^ The descending cerebral 
veins which come chiefly from the ventral part of the convex surface of the cere- 
brum open into the vena rhinalis posterior. 

The basal cerebral veins converge to a large common trunk, the vena rhinalis 
posterior ; this Ijegins at the anterior end of the piriform lobe, runs backward in a 
groove on the latter, enters the tentorium cerebelli, and opens into the dorsal 
petrosal sinus. 

The deep cerebral veins issue from the central or ganglionic parts of the brain 
at the transverse fissure. The principal ones come from the chorioid plexuses, the 
corpus striatum, and the septum pellucidum. These unite to form the internal 
cerebral veins (Vv. cerebri internse), which run backward in the roof of the third 
ventricle and unite to form the great cerebral vein (V. magna cerebri). This 
passes upward and backward behind the splenium of the corpus callosum and is 
continued as the straight sinus to join the longitudinal sinus. 

The dorsal cerebellar veins ramify on the upper surface of the cerebellum. 
They go chiefly to the occipital and tlorsal petrosal sinuses. The ventral cerebellar 
veins are larger and go chiefly to the basilar plexus. The veins of the medulla and 
pons end chiefly in the basilar plexus and the occipital and dorsal (and accessory) 
petrosal sinuses. 

The meningeal veins (X'enje meningcifi) arise in capillar j' plexuses in the su- 
perficial and deep faces of the dura mater. Some end in the sinuses of the dura, 
others accompany the meningeal arteries. 

The diploic veins (Venie iliploicse) are anastomosing channels in the spongy 
substance of the cranial bones. Their walls are thin, consisting in many places 
only of the endothelium, and the}' have no valves. Some open inward into venous 
sinuses, others into extracranial veins. 

Vertebral and Spinal Veins 
Two venous trunks, the longitudinal vertebral sinuses (Sinus vertebrales 
longitudinales), e.xtend along the floor of the vertebral canal, one on either side of 

' Most of these veins open into the sinus in the direction of the blood-stream in the sinus, but 
some of the posterior ones open about at a right angle, or even contrary' to the direction of the cur- 
rent. 

44 



690 



BLOOD-VASCULAR SYSTEM OF THE HORSE 




the dorsal longitudinal ligament. They are continuous in front with the basilar 
plexus. They lie in the grooves on the bodies of the vertebrae and are connected 
lay a series of transverse anastomoses which pass between the central part of the 
bodies of the vertebrae and the dorsal longitudinal ligament or in channels in the 
bone. They receive veins from the spinal cord, the meninges, and the bodies of the 
vertebrae (Vense basis vertebrae). Through the intervertebral foramina efferent 
vessels connect with the occipital, vertebral, intercostal, lumbar, and lateral sacral 
veins. The veins of the spinal cord are drained by dorsal and ventral longitudinal 

trunks. The ventral vein, which is the smaller, 
j^V:^' accompanies the ventral spinal artery. 



VEINS OF THE THORACIC LIMB 
The brachial vein (V. brachialis) (Fig. 566) 
is the satellite of the extrathoracic part of the 
brachial artery. It arises at the medial side of 
the distal end of the shaft of the humerus and 
ascends in the arm behind the artery under cover 
of a layer of fascia and the posterior superficial 
pectoral muscle. At the shoulder it is ventral to 
the artery, crosses the anterior border of the first 
rib, and concurs with its fellow and the two jugu- 
lars in the formation of the anterior vena cava. 
The roots of the vein are somewhat variable, but 
most often four veins in addition to a large ob- 
lique branch from the cephalic unite in its format 
tion; two or three of these radicles are satellites of 
the median artery. Its tributaries correspond in 
general to the branches of the artery, but a few 
differences are worthy of notice. The thoraco- 
dorsal vein (V. thoracodorsalis) often joins the 
external thoracic or the deep brachial vein. The 
external thoracic vein (V. thoracica externa)' is a 
large vessel which arises in the ventral wall of the 
abdomen, passes forward (embedded partly in the cutaneus muscle) along the lateral 
border of the posterior deep pectoral muscle, and joins the brachial vein close to 
the subscapular or in common with it. It may receive a vein which is the satellite 
of the external thoracic artery. 

The cephalic vein (V. cephalica) arises at the medial side of the carpus as the 
continuation of the medial metacarpal vein. It ascends on the deep fascia 
of the forearm at first in the furrow between the flexor carpi radialis and the 
radius. Toward the middle of the forearm it inclines gradually forward on the 
medial surface of the radius, accompanied liy a branch of the musculo-cutaneous 
nerve, and arrives at the insertion of the biceps. Here it detaches a large com- 
mimicating branch (Ramus communicans), which passes upward and backward over 
the medial insertion of the biceps and the median artery and median nerve, 
and joins the brachial vein. The vein to this point is often termed the internal sub- 
cutaneous vein of the forearm (V. cephalica antebrachii). It is continued (as the 
V. cephalica humeri) in the furrow between the brachiocephalicus and the anterior 
superficial pectoral muscle with a branch of the inferior cervical artery, crosses the 
deep face of the cervical cutaneus, and opens into the terminal part of the jugular 
or the brachial vein. It receives the accessory cephalic vein (V. cephalica accessoria) , 
which arises from the carpal network, rims upward on the deep fascia along the 
' Often termed the spur vein. 



Fig. 589. — Vehtebhal Sinuses of Horse. 
The vertebral canal has been opened 
by sawing off the arches. The nerve-roots 
are cut on one side and the spinal cord 
turned over to right. 1, Ventral spinal 
artery; £, reinforcing branches from verte- 
bral, intercostal, or lumbar arteries (ac- 
cording to region) ; 3, longitudinal verte- 
bral sinuses; a, ventral surface of spinal 
cord; 6, dura mater (cut) : c, nerve-roots; 
d, dorsal longitudinal ligament. (After 
Ellenberger, in Leisering's Atlas.) 



VEINS OF THE THORACIC LIMB 



691 



medial border of the extensor carpi, and joins the cephaHc vein at the proximal 
end of the forearm. 

The deep veins of the forearm are variable. Commonly two median veins 




Fig. .500. — Dissection of Pectohal Region and Anterior Part of Abdominal Wall of Horse. 
/, Jugular vein; 2, loose connective tissue of axillary space; 3, ascending branch of inferior cervical artery; 4. de- 
scending branch of same; 5, cephalic vein; f>, median nerve; 7, ulnar nerve; S, brachial artery; 9, brachial vein; 10, 
external thoracic vein; 11, anterior abdominal artery and vein; 12, branches of sixth cervical nerve; 13, cutaneous 
branch of axillary nerve; 1^, cutaneous branch of musculo-cutaneous nerve; 15, cervical cutaneus; 16, sterno-cephalicus ; 
17, scalenus; IS, brachiocephalicus; 19, anterior superficial pectoral; 20, posterior superficial pectoral; 21, anterior 
deep pectoral; 22, posterior deep pectoral; 23, abdominal cutaneus; 24, obliquus abdominis externus; 25, rectus 
abdominis; 26, coraco-brachialis; 27, tensor fascige antibrachii; a, prescapular lymph glands; h, prepectoral lymph 
glands; c, axillary lymph glands; d, cubital lymph glands; c. x., xiphoid cartilage. (After Schmaltz, Atlas d. Anat. 
d. Pferdes.) 



(Ven^e medians) accompany the artery of like name, one in front and one behind. 
A third vein arises by radicles emerging from the proximal part of the deep flexor; 



692 BLOOD-VASCULAR SYSTEM OF THE HORSE 

it joins the posterior satellite of the median artery or forms one of the roots of the 
brachial vein. The conunon interosseous vein joins the posterior satellite. The 
anterior radial vein (V. collateralis raclialis) is a satellite of the artery. The ulnar 
vein is usually double at its proximal part, and communicates with the deep brachial 
vein. 

There are three chief metacarpal veins. The medial metacarpal or common 
digital vein (V. metacarpea volaris superficialis medialis) arises from the volar 
venous arch above the fetlock. It is the largest vein of the region and lies in 
front of the common digital artery. It separates from the artery at the proximal 
end of the metacarpus, passes upward on the medio-volar surface of the carpus, 
under cover of the superficial layer of the volar annular ligament, and is con- 
tinued as the cephalic vein. It communicates at its proximal part with the origin 
of the median veins by a short but relatively large branch. The lateral metacaipal 
vein (V. metacarpea volaris superficialis lateralis) arises from the venous arch above 
the fetlock and passes upward behind the lateral border of the suspensory ligament 
in front of the lateral volar nerve and accompanied by a small artery. At the 
proximal end of the metacarpus it is connected with the deep metacarpal vein by 
two transverse anastomoses which pass across the suspensory ligament. It then 
ascends as a satellite of the lateral volar metacarpal artery and concurs in the 
origin of the ulnar and median veins. The deep metacarpal vein (V. metacarpea 
volaris profunda medialis) arises from the venous arch, passes forward between 
the two branches of the suspensory ligament, and ascends on the posterior surface 
of the large metacarpal bone. At the proximal end of the latter it communicates 
with the other metacarpal veins, ascends with the medial volar metacarpal artery, 
and concurs in forming tlie median veins. 

The venous arch (Arcus venosus volaris), from which the metacarpal veins 
arise, is situated above the sesamoids of the fetlock, between the suspensory liga- 
ment and the deep flexor tendon. It is formed by the junction of the two digital 
veins. 

The digital veins, medial and lateral (V. digitalis medialis, lateralis), drain the 
venous plexuses of the foot. They arise at the proximal edge of the cartilages of 
the third phalanx and ascend in front of the corresponding arteries. 

It is convenient to recognize the following venous plexuses of the foot, which, 
however, communicate very freely: 

1. The coronary plexus encircles the upper part of the foot. It covers the 
terminal part of the extensor tendon, the cartilages of the third phalanx, and the 
bulbs of the digital cushion. 

2. The dorsal (or laminal) plexus covers the dorsal surface of the third phalanx 
in the deep layer of the corium of the wall of the hoof. It forms the circumflex 
vein of the third phalanx, or vein of the distal border of the third phalanx, which 
corresponds to the artery of like name. 

3. The volar plexus is in the deep layer of the corium of the sole of the hoof 
and on the deep surface of the cartilages of the third phalanx. It communicates 
around the distal border of the third phalanx with the dorsal plexus and through the 
cartilages with the coronary plexus. 

The deep vein of the third phalanx accompanies the terminal part of the 
digital artery. It drains the intraosseous plexus contained in the third phalanx. 

THE POSTERIOR VENA CAVA (Figs. 554, 575) 
The posterior vena cava (V. cava caudalis) returns almost all of the blood from 
the abilomen, pelvis, and pelvic limits. It is formed by the confluence of the right 
and left common iliac veins at the fifth lumbar vertebra, above the terminal part 
of the aorta, and chiefly to the right of the median plane. 



THE PORTAL VEIN 693 

The mode of origin is variable. In some cases there is a common trunk formed by the 
union of the two internal iliac veins so that the arrangement resembles the termination of the 
aorta. In other cases the internal iliac vein does not exist. Exceptionally there is a small middle 
sacral vein on the middle of the pelvic surface of the saci-um. It opens at the angle of divergence 
of the common iliac veins. 

It passes forward on the ventral face of the psoas minor to the right of the 
abdominal aorta. At the last thoracic vertebra it separates from the aorta and 
runs forward between the right crus of the diaphragm and the pancreas till it 
reaches the liver. Here it inclines ventrally along the medial border of the right 
lobe and on the parietal surface of the liver, largely embedded in the gland sub- 
stance, and passes through the foramen vena cavse of the diaphragm. It then runs 
forward and somewhat ventrally between the intermediate lobe and the main mass 
of the right lung at the upper margin of a special fold of the right pleura, accom- 
panied by the right phrenic nerve, and opens into the posterior part of the right 
atriiun opposite the fifth intercostal space. It receives the following tributaries: 

1. The phrenic veins (Vv. phrenicse), two or three in number, return the blood 
from the diaphragm. They are very large in comparison with the arteries, and 
join the vena cava at the foramen venae cavse. 

2. The lumbar veins (Vv. lumbales) correspond to the arteries. Five pairs 
usually empty into the posterior vena cava. Sometimes the corresponding veins 
of opposite sides unite to form a common trunk. The first communicate with the 
vena azygos or hemiazygos, and the last usually enters the common iliac vein. 

3. The internal spermatic veins (Vv. spermaticie internee) (Fig. 575) accompany 
the arteries of like name. In the spermatic cord they form a very rich network, the 
pampiniform plexus (Plexus pampiniformis) about the artery and nerves. Their 
termination is variable. The right one commonly joins the vena cava near the 
renal vein, often by a common trunk with the left one. Frequently the left vein 
joins the left renal, and sometimes the right one ends similarly. 

3 a. The utero-ovarian veins are much larger than the preceding and are 
satellites of the arteries in the broad ligaments. The ovarian branch is plexiform 
near the ovary. The uterine branches form a rich plexus in the wall of the uterus. 
The trunk is very short and terminates like the corresponding vein of the male. 

4. The renal veins (Vv. renales), satellites of the arteries, are of large caliber 
and thin walled. The right vein passes medially and backward on the ventral face 
of the kidney, between the artery in front and the ureter behind. It joins the vena 
cava above the right adrenal. The left vein is somewhat longer. It passes medially 
at first like the right one, then bends around the posterior end of the adrenal, crosses 
the origin of the renal artery, and opens into the vena cava a little further back than 
the right one. They receive veins from the adrenals, but some adrenal veins (Vv. 
adrenales) open directly into the vena cava. 

5. The hepatic veins (Vv. hepaticse) return the blood from the liver, and open 
into the vena cava as it lies in the groove in the liver. Three or four large veins 
open into the vena cava just before it leaves the liver, and numerous small ones 
discharge into its embedded part. 

Of the foregoing, the phrenic and lumbar veins are termed parietal radicles 
(Radices parietales), and the remainder are visceral radicles (Radices viscerales). 

THE PORTAL VEIN 

The portal vein (V. portse) is a large trunk which returns the blood carried to 
the viscera by the gastric, splenic, and mesenteric arteries; its average diameter is 
a little more than an inch (ca. 3 cm.). Its peripheral tributaries correspond closely 
with the branches of the arteries, but the trunks do so in part only. The vein is 
formed behind the pancreas and below the posterior vena cava by the confluence 
of the anterior and posterior mesenteric ami splenic veins. It passes forward, 



694 



BLOOD-VASCULAR SYSTEM OF THE HORSE 



traverses the posterior part of the pancreas very obliquely, inclines ventrally and 
a little to the right, and reaches the portal fissure of the liver. Here it divides into 
three branches which enter the liver and ramify in the substance of the gland like 
an artery, terminating in the lobular capillaries. From the lobules the blood passes 
into the hepatic veins and through these to the posterior vena cava. Thus the 
blood which is distributed to the stomach, nearly the entire intestinal tract, the 
pancreas, and the spleen, passes through two sets of capillaries prior to its return 
to the heart, viz., the capillaries of these viscera and of the liver. 

1. The anterior mesenteric vein (V. mesenterica cranialis) is the largest of 
the portal radicles. It is situated to the right of the artery of like name, and its 
tributaries correspond in general to the branches of the artery. The dorsal colic 
vein usually unites with the ventral one at the pelvic flexure, thus forming a single 
trunk (V. colica dextra) which runs between the right parts of the colon. There is, 




Fia. 591.— Portal Vein < 

o, Intrahepatic part, b, extrahepatic part, of portal vein; c, anterior gastric vein; d, right gastro-epiploic vein; 
e, pancreatico-duodenal vein; /, splenic vein; /', left gastro-epiploic vein; g, posterior gastric vein; h, posterior mesen- 
teric vein; i, middle colic vein; k, left colic vein; h', anterior hffimorrhoidal vein; m, jejunal trunk; m', jejunal veins; 
o, right colic vein; o\ ventral colic vein; o", dorsal colic vein; o'", small collateral vein connecting dorsal colic and 
posterior mesenteric veins; p, ileal vein; g, caecal veins; /.liver; 7J, spleen; 777, stomach; 7T', duodenum; 1', jejunum; 
VI, caecum; r77, ventral parts of great colon; T777, pehdc flexure; 7.Y, dorsal parts of great colon; X, small colon; 
XI. rectum. (After Schmitz.) 



however, a small vein on the right dorsal colon which is connected by numerous 
branches with the right colic vein; it joins the posterior mesenteric vein or its 
middle colic radicle. The veins of the small intestine (Vv. intestinales) unite to 
form a short trunk. 

2. The posterior mesenteric vein (V. mesenterica caudalis) is the smallest of 
the radicles of the portal vein. It accompanies the artery in the colic mesentery, 
and its rectal branches (Vv. haemorrhoidales craniales) anastomose with those of 
the internal pudic vein. It receives the middle colic vein from the initial part of 
the small colon and also the small vein of the right dorsal colon, as mentioned above. 

3. ' The splenic vein (V. lienalis) is the very large satellite of the splenic artery. 
It is formed by the union of two radicles at the base of the spleen. On leaving the 
hilus of the spleen it passes medially between the anterior pole of the left kidney and 
the saccus cacus of the stomach and above the left end of the pancreas, receives 



THE COMMON ILIAC VEINS THE VEINS OF THE PELVIC LIMB 695 

commonly the posterior gastric vein (V. gastrica caudalis), and unites with the 
anterior mesenteric at the posterior l^order of the pancreas. Not uncommonly the 
splenic and posterior mesenteric veins form a short common trunk. 
The collateral tributaries of the portal vein are as follows: 

(1) Pancreatic veins (Kami pancreatici). 

(2) The gastro-duodenal vein (V. gastroduodenalis), when present, corresponds 
mainly to the extrahepatic liranches of the hepatic artery; but in most cases it does 
not exist, and the right gastro-epiploic vein (V. gastroepiploica dextra) and pan- 
creatico-duodenal vein (V. pancreaticoduodenalis) open directly into the portal 
vein. 

(3) The anterior gastric vein (V. gastrica cranialis) joins the portal vein at the 
portal fissure. 

THE COMMON ILIAC VEINS (Fig. 581) 
These (V. iliacte communes) ar(^ two very large but short trunks, which residt 
from the union of the internal and external iliac veins of each side at the sacro-iliac 
articulation. The left one is the longer, and crosses obliquely over the terminal 
part of the aorta. The chief tributaries of each are as follows: 

1. The last lumbar vein. 

2. The circumflex iliac veins (Vv. circumflexse ilium profundse) are the two 
satellites of the corresponding artery, on either side of which they are placed. 
They may open directly into the posterior vena cava or into the external iliac vein. 

3. The ilio-lumbar vein (V. iliolumbalis) may open into the common iliac, 
the external iliac, or the internal iliac vein. 

THE INTERNAL ILIAC VEINS 
The internal iliac or hypogastric veins (Vv. iliacte internte s. hypogastriciE), 
right and left, are usually formed by the confluence of lateral sacral, gluteal, and 
internal pudic veins. The obturator vein maj^ open into them also. They are 
short trunks, and are smaller than the external iliac veins. The tributaries corre- 
spond in general to the branches of the three arteries of like names. The internal 
pudic veins receive affluents from the anus and posterior part of the rectum ; from 
the venous plexuses of the prepuce and penis in the male ; and from those of the 
mammary gland, vulva, vagina, and vestibular bulb in the female. A large anas- 
tomotic branch connects the internal pudic and obturator veins at the lesser sciatic 
notch. 

THE VEINS OF THE PELVIC LIMB , 

The external iliac vein (V. iliaca externa) (Figs. 576, 581) lies behind the cor- 
responding artery at the lirim of the pelvis. It is the upward continuation of the 
femoral vein, and unites at the sacro-iliac joint with the internal iliac to form the 
common iliac vein. Its tributaries are as follows : 

1. The obturator vein (V. obturatoria) is a satellite of the artery, except in its 
terminal part; it usually opens into the external iliac at the insertion of the psoas 
minor. Its radicles anastomose with those of the internal and external pudic veins 
(Figs. 576, 658). 

2. The iliaco-femoral or lateral circumflex veins (Vv. circumflexiE femoris 
laterales) are the two satellites of the homonymous artery. They open a little 
higher than the obturator. 

The femoral vein (V. femoralis) (Figs. 575, 582) lies behind the artery in the 
proximal part of the thigh, lateral to it lower down. Its chief tributaries are: 

1. A large but short trunk is formed by the union of the deep femoral and 
the external pudic vein. The deep femoral vein (V. profunda femoris) corresponds 



696 BLOOD-VASCULAR SYSTEM OF THE HORSE 

otherwise to the artery. The external pudic vein (V. pudenda externa) arises 
chiefly from a rich plexus of large veins situated above and along the sides of the 
penis and prepuce in the male, the mammary glands in the female. It passes 
through a foramen in the anterior part of the tendon of origin of the gracilis and 
runs outward behind the pectineus to unite with the deep femoral vein. The right 
and left veins are connected by a large transverse anastomotic branch which lies 
in the subpubic groove, and each has a large connection with the obturator vein. 
Each receives the posterior abdominal vein (V. abdominalis caudalis), which ac- 
companies the artery of like name. The subcutaneous abdominal vein (V. ab- 
dominalis subcutanea) arises in the skin and cutaneous muscle of the ventral 
abdominal wall, anastomoses with the internal and external thoracic and deep 
abdominal veins, and joins the external pudic or the posterior abdominal vein. 
A small vein accompanies the external pudic artery in the inguinal canal. 

2. The anterior femoral vein (V. femoris cranialis) accompanies the artery. 

3. The saphenous vein (V. saphena) (Figs. 575, 576, 583) arises on the dorso- 
medial surface of the tarsus as the upward continuation of the medial metatarsal 
vein. Its course is distinctly visible. It ascends on the subcutaneous surface of 
the tibia and the popliteus muscle, enclosed between layers of the deep fascia, in- 
clines a little backward to the proximal part of the leg, then deviates slightly for- 
ward, runs upward on the gracilis, passes between that muscle and the sartorius, 
and joins the femoral or the external pudic vein.^ On the upper part of the capsule 
of the hock joint it forms an arch with the anterior tibial vein. The vein has 
numerous valves. The satellite artery is relatively small, and lies in front of the 
vein as far as the junction with the recurrent tibial vein, which it accompanies on 
the leg. It receives the recurrent tibial vein (V. recurrens tibialis) at the proximal 
fourth of the leg. This vessel arises at the distal third of the leg, where it forms an 
arch with the posterior tibial vein; here it is a satellite of the artery of like name. 
It ascends in the furrow in front of the gastrocnemius tendon, inclines forward at 
the proximal third of the leg, and joins the saphenous vein at an acute angle. It 
gives off a branch which ascends with the artery and joins the posterior femoral or 
the popliteal vein.= A smaller vein from the anterior face of the metatarsus joins 
the saphenous at the hock. 

4. Muscular branches which correspond to the arteries. 

5. The posterior femoral vein (V. femoris caudalis) is a satellite of the artery. 
It receives the recurrent tarsal vein (V. tarsea recurrens), which arises at the lateral 
side of the hock, ascends on the deep fascia of the lateral surface of the leg in front 
of the tendo Achillis, passes between the biceps femoris and semitendinosus, and 
joins the posterior femoral vein. It is connected with the recurrent tibial vein by 
a large anastomotic branch which crosses in front of the tuber calcis. Usually a 
branch from it ascends along the great sciatic nerve and anastomoses with the ob- 
turator vein. 

The popliteal vein (V. poplitea) lies along the medial side of the artery (Fig. 
584). It is formed by the confluence of anterior and posterior tibial veins. 

Two anterior tibial veins (Vv. tibiales anteriores) usually accompany the artery 
of like name; the lateral vein is much the larger.^ In other cases there is a single 

1 The place and mode of termination are quite variable. It may disappear from the surface 
of the thigh at any point above the distal third. In some cases it passes through the anterior 
part of the graciUs instead of dipping in between that muscle and the sartorius, and more rarely 
it joins the external pudic vem at the origin of the gracUis. 

2 The arrangement here is subject to variation. Some authors regard the ascending branch 
of this description as the trunk, and the connection with the saphenous as an anastomotic branch. 
The latter is u.sually, so far as size is concerned, the trunk. 

' The large size of this vein, the thinness of its wall, and the fact that it is separated only by a 
thin layer of muscle (lateral part of tibialis anterior) from the deep peroneal nerve should be noted 
with reference to section of that nerve. The vein is sometimes markedly varicose in the proximal 
part of the leg. 



LYMPHATIC SYSTEM OF THE HORSE THE THORACIC DUCT 697 

large vein in the proximal part, of the leg, two lower down. They arise from a 
number of anastomosing radicles on the front of the capsule of the hock joint, 
chiefly as the continuation of the perforating tarsal vein. A large branch from the 
saphenous vein concurs in the formation of the somewhat plexiform arrangement 
on the flexion surface of the hock. 

The posterior tibial vein (V. tibialis posterior) is commonly double (Fig. 583). 
It arises at the level of the tuber calcis, where it has a communication with the 
recurrent tibial vein. It is a satellite of the artery. 

The medial or great metatarsal vein (V. metatarsea dorsalis medialis (Figs. 
583, 585) arises from the venous arch above the sesamoids at the fetlock, but is 
practically the upward continuation of the medial digital vein. It ascends along 
the medial border of the suspensory ligament, then in the groove on the proximal 
part of the large metatarsal bone to the capsule of the hock joint, and is continued 
by the saphenous vein. The small middle dorsal metatarsal vein (V. met. dorsalis 
media) joins this vein or the saphenous at the hock. 

The lateral metatarsal vein (V. metatarsea dorsalis lateralis) is the very small 
satellite of the great metatarsal artery. It is inconstant, but may be double in the 
proximal part of the metatarsus. 

The medial plantar vein (V. melatarsea plantaris superficialis medialis) is very 
small, and is not always present. It ascends along the medial border of the deep 
flexor tendon in front of the correspontling nerve. It is connected below with the 
medial digital vein, and above with the deep metatarsal or the lateral plantar vein. 

The lateral plemtar vein (V. metatarsea plantaris superficialis lateralis) arises 
from the venous arch above the fetlock, but appears to be the upward continuation 
of the lateral digital vein. It ascends along the lateral border of the deep flexor 
tendon in front of the plantar nerve, and is connected with the deep metatarsal 
vein at the proximal part of the metatarsus by a transverse branch. It then passes 
upward along the deep flexor tendon in relation to the plantar nerves and the 
medial tarsal artery, and is continued by the recurrent tibial vein. 

The deep metatarsal vein (V. metatarsea plantaris profunda medialis) arises 
from the plantar venous arch, alaove the fetlock, passes forward between the branches 
of the suspensory ligament, and ascends on the posterior face of the large meta- 
tarsal bone. At the proximal end of the metatarsus it is connected w\ih the lateral 
plantar vein by a transverse branch, thus forming the deep plantar arch (Arcus 
plantaris profundus). It then passes, as the perforating tarsal vein (V. tarsea 
perforans), through the vascular canal of the tarsus and forms the chief radicle of 
the anterior tibial vein. 

The distal plantar venous arch (Arcus venosus plantaris distalis) and the digital 
veins are arranged like those of the thoracic limb. 



Lymphatic System of the Horse 

THE THORACIC DUCT (Figs. 553, 554) 
The thoracic duct (Ductus thoracicus) is the chief collecting trunk of the Ijnn- 
phatic system. It begins as an elongated irregular dilatation, the cistema chyli, 
which is situated between the right side of the aorta and the right crus of the 
diaphragm at the first and second lumbar vertebrae. The duct enters the 
thorax through the hiatus aorticus and runs forward on the right of the median 
plane, between the vena azygos and the aorta, covered by the pleura. At the sixth 
or seventh thoracic vertebra it inclines somewhat ventrally, crosses obliquely over 
the left face of the oesophagus, and passes forward on the left side of the trachea 
to the inlet of the thorax. The extrathoracic terminal part passes downward and 



698 BLOOD-VASCULAR SYSTEM OF THE HORSE 

forward a variable distance (3-4 cm.) on the deep face of the left scalenus muscle, 
bends inward and backward under the bicarotid trunk, and opens into the dorsal 
part of the origin of the anterior vena cava just behind the angle of junction of the 
jugular veins. The terminal bend is ampullate, and sometimes divides into two 
very short branches which open close together. 

Since the duct develops from a plexus of ducts in the embryo, considerable variation from 
the more usual course occurs. There is often a left duct which arises at the cisterna or at a var- 
iable point from the right duct, runs across the left intercostal arteries parallel to the latter, and 
unites with it over the base of the heart or further forward. The two are connected by cross- 
branches. In some cases the left duct is the larger, and there may indeed be none on the right 
side. Other variations are common. 

The chief tributaries of the thoracic duct are as follows: 

1. The two lumbar trunks (Trunci lumbales) are formed by the confluence 
of the efferent ducts of the lumbar glands, and commonly unite "udth each other 
and with the posterior intestinal trunk before opening into the cistern. 

2. The intestinal trunks (Trunci intestinal es), two or three in number, receive 
the efferents of the lymph glands of the intestine, stomach, liver, and spleen.' 

In its course through the thorax the thoracic duct receives efferents from the 
intercostal, mediastinal, and bronchial glands. At the thoracic inlet it is joined by 
ducts from the prepectoral and right axillary glands, and by the left tracheal duct. 
The duct is provided with several pairs of valves; the best developed are at its 
termination. 

THE RIGHT LYMPHATIC DUCT 
This vessel (Ductus lymphaticus dexter) — when present — collects the lymph 
from the right side of the head, neck, and thorax, and from the right thoracic limb. 
It is commonly absent, being represented by a number of short ducts which termin- 
ate in the thoracic duct, the right jugulo-brachial junction, or the origin of the 
anterior vena cava. When present in its typical form, it results from the con- 
fluence of efferent ducts from the right axillary and posterior cervical lymph glands 
with the right tracheal duct. It lies on the deep face of the scalenus muscle, above 
the terminal part of the right jugular vein. It is more or less ampullate and usually 
opens into the anterior vena cava to the right of the thoracic duct. It may be 
comiected with the latter by anastomoses or may join it. 

The duct is very variable in form and in regard to its afferents. Often it is a very short, 
irregular, and bulbous trunk; in some cases it is about an inch and a half (ca. 3-4 cm.) in length 
and receives the tracheal duct at its terminal bend. The lymphatico-venous connections here 
have not yet been satisfactorily worked out by modern methods. 



THE LYMPH GLANDS AND VESSELS OF THE HEAD AND NECK 
1. The mandibular or submaxillary lymph glands (Lgg. mandilnilares s. sub- 
maxillares) (Figs. 265, 587) are arrangeil in two elongated groups in the mandibular 
space along each side of the omo-hyoid muscles. The two groups are in apposition 
in front of the insertion of these muscles, and diverge posteriorly in the form of a V, 
extending backward about four or five inches (ca. 10-12 cm.). They are covered 
by the skin and a thin layer of fascia and cutaneus muscle, and are therefore pal- 
pable. Anteriorly they are firmly attached to the mylo-hyoidei, but otherwise they 
are freely movable in the normal state. Each group is related laterally to the 
external maxillary artery and the anterior belly of the digastricus, ventrally to the 
external maxillary vein, and dorsally to the lingual and sublingual veins. 

They receive afferent vessels from the lips, nostrils, nasal region, cheeks, the 

1 The lymph vessels of these organs appear to vary considerably in their mode of termina- 
tion, and the arrangement needs further study. Some lymph vessels from the stomach, liver, and 
spleen open directly into the cistern.. 



THK LYMPH GLANDS AND VESSELS OF THE HEAD AND NECK 699 

anterior part of the tongue, the jaws, the floor of the mouth, and the greater part 
of the hard palate and nasal cavity. The efferent vessels pass to the anterior 
cervical and pharyngeal glands. 

Most of the superficial lymph vessels of the face converge to twelve to fifteen trunks wliich 
turn around the lower border of the jaw with and m front of the facial vessels. Those of the lips 
form plexuses at the commissures. The nasal mucous membrane is richly supplied with lymph 
vessels which accompany the veins; posteriorly they communicate with the subdural and sub- 
araclmoid spaces and send efferents to the pharyngeal and anterior cerA'ical glands. 

2. The pharyngeal l5rmph glands (Figs. 562, 706) usually comprise two 
groups. One lies on the upper part of the lateral surface of the phar^^^x, along the 
course of the external carotid artery. These glands are related laterally to the 
occipito-mandibularis and digastricus, and often to the mandibular gland also, 
above to the guttural pouch; they maj" properly be termed the parapharyngeal 
lymph glands (Lgg. parapharjTigealcs) . Other small glands are commonly found 
on the guttural pouch along the course of the internal carotid artery; they are best 
designated as the suprapharyngeal lymph glands (Lgg. suprapharyngeales).^ They 
lie below the artery and arc covered by the aponeurosis of the brachiocephalicus 
and the cervical end of the manilibular glantl. In some cases a number of glands 
occur in the angle of divergence of the external and internal carotid arteries. 

They receive afferent vessels from the cranium, the posterior part of the tongue, 
the soft palate, pharynx, guttural pouch, larynx, posterior part of the nasal cavity, 
and efferents from the mandibular glands. 

3. The anterior cervical lymph glands (Lgg. cervicales craniales) (Fig. 646) are 
situated along the course of the common carotid artery, in the vicinity of the thyroid 

, gland, under cover of the cervical angle of the parotid gland. Some occur between 
the thyroid and the mandibular salivary gland, others above and partly upon the 
thyroid. They are related deeph' to the posterior part of the larynx, the trachea, 
the thyroid gland, and the cesophagus; below to the external maxillary vein and 
the lateral border of the omo-hyoideus.- 

These glands are variable. Often there are none in front of the thyroid and the group may 
extend back a considerable distance along the course of the carotid artery. 

Their afferents are deep lymph vessels from the head, the pharynx, lar\Tix, 
guttural pouch, and thyroid gland, and efferents from the mandibular and pharyn- 
geal glands. Their efferent vessels go to the middle and posterior cervical glands. 

4. The middle cervical lymph glands (Lgg. cervicales mediae) form an incon- 
stant group situated a little in front of the middle of the neck on the trachea below 
the carotid artery. The group is usually small, and in some cases is replaced by a 
number of glands occurring at intervals along the course of the carotid artery. In 
other subjects the group consists of several glands of considerable size. They are 
intercalated in the course of the tracheal lymph ducts. 

5. The posterior cervical or prepectoral lymph glands (Lgg. cervicales caudales) 
form a large group below the trachea at the entrance to the thorax (Fig. 590). 
They occupy the interstices between the vessels and muscles and extend forward a 
variable distance on the ventral aspect of the trachea. Posteriorly they are con- 
tinuous with the anterior mediastinal glands. They are covered by the cutaneus 
and sterno-cephalicus. Their afferent vessels come from the head, neck, thorax, 
and thoracic limb. They receive efferent ducts of the anterior and middle cervical, 
prescapular, and axillary glands. Their efferents go to the thoracic duct on the 
left, to the right lymphatic duct on the right, or open directly into the vena cava. 

6. The prescapular or superficial cervical lymph glands (Lgg. cervicales 

' Much confusion exists in the terminology used in regard to these glands and the next group. 
The terms here recommended appear to the author to be the best, all things considered. The 
pharyngeal and anterior cervical glands are all subparotid in the horse. 

^ Abscess here can be reached readily by an incision between the vein and the omo-hyoideus. 



700 BLOOD-VASCULAR SYSTEM OF THE HORSE 

superficiales) lie on the anterior border of the anterior deep pectoral muscle, in 
relation to the orao-hyoideus medially and the brachiocephalicus laterally (Figs. 
556, 566, 590). They are on the course of the ascending branch of the inferior 
cervical artery, and may form an elongated series which is continuous ventrally 
with the posterior cervical group. They receive afferents from the neck, breast, 
shoulder, and arm. Their efferents pass to the posterior cervical glands. 

The tracheal ducts, right and left (Ductus trachealis dexter, sinister), are col- 
lecting trunks for the lymph of the head and neck. They lie on the trachea in 
relation to the carotid arteries. The right one goes to the posterior cervical glands 
or to the right lymphatic duct, the left one to the terminal part of the thoracic duct. 



THE LYMPH GLANDS AND VESSELS OF THE THORAX 
The thoracic lymph glands (Lgg. thoracales) are in general of small size, but 
are numerous. They comprise the following : 

1. The intercostal lymph glands (Lg. intercostales) are small and are situated 
at the sides of the bodies of the thoracic vertebrse, in series corresponding to the 
intercostal spaces; others are between the aorta and the vertebrse. They receive 
afferents from the vertebral canal, the spinal muscles, the diaphragm, intercostal 
muscles, and pleura. The efferent vessels go to the thoracic duct.^ 

2. The anterior mediastinal lymph glands (Lgg. mediastinales craniales) 
are numerous. Some are situated on the course of the brachial arteries and 
their branches; on the right side they are related deeply to the trachea, on the left 
to the oesophagus also. They are variable in size and disposition and are continuous 
in front with the posterior cervical glands. Other glands lie along the ventral face of 
the trachea on the anterior vena cava and the right atrium of the heart; these are 
continuous Ijehind with the bronchial glands. A few glands usually occur along the 
dorsal surface of the trachea, and there is often one at the angle of divergence of 
the brachiocephalic trunk. The afferent vessels come chiefly from the pleura, 
the pericardium, the heart, the thymus or its remains, the trachea, the oesophagus, 
and the bronchial lymph glands. Their efferent vessels pass to the posterior 
cervical glands and the thoracic duct. 

The glands along the ventral face of the trachea are frequently enlarged and commonly pig- 
mented in dissecting-room subjects. The left recurrent nerve lies above them on the ventral 
face of the trachea. 

3. The bronchial lymph glands (Lgg. bronchiales) are grouped around the 
terminal part of the trachea and the bronchi. One group lies on the dorsal surface 
of the bifurcation of the trachea, and is continued a short distance backward under 
the oesophagus. Others lie below the trachea and bronchi and also occupy 
the angle between the aortic arch and the pulmonary artery, concealing the 
left recurrent nerve and often covering the vagus in this part of its course. 
Small glands occur along the chief bronchi in the substance of the lungs (Lg. pul- 
monales). They receive the deep and most of the superficial Ij'mph vessels of the 
lungs, and the efferents from the posterior mediastinal glands. Their efferent 
vessels go to the thoracic duct and the anterior mediastinal glands. The deep 
lymph vessels of the lung arise in plexuses which surround the terminal bronchi 
and accompany the bronchi to the root of the lung. The superficial vessels form 
a rich network under the pleura; most of them pass to the bronchial glands, but 
some go to the posterior mediastinal glands. 

The bronchial glands are commonly pifrmontod (except in young subjects) and are often 
enlarged and indurated. 

4. The posterior mediastinal lymph glands (Lgg. mediastinales caudales) are 
' These glands appear to be more numerous in the young subject than they are later in life. 



THE LYMPH GLANDS AND VESSELS OF THE ABDOMEN AND PELVIS 701 

usually small and are scattered along the posterior mediastinum chiefly above the 
oesophagus. They receive afferent vessels from the oesophagus, mediastinum, 
diaphragm, pleura, and liver. The efferents go to the bronchial and anterior medi- 
astinal lymph glands, partly to the thoracic duct directly. 

Sometimes one or two small glands are situated in the acute angle between the 
posterior vena cava and the diaphragm ; and the occurrence is recorded of a gland 
between the apex of the pericardium and the sternal insertion of the diaphragm. 



THE LYMPH GLANDS AND VESSELS OF THE ABDOMEN AND PELVIS 
The abdominal and pelvic lymph glands (Lgg. abdominales et pclvin£e) consist 
of two main groups, parietal and visceral. The parietal glands lie in the subserous 
or subcutaneous tissue; they receive the lymph vessels from the abdominal and 
pelvic walls, from parts of the viscera, and from the proximal lymph glands of the 
pelvic limbs. The visceral glands lie on the walls of the viscera or in the peritoneal 
folds which connect the organs with the wall or with adjacent viscera. They receive 
all or most of the lymph vessels from the organs with which they are connected. 
The parietal glands comprise the following: 

1. The lumbar lymph glands (Lgg. lumbales) lie along the course of the abdom- 
inal aorta and posterior vena cava (Fig. 575). Some are placed along the ventral 
surface and sides of the vessels, others above. A few small glands may be found 
above the sublumbar muscles. The small nodes which are situated at the hilus 
of the kidneys are often termed the renal lymph glands (Lgg. renales). They re- 
ceive afferent vessels from the lumbar wall of the abdomen and the paired viscera 
(kidneys, adrenals, genital organs), also the inguinal vessels and the efferents of the 
iliac glands. Their efferents go to the thoracic duct, constituting the lumbar trunks 
of origin of that vessel. 

2. The internal iliac lymph glands (Lgg. iliacse internse) are grouped about the 
terminal part of the aorta and the origins of the iliac arteries (Fig. 575). Their 
afferent vessels come chiefly from the pelvis, pelvic viscera, and tail, and they re- 
ceive efferent vessels of the external iliac and deep inguinal glands. 

3. The external iliac lymph glands (Lgg. iliaca externee) form a group on either 
side on the iliac fascia, at the bifurcation of the circumflex iliac artery (Fig. 575). 
Their afferent vessels come from the flank and abdominal floor, the lateral surface 
of the thigh, and the prefemoral glantls. The efferent vessels go to the lumbar and 
internal iliac glands. 

4. The sacral lymph glands (Lgg. sacrales) are small nodes situated along the 
borders of the sacrum and on its pelvic surface. They receive afi'erents from the 
roof of the pelvis and from the tail, and their efferent vessels pass to the internal 
iliac glands. 

5. The superficial inguinal lymph glands (Lgg. inguinales superficiales) lie on 
the abdominal tunic in front of the external inguinal ring (Fig. 582). ^ They form 
an elongated group along the course of the subcutaneous abdominal artery, on 
either side of the penis in the male, above the mammary glands in the female; 
in the latter they are often termed mammary. Their afferents come from the 
medial surface of the thigh, the abdominal floor, the sheath, penis, and scrotum in 
the male, and the mammary glands in the female. The efferent vessels ascend 
through the inguinal canal and go to the deep inguinal, internal iliac, and Imnbar 
glands. 

6. The ischiatic lymph glands (Lgg. ischiadicae) are small nodes on the upper 
part of the sacro-sciatic ligament along the course of the posterior gluteal artery. 
They receive lymph from the adjacent parts and from the popliteal glands, and send 
efferents to the sacral and internal iliac glands. 

1 In rare cases two or three of these glands are found behind the ring. 



702 BLOOD-VASCULAR SYSTEM OF THE HORSE 

The visceral glands include the following : 

1. The gastric lymph glands (Lgg. gastricre) are situated along the course of 
the gastric arteries. Several occur on the saccus csecus ventral to the left part of 
the pancreas, and along the attachment of the gastro-phrenic ligament. A group 
lies at the lesser curvature a short distance below the cardia. There is another 
small group on the visceral surface where the posterior gastric artery divides into 
its primary branches. There are usually two or three small nodes on the ventral 
aspect of the pylorus. Other small glands are scattered along the course of the 
gastro-epiploic and short gastric arteries, in the great and gastro-splenic omenta. 
The efferent vessels pass largelj^ to the coeliac radicle of the cisterna chyli, Ijut along 
the left part of the great curvature they go to the splenic glands. 

2. The hepatic lymph glands (Lgg. hepaticse) lie along the portal vein and 
hepatic arterj- ami in the lesser omentum. Their efferent vessels go to the 
ccEliac radicle of the cisterna chyli. 

Many of the lymph vessels from the parietal surface of the liver pass in the falciform and 
lateral ligaments to the diaphragm and join the lymphatics of the latter. Some pass through the 
diaphragm with the vena cava and go to the mediastinal glands. 

The pancreatic l3rmph vessels follow the course of the blood-vessels which 
supply the glanil ; most of t hem go to the splenic and hepatic glands. 

3. The splenic lymph glands (Lgg. lienales) lie along the course of the splenic 
blood-vessels in the hilus of the spleen and the gastro-splenic omentum. Their 
afferent vessels come from the subcapsular network of the spleen, from the greater 
curvature of the stomach, and from the left part of the pancreas. The efferents 
pass to the glands of the saccus csecus of the stomach and to the coeliac radicle of the 
cisterna chyli. 

4. The mesenteric lymph glands (Lgg. mesentericse) are situated in the great 
mesentery near its root. They are numerous and hence lie close together. They 
receive a very large number of afferent vessels (400 to 500) from the small intestine. 
They have several considerable efferents, which concur in the formation of the in- 
testinal radicles of the cisterna chyli. 

The lymph vessels of the intestine form three sets of capillary plexuses, viz., in the subserosa, 
submucosa, and mucosa. The lymph follicles, solitary and aggregate, lie in the zone of the plexus 
of the mucosa. The collecting vessels arise from the subserous plexus. 

5. The caecal lymph glands (Lgg. ctecales) are numerous and are distributed 
along \he course of the cajcal lilood-vessels. Their efferents enter into the formation 
of an intestinal radicle of the cisterna chyli. 

6. The colic lymph glands (Lgg. colicBe) comprise those of the great colon and 
those of the small colon. The glands of the great colon are extremely numerous 
and are placed close together along the colic blood-vessels. . Their efferent vessels 
are large and numerous. They converge to two large trunks which concur with 
those of the caecum and small intestine to form an intestinal radicle of the cisterna 
chyli. The glands of the small colon are situated in part on the wall of the bowel 
along the attachment of the mesentery, in part between the laj-ers of the latter 
along the course of the blood-ves.sels. The efferent vessels go to the lumbar glands 
and to the posterior intestinal radicle of the thoracic duct. 

' The intestinal radicles of the cisterna chyli are formed by the confluence of efferents from 
the intrstiiiiil lymph glands. The anterior trunk lies on the left side of the anterior mesenteric 
artery, i);is,^cs lirtween that vessel and the ca-liac artery, turns sharply backward across the right 
renal vessels, and opens into the cisterna. It is formed by the imion of the coeliac trunk with 
efferents from the glands of the small intestme, caecum, and colon. It is about four inches (ca. 
10 cm.) in length and is ampullate. The posterior tnmk receives vessels from the small intestine 
and small colon. It usually opens into a trunk formed by the imion of the right and left lumbar 
ducts. It is usually ampullate at its termination (Franck). The arrangement of these collecting 
trunks is, however, very variable. 

The rectal lymph glands (Lgg. rectales) form a chain along the dorsal surface 



THE LIIIPH GLANDS AND VESSELS OF THE PELVIC LIMB 703 

of the bowel. They receive afferent vessels from the rectum and anus, and their 
efferent vessels pass chiefly to the internal iliac glands. 

7. The anal lymph glands (Lg. anales) form a small group of three or four on 
either side of the sphincter ani externus (Figs. 578). They receive afferents from the 
anus, perineum, and tail. Their efferents go to the internal iliac glands. 



THE LYMPH GLANDS AND VESSELS OF THE THORACIC LIMB 

1. The axillary lymph glands (Lgg. axillarcs) (Fig. 590), some ten to twelve in 
number, are grouped on the medial face of the distal part of the teres major and the 
tendon of the latissimus dorsi at the angle of junction of the external thoracic and 
subscapular veins with the brachial (Fig. 566). Their efferents include most of the 
lymph vessels of the limb, which come directly or as efferents from the cubital glands. 
They receive also lymph vessels from the thoracic wall. The efferents accompany 
the brachial blood-vessels and end in the posterior cervical glands and the thoracic 
and right lymphatic ducts. 

2. The cubital lymph glands (Lg. cubitales), usually eight to ten in number, 
form a discoid oval group at the medial side of the distal part of the shaft of the 
humerus (Figs. 566, 590). They lie behind the biceps muscle on the brachial 
vessels and median nerve, and are covered by the deep fascia and the posterior 
superficial pectoral muscle. They receive as afferents most of the vessels from the 
limb below this point. Their efferents pass chiefly to the axillary glands, but in 
part to the prescapular glands also. 

In quite exceptional cases a IjTnph gland may be found on the brachial vessels about the mid- 
dle of the arm. 

A number of superficial lymph vessels ascend with or near the subcutaneous 
veins (cephalic and accessory cephalic), and join the prescapular ami prepectoral 
glands. Superficial vessels from the chest-wall and shoulder run across the latter 
to the prescapular glands. The superficial lymphatics of the pectoral region form 
a plexus which drains into the posterior cervical and prescapular glands by a number 
of vessels which accompany the cephalic vein. The deep lymph vessels of the pec- 
toral region run with the external thoracic vein to the axillary glands. 

In one subject the author observed several small glands along the posterior 
branch of the dorsal artery, under cover of the rhomboideus. 



THE LYMPH GLANDS AND VESSELS OF THE PELVIC LIMB 

1. The prefemoral or subiliac lymph glands (Lgg. prefemorales s. subiliacse) are 
situated in the fold of\the groin on the anterior border of the tensor fascise latae, 
about midway between the point of the hip and the patella (Figs. 575, 576, 582). 
They lie on the course of the posterior branch of the circumflex iliac arterv, and 
number usually about a dozen. They receive superficial lymph vessels from the 
hip, thigh, and flank. Their efferent vessels ascend with the posterior circumflex 
iliac vein, enter the abdomen near the tuber coxee, and join the external iliac IjTnph 
glands. 

2. The deep inguinal lymph glands (Lg. inguinales profunda) form a large 
group situated in the proximal part of the femoral canal, between the pectineus and 
sartorius muscles (Figs. 576, 582). The group is elongated and is commonly four 
or five inches (ca. 10-12 cm.) in length. They cover the femoral vessels and are 
related superficially to the inguinal ligament. They receive nearly all of the lymph 
vessels of the limb below them. Their efferent vessels ascend to the internal iliac 
glands. 

3. The popliteal lymph glands (Lg. popliteae), usually four to six in number, 



704 BLOOD-VASCULAR SYSTEM OF THE HORSE 

lie behind the origin of tlie gastrocnemius and between the biceps femoris and semi- 
tendinosus at tlie division of the posterior femoral artery into its primary Ijranches 
(Fig. 580). They receive the deep lymph vessels of the distal part of the limb. 
Their efferent vessels chiefly follow the course of the femoral vessels to the deep 
inguinal glands, but one or two ascend in company with a vein along the great 
sciatic nerve and may enter an ischiatic gland or accompany the internal pudic 
vein and join the internal iliac glands. 

Several superficial lymph vessels ascend with or near the medial metatarsal and saphenous 
veins, enter the femoral canal, and end in the deep inguinal glands. 



The Fcetal Circulation 

The blood of the foetus is oxygenated, receives nutrient matter, and gives off 
waste matter by close contiguity with the maternal blood in the placenta. The 
chief differences in the blood-vascular system as compared with that which obtains 
after liirth are correlated with this interchange. 

The umbilical arteries, right and left, are large vessels which arise from the 
internal iliac arteries and pass downward and forward in the umbilical folds of peri- 
toneum on either side of the bladder to the uml)ilicus. Here they are incorporated 
with the umljilical vein and the urachus in the umbilical cord, ramify in the allan- 
tois, and end as the capillaries of the fcetal placenta. They conduct the impure 
blood to the placenta. After birth these vessels retract with the bladder to the 
pelvic cavity; their lumen becomes greatly reduced and the wall thickened so 
that they are cord-like and are usually termed the round ligaments of the bladder. 

The umbilical vein receives the oxygenated blood from the placenta. Its 
radicles converge to form in the horse a single large trunk which separates from the 
other constituents of the umbilical cord on entering the abdomen and passes for- 
ward along the abdominal floor in the free border of the falciform ligament of the 
liver. It enters the latter at tlie umbilical fissure and joins the portal vein, so 
that the blood conveyed by it passes through the capillaries of the liver before 
entering the posterior vena cava. The vein contains no valves. 

In the ox and dog some of the blood in the umbilical vein is conveyed directly 
to the vena cava by the ductus venosus. This vessel is given off within the liver 
from a venous sinus formed l)y the confluence of the portal and umbilical veins 
and passes directly to the posterior vena cava. 

The foramen ovale is an opening in the septum between the atria of the heart, 
by which the latter communicate with each other. It is guarded by a valve (Val- 
vula foraminis ovalis) which prevents the blood from passing from the left atrium 
to the right. After birth the foramen soon closes, but this part of the septum 
remains membranous, and there is a deep fossa ovalis in the right atrium M'hich 
indicates the position of the former opening. In some cases the foramen persists 
to a varialjle extent in the adult without apparent disturbance of the circulation. 

The pulmonary circulation is very limited in the foetus, and most of the blood 
which enters the pulmonary artery passes through the ductus arteriosus to the 
aorta. This vessel is larger than the divisions of the pulmonary arter>- which go to 
the lungs, and joins the left side of the aortic arch. After birth the pulmonary 
circulation undergoes promptly an enormous increase and the ductus is rapidly 
transformed into a fibrous cord — the ligamentum arteriosum. 

The only arterial blood in the foetus is that carried by the umbilical vein. 
This blood is mixed in the liver with the venous blood of the portal vein, and after 
passing through the capillaries of the liver is carried by the hepatic veins to the 
posterior vena cava. The latter receives also the venous blood from the posterior 
part of the trunk and the pelvic limbs. It is generally believed that the blood car- 



THE BLOOD-VASCULAR SYSTEM OF THE OX 705 

ried into the right atrium by the posterior vena cava passes largely, if not entirely, 
through the foramen ovale into the left atrium, while the blood flowing into it 
through the anterior vena cava passes into the right ventricle. On this basis the 
blood received by the left atrium consists chiefly of mixed blood from the posterior 
vena cava, since the small amount of blood conveyed by the pulmonary veins is 
venous. This mixed blood passes into the left ventricle and is forced into the 
systemic arteries. The venous blood from the anterior part of the body and the 
thoracic limbs is conveyed by the anterior vena cava to the right atrium, passes 
into the right ventricle, and is forced into the pulmonary artery. A small amount 
is carried to the lungs, but the bulk of it passes by the ductus arteriosus into the 
aorta behind the point of origin of the brachiocephalic trunk, and is carried to the 
posterior part of the body, a large part passing by the umbilical arteries to the 
placenta. 



THE BLOOD-VASCULAR SYSTEM OF THE OX 
The Pericardium and Heart 

The pericardium is attached to the stermun opjDosite the facets for the sixth 
costal cartilages by two fibrous bands, the stemo-pericardiac ligaments (Ligg. 
sternopericardiaca) ; these ligaments, right and left, are embedded in the mass of fat 
which separates the ^pex of the pericardium from the floor of the thorax. On the 
left side the greater part of the pericardium is in contact with the chest wall as far 
back as the fourth intercostal space. On the right side the pericardium is com- 
monly covered by the lung, and has therefore no contact with the lateral chest wall. 
But in some cases there is a small cardiac notch on the right lung opposite to the 
ventral part of the third rib and intercostal space. 

The heart of the adult ox has an average weight of about five and a half pounds 
(ca. 2.5 kg.), or about 0.4 to 0.5 per cent, of the body-weight. Its length from base 
to apex is relatively longer than that of the horse, and the base is smaller in both 
its diameters. The ventricular part is more regularly conical and more pointed. 
A shallow intermediate groove (Sulcus intermedins) extends from the coronary 
groove down the left side of the posterior border, but dses not reach the apex. The 
amount of fat in and near the grooves is much greater than in the horse. Even 
more of the heart is situated to the left of the median plane than in the horse. The 
base is opposite the chest wall from the third rib to the fifth intercostal space, both 
inclusive. The apex is opposite to the fifth interchondral space; it is just to the 
left of the median plane, and is about an inch (ca. 2.5 cm.) from the diaphragm. 
The long axis is much less oblique than in the horse. The posterior border is 
opposite to the fifth intercostal space; it is practically vertical and is slightly con- 
cave. 

The pulmonary orifice is opposite to the third rib in part and the third intercostal space, 
about a handbreadth (ca. 10-12 cm.) above the sternal ends of the ribs. The aortic orifice is 
chiefly opposite to the fourth rib. The right atrio-ventricular orifice is opposite to the third inter- 
costal space and fourth rib and space. The left atrio-ventricular orifice is chiefly opposite to the 
fourth intercostal space and fifth rib. 

The left longitudinal groove corresponds to the fourth rib. The right groove is chiefly pos- 
terior; it begins below the termination of the posterior vena cava. The intermediate groo\'e 
begins below the posterior end of the left auricle, and m its descent inclines gradually to the left 
side of the apex. 

The vena hemiazj^gos usually unites with the terminal part of the great cardiac 
vein, thus forming a trunk which opens into the right atrium below the posterior 
vena cava. 

Two bones, the ossa cordis, develop in the aortic fibrous ring. The right one 



706 



THE BLOOD-VASCULAR SYSTEM OF THE OX 



is in apposition with the atrio-ventricular rings, and is irregularly triangular in 
form. Its left face is concave and gives attachment to the right posterior cusp of 
the aortic valve. The right surface is convex from before backward. The base 
is dorsal. The posterior border bears two projections separated by a notch. It 
is usually a little more than an inch (ca. 4 cm.) in length. The left bone is smaller 
and is inconstant. Its concave right border gives attachment to the left posterior 
cusp of the aortic valve. There is a large muscular moderator band in the right 

Aona 

Ligamentum arteriosum 

Left branch of pulmonary artery 
Anterior rena'-'WIS'f W/ I „ , 

cava lU^ M- I rmmonary veins 

Posterior rcna cava 



Pulmonary artery 




Right 7<cntrid' 
Left coronary artery 



Vena hemiazygos 
Left auricle 



Posterior branch of left 
coronary artery in 
intermediate groove 
Left ventricle 



Fig. 592.— Hea 
The ventricle 



ventricle, which extends from the base of the anterior septal papillary muscle to the 
lateral wall at the base of the papillary muscle there. In the left ventricle there 
are several branched moderator bands. 



The Arteries 1 

The great arterial trunks in the thorax resemble those of the horse in general 
disposition. 

1 Only the most important differential features of the arrangement of the vessels as compared 
with those of the horse will be considered. 



THE COMMON CAROTID ARTERY 707 

The left coronary artery is much larger than the right one; it gives off a branch 
which descends in the intermediate groove, and terminates by running dowTiward 
in the right longitudinal groove. The right coronary artery, after emerging from 
the interval between the right auricle and the puhnonary artery, divides into 
branches which are distributed to the wall of the right ventricle. 
' The brachiocephalic trunk (anterior aorta) is usually four or five inches (ca. 
10-12 cm.) in length. 

The brachial arteries give off in the thorax the following branches: 

1. A common trmik for the dorsal, deep cervical, and vertebral arteries. 

(1) The subcostal artery commonly arises separately and runs forward along 
the sides of the bodies of the vertebra. It supplies the second to the fifth inter- 
costal arteries. 

(2) The dorsal artery is relatively small. It usually ascends in front of the 
first costo-vertebral joint, and is distributed as in the horse. It gives off the first 
intercostal artery. 

(3) The deep cervical artery may arise from a common stem (Truncus vertebro- 
cervicalis) with the vertebral, or maj' constitute a branch of that arterj'. It passes 
up between transverse processes of the first thoracic and last cervical vertebra, or be- 
tween the sixth and seventh cervical, and is distributed as in the horse. 

(4) The vertebral artery passes along the neck as in the horse to the inter- 
vertebral foramen between the second and third cervical vertebra, gives off a 
muscular branch, and enters the vertebral canal (Fig. 594). It runs forward on 
the floor of the canal — connected with its fellow by two or three transverse anas- 
tomoses — and divides in the atlas into two branches. The smaller medial division 
(cerebrospinal artery) passes forward to the floor of the cranium and concurs with 
the condyloid artery and branches of the internal maxillary in the formation of a 
large rete mirabile. The large lateral branch emerges through the intervertebral 
foramen of the atlas and ramifies in the muscles of the neck in that region, com- 
pensating for the smallness of the branches of the occipital artery. It also sends a 
branch to the rete mirabile. The collateral branches detached to the cervical mus- 
cles are large and compensate for the small size of the deep cervical artery. The 
spinal branches pass through the intervertebral foramina, divide into anterior and 
posterior branches, and form two longitudinal trunks which are connected by cross- 
branches so as to form irregular polygonal figures. 

2. The internal thoracic artery presents no remarkable features. 

3. The inferior cervical artery corresponds usually to the ascending branch of 
that vessel in the horse. 

4. The external thoracic artery is large and usually gives off a branch which is 
equivalent to the descending branch of the inferior cervical artery of the horse. 



THE COMMON CAROTID ARTERY 

The carotid arteries usually arise from a common trunk about two inches (ca. 
5 cm.) in length, but in exceptional cases are given off separately from the brachio- 
cephalic. Each pursues a course similar to that of the horse, and is accompanied 
by the small internal jugular vein, but is separated from the external jugular vein 
by the omo-hyoid and sterno-mastoid muscles. It divides at the digastricus into 
occipital, external maxillary, and external carotid arteries. In addition to tracheal, 
oesophageal, and muscular tiranches, it gives off the thyroid, laryngeal and inferior 
parotid arteries. The thyroid artery (A. thyreoidea cranialis) bends around the 
anterior end of the thyroid gland, in which it ramifies. The accessory thyroid 
artery is usually absent. The laryngeal artery may arise with the thyroid. 

1. The occipital artery is relatively small. It gives off the following: 



708 THE BLOOD-VASCULAR SYSTEM OF THE OX 

(1) The pharyngeal artery (A. palatina ascendens) goes to the pharynx and 
soft palate; it may arise from the external carotid. 

(2) Muscular branches go chiefly to the ventral straight muscles of the head 
and supply twigs to the atlanto-occipital joint. 

(3) The condyloid artery passes into the cranium through the anterior foramen 
in the condyloid fossa, and joins the vertebral in the formation of the rete mirabile 
about the pituitary gland. Before entering the cranium it gives off a branch to 
the pharyngeal lymph glands and the middle meningeal artery; the latter passes 



Fig. 593. — Schema of Chief Ahteries of Heao of Cow. 
i, Common carotid artery; 5, thyro-laryngea!; 3, thyroid: 4. laryngeal: 5, pharyngeal ; &, occipital; 7, condyloid: 
8, middle meningeal; 0, pharyngeal; 10, external maxillary; 11. lingual: 12, sublingual; 13, superior labial; 14, in- 
ternal maxillary; 15, masseteric; 16, inferior alveolar; 17, buccinator; IS, great palatine: 19, sphenopalatine; 20, 
posterior auricular; 21, superficial temporal; 22, posterior meningeal: 23, anterior auricular: 24, artery to cerium of 
horn; ;S5, deep temporal ; ^6, arteries to rete mirabile; ^7, frontal; 2S, ma\aT; .35', dorsal nasal continuation of malar; 
29, infraorbital; 29^, lateral nasal continuation of 29. 

through the foramen lacerum. Another branch enters the temporal canal and gives 
twigs to the temporalis muscle and the mucous membrane of the frontal sinus. A 
muscular branch emerges from the intervertebral foramen of the atlas. A diploic 
branch goes into the occipital condyle and squama, and emits twigs to the occipital 
muscles. 

2. The external maxillary artery is smaller than that of the horse, but pursues 
a similar course.' It gives off several branches to the parotid and mandibular 
glands. The lingual artery is large, and often arises separately from the common 

• In the sheep the artery crosses the masseter muscle about its middle and is continued as 
the superior labial artery. 



THE COMMON CAROTID ARTERY 



709 



carotid; it gives off a branch to the mandibular gland, and the sublingual artery. 
After turning around the jaw the facial gives off the two labial arteries. The inferior 
labial artery is small; it runs forward along the ventral margin of the tlepressor 
labii inferioris. The superior labial is large; it passes forward ventral to the 
depressor labii superioris, and usually gives ofT a muscular branch which runs for- 
ward almost parallel with the lateral nasal. The angular artery is very small or 
absent, and the lateral and dorsal nasal arteries spring from branches of the in- 
ternal maxillary. 

3. The external carotid artery passes upward between the stylo-hyoideus 
and the great cornu of the hyoid bone, turns forward across the lateral face of the 
latter, and divides into superficial temporal and internal maxillary arteries. It 
gives off the following collateral branches: 

(1) The pharyngeal artery may be a branch of the external carotid, but often 
arises from the occipital. 

(2) The posterior aiuricular artery, which resembles that of the horse, sends a 




Fig. 594. — Floor of Cranium and Anterior Part op Vertebral Canal of Ox. 
1, Vertebral artery; J, muscular branches of 1 ; 3, branches of 1 to the rete mirabile; 4, 3, branches of internal max- 
illary artery to rete; 6, branch of internal maxillary artery entering cranium through foramen ovale; 7, condyloid ar- 
tery; 8, emergent artery from rete, distributed like internal carotid artery of horse; 9, 9', longitudinal vertebral sinuses; 
a, cribriform plate; b, optic formina; c, for. orbito-rotundum; d, foramen ovale; e, occipital condyle; /, g, h, first, 
second, and third cervical vertebrae. (After Leiserihg's Atlas.) 



stylo-mastoid branch into the tympanum. It may arise from the superficial 
temporal. 

(.3) The superior parotid artery arises near the termination of the external 
carotid and enters the upper part of the parotid gland. 

(4) The masseteric artery resembles that of the horse, but is smaller; it may 
arise from the internal maxillary artery. 

The superficial temporal artery is large and presents the following special 
features: (1) The transverse facial artery passes into the central part of the masse- 
ter. (2) It gives off a branch which corresponds to the posterior meningeal artery 
of the horse, enters the temporal canal, and ramifies in the dura mater, giving off 
twigs to the external ear, the temporal muscle, and the frontal sinus. (3) It 
usually gives off the anterior auricular artery. (4) A large branch passes around 
the outer side of the base of the horn-core, supplies the corium of the horn, and 
anastomoses across the back of the frontal eminence with the artery of the opposite 
side. (5) Other branches go to the frontal muscles and skin and to the orbital 
fat, the lacrimal glands, and the eyelids. 



710 THE BLOOD-VASCULAR SYSTEM OF THE OX 

The internal maxillary artery is entirely extraosseous, since the alar canal is 
absent. It passes forward along the side of the pharynx and the lateral pterygoid 
muscle and forms a double curve at the infratemporal fossa. It then runs forward 
to the pterygo-palatine fossa and divides into two terminal trunks; one of these 
divides into malar and infraorbital arteries, the other into sphenopalatine and 
greater palatine. It gives off branches to the pterygoid muscles, and the principal 
differential features in its branching are as follows: 

(1) The buccinator artery arises from the first curve of the internal maxillary; 
it is relatively large, supplies the superior buccal glands, and divides into two 
branches. One of these enters the buccinator; the other, which is much larger, 
ramifies in the deep part of the masseter. 

(2) The anterior deep temporal artery usually arises by a common trunk with 
the middle meningeal artery. The latter enters the cranial cavity through the 
foramen ovale antl concurs in the formation of the rete mirabile cerebrale. 

(3) The ophthalmic artery forms a rete mirabile within the periorbita.' Its 
frontal branch enters the sujjraorbital canal and ramifies chiefly in the frontal sinus. 

(4) Several branches which take the place of the internal carotid artery enter 
the cranial cavity through the foramen orbito-rotundum. They concur with the 
vertebral, middle meningeal, and condyloid arteries in the formation of an ex- 
tensive rete mirabile cerebrale on the cranial floor around the sella turcica. From 
each side of the rete an artery arises which is distributed in general like the internal 
carotid and basilar arteries of the horse. - 

(5) The malar artery is large; it arises Ijy a common trunk with the infra- 
orbital and gives off the dorsal nasal and the angular artery of the eye. 

(6) The infraorbital artery is large and emerges from the infraorbital foramen 
to form the lateral nasal artery. 

(7) The greater palatine artery usually arises by a common trunk with the 
sphenopalatine. It passes through the palatine canal and along the palatine groove, 
enters the nasal cavity through the incisive fissure, and does not go to the upper lip. 
It forms a rete mirabile about the incisive canal and terminates in the mucous 
membrane of the anterior part of the nasal cavity. 



ARTERIES OF THE THORACIC LIMB 
The brachial artery pursues the same course in the arm as that of the horse. 
At the elbow it becomes the median.^ The chief differential features in its branches 
are as follows: 

1. The subscapular artery is almost as large as the continuation of the brachial. 
The posterior circimifllex artery is large ; it sends branches backward and downward 
into the triceps, taking the place in part of the deep brachial artery. The thoracico- 
dorsal artery supplies branches to the pectoral muscles and the triceps as well as 
the teres major and latissimus dorsi; it may arise directly from the brachial. 

2. The smallness of the deep brachial artery is compensated, as noted above, 
by the large size of the posterior circumflex. 

3. The proximal collateral ulnar artery is often double, and does not extend to 
the carpus. Its superficial descending branch goes to the superficial pectoral 
muscle and the skin, and its ascending branch is distributed chiefly to the medial 
head of the triceps and the anconeus. 

(4) The (distal) collateral radial artery, which is given off at the elbow joint, 

' This may be distinguished as the rete mirabiU orbitale. 

2 The arteries which concur in the formation of the rete may be termed the arteria> retis 
mirabilis cerebralis. 

^ The homologies of the vessels of the lower parts of the limbs are still uncertain. The ac- 
coimt given here is mainly based on the views of Sussdorf and Baum. 



AKTERIES OF THE THORACIC LIMB 



711 



sends branches to the biceps, brachiahs, and extensor muscles; it also supplies the 
nutrient artery of the humerus. It does not descend to the carpus. 

The median artery descends along the medial part of the posterior surface of 
the radius antl divides near the middle of the forearm into the radial and lUnar 
arteries. It gives off at the proximal third of the forearm the common interosseous 
artery, a large vessel which anastomoses with the deep brachial, passes tlu'ough the 
jjroximal interosseous space, and descends as the dorsal interosseous artery in the 
groove between the radius and ulna, and concurs in the formation of the rete carpi 



■\^ 



Fig. 595. — Arteries of Distal Part > 
hiMB OF Ox; Dorsal View. 
a, Interosseous artery; b, dorsal branch of radiai 
artery; c, rete carpi dorsale; d, dorsal metacarpal ar- 
tery; e, dorsal common digital artery; /, /, dorsal proper 
digital arteries. 



Right Fore Fig. 596. — Arteries of Distal Part of Right Fork 
Limb of Ox; Volar View. 
g, Ulnar artery; h, radial artery; i, volar branch 
of common interosseous artery; k, I, m, deep volar 
metacarpal arteries; .-i.v., volar arches; n, volar com- 
mon digital artery; o, o', p, volar proper digital arteries. 



dorsale. At the distal end of the forearm it sends a l^ranch through the distal 
interosseous space, which passes downward, assists in forming the rete carpi volare, 
and is continued in the metacarpus as the lateral deep volar metacarpal artery. 
This is a small vessel which passes down under the lateral border of the suspensor}^ 
ligament and assists in forming the deep volar arch near the fetlock. The recurrent 
interosseous artery arises from the common interosseous and ascends to the lateral 
surface of the elbow. A large muscular branch arises from the median at the 
proximal end of the forearm ; it is distributed chiefly to the flexor muscles. 



712 THE BLOOD-VASCULAR SYSTEM OF THE OX 

The radial artery is the smaller of the two terminal branches of the median. It 
descends on the flexor carpi radialis, passes over the medio-volar surface of the 
carpus, and is continued as the medial deep volar metacarpal artery. At the distal 
end of the forearm and at the carpus it furnishes branches to the retia carpi. An- 
other branch (A. met. perforans proximalis) runs outward between the suspensory 
ligament and the large metacarpal bone, passes through the proximal foramen of 
the bone, and unites with the dorsal metacarpal artery ; before passing through the 
foramen it detaches the middle deep volar metacarpal artery (A. met. volaris prof. 
III.). This descends on the volar face of the metacarpal bone, receives an anasto- 
motic branch from the medial deep artery, and concm's in the formation of the deep 
volar arch above the fetlock. The medial deep volar metacarpal artery (A. met. 
volaris prof. II.) descends along the medial part of the volar surface of the large 
metacarpal bone and is continued as the medial volar proper digital artery. At the 
distal part of the metacarpus it is connected by a transverse branch with the middle 
deep volar metacarpal artery, and similarly with the volar common digital, forming 
with the latter the superficial volar arch. 

The ulnar artery, the larger of the two divisions of the median, descends under 
cover of the flexor carpi radialis without giving off any large branches in the fore- 
arm. It passes through the carpal canal and continues along the medial side of the 
deep flexor tendon as the volar common digital artery (A. met. volaris superficialis 
III.). At the distal third of the metacarpus this vessel is joined by a branch from 
the medial deep volar metacarj^al artery, forming the superficial volar arch. Near 
this another branch of the common digital (or of the medial digital) passes around 
the lateral border of the flexor tendons to the posterior face of the metacarpal bone 
and concurs with the deep volar metacarpal arteries in the formation of the deep 
volar arch. A branch from the arch (A. met. perforans distalis) passes forward 
through the distal foramen of the metacarpal bone and joins the dorsal metacarpal 
artery which descends from the rete carpi dorsale in the dorsal metacarpal groove. 

The volar common digital artery (A. metacarpea volaris superficialis III.) 
passes into the interdigital space and divides into two volar proper digital arteries, 
which descend along the interdigital surfaces of the chief digits and pass through 
the foramina at the proximal part of the interdigital surfaces of the third phalanges, 
enter the cavities in these bones, and ramif j' in a manner similar to the correspond- 
ing vessels in the horse. The volar common digital detaches a branch (A. inter- 
digitalis perforans) which passes forward through the upper part of the interdigital 
space and anastomoses with the dorsal metacarpal artery. 

The volar proper digital arteries (or the common digital) give off, in addition to other col- 
laterals, branches whiclj correspond to the arteries of the digital cushion of the horse. These 
pass to the bulbs of the claws and anastomose with each other and with the medial and lateral 
digital arteries, forming an arch from which numerous branches are distributed to the coriura 
of the hoofs. 

The dorsal metacarpal artery (A. met. dorsalis III.) is a small vessel which 
arises from the rete carpi dorsale, descends in the groove on the dorsal face of the 
metacarpal bone, and is joined by the distal perforating metacarpal artery from 
the deep volar arch to constitute the dorsal common digital artery. This vessel 
(A. digitalis communis dorsalis III.) divides into two dorsal proper digital arteries'. 

The medial volar digital artery (A. digiti III. medialis) is the continuation of the 
medial deep volar metacarpal artery. It descends on the medial side of the medial 
digit and terminates at the bulb of the claw by anastomosing with the corresponding 
volar proper digital artery. It gives off a branch to the rudimentary digit and 
forms a transverse anastomosis behind the first phalanx with the volar common 
digital or its medial division. 

The lateral volar digital artery (A. digiti IV. lateralis) arises from the deep volar 



BRANCHES OF THE ABDOMINAL AORTA 713 

arch, passes down on the lateral side of the lateral digit, and is distributed like the 
medial one. 

BRANCHES OF THE THORACIC AORTA 
The bronchial and oesophageal arteries often arise separately. 
There are thirteen ]3airs of intercostal arteries. The first comes from the 

dorsal, the next four from the subeostal, antl the remainder from the aorta directly. 
The two phrenic arteries are very variable in origin. They may come from 

the aorta, the coeliac, left ruminal, or an intercostal or lumbar artery. 



BRANCHES OF THE ABDOMINAL AORTA 
The cceliac artery is about four to five inches (ca. 10-12 cm.) in length. It 
passes ventrally and curves forward })etwcen the rumen and pancreas on the left 
and the right crus of the diaphragm and the posterior vena cava on the right. It 
gives off five chief branches. 

1. The hepatic artery arises from the convex side of the curve of the coeliac 
artery as it crosses the posterior vena cava. It passes downward, forward, ami to 
the right above the portal vein to the portal fissure, and gives off the following 
branches : 

(1) Pancreatic branches. 

(2) Dorsal and ventral branches go to the corresponding lobes of the liver. 
The ventral branch is the larger; it gives off the right gastric artery, which runs in 
the lesser omentum to supply the origin of the duodenum and the pylorus, anas- 
tomosing with the dorsal branch of the omaso-abomasal artery. 

(3) The cystic artery supplies the gall-bladder. 

(4) The gastro-duodenal artery divides into right gastro-epiploic and pan- 
creatico-duodenal branches. The right gastro-epiploic artery anastomoses with 
the left gastro-epiploic. The pancreatico-duodenal artery anastomoses with the 
first intestinal branch of the anterior mesenteric artery. 

2. The right ruminal artery (A. ruminalis dextra) is the largest branch, and 
usually arises by a short conmion trunk with the splenic. It runs downward and 
backward on the right face of the dorsal sac of the rumen to the posterior transverse 
fissure, in which it turns around to the left and anastomoses with branches of the 
left ruminal artery. It gives off a pancreatic branch, dorsal and ventral coronary 
arteries, branches to the great omentum, and ramifies on both surfaces of the rumen. 

3. The left ruminal artery (A. ruminalis sinistra) descends on the anterior part 
of the right face of the rumen, enters the anterior furrow, in which it runs from 
right to left, and continues backwartl in the left longitudinal groove, anastomosing 
with branches of the right artery. It supplies chiefly the left face of the nnnen, 
but not its posterior part. It usually gives off near its origin the reticular artery 

(A. reticularis) ; this rather small vessel passes forward on the dorsal curvature of 
the rumen and turns dowmward in the rumino-reticular groove, in the bottom of 
which it runs around ventrally to the right side. It gives off a branch which passes 
to the left of the cardia and along the lesser curvature of the reticulum to the neck 
of the omasum. The reticular branches anastomose with the omaso-abomasal and 
left ruminal arteries. 

4. The omaso-abomasal artery (A. gastrica sinistra) appearsas the continua- 
tion of the ctt'liac. It passes forward and downward to the greater curvature of 
the omasum, and divides after a course of four or five inches into two branches. 
The dorsal branch curves sharply backward on the dorsal surface of the omasum, 
continues along the lesser curvature of the abomasum, and anastomoses with the 
hepatic artery. It supplies branches to the omasum and to the lesser curvature 



714 



THE BLOOD-VASCULAR SYSTEM OF THE OX 




Fig. 597. — Gastric Arteries of Ox; Right View (Partly Schematic). 
7, Cceliac; ;?, right ruminal; S, splenic; 4, reticular; 5, left ruminal; 5, omaso-abomasal; 7, dorsal branch of ^; 



8, ventral branch of 6 (= left gastro-epipli 
sacs; D, oesophagus; E, reticulum; F, 
By an oversight the reticular artery is show 



, dorsal i 
G, abon 
arising from the ( 



umen; B, ventral sac of rumen; C, C, posterior blind 
H, duodenum; /, right longitudinal furrow of rumen- 
maso-abomasal. 




Fig. 59S. — Gastric Arteries of Ox; Left View (Partly Schematic). 
i, Left ruminal artery; 2, continuation of right ruminal artery; 5, reticular arterj-, which disappears into rumino- 
reticuiar groove ; A, dorsal sac of rumen; 5, ventral sac of rumen; C, C, posterior blind sacs; D, oesophagus; £?, reticu- 
)-reticular groove; G, left longitudinal furrow of rumen. 



BRANCHES OF THE ABDOMINAL AORTA 



715 



and pyloric part of the abomasum. The ventral branch (A. gastro-epiploica 
sinistra) runs forward and downward over the anterior extremity of the omasum, 
passes backward in the great omentum close to the ventral curvature of the aboma- 
sum, and anastomoses with the right gastro-epiploic. A considerable branch from it 
curves around in front of the neck of the omasum to communicate with the reticular 
artery. Another branch runs liack across the left side of the omaso-abomasal 
junction, and a third goes to the lesser curvature of the omasum. 

5. The splenic artery usually arises liy a common trunk with the right ruminal 




■Small 



Fig. 599.— Plan of Branches of A 
1, Anterior mesenteric artery; i?, middle colic artery; 
tion of anterior mesenteric artery, giving off branches to i 
mesenteric artery; ,-1, termination of duodenum. 



:8ENTERIC .\rTEHY OF Ox. 

ileo-CEeco-colic artery; 4> ramus collateralis; S, continua- 
all intestine; 6, csecai artery; 7, colic branch of posterior 



artery. It passes forward and to the left across the dorsal curvature of the rumen 
and enters the hilus of the spleen. 

The anterior mesenteric artery arises from the aorta just behind the coeliac, 
and has about the same caliber as the latter. It descends, inclining a little to 
the right, and crosses the colon as the latter emerges from the spiral to run backward. 
After detaching twigs to the pancreas it gives off in succession the following branches: 

1. The middle colic artery (A. colica media) passes to the colon as it emerges 
from the spiral arrangement. This artery is comparable to the middle colic or 
artery of the small colon of the horse ; it runs backward along the terminal part of 
the colon, which it supplies. 



716 



THE BLOOD-VASCULAR SYSTEM OF THE OX 



2. The ileo-caeco-colic artery ramifies on the right face of the spiral part of the 
colon. It gives off the ik'o-("f cal artery, which divides into ileal and ceecal arteries. 

3. The ramus coUateralis riuis in the mesentery in a curve along the ventral 
border of the coils of the colon. (This vessel is absent in the sheep.) 

4. The continuing trunk (Truncus intestinalis) of the anterior mesenteric 
pursues a course in the mesentery corresponding to the series of mesenteric lymph 
glands and is connected with the ramus coUateralis. 

The two preceding vessels are essentially the arteries of the small intestine, 
which they supply with the exception of its initial and terminal parts. The ramus 
coUateralis gives off no considerable branches in its course along the ventral border 
of the coils of the colon, but on curving upward along the latter it anastomoses with 




Fig. 600. — Pelvic Arteries of Cow. 
Part of the right wall of the uterus and vagina is removed and the cervix uteri is shown in sagittal section, a, 
Aorta; 6, utero-ovarian artery; 6', ovarian, and b" , uterine branch of 6; c, external iliac artery; d, right internal iliac 
artery; e, common trunk of umbilical artery (e') and middle uterine artery (/); g, ilio-lumbar artery: h, anterior gluteal 
arteries; i, middle heemorrhoidal artery; k, posterior uterine artery: I, perineal artery: m, posterior gluteal artery; n, 
obturator arteries; o, artery of clitoris; p, posterior mesenteric artery; r, anterior hemorrhoidal artery: s, middle 
sacral artery; 1, ovary; 2, apparent body of uterus, really apposed horns; 2', horn of uterus: 3, vagina; .(, neck of uterus; 
Jf, external orifice of uterus (os uteri); o, 5', broad ligaments, large part of right one removed; 6, urinary bladder; 7» 
rectum; 5, sacrum; 9, symphysis pelvis. (After Zieger.) 



the continuing trunk of the anterior mesenteric artery and detaches numerous 
branches to the small intestine which form series of superposed anastomotic arches. 
It supplies, roughly speaking, about one-third of the small intestine and terminates 
by joining the ileal artery. The continuing trunk gives off numerous branches 
which also form arches and supply about the first two-thirds of the small intestine, 
exclusive of the small part supplied by branches of the coeliac artery. Both arteries 
give branches to the lymph glands.^ 

The posterior mesenteric artery arises from the aorta near its termination. It 
is small antl supplies branches to the terminal part of the colon antl to the rectum 
(A. colica sinistra; A. haemorrhoidalis cranialis). 

' It is difficult to make the arrangement of these vessels clear in a brief textual description, 
but a reference to the schematic figure will explain the main facts. 



ARTERIES OF THE PELVIC LIMB 717 

The renal arteries arise from the aorta close together. The right one passes 
outward antl forward across the dorsal face of the posterior vena cava to the hilus 
of the kidney. The left one runs backward, but necessarily varies in direction in 
conformity with the position of the kidney (g. v.). 

The spermatic arteries resemble those of the horse. 

The utero-ovarian arteries are small. 

The five pairs of lumbar arteries derived from the aorta are distributed much 
as in the horse. The sixth usually comes from the internal iliac artery. 

The middle sacral artery is a vessel about 5 mm. in diameter which continues 
the aorta. It arises from the dorsal face of the aorta at the angle of divergence of 
the internal iliacs, runs backward on the pelvic surface of the sacrum a little to the 
left of the median line, and is continued as the middle coccygeal artery. It gives 
off small collateral branches to the spinal cord and the muscles of the tail and the 
lateral coccygeal arteries. The latter may have a common tnmk of origin, and 
each divides into dorsal and ventral branches. The middle coccygeal artery runs 
through the ventral (hismal) arches of the coccygeal vertebrce. The coccygeal 
arteries are connected at pretty regular intervals by segmental anastomoses. 

The internal iliac arteries are much longer than in the horse. Each passes 
Ijackward on the sacro-sciatic ligament and divides al^out the middle of the pelvic 
wall into posterior gluteal and internal pudic branches. The chief differences in 
its distribution are: (1) A large trunk gives origin to the umbilical and middle 
uterine arteries. The umbilical artery is usually largely obliterated, and its terminal 
branches receive their blood through anastomoses with the internal pudic. It 
gives off near its origin two small vessels, the ureteral artery (A. ureterica) and the 
deferential artery (A. deferentialis), which accompany the ureter and the ductus 
deferens respectively. The middle uterine artery (A. uterina media) is very large. 
It is distributed chiefly to the cornu of the uterus, and compensates for the small 
size of the utero-ovarian artery. (2) The ilio-lumbar artery is relatively small 
and is distributed chiefly to the sublumliar muscles. It is sometimes replaced by 
branches of the circumflex iliac antl gluteal arteries. (3) The anterior gluteal 
artery is commonly represented by several vessels. (4) The obturator artery is 
represented by several small branches which supply the obturator and adductor 
muscles. (5) The iliaco-femoral and lateral sacral arteries are absent. The 
absence of the latter is compensated by the middle sacral and gluteal arteries. (6) 
The posterior gluteal artery is large. It emerges through the lesser sciatic notch 
and ramifies in the biceps femoris and adjacent muscles. (7) The internal pudic 
artery (A. urethro-genitalis) is the direct continuation of the internal iliac. It 
gives off branches to the rectum, bladder, urethra, and genital organs. In the 
male it supplies the accessory genital glands and divides into dorsal and deep arteries 
of the penis; the a. dorsaUs penis runs along the dorsum penis to the glans and gives 
twigs to the prepuce; the a. profunda penis gives off' a perineal branch and enters 
the corpus cavernosum penis. In the female it gives oft' the large posterior uterine 
artery, which supplies the posterior part of the uterus and gives branches to the 
vagina and bladder. It ends as the a. clitoridis, which supplies the clitoris and 
adjacent parts. 

ARTERIES OF THE PELVIC LIMB 

The external iliac artery has the same course as in the horse. The circumflex 
iliac artery is large. A branch from it emerges between the abdominal and lumbar 
muscles near the tuber coxae and ramifies like the terminals of the ilio-lumbar 
artery of the horse. 

The femoral and popliteal arteries jjursue a similar course to those of the horse. 
The chief differences in their Ijranches are as follows: 

1. The external pudic artery is distributed chiefly to the scrotum in the male. 



•18 



THE BLOOD-VASCULAR SYSTEM OF THE OX 



In the cow it is usually termed the mammary and is very large, especially during 
lactation. Each divides at the base of the mammary gland into two branches 
which are distributed to the anterior and posterior parts ("quarters") of the gland. 
A small branch accompanies the subcutaneous abdominal vein to the xiphoid region. 
2. The deep femoral artery gives off an obturator branch which passes up 
through the obturator foramen to supply the obturator internus and compensates 
otherwise for the absence of the obturator artery. 



Fig. 601. — Arteries of Distal Part of Right Hind 
Limb of Ox; Dorsal View. 
a. Anterior tibial artery; b, proximal perforatiDg 
metatarsal artery; c, dorsal metatarsal artery; d, dorsal 
common digital artery; e, e\ dorsal proper digital ar- 
teries. 



Fig. C02. — Arteries of Distal Part of Right Hind 
Limb of Ox; Plantar View. 
e. Saphenous artery; /, /', internal and external 
plantar arteries; g, g\ medial and lateral superficial 
plantar metatarsal arteries; k, deep plantar metatarsal 
artery; i, j, medial and lateral plantar digital arteries, 
k, plantar common digital artery; I, I', medial and lat- 
eral plantar digital arteries. 



3. The anterior femoral artery is large. It often gives off the external cir- 
cimiflex artery of the thigh, which perforates the proximal end of the quadriceps, 
gives Ijranches to that muscle, the iliacus, glutei, and tensor fasciffi latse. 

4. The saphenous artery is large. It descentls in front of the homonymous 
vein over the medial surface of the leg, and divides near the hock into lateral 
and meilial tarsal arteries. The lateral tarsal artery is small and is distributed 
on the outer part of the hock. The medial tarsal artery is the direct continuation 



THE VEINS 719 

of the saphenous. It descends along the medial border of the superficial flexor 
tendon and divides into medial and lateral plantar arteries. The medial plantar 
artery descends along the medial side of the deep flexor tendon with the medial 
jilantar nerve. It anastomoses at the proximal end of the metatarsus with the 
perforating tarsal artery, assisting in the formation of the proximal plantar 
arch, and continues distally as the a. met. plant, superfic. med. along the medial 
border of the deep flexor tendon. Near the fetlock it concurs with the perforating 
branch of the dorsal metatarsal artery and with a branch of the corresponding 
lateral artery in the formation of the distal plantar arch. Below this it is continued 
as the medial digital artery. The lateral plantar artery is small. ^ It descends 
along the lateral border of the tlecp flexor tendon with the lateral plantar nerve, 
concurs with the perforating tarsal and meilial plantar arteries in the formation 
of the proximal plantar arch, and gives branches to the rete tarsi dorsale. Continu- 
ing do^^'nward along the deep flexor tendon as the a. met. plant, superfic. lat., it 
assists in forming the distal plantar arch and becomes the lateral digital artery. 

The posterior tibial artery is relatively small and is distriljuted chiefly to the 
muscles on the posterior surface of the tibia. Lower tlown it is replaced by the 
saphenous artery, as described above. 

The anterior tibial artery has thesame course as in the horse. It is continued 
down the groove on the front of the metatarsal bone as the dorsal metatarsal artery. 
At the tarsus branches are given off which concm' ■nith the lateral tarsal artery in 
the formation of the rete tarsi dorsale. The perforating tarsal artery passes back 
through the vascular canal and anastomoses with the plantar arteries, thus forming 
the proximal plantar arch. From this the small deep plantar metatarsal artery 
descends in the plantar groove of the large metatarsal bone to the distal plantar 
arch. The dorsal metatarsal artery (A. met. dorsalis) is the chief artery of the 
region and is accompanied by two veins. Near the distal end of the metatarsal 
bone it gives off the perforating metatarsal artery, which passes back through the 
distal metatarsal foramen and assists in forming the distal plantar arch. 

The dorsal common digital artery is the direct continuation of the dorsal 
metatarsal. It divides into two branches which unite in the interdigital space with 
the corresponding branches of the plantar common digital to form the proper 
digital arteries. 

The plantar common digital artery descends from the distal plantar arch, 
anastomoses in the interdigital space with the medial and lateral digitals, and 
divides into two branches which join those of the dorsal common digital artery as 
before mentioned. 

The foregoing is a brief statement of the more common arrangement of the 
vessels in the distal part of the limb, but minor variations are very common. 



The Veins = 

The vena hemiazygos takes the place of the vena azygos. It lies along the 
left side of the aorta and the bodies of the thoracic vertebrae, turns down across 
the left face of the aorta and left pulmonary artery, runs back over the left auricle, 
and usually joins the great cardiac vein, but may open into the right atrium. It 
receives the dorsal intercostal veins. 

Two jugular veins occur on either side. The internal jugular vein (V. jugu- 
laris interna) is a relatively small vessel which accompanies the carotid artery. It 

' This vessel may arise instead from the rete tarsi dorsale. 

- Most of the differences in the veins of the ox are correlated with those of the arteries of 
which they are sateUites, and will not be described. The account here given consists chiefly of 
those differential features which could not be deduced from a knowledge of the arteries. 



720 THE BLOOD-VASCULAR SYSTEM OF THE OX 

arises by occipital, laryngeal, and thyroid radicles, receives tracheal, oesophageal, 
and muscular branches, and joins the external jugular near its termination. It is 
sometimes absent, but in some cases it appears, on the other hand, to be large 
enough to interfere with venesection practised on the external jugular. The 
external jugular vein (V. jugularis externa) is very large and corresponds to the 
jugular of the horse. It is separated from the carotid artery in the greater part 
of its course by the sterno-cephalicus and omo-hyoideus muscles. 

The ventral cerebral vein usuallj' does not unite with the occipital ; the latter 
is continued by the internal jugular vein. 

The ventral longitudinal sinus is represented by a vein. There is an anterior intercavernous 
sinus. The transverse sinus is connected with the basilar plexus by a vein which traverses the 
condyloid canal. In the sheep there are two ventral occipital sinuses in place of the basilar plexus. 

The orbital veins form a network between the periorbita and the muscles of 
the eyeball. This plexus communicates with the cavernous sinus and with the 
dorsal cerebral vein. It is also drained by the frontal vein, which runs in the 
supraorbital canal and groove and joins the angular vein of the eye. 

The dorsal nasal vein is usually double. 

The superior labial vein usually joins the infraorbital. 

The vena reflexa is absent, and the radicles which are received by it in the horse 
go to the internal maxillary vein. 

The sublingual vein is very large. 

The veins of the thoracic limb differ chiefly in the distal part; the special 
features are as follows: 

The dorsal digital veins ascend on the front of the digits and are connected 
with the other digital veins by transverse branches. They unite near the fetlock 
to form the dorsal metacarpal vein. This runs upward on the dorsal face of the 
metacarpus and carpus, inclines to the medial surface of the radius, and joins the 
cephalic or the accessory cephalic vein. 

The volar digital veins are larger than the dorsal veins. They lie on the inter- 
digital surfaces of the tligits and unite in the interdigital space to form a trimk which 
is a satellite of the volar common digital artery. This trunk, the volar common 
digital vein, which is often double, is connected distally by transverse branches 
with tlic lateral and medial digital veins to form the superficial volar arch; it is 
continued upward as the satellite of tlie ulnar artery. 

The medial and lateral digital veins lie in front of the corresponding arteries. 
They are connected with the volar digital vein by a large branch which passes 
between the flexor tendons and the first phalanx. At the distal end of the meta- 
carpus each inclines forward and anastomoses with the volar common digital vein 
to form the volar venous arch. The medial vein is continued as the medial volar 
metacarpal vein along the medial border of the suspensory ligament, and becomes a 
satellite of the radial artery in the forearm, while the lateral one is continued on the 
volar face of the metacarpal bone by the lateral volar metacarpal vein. The latter 
unites at the proximal part of the metacarpus vrith the middle volar metacarpal 
vein, and the trimk thus formed joins the medial vein to form the deep plantar arch. 
They unite below the carpus or join the volar common digital vein. 

The digital veins arise from the venous plexuses of the corium of the hoof. They form ljy 
anastomotic branches a venous circle at the coronary border of the hoot, which may be termed the 
coronary circle. A vein which emerges from the foraiiien on the proximal part of the interdigital 
surface of the third phalanx is the principal radicle of the dorsal digital vein. 

The accessory cephalic vein is the upward continuation of the dorsal meta- 
carpal vein and is much larger than in the horse. 

The posterior vena cava is partially embedded in the metlial Itorder of the 
liver. Its abdominal part has a thicker wall than in the horse. Its affluents 



THE VEINS 721 

correspond to the arteries of which they are satelhtes. The renal veins are large 
and thick-walled; they run obliquely forward and join the vena cava at an acute 
angle. The left one is much the longer. 

Two middle sacral veins usually accompany the artery. 

The veins of the mammary glands deserve special notice. They converge to 
a venous circle at tlie base of the udder, which is drained chiefly by two pairs of 
veins. The subcutaneous abdominal vein (anterior mammary or "milk" vein) 
is very large in animals of the dairy breeds, and its course along the ventral wall of 
the abdomen is easily followed. It is usually flexuous. It emerges at the anterior 
border of the udder about two or three inches (ca. 5-8 cm.) from the linea alba, 
runs forward (deviating a little outward) , dips under the cutaneus, passes through 
a foramen in the abdominal wall about a handbreadth from the median plane, and 
joins the internal thoracic vein. The two veins are connected by a transverse 
anastomosis at the anterior border of the base of the udder, anil each anastomoses 
behind with a branch of the external pudic vein. The external pudic vein (middle 
mammary vein) is also of consideraljle size. It ascends in the inguinal canal as a 
satellite of the artery and joins the external iliac vein. The right and left veins 
are connected at the posterior l)order of the base of the udder by a large transverse 
branch. From the latter arises the- perineal vein (posterior mammary vein), 
which runs medially upward and backward to the perineum, turns around the 
ischial arch, and joins the internal pudic vein. Two veins may present. In the 
male these veins are relatively small. 

The deep veins of the thigh and leg resemble those of the horse, but there is 
no recurrent tibial vein. 

The saphenous vein is much smaller than in the horse. It may be regarded 
chiefly as the upwartl continuation of the medial tarsal vein, which arises from the 
deep plantar arch. 

The recurrent tarsal vein' is large. It is the upward continuation of the dorsal 
metatarsal vein and anastomoses with the anterior tibial and saphenous veins. It 
arises on the lateral face of the hock, ascends at first in front of the tendo Achillis, 
then crosses the latter laterallj', passes up between the biceps femoris and semi- 
tendinosus, and joins the posterior femoral vein. 

There are three chief metatarsal veins. The large dorsal metatarsal vein 
arises at the distal part of the metatarsus by the union of the dorsal digital vein 
and a large branch from the venous arch above the sesamoids. It ascends super- 
ficially between the long and lateral extensor tendons and may be regarded as being 
continued in the leg by the recurrent tarsal vein; it also furnishes a large chief 
radicle of the anterior tibial vein. The medial plantar metatarsal vein arises from 
the venous arch above the fetlock, ascends l)etween the medial border of the sus- 
pensory ligament and the plantar surface of the metatarsal bone; it is connected 
with the corresponding lateral vein at the i>roximal end of the metatarsus by a 
transverse anastomosis, thus forming the deep plantar arch. From this the per- 
forating tarsal vein passes through the vascular canal of the metatarsus and centro- 
tarsal (as the perforating tarsal) and joins the anterior tibial vein. The lateral 
plantar metatarsal vein pursues a similar course laterally, and is continued by the 
lateral tarsal vein, which joins the recurrent tarsal vein above the hock. It passes 
superficially over the lateral face of the hock and is continued by the recurrent tarsal 
vein. 

The digital veins differ from those of the forelimb chiefly in that the dorsal 
common vein is large and the plantar absent or small. 

The dorsal common digital vein arises at the distal part of the interdigital space by the union 
of branches coming from the venous plexuses of each digit. It deviates outward at the fetlock and 
joins the lateral digital vein to form the dorsal metatarsal vein. The medial digital vein ascends 

' Also termed the external saphenous vein. 
46 



722 LYMPHATIC SYSTEM OF THE OX AND SHEEP 

along the medial surface of the medial chief digit, turns laterally above the fetlock joint, and is con- 
nected with the corresponding lateral vein to form the plantar venous arch. From this the three 
chief metatarsal veins ascend and to it come small veins from the rudimentary digits. 

The portal vein is formed usually by the confluence of two radicles, gastric 
and mesenteric. It receives the gastro-duodenal vein and veins of the pancreas. 
The gastric vein is the largest affluent. It is formed by the junction of two trunks. 
One of these, the right ruminal vein, receives the splenic vein. The other is a 
short trunk which is formed by the confluence of the left ruminal and omaso- 
abomasal veins; it receives the reticular vein. The anterior mesenteric vein is 
formed by the confluence of three chief radicles which return the blood from the 
entire intestine, with the exception of part of the duodenum and rectum; from 
these the blood is conveyed by the gastro-duodenal and internal pudic veins. The 
portal tributaries are in general satellites of the corresponding arteries. 



LYMPHATIC SYSTEM OF THE OX AND SHEEP 

The lymph glands of the ox are in general less numerous but larger than those 
of the horse; in some situations a single large gland occurs instead of a group of 
small ones, as found in the latter animal. 

The thoracic duct arises from the cisterna chyli at the hiatus aorticus. In 
some cases it remains single, as is most common in the horse, pursues a similar 
course and opens into the origin of the anterior vena cava, or into the left common 
jugular vein. But in many cases the duct divides into two branches which lie on 
the right and left sides of the dorsal face of the aorta. The two ducts are united 
by anastomotic branches and are embedded in fat. Thej' usually unite about the 
fifth thoracic vertebra. The terminal part is often ampullate, but the lymphatico- 
venous opening is small. Wlien single, the duct is 6-10 mm. in diameter. The 
duct may receive efferent vessels from the intercostal, mediastinal, and bronchial 
lymph glands. 

Many other variations have been described. In the anterior mediastinum there may be 
three or even four ducts (with connecting branches), which usually imite just before the lym- 
phatico-venous opening, but may open separately. 

The cistema chyli lies in tlic hiatus aorticus, dorsal to the aorta and ventral 
to the last thoracic and first luml)ar vertebrae. It receives the lumbar and intestinal 
lymph trunks. It is very variable in form and is commonly alaout three-fourths 
of an inch (1..5-2 cm.) wide. 

The intestinal trunk (Truncus intestinalis) is formed at the ventral face of the 
posterior vena cava, just behind the dorsal border of the liver. It results from the 
union of the common efferent vessels of the gastric and intestinal lymph glands. 

The trunk is a centimeter or less in diameter in the adult. It runs backward a short distance, 
bends sharply dorsally between the aorta and vena cava, and imites (usually) with the lumbar 
trunk to form the cisterna chyli. 

The lumbar trunk (Truncus lumbalis) is formed in the sublumbar region by 
the confluence of efferent vessels from the iliac lymph glands. It concurs with the 
intestinal trunk in the formation of the cisterna chyli. It receives efferent vessels 
of the lumbar and renal lymph glands. The trunk is very variable in regard to 
its mode of formation and two may be present. 

The mandibular lymph glands are usually two in number, one on each side. 
The gland is situated between the sterno-cephalicus muscle and the ventral part of 
the mandibular salivary gland, and is usually related dorsally to the external maxil- 
lary vein. The gland is oval and is commonly about an inch and a half (ca. 3-4 cm.) 



LYMPHATIC SYSTEM OF THE OX AND SHEEP 



723 



long and an inch (ca. 2-3 cm.) wide. In some cases a second, smaller gland is 
present. Its position is variable; it may be behind or dorsal-medial to the large 
gland, or may be on the deep face of the ventral end of the mandibular salivary 
gland. Haemolymph often occur in this vicinity. The efferent vessels come from 
the muzzle, lips, cheeks, hard palate, the anterior part of the turbinates and septum 
nasi, the gums (in part) ; the sublingual and parotid glands; the tip of the tongue, 
the muscles of the head, except those of the eye, ear, tongue, and hyoid bone; the 
mandible, premaxilla, and nasal bone ; the skin of the face in part. It also receives 
the efferent vessels of the pterygoid lymph gland when present. The efferent 
vessels, two to four in number, go to the atlantal gland. 

The parotid lymph gland (Lg. parotidea) lies on the posterior part of the mas- 
seter muscle and is partly covered by the dorsal end of the parotid salivary gland. 
It is related deeply to the internal maxillary and superficial temporal vessels and 
the superficial temporal nerve. It is about three inches (ca. 6-8 cm.) long and about 
an inch (ca. 2-3 cm.) wide. In some cases there are instead two smaller glands. 




Fig. 603.— Superfici.vl Lym 

; 2, parotid; 3, atlantal: 4. p 

S, prefemoral. (With \ 



apharyngeal; 5, anterior 
i of fig. in EUenberger-Ba 



Projected on SrRFACE of Body. 

erior cer\'iral: 0. middle cervical: 7, prescapula 



, Anat. f. Kijnstler.) 



The afferent vessels come from the muzzle, lips, the gums (in part), the anterior 
part of the turbinates and septum nasi; the parotid salivary gland; most of the 
muscles of the head, including those of the eye and ear ; the eyelids, lacrimal gland 
and external ear; the frontal, malar, nasal and premaxillary bones and the mandible; 
the skin of the head in great part. The efferent vessels, eight to twelve in number, 
go to the atlantal gland. 

The suprapharyngeal lymph glands (Lgg. suprapharyngese)' are usually two 
in number, rigjit antl left. They are situated about an inch apart, medial to the 
great cornu of the hyoid bone, and between the pharynx and the ventral straight 
muscles of the head (Fig. 386). They average about three inches (ca. 6-8 cm.) 
in length. In some cases an additional gland is present. The afferent vessels come 
from the tongue, the floor of the mouth, the hard palate, the soft palate, the gums 
(in part), the pharynx, the sublingual and mandibular salivary glands; the posterior 
' Also commonly termed the retropharyngeal glands. 



724 LYMPHATIC SYSTEM OF THE OX AND SHEEP 

part of the nasal cavity, the maxillary and palatine sinuses, and the larynx; and the 
rectus capitis ventralis major. The efferent vessels, four to eight in number, con- 
cur in forming the tracheal lymph duct. 

A small paraphar5mgeal lymph gland is usually present on the lateral wall of 
the pharynx, under cover of the mandiljular salivary gland or at its posterior border. 
It is ventral to the carotid artery and the atlantal gland. Its afferent and efferent 
vessels are similar to those of the atlantal gland. 

The atlantal lymph gland is situated ventral to the wing of the atlas, on the 
cleido-mastoideus tendon, and partly under cover of the mandibular salivary gland. 
It is related ventrally to the carotid artery. It is usually discoid and an inch and a 
half to two inches (ca. 4-5 cm.) in length. One or more small lymph nodes may 
occur near the large constant one, and small hsemolymph glands are commonly 
present here. The afferent vessels come from the tongue, the salivary glands, the 
gums in part; the cervical part of the thymus; most of the hyoid and cervical 
muscles. It also receives vessels from the parotid, mandiljular, and suprapharyn- 
geal Ij'mph glands. The efferent vessels, three to six in number, concur in forming 
the tracheal lymph duct. 

The pterygoid lymph gland (Lg. pterygoidea) , which is present in the majority 
of cases, is situated on the dorsal part of the lateral face of the pterygoid muscle, 
close to the maxillary tuberosity. It is usually about half an inch (ca. 1-1.5 cm.) 
in length and width, but may be much smaller and escape observation. Its affer- 
ent vessels come from the hard palate and adjacent part of the gums. The efferent 
vessels, to or three in number, go to the mandibular lymph gland. 

The hyoid lymph glands (Lgg. hyoidese) occur in about 20 per cent, of cases. The anterior 
hyoid gland (Lg. hyoidea oralis) lies on the thyroid cornu of the hyoid bone, at the insertion of the 
stylohyoideus muscle. It is about half an inch (ca. 1-1.5 cm.) long. It receives aiTerent vessels 
from the tongue. The efferent vessels, two or three in number, go to the atlantal gland, and may 
go in part to the suprapharjTigeal gland. The posterior hyoid gland (Lg. hyoidea aboralis) lies 
on the dorsal end of the great cornu of the hyoid bone or in the angle between the bone and the 
occipito-hyoidcus muscle. It receives lymph vessels from the mandible which issue from the 
mandibular foramen. The efferent vessels go to the atlantal gland. 

The anterior cervical lymph glands (Lgg. cervicales craniales) are situated on 
the anterior part of the trachea, along the course of the carotid artery. They are 
variable in number and size. Four or five may be present. They vary in length 
from about half an inch to two inches (ca. 1-2.5 cm.). 

The middle cervical lymph glands (Lgg. cervicales mediae) lie on each side of 
the trachea, in the middle third of the neck. They vary in position, number, and 
size. The series may extend to the anterior group, or may reach ]:)ack almost to 
the posterior group. The nimiber appears to vary from one to seven on either side. 
Their length ranges from alwut one-fourth inch to an inch or more (ca. 0.5-3 cm.). 
There are usually hsemolymph glands near them. 

The posterior cervical lymph glands (Lgg. cervicales caudales) are situated 
near the thoracic inlet. One of them lies dorsal to the manubrium sterni and the 
cervical muscles attached to it. It is usually about half an inch (ca. 1-1.5 cm.) 
long. Three or four others usually occur on either side. Of these, one is ventral 
to the brachial vein at the first rib, one or two lie on the brachial vessels here, and 
others are dorsal and ventral to the jugular vein. HsemolymiDh glands usually are 
present in the fat about this group. 

The cervical lymph glands receive afferent vessels from the ventral muscles of 
the neck, the oesophagus, the larjaix, the trachea, the thyroid gland, and the cervical 
part of the thymus. The anterior cervical glands receive efferent vessels of the 
atlantal gland. The efferent vessels go in general to the tracheal lymph ducts, but 
efferents from some of the posterior group may go to the terminal part of the thora- 
cic duct or to the common jugular vein. 



LYMPHATIC SYSTEM OF THE OX AND SHEEP , 725 

The costo-cervical lymph gland (Lg. costo-cervicalis)^ is situated lateral to the 
trachea and oesophagus and tlorsal to the carotid artery and the vago-sympathetic 
trunk. It lies usually just in front of the first rib, under cover of the scalenus 
muscle, but it may be partly medial to the first rib. Its length varies from about 
half an inch to an inch or more (1.5-3 cm.). Its afferent vessels come from the 
muscles of the neck and shoulder, the costal pleura, the trachea, and the intercostal 
and anterior mediastinal glands. The efferent vessels on the right side usually go 
to the right tracheal duct or join the efferent vessel of the prescapular gland; on the 
left they go most often to the end of the thoracic duct, but are very variable. 

The tracheal lymph ducts (Ductus tracheales), right and left, are formed 
essentially by the confluence of efferent vessels from the atlantal gland. They 
usually receive efferent vessels from the cervical, costo-cervical, and prescapular 
glands. The ducts pass along each side of the trachea and oesophagus; the right 
one usually opens into the right common jugular vein; the left one joins the terminal 
part of the thoracic duct or opens into the left common jugular vein. 

These ducts are very variable in regard to formation, affluents, and termination. There 
may be an accessory tracheal duct, which receives part of the lymph vessels that otherwise go to 
the chief duct; this accessory duct runs a variable distance along the neck practically parallel 
with the chief duct, and imites with the latter. 

A short right lymphatic duct may be formed by the junction with the terminal 
part of the right tracheal duct of efferent vessels from the right cervical, costo-cer- 
vical, and prescapular lymph glands. It also usually receives an efferent vessel 
from the anterior sternal Ijaiijjh gland. 

The prescapular or posterior superficial cervical lymph gland (Lg. cervicalis 
superficialis caudalis) is situated at the anterior border of the supraspinatus, a little 
above the level of the shoulder joint; it is covered by the omo-transversarius and 
brachiocephalicus muscle. It is elongated and may attain a length of four or five 
inches (ca. 10-12 cm.) and a mdth of an inch or more (ca. 3 cm.). Its deep face 
has a long and distinct hilus. It receives afferents from the skin of the neck, 
shoulder, part of the ventral and lateral surfaces of the thorax, and the thoracic 
limb; from the muscles of the shoulder-girdle, and from the external scapular 
muscles; from the tendons of the muscles of the forearm and digit and the fascia 
of the forearm; from the joints of the carpus and digit. The efferent vessel de- 
scends over the scalenus muscle and opens on the right side into the end of the right 
tracheal duct, on the left into the terminal part of the thoracic duct or the left 
tracheal duct. 

In one case Baum found two efferent vessels on the right side: one opened mto the end of 
the tracheal duct, the other went to a posterior cervical gland. 

A chain of small nodes, five to ten in number, extends along the border of the supraspinatus, 
dorsal to the prescapular gland, and covered by the trapezius and omo-transversarius. These 
nodes, termed by Baum lymphoglandulae cervicales nuchales, are in most cases dark red in color, 
and most of them are hsemolymph glands. But some are lymph glands, since they receive afferent 
vessels from adjacent muscles and send efferent vessels to the prescapular lymph gland or to 
another gland of the group. 

The intercostal lymph glands are situated in the dorsal ends of the intercostal 
spaces, on the course of the intercostal vessels, and embedded in fat. Most of them 
are small, but some may be nearly an inch (ca. 2 cm.) long. Not all of the spaces 
contain glands, and quite exceptionally two may occur in one space. Associated 
with them are haemolymph glands. The afferent vessels come chiefly from the 
intercostal and spinal muscles, the serrati, latissimus dorsi, trapezius, subscapularis, 
longus colli, obliquus abdominis externus; from the costal pleura and the peri- 
toneum; from the thoracic vertebrae and the ribs. The efferent vessels go to the 
mediastinal lymph glands. 

' This gland has been included in the posterior cervical group, but forms a connecting link, 
as it were, between the cervical and mediastinal glands. Baum has given it the above name and 
has shown that it receives lymph vessels from the pleura. 



726 LYMPHATIC SYSTEM OF THE OX AND SHEEP 

The dorsal mediastinal Ijrmph glands (Lgg. mediastinales dorsales) are situated 
on each side of the thoracic aorta, in the fat which levels up the space Ijetween that 
vessel and the bodies of the vertebrae. On the right side they lie chiefly dorsal to 
the thoracic duct, and on the left side they are related to the vena hemiazygos. 
They are irregular in arrangement and their length varies from about half an inch 
to an inch and a half (ca. 1-3.5 cm.). They are in series with the anterior medias- 
tinal glands. 

Their afferent vessels come from the same parts as those of the intercostal 
glands; also from the diaphragm, the mediastinum, the pericardium, the ribs, and 
the intercostal lymph glands. The efferent vessels go chiefly to the thoracic duct 
or join the common efferent duct of the posterior mediastinal glands. 

The ventral mediastinal lymph glands (Lgg. mediastinales ventrales) are 
situated on the transversus thoracis muscle. Several (2-5) occur constantly in 
the fat about the apex of the pericardium; they vary in length from about half an 
inch to an inch or more (ca. 1-3 cm.). In some cases other glands are present 
further forward. The afferent vessels come from the costal and mediastinal 
pleura, the diaphragm, the pericardium, and the ribs. The efferent vessels usually 
unite to form a trunk which goes to the anterior sternal lymph gland. Hsemolymph 
glands may be present in this region. 

The anterior mediastinal lymph glands (Lgg. mediastinales craniales) are 
situated in part at the thoracic inlet, in part along the oesophagus, trachea, anterior 
vena cava, and brachiocephalic trunk. The former group comprises two to four 
glands on either side, ventral to the trachea and cEsophagus. Usually the largest 
of these, which may be an inch or more (ca. 2-3 cm.) in length, lies along the origin 
of the internal thoracic artery. The second group differs somewhat on the two sides. 
On the right side there is usually a large gland, which may be two or three inches 
(ca. 5-7 cm.) in length; it lies on the oesophagus and is crossed laterally by the 
dorsal vein. Behind this there are commonly two or three glands on the oesophagus 
or the longus colli, and in front two or three are placed similarly and on the trachea. 
On the left side a varial^le number (2-7) are situated on the oesophagus, trachea, 
brachiocephalic trunk, and anterior vena cava; glands may be between the vessels, 
or between the vessels and the trachea, and escape superficial examination. HiBnio- 
lymph glands are often present in the vicinity of these glands. The afferent vessels 
come from the thoracic part of the oesophagus, trachea, and thymus; from the lungs, 
pericardium, heart, costal and mediastinal pleura; from the intercostal glands of 
the first four spaces and from the gland on the apical bronchus. In some cases these 
glands receive also efferent vessels from the anterior sternal, left bronchial, and 
other mediastinal glands. The efferent vessels for the most part go to the thoracic 
duct, the right tracheal duct, and the costo-cervical glands. 

The posterior mediastinal lymph glands (Lgg. mediastinales caudales) are 
situated along the oesophagus, from tlie aortic arch backward. The largest of these 
may be eight inches (ca. 20 cm.) or more in length; its anterior part is dorsal to the 
oesophagus, while posteriorly it lies in the angle between the aorta and the diaphragm 
(Fig. 389). But in some subjects there are two glands in place of this large one; in 
these cases the additional posterior one is usually the smaller. Several other glands 
of smaller size lie in front of the large one, in the angle between the aorta and the 
oesophagus. In front of these there are usually two or three on the right side on the 
aorta and the oesophagus.^ The afferent vessels come from the oesophagus, the 
lungs, the pericardium, the mediastinum, the diaphragm, the peritoneum, the liver, 
and the spleen. The efferent vessels unite to form a common trunk which joins the 
thoracic duct. 

The diaphragmatic lymph glands (Lgg. diaphragmaticse) are small nodes which 
may be present at the foramen venae cavae and the termination of the phrenic 
1 These are termed by Baum the middle mediastinal lymph glands. 



LYMPHATIC SYSTEM OF THE OX AND SHEEP 727 

nerves. The one most often present is at the acute angle between the vena cava 
and the diaphragm. The afferent vessels come from the diaphragm and medias- 
tinum. The efferent vessels go to the posterior mediastinal glands. 

The bronchial l3nnph glands (Lgg. bronchiales) are situated on the termination 
of the trachea and on the bronchi. Commonly three or four are present. One (Lg. 
bifurcationis sinistra) constantly occurs on the left side in the angle between the aortic 
arch and the left division of the pulmonary artery (Fig. 389) ; it is crossed laterally 
by the vena hemiazygos. This gland is about an inch to an inch and a half (ca. 2.5- 
3.5 cm.) in length and an inch (ca. 2.5 cm.) in width; it is often very irregular in 
shape. A gland (Lg. bifurcationis dextra) is similarly situated on the right side in 
the majority of cases. It is smaller than the left gland and appears to be absent 
in about 25 per cent, of subjects; in some cases, on the other hand, two glands occur 
here. In about half of the cases a small gland (Lg. bifurcationis dorsalis) is situated 
above the bifurcation of the trachea. Another gland (Lg. eparterialis) occurs at the 
origin of the bronchus of the apical lobe of the lung. Exceptionally a second small 
gland is present here. The afferent vessels of these glands come chiefly from the 
lungs and the pulmonary lymph glands, the thoracic part of the oesophagus, and the 
heart. ^ The efferent vessels of the left gland are quite variable. They may join the 
common efferent of the posterior mediastinal glands. Those of the right gland go 
to a middle mediastinal gland, those of the dorsal gland go to the right gland, and 
those of the apical gland go to anterior mediastinal glands. 

The pulmonary lymph glands (Lgg. pulmonales) are inconstant and variable 
nodes which may be found on the chief bronchi in the lungs. They appear to be 
absent in one-third to one-half of the cases on one side or both. They vary in size 
from a fifth to half an inch or more (ca. 0.5-1.5 cm.) in length. The afferent vessels 
come from the lungs, and the efferent vessels go to the bronchial and posterior 
mediastinal glands. 

It is worthy of note that in some ca.ses lymph vessel.s of the left lung go to glands on the right 
(middle mediastinal ghxnds), and lymph vessels of the right lung go to the left bronchial gland. 

The pericardiac l5rmph glands (Lgg. pericardiacse) are small and variable nodes 
which lie on the pericarclium. The left gland is usually present and is situated at 
the space between the aortic arch and the vena hemiazygos. In some cases it may 
be unusually large — nearly three inches (ca. 7 cm.) in length — and extend back to 
the left bronchial gland. Other small glands may be found in this vicinity or lower 
down. The right gland is only exceptionally present. It is situated just ventral 
to the termination of the posterior vena cava. The afferent vessels come from the 
pericardium, and the efferents go to the dorsal mediastinal glands (or their efferents) 
or to the left bronchial gland on the left side, to the apical bronchial gland or an 
anterior mediastinal gland on the right side. 

The sternal lymph glands (Lgg. sternales) are situated along the course of the 
internal thoracic vessels. The largest, distinguished as the anterior sternal gland 
(Lg. sternalis cranialis), is embedded in the fat in front of the transversus thoracis. 
It is about half an inch to an inch (ca. 1.5-2.5 cm.) in length. The other glands are 
covered by the transversus thoracis, and vary in size, number, and arrangement. 
There is not one at every interchondral space, and, on the other hand, two may occur 
at one space. The last of the series is often situated in the angle between the eighth 
and ninth costal cartilages and the sternum and may escape notice." The afferent 
vessels come from the diaphragm, the intercostal, deep pectoral, serratus ventralis, 
rectus thoracis, and abdominal muscles; the costal and mediastinal pleura, the 

' Baum notes the curious fact that in many cases in which he injected the lymph vessels of 
the diaphragmatic lobes the vessels went around the dorsal gland without entering it. 

^ Attention was recently drawn to this gland by Stroh, who designated it the xiphoid glands. 
It is not always present. 



728 LYMPHATIC SYSTEM OF THE OX AND SHEEP 

pericardium, the peritoneum; the Hver; the ribs, costal cartilages, and sternum; 
the ventral mediastinal glands. The efferent vessels usually concur in forming 
one or two trunks which run forward along the internal thoracic vessels to the 
anterior gland. From the latter one or two efferents go to the anterior mediastinal 
glands or directlj^ to the end of the right tracheal duct or the thoracic duct (on the 
left side). 

The axillary lymph gland lies on the medial face of the distal part of the teres 
major on the course of the vein from the latissimus dorsi. It is oval in outline and 
is usually a little more than an inch (ca. 3 cm.) in length. Quite exceptionally two 
glands may be present. The efferent vessels come from most of the muscles of the 
shoulder and arm, the muscles of the forearm, the trapezius, latissimus dorsi, pec- 
toralis profundus, and cutaneus; the fascia of the forearm; the shoulder, elbow, and 
carpal joints; the scapula, humerus, radius, ulna, and carpus; the infraspinatus 
gland. The efferent vessels (one to three) go to the posterior cervical glands. 

The infraspinatus lympli gland (Lg. infraspinata) is a small node which is present in 
somewhat less than a fourth of the cases (Baum). It is situated at or near the posterior border of 
the infraspinatus, about on a level with the proximal end of the caput longuni. It receives lymph 
vessels from the latissimus dorsi and sends an efferent vessel to the axillary gland. 

The rhomboid lymph gland (Lg. rhoniboidea) is .small and only present in about 15 per 
cent, of subjects (Hauin). It is situated under the rhomboideus cervicalis near its ventral border 
and the cervical angle of the scapula. It receives afTercnts from the rhomboideus, supras- 
pinatus, and serratus -v-cntralis, and sends efferents to the costocervical gland. 

The lumbar lymph glands (Lgg. lumbales) are situated along the abdominal 
aorta and the posterior vena cava, and in some of the spaces between the transverse 
processes.^ Some of the glands are dorsal to the vessels. Hsemolymph glands also 
occur in this region. The afferent vessels come from the spinal, sublumbar, ab- 
dominal, and serratus dorsalis muscles; the lumbo-dorsal fascia; the kidneys, 
adrenals, and the peritoneiun; the lumbar vertebra^. The efferent vessels go to 
the lumbar trimk and the cisterna chyli. 

The renal lymph glands (Lgg. renales) belong in reality to the preceding group, 
from which the\' are only conventionally distinguished. They are situated on the 
course of the renal vessels and vary m size and number. Their afferent vessels come 
from the kidneys and adrenals, and the efferent vessels go mainly to the cisterna 
chjli. 

The cceliac lymph glands (Lgg. coeliacse), two to five in number, are situated on 
and near the ca'liac and anterior mesenteric arteries, and in relation to the left 
extremity of the pancreas, the dorsal curvature of the rumen, and the posterior 
vena cava. One is a large discoid gland which lies on the coeliac artery and the 
origin of the chief branches of that vessel (Fig. 389). It is heart-shaped, marked 
by a deep notch, and is aliout two inches (ca. 5-6 cm.) long and an inch and a half 
(ca. 3-4 cm.) wide. Their afferent vessels come from the spleen. The efferent 
vessels go to the common efferent vessel of the gastric lymph glands, or to the 
intestinal trunk, or to the cisterna chyH. 

The internal iliac lymph glands are situated in relation to the terminal branches 
of the aorta and the radicles of the posterior vena cava. They number commonly 
six to eight and vary in length from half an inch to two inches (ca. 1-5 cm.). Their 
afferent vessels come chiefly from muscles of the sublumbar region, pelvis, tail, and 
thigh; from the genital organs; from the kidneys, bladder, and urethra. They also 
receive vessels which are efferents of the external iliac, sacral, ischiatic, deep in- 
guinal, prefcmoral, and coxal glands. Their efferent vessels go chiefly to the luml^ar 
trunk. 

1 Baum distinguishes those about the vessels as lgg. lumbales aortica", and terms those in 
the intertransverse spaces lgg. lumbales proprise, and regards them as corresponding to the dorsal 
mediastinal and intercostal .glands respectively. 



LYMPHATIC SYSTEM OF THE OX AND SHEEP 729 

The deep inguinal lJ^nph glancU is situated ventral to the psoas minor, at the 
angle of divergence of the circumflex iliac from the external iliac artery. It is 
discoid and is commonly two to three inches (ca. 5-7.5 cm.) in length. A smaller 
gland may be present near the large one or at the origin of the prepubic artery. The 
afferent vessels come chiefly from the abdominal muscles; the pelvic limb; the 
urinary organs, the vesiculse seminales, tunica vaginalis, cremaster muscle; and 
the superficial ingumal, external iliac, sacral, prefemoral, and popliteal glands. 
The efferent vessels go in part to the internal iliac glands, in part dii-ectlj' to the 
lumbar trunk. 

The external iliac lymph glands (Lgg. iliacee laterales) number one or two on 
each side, and are situated at the bifurcation of the circumflex iliac artery. In the 
majority of cases a single gland is found just in front of the origin of the anterior 
branch of the artery, but another may lie in the angle between the two branches. 
The more constant one is half an inch to an mch (ca. 1.25-2.5 cm.) in diameter. 
They may be absent on one side or (quite exceptionally) on both sides. The 
afferent vessels come from the abdominal muscles, the gluteus profundus, the tensor 
fasciae latse, the fascia lata; the peritoneum of the adjacent region; the pelvic bones. 
They also receive vessels from the prefemoral and coxal glands. The efferent ves- 
sels go in part to the lumbar trunk, in part to the internal iliac or deep inguinal 
glands. 

The epigastric lymph gland (Lg. epigastrica) is small and inconstant. It is situated 
on the course of the posterior abdomuial artery near the pubis. It receives afferent vessels from 
the adjacent part of the peritoneum and abdominal muscles, and sends an efferent vessel to the 
deep mguinal gland. 

The paralumbar lymph glands (Lgg. paralumbales) are small and inconstant 
nodes, one or two in nuniljer, which may be found under the skin of the upper part 
of the flank. Their afferent vessels come from the adjacent skin, and the efferents 
go in part to the prefemoral gland, in part to the deep inguinal gland. Hsemolymph 
glands occur in this region. 

The superficial inguinal lymph glands (Lgg. inguinales superficiales) differ in 
the two sexes. (1) In the bull they are situated below the prepubic tendon and in 
the narrow interfemoral space. They lie in the mass of fat about the neck of the 
scrotum and behind the spermatic cord, and are covered (in part) by the retractor 
of the prepuce. It is usual to find one or two on each side of the penis, but in ex- 
ceptional cases one or two more may be present. A central one above the penis 
has been observed, and there may be one further back. The afferent vessels come 
from the external genital organs (except the testicles) ; also from the skin of the 
adjacent region, the medial and posterior surface of the thigh, and the medial sur- 
face of the leg. The efferent vessels ascend through the inguinal canal to the deep 
inguinal gland at the side of the pelvic inlet. (2) In the cow they are usually 
termed the supramammary lymph glands (Lgg. supramammaricse), since they are 
situated above the posterior border of the base of the mammary glands.^ Usually 
two are present on either side. The larger ones are in apposition medially and are 
sometimes united. The smaller glands are above or in front of the large ones. 
Exceptionally a third gland may be present or there may be only one on one side. 
The large glands are usually two or four inches (ca. 6-10 cm.) long, the smaller 
ones a fourth to one-half as large. The afferent vessels come from the udder, the 
external genital organs, and part of the skin of the thigh and leg. The efferent 
vessels converge to two or three large trunks which go to the deep inguinal glands 
at the side of the pelvic inlet. 

' This gland, designated by Chauveau-Lesbre as external iliac, is here named in accordance 
with the observations of Baum, who found that it, together with the deep femoral gland, derives 
its afferent vessels from substantially the same region as the deep inguinal glands of the horse. 

= When enlarged, they can easily be felt, and when much enlarged, may produce a prominence. 



730 LYMPHATIC SYSTEM OF THE OX AND SHEEP 

The efferent vessels run forward on the base of the udder, then incline outward and pass 
through the aponeuroses of the obhque abdominal muscles at the lateral edge of the rectus ab- 
dominis, a handbreadth or more in front of the pubis. On reaching the femoral ring they follow 
the course of the external iliac vessels to the deep inguinal gland. When the deeper gland (Ig. 
profmida femoris) is present, some efferents go to it. Baum has recorded the remarkable fact that 
efferents of one side may go to a supramammary or deep inguinal gland of the opposite side. 

The sacral lymph glands (Lgg. sacrales) may be subdivided into two groups.^ 

(1) The internal sacral lymph glands (Lgg. sacrales mediales) are quite m- 
constant. When present, there is a gland on either side on the deep surface of the 
sacro-sciatic ligament, in the fat between the ligament and the rectum or the re- 
tractor ani. Its afferent vessels come from the pelvic urethra and urethral muscle, 
the root of the penis and its muscles, the prostate, the vagma and urethra, and the 
coccygeal muscles. The efferent vessels usually go to the mtemal iliac glands. 

(2) The external sacral lymph glands (Lgg. sacrales laterales) comprise one 
or two mconstant nodes on the upper part of the outer surface of the sacro-sciatic 
ligament. One occurs in the majority of cases at the greater sciatic foramen; the 
other, which is further back, under the origin of the biceps femoris, is absent on one 
side or both in more than half the cases. Their afferent vessels come from the 
gluteus profundus, the luml)o-dorsal fascia, the pelvic bones, and the hip jomt. 
The efferent vessels go to the internal iliac and deep inguinal glands. 

The ischiatic lymph glands (Lgg. ischiadicse) are one or two in number. The 
one which appears to be constant lies on the sacro-sciatic ligament, about an inch 
(ca. 2-3 cm.) above the lesser sciatic notch, and mider cover of the biceps femoris. 
It is discoid and is an inch or more (ca. 2.5-3.5 cm.) in diameter. A second gland 
occurs in the majority of cases at the medial side of the tuber ischii and the attach- 
ment of the sacro-sciatic ligament, covered only by the skin and subcutaneous fat.^ 
The afferent vessels come from the rectum and anus; the vulva, the root of the 
penis, the prostate, the bulbo-urethral glands, the urethra and urethral muscle; 
the glutei, biceps femoris, semitendinosus, obturator mternus, and gemellus, and 
the lumljodorsal fascia; the skin of the hip and tail; the hip joint. They also 
receive efferent vessels of the popliteal gland. The efferent vessels go to the internal 
iliac glands.* 

The gastric lymph glands (Lgg. gastricse) are numerous, as might be expected, 
and are difficult to group satisfactorily. They comprise the follo%ving: 

(1) The atrial lymph glands (Lgg. atriales) lie chiefly on the visceral surface 
of the atrium, just behind the cardia; commonly three or four are present. Their 
afferent vessels come from the atrium, from the adjacent part of the rumen and 
reticulum, and from the spleen. They receive efferent vessels of the right and 
anterior rummal, reticular, omasal, and dorsal abomasai glands. Their efferent 
vessels commonly converge to a large trmik, the common efferent vessel (Vas 
efferens commune) of the gastric lymph glands. This rims upward and backward 
in relation to the cceliac artery and reaches the ventral face of the posterior vena 
cava; here it miites wdth the common efferent vessels of the mesenteric glands to 
form the intestinal trimk. 

(2) The right ruminal lymph glands (Lgg. ruminales dextrse) lie along the 
course of the right ruminal artery. Commonly four or five are present, and they 
are half an inch to an inch and a half (ca. 1-3.5 cm.) long. Their afferent vessels 
come chiefly from the rumen. They also receive efferent vessels of the other 
rmninal glands. The efferent vessels go from the anterior part of the series to the 
reticular glands and the common gastric efferent. 

' Baum distinguishes three groups of sacral glands and terms the glands about the termina- 
tion of the aorta and the origin of the vena cava as the lgg. sacrales hypogastricae. These have 
been included in the internal iliac group of this description. 

^ This gland is termed by Baum the Ig. tuberosa. 

' Many variations occur in the arrangement of those efferent vessels. An efferent may go 
to a coeliac or mesenteric gland or to the intestinal trunk or cisterna chyli directly. 



LYMPHATIC SYSTEM OF THE OX AND SHEEP 731 

(3) The left rmninal lymph glands (Lgg. ruminales sinistrae) are inconstant. 
One or two may be present in tlie left groove of tlie rumen. Thieir afferent vessels 
come from the rmnen, and tlie efferent vessels go to the anterior or the right ruminal 
glands. 

(4) The anterior ruminal glands (Lgg. ruminales craniales) are deeply situated 
in the anterior groove of the rumen. They average four or five in number and about 
half an inch (ca. 1.5 cm.) in length. They receive Ijanph vessels from the rumen 
and from the left ruminal glands, and their efferent vessels go to the right ruminal 
and atrial glands. 

(5) The reticular lymph glands (Lgg. reticulares) are situated on the reticulum 
above and below its junction with the omasum. They receive afferent vessels 
chiefly from the reticulum and the adjacent parts of the omasum and abomasum. 
Their efferent vessels go chiefly to the atrial Ijinph glands. 

(6) The omasal lymph glands (Lgg. omasicse) lie on the omasum chiefly along 
the course of the dorsal omasal vessels. Their afferent vessels come from the 
omasum, and the efferent vessels go chiefly to the atrial lymph glands. 

(7) The dorsal abomasal lymph glands (Lgg. abomasicae dorsales) form a series 
along the lesser curvature of the abomasum. They receive afferent vessels from 
the abomasum, duodenum, and ventral part of the omasum. The efferent vessels 
go chiefly in the lesser omentum to the hepatic lymph glands, but some from the 
anterior part of the series go to tlie omasal and reticular glands. 

(8) The ventral abomasal lymph glands (Lgg. abomasicae ventrales) comprise 
a few nodes in the fat along the greater curvature of the pyloric part of the abo- 
masum or in the omentum an inch or two distant from the abomasum. "^ They 
receive afferent vessels from the abomasum and the duodenum and their efferent 
vessels go to the hepatic lymph glands. 

The mesenteric lymph glands (Lgg. mesentericae) comprise a large number of 
nodes which receive lymph from the intestine. The following groups may be 
recognized, although the distinction is in part conventional. 

(1) The duodenal lymph glands (Lgg. duodenales) are small nodes in the 
anterior part of the mesoduodcnum. They receive afferent vessels from the duo- 
denum and their efferent vessels go to the hepatic lymph glands. 

(2) The jejuno-ileal lymph gland (Lgg. jejuno-ileales) lie in the part of the 
mesentery to which the coils of the jejuno-ileum are attached. They vary in 
number from ten to fifty, and in length from about a quarter of an inch to four feet 
(ca. 0.5-120 cm.) . As a rule, the long narrow glands are in the peripheral part of the 
mesentery, while numerous small nodes are scattered throughout the mesentery 
and extend centrally to the coils of the colon. Their afferent vessels come from the 
mesenteric part of the small intestine. The efferent vessels converge to form a 
large common efferent vessel. This receives efferent vessels of the caecal and colic 
lymph glands, runs upward and forward on the right side of the spiral mass of the 
colon, and reaches the ventral face of the posterior vena cava just behind the an- 
terior mesenteric artery; here it unites with the common efferent vessel of the 
gastric IjTiiph glands to form the intestinal trunk. 

(3) The cascal lymph glands (Lgg. caecales), usually not more than two or three 
in number, are situated along the attached surface of the caecum. Their efferent 
vessels come from the caecum and ileum. The efferent vessels go to colic or ileal 
glands or to the common efferent vessel. 

(4) The colic lymph glands (Lgg. colicae) are situated in part superficially on 
the right side of tlie spiral mass of the colon, in part deeply between the coils. One 
or two are constantly present on the initial part of the colon, near the termination 
of the ileum. The afferent vessels come from the colon chiefly, but some of the 

• These glands are often difficult, to find in the large mass of fat in which they are usually 
embedded; they are not always present. 



732 LYMPHATIC SYSTEM OF THE OX AND SHEEP 

glands receive vessels from the ileum and caecum and their lymph glands. The 
efferent vessels go to the common intestinal efferent or to other colic glands. 

(5) The rectal lymph glands (Lgg. rectales) are situated along the dorsal and 
lateral surfaces of the rectmn. They receive afferent vessels from the rectum, 
anus, and terminal part of the colon. ]\Iost of the efferent vessels go to other 
glands of the group, but some unite to form one or two large trunks which end in the 
internal iliac lymph glands. There are many small hsemolymph glands in relation 
to the rectal lymph glands. 

(6) The pancreatico-intestinal Ijrmph glands (Lgg. pancreatico-intestinales) 
lie on the ventral surface of the pancreas and along the right part of the latter in 
relation to the duodenum. Some are at the pancreatic notch about the portal vein 
and its affluents, and others are covered by the adhesion of the colon to the gland. 
Their afferent vessels come from the pancreas, the duodenum, and the adjacent 
part of the colon. The efferent vessels go to the common intestinal efferent. 




Fig. 604. — Intestine of Ox, Spread Out. 
r«, Caecum; C, colon; D, duodenum; //, ileum; J, jejunum; R, rectum; m, mesenteric lymph glands. (After 

Edelmann.) 

(7) The hepatic lymph glands (Lgg. hepaticae) are situated in and ventral to 
the portal fissure. Most of them are grouped about the portal vein, the hepatic 
artery, and the bile duct, and are covered by the pancreas; but some are ventral 
to the pancreas. Their average number is ten to fifteen, but twenty or more have 
been counted. Their length varies from less than half an inch to three inches (ca. 
1-7 cm.). They receive vessels from the liver, pancreas, and tluodenum, and from 
the abomasal lymph glands. Their efferent vessels converge to a large trunk 
which passes along the jiortal vein and joins the common efferent vessel of the 
intestinal glands or that of the gastric glands. 

The pref amoral or subiliac lymph gland' is situated on the aponeurosis of the 

obliquus abdominis externus, at the anterior border of the tensor fasciae latiB and 

about a handlsreadth above the patella. It has an elongated elliptical outline 

and is flattened. Its average length is three or four inches (ca. 8-10 cm.), and its 

■ This is also termetl the precrural or suprapatellar gland. 



LYMPHATIC SYSTEM OF THE OX AND SHEEP 733 

wadth about an inch (ca. 2.5 cm.) in the adult, but it may be considerably larger. 
In some cases a second small gland is present alcove or below the large one. It 
receives afferent vessels from the skin of the posterior part of the thorax, the ab- 
domen, pelvis, thigh, and leg; also from the tensor fasciffi latae and the prepuce. 
The efferent vessels ascend on the deep face of the tensor fasciae latse and end 
chiefly in the deep inguinal gland, but in some cases some go to the iliac glands. 

The popliteal lymph gland (Lg. poplitea) is situated in a mass of fat on the 
gastrocnemius nuisclo, behind the tibial and peroneal nerves and between the biceps 
femoris and semitendinosus. Its average length is about an inch and a half (ca. 
3^ cm.) and its width about an inch (ca. 2-3 cm.). The gland receives afferent 
vessels from the lateral and posterior part of the leg and from the distal part of the 
limb; vessels from the biceps femoris and semitendinosus also go to it. The 
efferent vessels go chiefly to the deep inguinal gland, but some end in the ischiatic 
or internal iliac glands. 

The coxal lymph gland (Lg. coxalis) is situated in front of the proximal part of 
the quadriceps femoris, under cover of the tensor fasciee latse. It is present in the 
majority of subjects on one side or both and may be an inch or more (ca. 2.5-3 cm.) 
in length. It receives vessels from the quadriceps femoris, tensor fasciae latse, 
fascia lata, and the prefemoral gland.' The efferent vessels go to the iliac or the 
deep inguinal glands. 

One or two Ijmiph glands are commonly present on the superficial face of the 
tensor fasciae latae, an inch or two from the anterior border of the muscle and five 
or six inches from the tuber coxte. They are often partially embedded in the muscle, 
and are usually small, but may be almost an inch (ca. 2 cm.) long. Haemolymph 
glands may be found here and in some cases appear to take the place of the Ijmiph 
gland. The afferent vessels come from the skin of the hip and the efferent vessels 
go to the prefemoral or deep inguinal gland. 

The lymph glands of the sheep resemble in general those of the ox, but a few 
special features may be noted. Hemohinph glands are numerous, especially along 
the course of the aorta; they are dark red or black and hence are easily seen, in 
spite of their small size, in the fat in which they are chiefly embedded. 

The mandibular l5rmph glands are usually two in number on each side, and are 
situated behind the angle of the jaw on the course of the external maxillary vein. 
The larger one is flattened and kidney shaped and may be nearly an inch (ca. 2 cm.) 
long. 

The parotid lymph gland lies on the posterior border of the masseter muscle, 
about midway between the mandibular joint and the angle of the jaw. It is 
related to and commonlj^ partly covered by the anterior border of the parotid 
salivary gland. It is flattened and has a deep notch posteriorly. It is usually a 
little less than an inch (ca. 2 cm.) long. 

The suprapharyngeal lymph glands, two in number, have an elongated oval 
outline. They are situated on the dorsal wall of the pharjmx, a quarter of an inch 
or less (ca. 0.5 cm.) apart. They are related laterally to the dorsal end of the great 
cornu of the hyoid bone, and dorsally to the ventral straight muscles of the head. 
They are about an inch (ca. 2-3 cm.) long, and half as -wide. 

The atlantal l5Tnph gland is related to the ventral part of the parama.stoid 
process and is dorsal to the carotid arterJ^ It is discoid, oval in outline, and about 
half an inch (ca. 1.5 cm.) long. Commonly there is a small node behind the at- 
lantal gland and one or more haemoljanph glands occur here. 

The sternal lymph gland, which overlies the first segment of the stenmm, is 
about the size of a hazel nut. 

The mesenteric lymph glands consist chiefly of long narrow elongated masses 
instead of isolated small nodes. 

The prefemoral lymph gland is in front of the anterior border of the tensor 



734 



CIRCULATORY SYSTEM OF THE PIG 



fasciae latse, about midway between the tuber coxse and the patella. It is kidney- 
shaped and is a little more than an inch (ca. 3 cm.) long and nearly an inch (ca. 
2 cm.) wide. 

The superficial inguinal or mammary lymph glands are usually two in number 
on each side. The larger one is kidney-shaped; it may be an inch and a half (ca. 
3..5 cm.) long and about half as wide. The smaller gland is oval and usually about 
half an inch (ca. 1 cm.) in length. 



CIRCULATORY SYSTEM OF THE PIG 

THE HEART 

The pericardium is attached to the sternum from a point opposite to the third 
rib as far as the xiphoid cartilage, and also to the sternal part of the diaphragm. 



Vena hemiazygos 



Aorta 

Left brachial artery -Jj 

Pulmonary arlery ~!^^ 
Brachiocephalic 
artery \ 



Anterior vena 
cava 
Right auricle 




Pulmonary veins 



Posterior verm 
cava 



Left auricle 
Left ventricle 



Right ventricle 



Fig. 605.— Heart or Pig; Left Vi 
1, Conus arteriosus; 2, great cardiac vein in left longitudinal groove: S, cardii 



intermediate groove; 4> apex. 



It has extensive contact with the chest wall from the second intercostal space to the 
fifth rib. 



THE HEART 



735 



The heart is small in proportion to the body-weight, especially in fat animals. 
Its weight in a large adult is usually less than a pound. It is broad, short, and blunt. 
When hardened in situ it is compressed dorso-ventrally. The ventral or sterno- 
costal surface (Facies sternocostalis) is only moderately convex; it overlies the 
sternum from the second sternebra to the anterior part of the last one. The left 
longitudinal groove is on its left part, and is almost parallel with the left border. 
The dorsal or diaphragmatic surface is more convex. The right longitudinal groove 
runs oblicjuely across this surface ; it begins below the end of the posterior vena 
cava and extends to the left border. There is often an intermediate groove on the 
left border; it may extend to the apex, but it is frequently small and is sometimes 



Vena hemiazygos 
Pulmonary artery 
Left au: 



Left ventricle 




Right ventricle 



Fig. 606. — Heart of Pig, Diaphragmatic Surface. 

1-6. Pulmonary veins; 6, left pulmonary artery; 7, 8, branches of right pulmonary artery; 9, vena azygos; 10, 

fat in coronary groove; 11, vessels and fat in right longitudinal groove; 13, apex. 



absent. The apex is blunt and is almost median; it overlies the anterior part of 
the last sternebra, and is about a quarter of an inch (ca. 5-6 mm.) from the sternal 
part of the diaphragm. When the ventricles are dilated, there is a notch at the apex 
(Incisura apicis cordis). The lower border of the left auricle is marked by several 
notches and is situated at a lower level than the right one. 

In the right atrium the large orifice of the vena hemiazygos is seen below that of the posterior 
vena cava; the two are separated by a valvular fold with a concave free edge. The intervenous 
crest is broad and rounded, not prominent, as in the horse. The musculi pectinati radiate from 
a distinct crista terminalis and form a highly developed network in the auricle. The fossa 
ovalis is extensive. There is a large moderator band in the right ventricle. 



736 CIRCULATORY SYSTEM OF THE PIG 

The Arteries 

The pulmonary vessels present no remarkable features. 

The aorta resembles that of the horse and ox in its course and relations, but the 
arch is much more strongly curved. There is no common brachiocephalic trunk. 

The brachiocephalic artery arises first from the aortic arch and jjasscs forward 
below the trachea to the first rib. Here it gives off the common carotid arteries, 
separately or by a very short bicarotid trunk, and is continued around the first rib 
as the right brachial artery. 

The left brachial artery arises from the aortic arch just above the brachio- 
cephalic. It curves forward and do\\iiward and turns around the anterior border 
of the first rib. 

The branches given off by the brachial arteries are as follows: 

There is usually a common trunk for the dorsal, dec]! cervical, and vertebral 
arteries. This trunk or the dorsal artery gives off the subcostal artery, which sup- 
plies usually the third, fourth, and fifth intercostal arteries. The second inter- 
costal artery arises separately. The dorsal artery emerges through the dorsal end 
of the second intercostal space and tlivides into dorsal and cervical branches ; the 
dorsal branch passes upward and backward and ramifies in the deep muscles of the 
anterior part of the back ; the cervical branch passes deeply to the atlantal region, 
where it anastomoses with the occipital artery. The deep cervical artery is a 
much smaller vessel, which emerges through the first intercostal space; it gives off 
the first intercostal artery, passes upward and forward deeply, and ramifies chiefly 
in the complexus and multifidus. The vertebral artery resembles that of the horse. 

The inferior cervical artery is large; its ascending branch gives off the posterior 
thyroid artery and parotid branches. 

The internal and external thoracic arteries give branches to the pectoral 
mammary glands; the external artery ma>' l)e alisent. 

The common carotid arteries arise from the brachiocephalic close together or 
by a very short common trunk; they are accompanied by an internal jugular vein 
of considerable size, anil their collaterals are similar to those of the horse. They 
terminate in occipital and internal and external carotid divisions. 

The occipital artery resembles that of the horse. 

The internal carotid artery usually arises by a common trunk with the occipital. 
After giving oft' a large meningeal Ijranch which enters the cranium through the 
mastoid foramen, it passes through the foramen lacerum and forms with the oppo- 
site artery a rete mirabile which resembles that of the ox, but is smaller; it is not 
connected with the vertebral and condyloid arteries, but the meningeal l)ranch just 
mentioned and the middle meningeal artery concur in its formation. 

The external carotid artery has the same course and termination as in the horse. 
Its collateral branches present the following special features: (1) The lingual 
artery is relatively' large and sujjplies the pharj-ngeal artery, the sublingual artery, 
muscular Ijranches, and branches to the soft palate, mandibular gland, and larynx. 
(2) The external maxillary artery is represented by a small vessel which ends in the 
masseter muscle; it gives branches to the pterygoideus medialis, the parotid and 
mandibular glands, and the mandibular lymph glands, the masseter and the cuta- 
neus. It does not extend upon the lateral surface of the face. (3) The posterior 
auricular artery is long and relatively large ; it ascends along the anterior border of 
the paramastoid process and ramifies on the convex surface of the external ear. It 
gives off the posterior meningeal artery, which enters the cranial cavity tlirough the 
mastoid foramen. 

The internal maxillary artery pursues a flexuous course between the ramus of 
the mandil)le and the pterygoid muscles to the maxillary recess and divides into 
infraorbital and palatine branches. Its branches offer the following special features: 



THE ARTERIES 737 

(1) The inferior alveolar artery is large; branches from it emerge through four or 
five mental foramina and take the place of the inferior labial. (2) The middle 
meningeal artery enters the cranial cavitj^ through the foramen ovale and concurs 
in the formation of the rete mirabile. (3) The buccinator artery is large and partly 
compensates for the lack of a facial artery. It ramifies in the cheek and its fine 
terminal branches extend to the lips. (4) The large infraorbital artery extends to 
the snout and replaces the superior labial largely and the lateral nasal in part. The 
malar branch compensates largely for the absence of the lateral and dorsal nasal 
arteries. (5) The palatine artery is small. 

The superficial temporal artery ascends behind the temporo-mandibular 
articulation and ramifies in tlie temporalis muscle; it is small and may be absent. 
In the latter case the anterior auricular and transverse facial arteries arise separately 
from the external carotid artery, which is directly continued by the internal maxil- 
lary artery. 

The intercostal arteries number usually fourteen or fifteen on either side; of 
these ten to twelve arise from the aorta, usually by short common trunks. Fre- 
quently an intercostal artery is given off from that of an adjacent space. 

The bronchial and CESophageal arteries usually arise separately. 

The cceliac artery is half an inch to an inch long. It supplies a branch to the 
left crus of the diaphragm, and divides into two primary branches, gastro-hepatic 
and splenic. The gastro-hepatic artery is the larger. It gives off pancreatic 
branches, the anterior gastric artery, l)ranches to the lesser curvature of the stomach, 
pyloric, and gastro-duodenal arteries. The latter divides into pancreatico-duo- 
denal and right gastro-epiploic. The anterior gastric usually supplies the oesopha- 
geal artery. The continuing trunk (A. hepatica propria) gives off a cj'stic branch 
and divides in the portal fissure into three or four branches which ramify in the 
liver. The splenic artery gives off the posterior gastric (usually), a branch to the 
stomach above the cardia (A. diverticuli), t\vigs to the pancreas, short gastric 
arteries to the left part of the great curvature, and splenic branches, and is con- 
tinued as the left gastro-epiploic artery. 

The posterior gastric may arise from the gastro-hepatic or in the angle of divergence of the 
two primary divisions of the cceliac. The (esophageal branch may come from the posterior gas- 
tric or the splenic. Other variations occur. 

The anterior mesenteric artery arises an inch or more behind the coehac and 
is long, like that of the ox. It gives twigs to the pancreas and is continued in the 
mesentery as the artery of the small intestine or truncus intestinalis. This gives off 
about a dozen branches which form a series of arches along the mesenteric lymph 
glands. From these is formed a ricli netw(_)rk which gives off innumerable fine 
branches placed close together. The ileo-cseco-colic artery gives off ileal and caecal 
arteries, antl enters the axis of the spiral coil of the colon. Here it pursues a spiral 
course and gives off branches which form remarkable plexuses; from the latter 
nvunerous fine branches go to the centri]3etal coils. A short trunk gives origin to 
right and middle colic branches. The right colic artery is arranged like the colic 
branch of the ileo-c£eco-colic artery, with which it anastomoses at the apex of the 
coil; it supplies the centrifugal parts of the coil. The middle colic artery goes to 
the colon as it emerges from the coil and anastomoses with the posterior mesenteric 
artery. 

A phrenico-abdominal artery arises on either side a little in front of the renal 
arteries. It divides into branches which go to the costal part of the diaphragm 
and the abdominal muscles. 

The renal and spermatic arteries j^iresent no special characters. 

The posterior mesenteric artery aiises near the termination of the aorta. It 
is small and is ilistributed like that of the ox. 
47 



738 



CIRCULATORY SYSTEM OF THE PIG 



Six pairs of Ivimbar arteries arise from the aorta. The seventh comes from 
the micklle sacral. 

The terminal branches of the aorta resemble those of the ox. 

The arteries of the shoulder, arm, and forearm resemble in general those of 
the ox. 

The brachial artery is continued over the medial surface of the elbow by the 
median artery. The latter divides near the middle of the forearm into radial and 
ulnar arteries. 

The radial artery is the smaller of the two terminal branches of the median. 
It descends along the medial border of the radius and divides at the proximal end 





Fio. fi07.— Arteries of Di3tal Part of Right Fore 
Limb of Pig; Dorsal View. 
n. Terminal part of volar interosseous artery; b, 
dorsal interosseous artery; c, rete carpi dorsale; d, dorsal 
metacarpal arteries; c, dorsal common digital arteries: 
/, dorsal proper digital arteries. 



KiG, 608. — Arteries op Distal Part of Right Fore 
Limb of Pig; Volar View. 
g. Ulnar artery; h, super6cial branch of radial 
artery; i, collateral ulnar artery* j, volar interosseous ar- 
tery; h, deep branch of radial artery; k, deep volar meta- 
carpal arteries: /, superficial volar metacarpal arteries; 
m, volar common digital artery; n, volar proper digital 
arteries. 



of the metacarpus into two branches. The superficial branch descends in the space 
between the second and third metacarpal bones and unites with the ulnar artery 
or with the lateral superficial volar metacarpal artery to form the superficial volar 
arch. The deep branch joins the volar interosseous artery at the proximal end of 
the metacarpus to form the deep volar arch. There is also a communicating branch 
between the radial and ulnar arteries at the carpus. 

The ulnar artery descends along the meilial side of the deep digital flexor and 
connects with the superficial branch of the radial artery to form the superficial 
volar arch. 



THE ARTERIES 



739 



The main facts as to the metacarpal and digital arteries are as follows: The 
rete carpi dorsale is formed essentially by the terminals of the interosseous artery 
of the forearm. It gives rise to three dorsal metacarpal arteries, which descend in 
the corresponding interosseous spaces and unite with branches of the volar meta- 
carpals to form three common digital arteries. Each of these divides into two 
proper digital arteries, which descend along the interdigital surfaces of the digits. 
From the superficial and deep volar arches described above there arise three super- 
ficial and three deep volar metacarpal arteries. The deep arteries unite near the 
distal end of the space between the principal metacarpal bones to form a stem 
which unites with the middle (third) superficial artery. The superficial arteries 





Fig. 609. — ^Arteries of Distal Part of Right Hin-d 
Limb of Pig; Dorsal View. 
a. Anterior tibial arterj', continued on tarsus as the 
dorsalis pedis: b. perforating tarsal arter>': c, dorsal 
metatarsal arteries: d, common digital arteries: e, 
proper digital arteries. 



Fig. 610. — Arteries of Distal Part of Right Hind 
Limb of Pig: Plantar \'iew. 
/, Saphenous artery, continued as medial tarsal 
artery: ff, lateral tarsal arterj': /i, medial plantar arterj', 
h' , lateral plantar arter>': i, perforating tarsal artery; 
J, deep plantar metatarsal arteries; k, common digital 
arter>'; I, proper digital arteries. 



unite to form an arch from which proper digital arteries are given off to the axial 
aspect of the small digits, and a common digital which supplies two volar proper 
digital arteries to each of the chief digits. 

Tlic arteries of the hip, thigh, and leg are arranged much as in the ox. A few 
special features may be noted. 

The ilio-lumbar artery gives off a branch to the quadriceps femoris and lateral 
muscles of the thigh, anrl ramifies in the abdominal muscles. It may also supply 
the posterior abdominal artery, which otherwise arises from the deep femoral. 

The deep femoral artery is given off above the level of the pubis. It is large 
and compensates for the ab.sence of the obturator artery. The posterior abdominal 



740 CIRCULATORY SYSTEM OF THE PIG 

and external pudic arteries may arise from it by a short common trunk or separately. 
The external pudic gives branches to the prepuce and preputial bursa but not to 
the penis. In the female it supplies the inguinal and abdominal mammary glands 
and anastomoses with the external thoracic artery. The popliteal artery gives off 
the peroneal. 

The femoral artery gives off a short trunk which divides into anterior femoral 
and lateral circumflex arteries, the latter being much the larger. 

The saphenous artery is large. It descends as in the ox on the medial surface 
of the leg and divides near the hock into lateral and medial tarsal arteries. The 
latter is the real continuation of the saphenous; it divides into medial and lateral 
plantar arteries, which concur with the perforating tarsal artery in forming the 
proximal plantar arch. 

The posterior tibial artery is small, being replaced distally by the saphenous. 
It gives branches to the muscles on the posterior face of the tibia and supplies the 
nutrient artery of that bone. 

The anterior tibial artery is continued as the dorsalis pedis on the dorsal sur- 
face of the tarsus. This gives off the perforating tarsal artery, which passes back 
through the vascular canal of the tarsus and unites with the plantar arteries to 
form the proximal plantar arch. 

The metatarsal and digital arteries resemble in arrangement the corresponding 
vessels of the limb. 

The Veins 

The veins resemble in general those of the ox. Thus there is a hemiazygos 
vein and two jugular veins, the internal one being relatively larger than in the ox. 
A few differential features maj' be noted. 

The buccinator vein resembles that of the horse, and unites with the vena 
refiexa to form a short common trunk which joins the external maxillary vein. 

The external maxillary vein resembles in general that of the horse. The dorsal 
nasal vein is large, receives the veins from the snout, runs backward in the groove 
of the nasal bone, and joins the frontal vein; it is connected with its fellow by a 
transverse branch, and anastomoses freely with the malar and facial veins. 

The veins of the distal parts of the limbs naturally present differences which 
are correlated with those of the arteries. 

The Lymphatic System 

The thoracic duct often divides near its termination into two branches which 
unite to form an ampulla. The latter suddenly contracts and opens into the termi- 
nal part of the left jugular vein. The lymph glands of animals in good condition 
are almost all embedded in fat. 

The mandibular lymph glands are situated in the space between the omo- 
hyoid and medial pterygoid muscles, in relation to the lower part of the anterior 
border of the mandibular salivary gland. There are commonly two on each side, 
one large, the other small. 

The parotid lymph glands (Fig. 415) are reddish-brown in color. There are 
usually four of considerable size and several smaller ones on either side. One is 
situated at the upper part of the posterior border of the masseter, partly covered 
by the parotid salivary gland. A large subparotid gland lies below the base of the 
ear on the terminal part of the brachiocephalicus muscle. Ventral to this are two 
smaller glands, one above and one below the external maxillary vein. 

The suprapharyngeal lymph glands (Fig. 416) are situated on the dorsal wall 
of the pharj-nx, dorsal to the external carotid artery and below and l^ehind the 
paramastoid process. There are usually two of considerable size on either side. 



THE LYMPHATIC SYSTEM 



741 



They are related deeply to the rectus capitis veiitralis major and are covered by the 
cleido-mastoiileus. 

The middle cervical lymph glands form a grouj) on the brachiocephalicus 
on the course of the external jugular vein. Other small nodes are present in the 
fat around the trachea. 

The prescapular lymph glands are situated at the anterior border of the an- 
terior deep pectoral muscle, under cover of the trapezius and omo-transversarius. 

The posterior cervical or prepectoral l5rmph glands are reddish in color and 
usually three in number. The largest is placed centrally under the trachea; the 
others are situated on the brachial vessels as the^• tin-n aroimd the first rib. 




Fig. 611. — Stomach .\nd Part of Intestine op Pig, Spread Otrr. 

a, Pyloric part of stomach; b, duodenum; c, jejunum; d. caecum; e, /, colon; g, pancreas; h, epiploic foramen; 

i, portal vein; k, hepatic lymph glands; I, gastric lymph glands: m, oesophagus. (After Edelmann.) 



The axillary lymph glands are usually absent, but very small nodes may be 
found near the ins(>rtion of the latissimus dorsi. Cubital glands are not present. 

The thoracic lymph glands comprise the following: 

(1) A sternal lymph gland of relatively large size lies on the first segment of the 
sternum. (2) The mediastinal lymph glands include: a number of small reddish 
nodes in the fat along the dorsal surface of the aorta ; a gland on the left side of the 
trachea in front of the aortic arch ; a gland on the aorta where it is crossed by the 
vena hemiazygos; two or three glands in the posterior mediastinum along the 
ventral surface of the aorta; several glands along the ventral surface of the trachea. 
(3) The bronchial lymph glands include one on the bifurcation of the trachea and 
another at the apical bronchus of the right lung. 



742 CIRCULATORY SYSTEM OF THE DOG 

The lumbar lymph glands are scattered along the abdominal aorta and the vena 
cava. Those placed near the hilus of the kidney are often designated renal. 

The internal iliac lymph glands are rounded and relatively large. They 
comprise: (1) Three or four glands situated on and between the origin of the cir- 
cumflex iliac and the external and internal iliac arteries; (2) a gland in the angle 
of divergence of the internal iliac arteries; (3) several glands along the course of 
the external iliac arterj', the most ventral of which is usually the largest, and might 
be regarded as a deep inguinal gland. 

The external iliac lymph glands are small, three or four in number, and lie in 
front of the circumflex iliac vessels. 

The visceral lymph glands of the abdomen comprise the following: 

1. The gastric lymph glands are situated on the lesser curvature of the stomach, 
covered by the pancreas in situ. They are commonly five or six in number and are 
in series with the hepatic glands. 

2. Several hepatic lymph glands (Fig. 429) are present about the portal vein 
at the portal fissure. The largest ones are about an inch (ca. 2-3 cm.) long. 

3. A long splenic Ijrmph gland lies on the splenic vessels near the dorsal end 
of the spleen. 

4. The mesenteric lymph glands are situated along the anastomotic arches 
formed by the vessels of the small intestine. 

5. Several caecal lymph glands are situated along the first part of the csecal 
vessels. 

6. Two series of coUc lymph glands accompany the arteries of the spiral part of 
the colon, and are exposed by separating the coils of the bowel. Small glands are 
placed in the colic mesentery and above the rectum. 

7. The anal lymph glands are situated on either side on the retractor ani. 

A small ischiatic lymph gland is found on the sacro-sciatic ligament near the 
lesser sciatic notch. 

The prefemoral lymph gland is situated on the aponeurosis of the external 
oblique muscle at the anterior border of the tensor fasciae latae, and a little above the 
middle of the thigh. It has an elongated oval outline, and in the adult may be 
about two inches (ca. 5 cm.) long, and nearly an inch (ca. 2 cm.) wide. It is em- 
bedded in fat. 

The superficial inguinal lymph glands form an extensive group, which may be 
five inches or more (ca. 10-12 cm.) in length. The middle part of the group is at 
the external inguinal rmg, and the series extends back on the upper part of the 
gracilis and forward and outward on the aponeurosis of the obliciuus abdominis 
externus. They number aliout a dozen; the largest are about an inch (ca. 2-3 cm.) 
long, antl the others about the size of a pea. 

The popliteal lymph glands are small normally and may escape notice. They 
are more superficially placed than in the other animals, and are in part in contact 
with the skin. 

A few small tarsal glands occur in front of the distal part of the tendo Achillis. 
The occurrence of a gland in the subcutaneous fat about a handbreadth above the 
tuber calcis has been noted by Hartenstein ; it varies from the size of a pea to that 
of a hazel nut. 



CIRCULATORY SYSTEM OF THE DOG 
The Pericardium and Heart 

The pericardiimi is attached to the sternal part of the diaphragm by a fibrous 
band, the pericardiaco-phrenic ligament (Lig. pericardiaco-phrenicum). and is con- 
nected with the sternum only by the mediastinal pleura. 



THE PERICARDIUM AND HEART 



743 



The area of contact of the pericardium with the chest wall is chiefly ventral, and is best seen 
with the subject on its back. In this position (after removal of the intercostal and rectus thoracis 
muscles), the area is seen to be almost triangular. The anterior border of the triangle (formed by 
the apical lobe of the right huig) is at the right fourth costal cartilage and extends across the median 
plane, ending at the third interchondral space near the costo-ehondral junction. The right border 
extends from the sternal end of the fourth rib to the eighth chondro-sternal joint. The left border 
begins at the left end of the anterior border, crosses the fourth cartilage nearly an inch from its 
junction with the rib and the fifth and sixth chondro-costal junctions. 

The heart differs greatly in form and position from that of the larger animals. 
In diastole it is ovoid and the apex is blunt and rounded. Its long axis is very 
oblique. Thus the base faces chiefly toward the thoracic inlet and is opposite to 
the ventral part of the third rib. The apex is on the left side at the sixth inter- 
chondral space or seventh costal cartilage, and in close relation to the sternal part 
of the diaphragm. The stemo-costal surface corresponds largely to the floor of 
the thorax from the fifth chondro-sternal joint backward. It is crossed obliquely 



Aorta 



Pulmonary veins 



Left brachial 
artery 

Brachiocephalic 
artery 
Anterior vena 
cava 

Right auricle 

Pulmonary art<ri/ 
Conus arteriosii 



iht ventricle 




Posterior vena cava 



Left ventricle 



•ipex 



1, Pulmonary veins; 2, left : 



Fig, 612. — Heart op Dog; Left View. 
vessels and fat in coronary groove; 4. vessels and fat i 
■oove; 5 J vessels and fat in intermediate groove. 



by the left (or ventral) longitudinal groove, which begins behind the origin of the 
pulmonary artery, and joins the right (or dorsal) groove at the right border, thus 
forming a notch not far from the apex. The diaphragmatic surface is less ex- 
tensive and less convex. On it is the right (or dorsal) longitudinal groove, which 
begins at the coronary groove just behind the termination of the posterior vena 
cava and joins the left (or ventral) groove to the right of the apex. There is fre- 
quently an intermediate groove between these on the left ventricle, which extends 
a variable distance toward the apex. The weight of the heart of a dog of medium 
size is five to six ounces, and is about 1 per cent, of the body weight. 

The relative weight is subject to wide variation. It is large in hunting dogs and such as are 
trained for speed or worked. In fat dogs of sedentary habit it may be only about 0.5 per cent. 

The fossa ovalis is very shallow and is bounded in front by the intervenous crest. The musculi 
pectinati form a rich network in the right auricle. The tricuspid valve has two chief cusps and 
three or four small ones. There are four musculi papillares in the right ventricle, all of which 
spring from the septal wall. They diminish in size from before backward, the anterior ones being 
long and cylindrical. Their bases are connected with the lateral wall by trabecute camese. Usu- 



744 



CIRCULATORY SYSTEM OF THE DOG 



ally six pulmonary veins open into the left atrium. The bicuspid valve consists of two large cusps 
and four or five small ones. There are two musculi papillares in the left ventricle, both of which 
arise from the lateral wall ; they are much larger than those of the right ventricle. 



The Arteries 

The two coronary arteries usually spring separately from the origin of the aorta, 
but may arise by a common trunk. Each divides into circumflex and descending 
branches. The left artery is twice as large as the right one ; it commonly gives off 
a branch of considerable size which runs in the intermediate groove. 

22 p 

" /I/ t (Ai. 




Fig. 613. — Vessels, Nerves, Etc, of Thorax op Dog; Right View. 



I, First rib (stump); 2, sternum; 2\ mauubrium sterni; J", .\iphQid cartilage; 3, trachea; 4. oesophagus; 5-5, 
ventral branches of fifth to eighth cervical nerves; 9, ventral branch of first thoracic nerve; it>, iO^, muscular and ten- 
dinous parts of diaphragm; 11, 11', left ventricle and atrium of heart; 12, IW , right ventricle and auricle of heart; -/5, 
coronary groove; i^, right coronary artery; 15, middle cardiac vein; 16, pulmonary veins; 17, aorta; 18, thoracic 
duct; i5, anterior vena cava; ^(>, posterior vena cava ; ^i, dorsal intercostal vessels; ;^;3, intercostal nerve; ;25, inferior 
cervical (or omo-cervical) artery; 21^, external thoracic artery; 25, brachial vessels; 26, common jugular vein; 27, in- 
ternal thoracic vessels; 28, sternal branches of internal thoracic vessels; 29, mediastinal arteries; SO, musculo-phrenic 
artery; SI, anterior abdominal artery; 32, m. longus coUi; 33, anterior mediastinal lymph glands; 54, sternal lymph 
glands; a, a' , right brachial artery and vein; 6, common carotid artery; c, deep cervical vessels; d, vertebral vessels; 
e, dorsal vessels; /, subcostal vessels; g, h, dorso-cervical trunks; i, vena azygos; k, recurrent nerve; I, vago-sympathetic 
nerve; /', /", dorsal and ventral branches of vagus; m, phrenic nerve; n, roots of phrenic nerve; o, thoracic trunk of 
sympathetic; o' , nerve loop formed around brachial artery by branches which connect posterior cervical and first tho- 
racic ganglia of sympathetic (Ansa subclavia); p, thoracic ganglia of sympathetic; q, rami communicantes; r, posterior 
cervical ganglion; s, first thoracic ganglion; /, u, d, rami communicantes between s and seventh cervical, first thoracic, 
and eighth cer\'ical nerves; w, cardiac branch of first thoracic ganglion; x, cardiac branches of posterior cervical gan- 
glion; y, bronchial branches of vagus; z, depressor nerve. (After Bucher.) 



The aorta runs at first almost straight forward and then turns backward, 
forming a very sharply curved arch. It gives off at its origin the two coronary 
arteries. From the convexity of the arch two large vessels arise. The first and 
larger of these is the brachiocephalic artery; this runs forward at first on the 
ventral surface of the oesophagus, then under the trachea. It gives oft" in succession 
the left and right common carotid arteries, and turns around the first rib as the 
right brachial artery. The left brachial artery passes forward on the left face of 
the oesophagus, forming a slight arch (concave ventrally), and turns around the first 
rib. The intrathoracic branches of the brachial arteries are as follows: 



THE ARTERIES 



745 



(1) The vertebral artery arises opposite the first intercostal space from the 
dorsal face of the parent trunk. It runs forward on the longus coUi (crossing the 
trachea on the right side), and passes along the neck in typical fashion to the third 
cervical vertebra, where it divides into three branches. The largest of these supplies 
the muscles in this region, compensating for the absence of branches of the deep 
cervical artery. The second passes between the second and third cervical vertebrae 
into the vertebral canal and unites with the opposite artery and a branch of the 
occipital artery to form the basilar artery. The third branch is the small continua- 




FiG. 614. — Vessels, Nerves, Etc., of Thorax of Dog; Left View. 
1, First rib (stump) : 2, sternum; 2', manubrium sterni; 2'', xiphoid cartilage; 3, trachea; 3', bifurcation of trachea; 
4, cesophagus; 5-8, ventral branches of fifth to eighth cervical nerves; 9. ventral branch of first thoracic nerve; W, W, 
muscular and tendinous parts of diaphragm; //, 11', left ventricle and auricle of heart; 12, 12', right ventricle and auricle 
of heart; 13, 13', left coronary artery (descending branch) and great cardiac vein; 14, branch of left coronary artery in 
intermediate groove; i5, pulmonary artery; i5, pulmonary veins; J 7, 75, aorta; /5, anterior vena cava; 20, 20', 20", 
intercostal nerve, artery, and vein; j?/, thoracic duct; ;S^, ^^', internal thoracic vessels; ;?3, sternal branches of 25; 24, 
mediastinal arteries; 25, musculo-phrenic artery; 26, anterior abdominal artery; 27, inferior cervical (or omo-cervical) 



', left common jugular vein; 31, m. longus colli; 32, an- 

a, brachiocephalic artery; h, b', common carotid arteries; 

essels; /, /', vertebral vessels; g, dorsal vessels; h, 

I, vago-sympathetic trunk; /', /", dorsal and ventral 

from fifth to seventh cervical nerves; o, thoracic trunk 

isa subclavia formed by branches connecting posterior cerNacal and first thoracic ganglia; o", 

; p, thoracic ganglia of sympathetic; q, rami communicantes; r, posterior cervical ganglion; s, 

of sympathetic; t, u, v, rami communicantes connecting s with seventh and eighth cervical and 

w, cardiac branch of first thoracic nerve; :r, cardiac nerves from posterior cervical ganglion; y. 



artery; 28, brachial vessels; 29, external thoracic artery; 
terior mediastinal lymph glands; S3, sternal lymph gland; 
c, c', brachial arteries; d, left brachial vein; e, e', dorso- 
subcostal vessels; {, deep cervical vessels; k, recurrent i 
branches of vagus: m, phrenic nerve; n, roots of phrenic 
of sympathetic; o', 
great splanchnic nei 
first thoracic gangli( 
first thoracic nerves 



bronchial branches of vagus: -, depress 



(After Bucher.) 



tion of the parent trunk; it passes to the wing of the atlas and anastomoses with 
the occipital artery. 

(2), (3) The dorsal and deep cervical arteries arise by a common trunk close 
to the vertebral. The trunk crosses the lateral face of the latter, ascends on the 
longus colli, and divides into two branches. The anterior branch, the deep cervical 
artery, emerges medial to the upper end of the first rib and ramifies in the deep 
muscles of the neck. The dorsal artery gives off the subcostal artery (which 
supplies two or three intercostal arteries) and emerges through the dorsal end of 
the first intercostal space and ramifies in the spinal muscles. 



746 



CIRCULATORY SYSTEM OF THE DOG 



(4) The inferior cervical artery arises at the first rib, and gives off the ascending 
cervical and transverse scapular arteries. The former runs on the deep face of the 
brachiocephalicus, in which it ramifies. The latter goes to the anterior border of 
the subscapularis, and its largest branch (equivalent to the prescapular of the horse) 
accompanies the suprascapular nerve. 

(5) The internal thoracic artery is large and sends perforating branches to the 
pectoral mammary glands. 

The axillary part of the brachial artery gives off the thoraco-acromial and ex- 
ternal thoracic arteries. 

The thoraco-acromial artery supplies branches to the deltoid and pectoral 
muscles. 

The external thoracic artery passes backward under cover of the deep pectoral 




Fig. 615. — Superficial Vessels of Head of Dog. 
1, Facial artery; 2, inferior labial artery; 3, artery of angle of mouth; 4, superior labial artery; 6, lateral nasal 
artery; 6, dorsal nasal artery; 7, superficial temporal arterj'; 5, transverse facial artery; 9, anterior auricular artery; 
iO, zygomatico-orbital artery; ^1, satellite vein of 20; J5, ant. auricular vein; i5, superficial temporal vein; i^. internal 
maxillary vein; /5, post, auricular vein; i(?, ?/", external jugular vein; i5, external maxillary vein; 7P, 53, facial vein; 
50, inf. labial vein: 5i, buccinator vein; 55, vena reflexa; .?4, superior labial vem; 55, vena angularis oeuli; 5^, dorsal 
nasal vein; a, concha; 6, parotid gland; c, mandibular gland; d, mandibular lymph glands; e, mylo-hyoideus; /, 
digastricus; g, masseter; h, zygomaticus; i, scutularis; k, temporalis; I, orbicularis oculi; m, zygomatic arch; h, re- 
tractor anguli oris; o, buccinator. (Ellenberger-Baum, .\nat. d. Hundes.) 



muscle and ends in the abdominal cutaneous muscle. It sends branches to the 
mammary glands. 

The common carotid arteries, left and right, arise in that order from the 
brachiocephalic. In the neck the right one lies on the trachea, the left on the 
oesophagus. Collateral branches arc the posterior thyroid (which may, however, 
arise from the right or left brachial or the inferior cervical), pharjmgeal, anterior 
thyroid, laryngeal, muscular, tracheal, and glandular (to the mandil:)ular gland). 
Each carotid divides under the wing of tlie atlas into occipital and internal and ex- 
ternal carotid branches. 

The occipital artery is small; it ascends behind the hypoglossal nerve to the 
paramastoid process, crossing laterally the internal carotid artery and vagus and 
sympathetic nerves. It curves over the paramastoid process and pursues a f.exuous 



THE ARTERIES 747 

course on the nuchal surface of the occipital bone parallel with the nuchal crest, 
anastomoses with the opposite artery, and ramifies in the nuchal muscles. It 
gives collateral branches to the ventral straight muscles and to the pharjiix. It 
also gives off the condyloid and posterior meningeal arteries. The latter passes 
through the mastoitl foramen and ramifies in the dura mater. The cerebrospinal 
artery passes through the intervertebral foramen, and unites in the vertebral canal 
■(vith its fellow and a branch from the vertebral artery to form the basilar artery. 
The recurrent branch anastomoses with the vertebral as in the horse. 

The internal carotid artery, also small, arises just behind the occipito-mandib- 
ularis muscle; it passes to the foramen lacerum posterius, enters the carotid canal, 
and forms a bend before entering the cranial cavity through the carotid foramen. 
It forms a plexus which is connected by branches with the middle meningeal and 
external ophthalmic arteries. It then perforates the dura mater and enters into 
the formation of the circulus arteriosus, which is formed in a manner similar to that 
of the horse. The anterior cerebral artery gives off the internal ophthalmic artery 
which accompanies the ojitic nerve to the eyeball. The middle cerebral artery is 
large, and gives off the ch(jroid artery. 

The external carotid artery is the direct continuation of the common carotid. 
It passes along the lateral wall of the pharynx, emerges from beneath the occipito- 
mandibularis, and divides Ijehind the postglenoid process into superficial temporal 
and internal maxillary arteries. It gives off the following collateral branches: 
The large flexuous lingual artery passes to the side of the root of the tongue, runs 
forward under cover of the hyo-glossus, and continues to the tip of the tongue in 
company with a satellite vein and the hypoglossal nerve. It ramifies in the 
tongue and gives collateral branches to the phar^Tix and soft palate. The external 
maxillary artery, smaller than the lingual, passes along the upper border of the occipi- 
to-mandibularis, gives off the sublingual, gains the anterior border of the masseter, 
and divides into superior and inferior labial and the angularis oris. The last-named 
vessel passes forward on the cheek between the labials to the angle of the mouth. 
The sublingual artery passes along the upper border of the occipito-mandihularis, 
then between the mylo-hyoideus and the ramus of the mandible. The great auric- 
ular artery arises at the anterior border of the occipito-mandibularis, gives branches 
to the parotid and mandibular salivary glands and the adjacent muscles, and ter- 
minates in three auricular branches which ramify on the convex face of the concha. 
These branches anastomose with each other and the anterior auricular artery. 

The superficial temporal artery, after giving off the anterior auricular artery 
and a small transverse facial artery, turns forward under the temporal fascia towartl 
the eye, and divides into upper and lower branches which supply the frontal region 
and the eyelids. It also supplies branches to the parotid gland and the masseter 
and temporalis muscles. 

The internal maxillary artery pursues a course similar to that of the horse, 
and ends in tlie pterygo-jDalatine fossa by dividing into the infraorbital artery and a 
common trunk for the greater palatine and splienopalatine arteries. The mental 
branches of the inferior alveolar artery are of consiclerable size and are distributed 
in the lower lip and gums. Two or three deep temporal arteries are present; the 
anterior one may arise from the buccinator artery. The middle meningeal artery 
enters the cranium through the foramen ovale, ramifies in tlie dura mater, and sends 
a branch to the carotid plexus. The external ophthalmic artery is connected ^vith 
the internal carotid by a large ramus anastomoticus which passes through the 
orbital foramen. The superficial branches of the infraorbital artery replace the 
dorsal and lateral nasal arteries, and compensate for the small size of the superior 
labial. 

The brachial artery in its course in the arm presents no special features. At 
the elbow it passes between the biceps and the pronator teres, descends as the 



748 



CIRCULATORY SYSTEM OF THE DOG 



median artery under the flexor carpi radialis about a third of the way down the 
forearm, and divides into radial and ulnar arteries. Among its collateral l)ranches 
are the following: (1) The large subscapular artery passes up between the sub- 




Fin. fil6. — VESSELa AND Nehves of Medial Surface 
OF Shoulder and Arm of Dog. 
a , b. Brachial artery ; c, subscapular vessels ; d, 
thoraco-dorsal vessels; e, deep brachial vessels; /.prox- 
imal collateral ulnar vessels; g, brachial vein; k, k", 
cephalic vein; h', mediano-radial vein; i, anterior tho- 
racic nerves ; k, musculo-cutaneous nerve ; I, median 
nerve ; m, ulnar nerve ; it, radial nerve ; o, thoraco- 
dorsal nerve; 1, subscapularis muscle; 2, supraspinatus 
muscle; 3, teres major; ^, latissimus dorsi; 5, deep 
pectoral muscle; 6, biceps brachii; 7, long head^ofitri- 
ceps; S, tensor fascise antibrachii; 9, medial head of 
triceps; 10, pronator teres* (Ellenberger-Baum, Anat. 
d. Hundes.'' 




Fig. 617. — Arteries of Forearm of Do 



Arteries: «, Brachial; a', median 
seous; d, volar antibrachial; e, radial; e', e", dorsal 
and volar branches of e; f, /', cutaneous branches of e; 
g, ulnar. Muscles: 1, Biceps brachii; 3, extensor carpi 
radialis; 3, pronator teres; j}, deep digital flexor; 5, 
radius; 6, superficial digital flexor; 7, flexor carpi radi- 
alis: S, ulnaris lateraUs; 9, humerus. (Ellenberger- 
Baum, Anat. d. Hundes.) 



scapularis and teres major, turns around the posterior angle of the scapula, and 
terminates in the supraspinatus, deltoid, trapezius, and brachiocephalicus. In 
about half the cases it gives off the anterior circumflex, which often arises with the 



THE ARTERIES 749 

posterior circumflex. Its other branches resemble those of the horse. (2) The 
anterior circumflex artery in about half the cases arises from the brachial. (3) 
The deep brachial artery arises about a third of the way down the arm. (4) The 
bicipital artery (for the biceps) is given off at the distal third of the arm. (.5) The 
proximal collateral ulnar artery arises almost opposite to the preceding vessel. It 
ramifies chiefly in the distal part of the triceps, and sends a superficial branch to the 
medial and posterior surfaces of the proximal part of the forearm. (6) The proxi- 
mal collateral radial artery (not present in the horse) arises at the distal fourth of 
the arm, crosses over the terminal part of the biceps, descends on the extensor 
carpi radialis, and concurs with a branch of the volar interosseous artery in forming 
the rete carpi dorsale. It often supplies the bicipital artery. (7) The distal col- 
lateral radial artery is very small; it accompanies the deep branch of the radial 
nerve on the dorsal surface of the forearm and supplies branches to the elbow joint 
and the brachialis, supinator, and extensor muscles. (8) The common interosseous 
artery is given off from the median a little below the elbow. It suiijilies 
branches to the flexor muscles and gives off the dorsal interosseous artery, 
which passes through the interosseous space, gives branches to the extensor muscles, 
and by its terminal twigs concurs in the formation of the rete carpi dorsale. The 
direct continuation of the trunk is the volar interosseous artery, which descends 
along the interosseous space under cover of the pronator quadratus, gives off a 
branch to the rete carpi dorsale and the fifth volar metacarpal artery, and termin- 
ates by joining the volar branch of the radial arter\^ to form the deep volar arch. 
(9) The volar antibrachial artery (Ramus volaris antibrachii) arises below the 
interosseous and descends at first imder the flexor carpi radialis, then between the 
heads of the deep flexor, and divides into ascending and descending branches which 
ramify in the rtiuscles mentioned. 

The radial artery, the smaller terminal of the median, descends along the 
medial border of the radius, and divides near the carpus into dorsal and volar 
branches. The dorsal branch assists in forming the rete carpi dorsale. The larger 
volar branch descends behind the medial border of the carpus and joins the end of 
the volar interosseous in forming the deep volar arch. The arch extends across 
the interossci at the proximal part of the metacarpus. From this arch three deep 
volar metacarpal arteries descend in the second, third, and fourth intermetacarpal 
spaces and concur with the corresponding superficial volar and the dorsal meta- 
carpal arteries to form the common digital arteries. 

The ulnar artery is much the larger of the two terminal l^ranches of the median. 
It descends with the median nerve along the medial border of the deep flexor of the 
digit, and sends a connecting branch to the radial above the carpus. It then in- 
clines somewhat laterally and passes between the superficial and deep flexor tendons. 
Near the middle of the metacarpus it gives off the first volar metacarpal artery and 
divides into the second, third, and fourth superficial volar metacarpal arteries. 
The first volar artery unites with the corresponding dorsal arterj' to form the first 
common digital artery, which supplies proper digital arteries for the opposed sur- 
faces of the first and second digits. The superficial volar arteries descend in the 
spaces between the other metacarpal bones, and unite near the metacarpo-phalangeal 
joints with the corresponding deep volar and dorsal metacarpal arteries to form 
three common digital arteries. Each of the latter divides after a short course into 
two proper digital arteries, which run along the opposed surfaces of the second to 
the fifth digits. The lateral digital artery of the fifth digit comes from the super- 
ficial volar arch formed by the union of a branch of the volar interosseous with the 
fourth superficial volar metacarpal artery. 

The rete carpi dorsale gives off four dorsal metacarpal arteries which descend 
in the intermetacarpal spaces and unite near the metacarpo-phalangeal joints with 
the volar arteries to form the common digitals. 



750 



CIRCULATORY SYSTEM OF THE DOG 



The thoracic aorta supplies the last nine or ten pairs of intercostal arteries, 

but no anterior phrenic arteries. It gives off two or more oesophageal branches, in 
addition to the broncho-cesophageal, which arises close to or with the sixth inter- 
costal and ramifies in the usual manner. 

The abdominal aorta, after giving off the external iliac arteries, continues 
about half an inch to an inch (ca. 1-3 cm.) under the last lumbar vertebra, gives 
off the internal iliac arteries, and is continued by the middle sacral artery (Fig. 
624). This small vessel runs backward under the sacrum and coccygeal vertebrae 
and gives off branches in segmental fashion. Six pairs of lumbar arteries are given 
off from the aorta, the seventh coming from the internal iliac artery. 





Fig. 618. — .Arteries of Distal Part of Right Fore 
Limb of Dog, Dorsal View. 
a, Branch of volar interosseous artery: 6, proximal 
collateral radial artery (lateral branch) ; c, radia! artery 
(dorsal branch): d, rete carpi dorsaie: e, deep dorsal 
metacarpal arteries; /, superficial dorsal metacarpal 
arteries: g, common digital arteries; h, proper digital 
arteries. 



Fig. ()19. — .\hterie.'5 op Distal Part of Right Fore 
Limb of Dog; Volar View. 
(", Radial artery; j\ ulnar artery; k, volar inter- 
osseous arter>'; I, deep volar arch; /«, fifth volar meta- 
carpal artery: 71, deep volar metacarpal arteries: p, super- 
ficial volar metacarpal arteries; o, q, common digital 
arteries; r, proper digital arteries. 



The cceliac artery gives off the hepatic artery and forms a short trunk from 
which the gastric anil splenic arteries arise. The hepatic artery, after giving off 
several proper hepatic arteries, and the right gastric artery, which passes along the 
lesser curvature of the stomach and anastomoses with the left gastric artery, is con- 
tinued by the gastro-duodenal artery. This divides near the pylorus into right 
gastro-epiploic and pancreatico-duodenal arteries; the former supplies branches 
to the jjyloric part of the stomach and passes along the greater curvature of that 
viscus in the omentum and anastomoses with the left gastro-epiploic. The left 
gastric artery passes to the lesser curvature of the stomach and ramifies chiefly on 



THE ARTERIES 751 

the left part of the stomach, giving off a branch which anastomoses with the right 
gastric arterj'. The splenic artery gives off pancreatic branches, antl reaches the 
ventral part of the spleen. It gives off the left gastro-epiploic and a gastro- 
splenic branch which passes to the dorsal end of the spleen, which it supplies, 
besides giving off t\vigs to the left extremity of the stomach. 

The anterior mesenteric artery arises close behind the coeliac. It gives off a 
common trunk for two colic arteries and the ileo-cseco-colic. The right colic 
artery is a small vessel which goes to the right part of the colon. The middle 
colic artery is much the largest of the colic vessels ; it supplies the transverse colon 
and part of the right colon. The ileo-cseco-colic gives off ileal, csecal, and colic 
branches. Anastomoses are established between the colic arteries, and the ileal 
branch anastomoses with the last jejunal artery. The trunk is contiimed as the 




Fig. 620. — End Bbanches or Aorta and Radicles of Posterior Vena Cava of Dog. 

a, Abdominal aorta; 6, posterior mesenteric artery; c, lumbar arteries; (/, circumflex iliac artery ; e, external iliac 
artery; /, deep femoral artery ; p, posterior abdominal artery ; A, external pudic artery; a, femoral artery; i, t, internal 
iliac arteries; fc, visceral branch of i; ^ parietal branch of t; ?«, ilio-lumbar artery; «, anterior gluteal artery; o. lateral 
coccygeal artery; p, posterior gluteal artery; g, umbiUcal artery; r. middle hsemorrhoidal artery; /9, posterior hsemor- 
rhoidal artery; s, perineal arterj-; (, art. profunda penis; /;, art. bulbi urethrae; v, art. dorsalis penis; w, middle sacral 
artery; a', posterior vena cava; other veins are satellites of arteries and correspondingly named; 1, iUo-psoas muscle; 
2, tendon of psoas minor; 3, abdominal muscles; 4. sartorius; 6, rectus femoris; o', vastus medialis: 6, pectineus; 6"', 
adductor; 7, graciUs; 5, symphysis pelvis; 9, ihum; 10, piriformis; 11, gluteus superficialis; 1^, obturator internus; 
13, penis; 14, lumbar vertebrse. (After EUenberger, in Leisering's Atlas.) 

artery of the small intestine, giving off fourteen to sixteen branches (Aa. jejunales), 
which form a series of anastomotic arches in the mesentery near the bowel. 

Two phrenico-abdominal arteries (Aa. phrenicee caudales) come off from the 
aorta behind the anterior mesenteric, and divide into phrenic and abdominal 
branches. Each phrenic artery diverges from its fellow in descending on the ab- 
dominal surface of the corresponding crus of the diaphragm to the sternal part. 
The medial branches anastomose with those of the opposite artery, the lateral 
branches with intercostal arteries chiefly. The abdominal arteries pass outward 
across the psoas muscles, give branches to the lumbar muscles, the renal fat and 
adrenals, and ramify in the oblique abdominal muscles. 

The renal and spermatic arteries offer no special features. 

The utero-ovarian artery divides near the ovary into three or four branches 



752 



CIRCULATORY SYSTEAI OF THE DOG 




Fig. 621, — Arteries 
Limb of Dog; Me 
a, Abdominal aorta; 6, fem- 
oral; c, c', deep femoral; d, pos- 
terior abdominal; e, external pudic; /, medial cir- 
cumflex; g, anterior femoral (accompanied by an- 
terior branch of^ femoral nerve); h, lateral circum- 
flex; i, kf muscular branches; t, articular branch; m, 
saphenous; n, o, plantar and dorsal branches of saphen- 
ous; q, saphenous nerve; r, obturator nerve; i, ilio- 
psoas; f, ilium; S, gracilis; 4, semitendinosus; a, 
adductor magnus; 6, adductor longus; 7, quadri- 
ceps femoris; S, sartorius; 9. semimembranosus; 10, 
gastrocnemius; 11, tibialis anterior; 12, tibia. (Ellen- 
berger-Baum, Anat. d. Hundes.) 



which supply the ovary and uterme tube 
and anterior part of the cornu of the 
uterus, anastomosing with the uterine 
artery. 

The posterior mesenteric artery is 
small. It divides into two branches which 
supply the terminal part of the colon and 
the anterior part of the rectum; the 
former (A. colica sinistra) passes forward 
along the left part of the colon and anas- 
tomoses with the middle colic branch of 
the anterior mesenteric artery; the latter 
(A. htemorrhoidalis cranialis) anastomoses 
with the middle hsemorrhoidal branch of 
the internal pudic artery. 

The circumflex iliac artery usually 
arises from the terminal part of the 
aorta. 

The external iliac artery usually gives 
off no collateral branches. 

The femoral artery has the usual 
course in the femoral triangle and canal. 
The deep femoral artery gives off the 
posterior abdominal and external pudic 
arteries by a very short common trunk 
or separately. In the female the external 
pudic divides into anterior and posterior 
branches; the former runs forward, sup- 
plies branches to the superficial inguinal 
lymph glands, the mammary glands and 
skin, and anastomoses with the mammary 
branch of the internal thoracic artery; the 
posterior branch pursues a flexuous course 
between the thighs to the vulva, where its 
terminal branches anastomose with the 
internal pudic artery. In the male the 
artery crosses the medial side of the sper- 
matic cord and runs forward to the 
umbilical region; it supplies the inguinal 
lymph glands, prepuce, and skin. The 
anterior femoral artery may arise by a 
sliort common trunk with the lateral cir- 
cumflex. The former, accompanied by 
the anterior branch of the femoral nerve, 
dips in between the rectus femoris and 
vastus medialis. The lateral circumflex 
artery passes forward between the sar- 
torius medially and the rectus femoris 
and tensor fasciae latse laterall}^ and sup- 
plies branches to these muscles and the 
glutei. In addition to muscular branches 
of considerable size, an articular branch 
(A. genu suprema) arises a little below 
the middle of the thigh and runs dowai- 



THE ARTERIES 



753 



ward and forward to the medial face of the stifle joint. The saphenous artery is 
large. It arises from the medial surface of the femoral a little below the middle of the 
thigh, descends superficially to the proximal part of the leg, and divides into two 
branches. The smaller dorsal branch (Ramus dorsalis) passes obliquely downward 
and forward across the medial surface of the tibia to the flexion surface of the hock and 
gives off the second, third, and fourth superficial dorsal metatarsal arteries. These 
descend along the grooves between the metatarsal bones and each divides into two 
proper digital arteries. The plantar branch (Ranms plantaris), which is much the 





Fig. 622. — Arteries of Distal Part of Right Hind Fig. 623. — Arteries of Distal Part of Right Hind 



Limb of Dog; Dors.4l View. 
a, Lateral branch of anterior tibial artery; b, an- 
terior tibial artery; c, saphenous artery (dorsal branch): 
d, perforating metatarsal artery; e, dorsal metatarsal 
arteries: /, deep dorsal metatarsal arteries: g, super- 
ficial dorsal metatarsal arteries; h, anastomoses between 
dorsal and plantar arteries; i, common digital arteries; 
j, proper digital arteries. 



Limb of Dog; Plantar View. 
k. Saphenous artery (plantar branch); I, V , medial 
and lateral plantar arteries: m, perforating metatarsal 
artery; n, deep plantar metatarsal arteries; o, super- 
ficial plantar metatarsal arteries; p, common digital 
artery: g, proper digital arteries. 



larger, descends on the medial face of the gastrocnemius and the long digital flexor. 
It gives off the lateral tarsal artery to the lateral surface of the tarsus, and at the 
plantar face of the tarsus detaches the medial and lateral plantar arteries; these 
descend on either side of the deep flexor tendon and unite with the perforating 
metatarsal artery to form the proximal plantar arch. The artery continues 
down the middle of the plantar surface of the metatarsus and divides near the 
metacarjjo-phalangeal joints into three superficial plantar metatarsal arteries 
(II, III, IV). These vessels unite with three deep plantar metatarsal arteries, which 
descend from the proximal plantar arch ami with branches from the dorsal meta- 
48 



754 CIRCULATORY SYSTEM OF THE DOG 

tarsal arteries. From these anastomoses four plantar digital arteries result; of 
these, the central two have a common digital trunk. 

The popliteal and posterior femoral arteries present nothing of special interest. 

The posterior tibial artery is very small, being replaced largely by the saph- 
enous. It supplies twigs to the flexor muscles at the proximal part of the leg. 

The anterior tibial artery descends on the anterior face of the tibia and tarsus 
and is continued as the perforating metatarsal artery, which passes through the 
upper part of the space between the second and third metatarsal bones and concurs 
with the plantar arteries in the formation of the proximal plantar arch. Besides 
muscular and articular branches, the anterior tibial supplies the fifth dorsal meta- 
tarsal artery for the lateral side of the fifth digit. At the proximal part of the meta- 
tarsus it gives oft three deep dorsal metatarsal arteries which descend in the in- 
tervals between the metatarsal bones and concur with the superficial dorsal meta- 
tarsal and the plantar arteries in the formation of the digital arteries. The latter 
resemble in general arrangement the corresponding arteries of the thoracic limb. 

The internal iliac artery (Fig. 620) runs backward and a little outward across 
the ilio-psoas, and on reaching the ilium divides into parietal and visceral branches; 
it gives off the seventh lumliar artery. The parietal branch is the larger. It runs 
backward on the lateral wall of the pelvis, passes out through the lesser sciatic 
notch, and breaks up into branches which supply the muscles of this region; this 
terminal part may be regarded as the posterior gluteal artery. It gives off the 
following branches: (1) The ilio-lumbar artery passes outward between the ilio- 
psoas and the shaft of the ilium and ramifies in the gluteus medius, giving branches 
to the ilio-psoas and tensor fascise latie; it may arise from the internal iliac. (2) 
The anterior gluteal artery passes out through the greater sciatic foramen and sup- 
plies branches to the glutei. (3) Muscular branches go to the oljturator internus, 
coccygeus, and retractor ani. (4) The superficial lateral coccygeal artery (A. cau- 
dalis lateralis superficialis) passes back at first on the lateral face of the coccygeus and 
continues beneath the skin along the side of the tail. The visceral branch is equiva- 
lent to the internal pudic artery; it passes back below the parietal branch on the 
lateral face of the rectum, retractor ani, and coccygeus. Its chief collateral branches 
are: (1) The imibilical artery, which pursues a flexuous course and supplies twigs to 
the bladder, ureter, and ductus deferens. In the bitch it gives off a large uterine 
artery which ramifies chiefly in the body and neck of the uterus and the vagina 
and anastomoses with the utero-ovarian. (2) The middle hsemorrhoidal artery 
arises near the ischial arch, passes upward and forward on the lateral surface of the 
rectum, gains its dorsal surface, and anastomoses with the posterior mesenteric ; it 
supplies the rectum and the anus, together with its muscles and glands. (3) A 
small perineal artery is detached to the perineum. In the male the trunk turns 
around the ischial arch as the artery of the penis (A. penis). This vessel, after 
giving off the deep artery of the penis (A. profunda penis), which supplies the 
artery of the bulb (A. jjulbi urethra>) and enters the corpus cavernosum, is con- 
tinued as the dorsal artery of the penis (A. dorsalis penis) along the dorsum penis. 
In the female the terminal branches of the trunlv go to the vulva, vestibular bulb, 
and clitoris. 



The Veins' 

The arrangement of the veins is, of course, correlated in general with the 
arterial system, but a few special features are worthy of mention. 

The coronary sinus is a large liut short trunk formed by the confluence of the 
cardiac veins; it opens into the right atrium below the posterior vena cava. The 

1 Manv of the veins are shown in the illustrations of the arteries. 



THE VEINS 755 

great cardiac vein ascends in the left longitudinal groove of the heart to the coronary 
groove, in which it courses to the diaphragmatic surface. Here it is joined bj' one 
or two lesser cardiac veins, which are satellites of the right coronary artery, thus 
forming the coronary sinus. There is commonly a vein in the intermediate groove 
which joins the great cardiac vein. 

The anterior vena cava (Figs. 613, 614) is formed by the jimction of short right 
and left brachiocephalic veins, and each of the latter results from the confluence 
of jugular and brachial veins. 

The vena azygos (Fig. 61.3) is continuous behind with the first lumbar vein; it 
reseml^les that of the horse, and receives at the ninth or tenth thoracic vertebra a 
vena hemiazygos. 

Two jugular veins are present on each side. The external jugular vein is the 
chief vein of the neck; it is formed by the union of external and internal maxillary 
veins at the posterior border of the mandibular gland. The two external jugulars 
are commonly united l^y a transverse branch below the cricoid cartilage. Each 
passes along the neck on the sterno-cephalicus, covered only by the skin and cu- 
taneous muscle, dips imder the cleido-cervicalis, and joins the internal jugular. 
The internal jugular vein is the satellite of the common carotid artery. It results 
usually from the junction of laryngeal and thyroid veins, but in some cases it is 
formed l^y the confluence of the ventral cerebral and occipital veins. 

The external maxillary vein arises on the lateral nasal region by the junction 
of the dorsal nasal vein with the angularis oculi. Near the infraorbital foramen it 
receives the lateral nasal vein, and a little lower the superior labial. In its course 
along the anterior border of the masseter it receives the vena reflexa, which arises 
in the pterygo-palatine fossa by the junction of infraorbital, sphenopalatine, and 
palatine radicles, together with a branch from the cavernous sinus. At the ventral 
border of the mandible it is joined by the inferior labial vein, which receives the 
buccinator vein. The lingual vein is connectetl with its fellow by a superficial 
transverse branch at the insertion of the sterno-hyoidei. The sublingual and 
submental veins terminate in a variable manner, but often form a common trunk 
which joins the lingual. 

The internal maxiUeiry vein arises from the pterygoid plexus, formed chiefly 
by dorsal lingual, inferior alveolar, deep temporal, pterj'goid, and meningeal tribu- 
taries. It receives the dorsal cerebral, auricular, superficial temporal, transverse 
facial, and masseteric veins, and often a trunk formed by the union of the ventral 
cerebral and occipital veins. 

The brachial and radial veins are satellites of the arteries. 

The ulnar vein is usually double. It unites below the carpus with a branch of 
the interosseous vein to form the superficial venous arch. 

The cephalic vein accompanies the ulnar artery in the forearm and joins the 
superficial venous arch below. 

The accessory cephalic vein arises from the union of three dorsal metacarpal 
veins. It joins the cephalic vein about the middle of the forearm. 

There are three short volar metacarpal veins which open into the superficial 
venous arch. They are formed above the metacarpo-phalangeal joints by the 
junction of the volar digital veins, of which there are two for each of the chief 
digits. The volar vein of the first digit joins the superficial venous arch. 

Each of the chief digits has two dorsal digital veins, while the first digit has one. 

The portal vein (Fig. 625) is formed by the union of a common intestinal or 
mesenteric vein wth the gastro-splenic vein. It receives the gastro-duodenal vein. 
The intestinal trunk is formed in the mesentery by the confluence of veins from 
the jejunum; it receives an ileo-cseco-colic vein. 

The posterior vena cava, its collateral affluents, and common iliac radicles 
present no special features of importance. 



756 CIRCULATORY SYSTEM OF THE DOG 

The internal iliac vein corresponds in regard to its tributaries with the branches 
of the artery, except that it is not divided into parietal and visceral branches. 

The external iliac, femoral, and popliteal veins with their collateral tributaries 
are satellites of the arteries. 

The anterior tibial vein is usually double, and the posterior tibial vein is very 
small. 

The saphenous vein is the upward continuation of the medial plantar meta- 
tarsal vein. It communicates by a large branch ^vith the dorsal metatarsal vein, 
and ascentls the leg as a satellite of the saphenous artery and its plantar branch. 
The recurrent tarsal vein is larger. It is formed at the lower part of the leg by the 
union of dorsal metatarsal and lateral plantar metatarsal veins, crosses the lateral 
surface of the leg obliquely upward and backward, ascends behind the gastrocnemius, 
and joins the femoral vein. 

The metatarsal and digital veins resemble in general the corresponding vessels 
of the forelimb. 

The Lymphatic System 

The cistema chyli is relatively large and is fusiform; it is ventral to the last 
thoracic and first lumljar vertebrae and is related ventro-medially to the aorta, 
dorsally and laterally to the right crus of the diaphragm and the psoas minor. The 
thoracic duct passes forward to the right of the aorta and ventral to the vena azygos 
as far as the sixth thoracic vertebra; here it crosses to the left face of the oesophagus 
and runs forward, turns ventrally at the thoracic inlet, and opens into the left 
brachiocephalic or the common jugular vein. The duct may be single throughout, 
but often divides anteriorly into two branches, which may then unite and form a 
dilatation which receives the left tracheal duct and the vessels from the forelimb. 
Other variations occur and the primitive plexiform arrangement persists in varying 
degree. The tracheal lymph ducts accompany the internal jugular veins. The 
right duct opens into the right l)rachiocephalic vein. 

The mandibular lymph glands (Fig. 615) are commonly two or three in number 
on each side, but as many as five have been observed. They are situated in the 
angle between the masscter and the mandibular salivary gland, above and below 
the external maxillary vein, and covered only by the skin and cutaneus muscle. 

A small rountl parotid lymph gland is situated superficially between the upper 
part of the posterior border of the masseter and the parotid salivary gland or partly 
or completely under cover of the latter. Exceptionally two or three may be present. 

The supraphar3nigeal l5rmph glands, usually one on each side, lie dorsal to the 
pharynx, under cover of the sterno-mastoideus and the mandibular salivary gland. 
They are related deeplj' to the rectus capitis ventralis and the carotid artery, and 
the anterior end is just behind the occipito-mandibularis (Fig. 433). Each is about 
two inches (ca. 5 cm.) long in a good-sized dog. In a good many cases a second 
gland is present. 

Anterior cervical lymph glands ajipear to be absent in the majority of subjects, 
but in other cases small nodes may be present in relation to the anterior end of the 
thyroid gland. It should be noted, however, that parathyroids may be mistaken 
ior lym]ih nodes unless a microscopic examination is made. Middle cervical 
lymph glands are apparenth' not present, and the same is usually the case in regard 
to the posterior cervical lymph glands ; liut in some cases one or more of the latter 
occur on the ventral face of the trachea near the thoracic inlet. 

The prescapular or superficial cervical lymph glands lie on the serratus ven- 
tralis, at tlie anterior Ixjrder uf the sui)raspinatus, embedded in a mass of fat. Usu- 
ally two are present on each side, but there may Ije tliree or only one. They are 
oval and are about an inch long in a dog of medium size when two are present. 



THE LYMPHATIC SYSTEM 



757 



The axillary lymph gland lies in a mass of fat on the medial face of the distal 
part of the teres major. It is discoid and is about an inch (ca. 5 cm.) wide in a 
large dog. Exceptionally a second smaller 
gland is present. 

The cubital lymph gland is usually 
absent. When present, it is situated on 
the medial face of the long head of the 
triceps or on the latissimus dorsi. 

Intercostal lymph glands do not ap- 
pear to be present. 

Two sternal lymph glands (Fig. 613) 
are usually present, one on each side. 
They are situated on the course of the 
internal thoracic vessels, usually at the 
second sternebra. A third node may be 
present in front of the more constant one, 
and in some cases, on the other hand, the 
gland is absent on one side. In large dogs 
the gland may be nearly an inch long. 

The mediastinal lymph glands are 
variable in number and arrangement. 
None have been found in the posterior 
mediastinum, and the following statement 
is to be understood merely as an account 
of what is most often found. Two or three 
glands usually occur on the ventral face of 
the trachea, oesophagus, and brachioceph- 
alic artery to the left of the anterior vena 
cava; they are related ventrallj'to the thj'- 
mus, when the latter is not too much re- 
duced. Others may be found on the lateral 
face of the brachiocephalic artery. One 
or two glands are usually present between 
the trachea and the anterior vena near 
the thoracic inlet, and one or two are on 
the right side of the trachea, dorso-lateral 
to the right brachial artery. Another lies 
on the trachea at the crossing of the vena 
azygos over that tube. 

The bronchial lymph glands are usu- 
ally four in number. The largest one (Lg. 
bifurcationis) is situated in the angle of 
divergence of the chief bronchi, to which 
it is adapted, so that it is somewhat V- 
shaped. Another lies on the left bronchus 
at its bifurcation and in the angle between 
the aortic arch and the left pulmonary 
artery. A third smaller one lies on the 
right bronchus, lateral to the oesophagus; 

it is not always present. A fourth is anterior to the root of the apical bronchus, in 
relation in front to the vena azygos. These glands are commonly black, and the 
same is true of the gland on the right side of the trachea in relation to the vena 
azygos, indicating that all of these glands receive lymph from the lungs. 

Minute pulmonary lymph glands occur in the lungs along the bronchial branches. 




Fig. 624. — Sdblumbar and Pelvic Lymph Glands 
OF Dog. 
1, 1', Renal lymph glands; 2, lumbar lymph glands; 
3, 3', 4, 4', internal iUac lymph glands; 5, 5', medial 
sacral lymph glands; 6, 6', lateral sacral lymph glands; 
7, 7', external iliac lymph glands: a, a', kidneys: b, b', 
crm-a of diaphragm; c, c', psoas minor; d, d' , ilio- 
psoas: e, e', sacro-coccygeus ventralis; /, /', cocey- 
geus; 7, posterior vena cava; //, abdominal aorta; 
///, ///', renal arteries; IV, IV', renal veins; 1', T"', 
VI. VI', circumflex iliac vessels; VII, VII', external 
iliac arteries; VIII, VIII', internal iliac arteries; IX, 
middle sacral artery; X, X' , parietal branches of in- 
ternal iUac arteries; XI, XI', visceral branches of in- 
ternal iliac arteries: XII, XII', common iliac veins; 
XIII, Xlir, external iUac veins; XIV, XIV, in- 
ternal iUac veins. (After Merzdorf). 



758 



CIRCULATORY SYSTEM OP THE DOG 



The lumbar lymph glands are situated in the sublumbar region around and 
between the aorta and posterior vena cava. Most of them are very small and are 
difficult to find in the fat in which they are usually embedded. Their number is 
very variable; as many as fifteen have been counted. 

Usually two large internal iliac lymph glands are present. The right one lies 
along the posterior part of the posterior vena cava and the common iliac vein; the 
left one is similarly placed in relation to the aorta and left common iliac vein. They 
may be two inches or more (ca. 5-6 cm.) in length and nearly an inch (ca. 2 cm.) 
wide in large dogs. In some cases there is a third small gland anterior to the large 
one in relation to the origin of the circumflex iliac vessels. Iia most cases there is a 
gland on each sitle of the middle sacral artery, between that vessel and the internal 
iliac artery and its visceral branch. The gland may be absent on one side or there 
may be instead two or three glands. 




Fig. 625. — Ltmph Glands op Abdominal Visceha of Dog. 
1-6, Portal lymph glands; 7, 8, mesenteric lymph elands; 9-11, CEeco-colic lymph glands; a, liver; b, stomach; 
c, spleen; rf, duodenum {cut off and indicatetl by dotted line) ; e, jejunum; /.ileum; (/.caecum; A, i, t, right, transverse, 
and left parts of colon; /, portal vein; /J, gastro-duodena! vein; 7//, gastro-splenic vein; /T, splenic vein; T, common 
gastric vein; VJ, radicles of splenic vein; T"//, ileo-cseco-coUc vein; 1'///, left coUc vein; JA', middle colic vein; A', 
right cohc vein ; A'l, caecal vein; A'//, ileal vein; A///, jejunal venous trunk. (After Merzdorf.) 



The external iliac lymph glands are situated on the ventral surface of the psoas 
minor, between the diverging external and internal iliac veins. ^ They are inconstant 
and variable. One may occur on each side or two on one side and none on the other. 

The sacral lymph glands arc situated along the roof of the pelvic cavity and 
may easily escape notice on account of the fat in which they areem bedded. Their 
size, number, and arrangement are very variable. In the majority of subjects 
there are two or three glands on the anterior part of the sacro-coccygeus ventralis 
in relation to the middle coccygeal artery. In some cases one or two glands occur 
at the interspace between the sacro-coccygeus ventralis and the coccygeus. In 
other cases glantls are present centrally or on one side only or appear to be absent. 

The term portal lymph glands may be aiJijlied to those which occur along the 
course of the portal vein and some of its affluents. The larger and more constant 
of these are as follows: One lies to the left of the portal vein, on the origin of the 



1 It seems not unlikely that these gland 
of the horse. 



correspond regionally to the deep inguinal glands 



THE LYMPHATIC SYSTEM 759 

duodenum and the duodenal angle (or head) of the pancreas. In most cases two 
glands occur on the right of the portal vein and further back along the mesenteric 
vein. Glands of variable size and number occur in the gastro-splenic part of the 
omentum along the splenic vein and its radicles. 

The mesenteric lymph glands consist chiefly of two elongated nodes which 
extend from the root of the mesentery of the jejuno-ileum along the course of the 
artery of the small intestine and the corresponding vein. 

The colic lymph glands comprise a variable number of nodes (5-8) in the meso- 
colon. One is at the origin of the ileo-cseco-colic vein; a second one may be found 
here. One or two may be fountl in the transverse mesocolon and others (2-5) 
occur at the terminal part of the colon. 

The renal lymph glands, one on each side of the aorta, are in relation to the 
origin of the renal arteries; the riglit one is concealed by the vena cava. 

The superficial inguinal lymph glands are embedded in the fat about the ex- 
ternal inguinal ring in relation to the external pudic vessels. In the male they are 
related medially to the penis; in the female they are commonly termed supra- 
mammary on account of their relation to the base of the inguinal mammary glands. 
In the majority of cases two are present on each side, but there is often only one, 
and sometimes three occur on one side. 

The popliteal lymph gland is situated in a mass of fat on the gastrocnemius 
at the level of the stifle joint. It is between the biceps femoris and semitendinosus, 
but is more superficial than in the other animals, and hence is commonly palpable. 
It is oval and in large clogs may be nearly two inches (ca. 4.5 cm.) long and more 
than an inch (ca. 3 cm.) wide. 



NEUROLOGY 

THE NERVOUS SYSTEM 

The nervous system (Sj'stema nervorum) is a complex mechanism by which the 
organism is brought into functional relation with its environment, and its various 
parts are coordinated. For purposes of gross description it is divided primarily 
into two parts, central and peripheral. The central nervous system (Systema ner- 
ve 1 centrale) comprises — (a) the spinal cord (Medulla spinalis), and (b) the brain 
(El phalon) . The peripheral nervous system (S>'stema nervorum perijihericuni) 
includes — (a) the cranial and spinal nerves with their ganglia, and (6) the sympa- 
thetic nervous system. 

The division into central and peripheral parts is quite arbitrary, and is employed purely 
as a matter of convenience of description. The fibers of which the nerves are composed either 
arise or end within the central system, and therefore constitute an integral part of the latter. 
The structural and fmictional unit of he nervous system is the neurone, which consists of the 
cell-body, usually termed the nerve-cell, a-d all its processes. The processes arise as out- 
growths from the cell-body and conduct impulses to or from the cell ; they vary greatly in length, 
some being less than a millimeter long, while others extend from a cell in the spinal cord to the 
distal end of a limb. A nerve is composed of such processes, usually enclosed in a protecting 
and insulating sheath, and united into bundles by areolar tissue. The neurones are embedded 
in a ]3eculiar supporting tissue termed neuroglia. This consists of a very intricate feltwoik 
of glia-fibers, many of which are connected with the small glia-cells or astrocytes. In addition 
the nervous tissue is invested closely by a vascular layer of connective tissue, the pia mater, from 
which ingrowths extend mto the nervous substance proper.' 

To the naked eye the central nervous system appears to be composed chiefly 
of two kinds of substance, white and gray. The white matter (Substantia alba) is 
dead white in color and is soft in the natural state. It consists largely of medullated 
nerve-fibers, packed closely together and arranged more or less clearlj^ in large or 
small bundles or tracts (funiculi, fasciculi). The gray matter (Substantia grisea) 
is usually brownish-gray in color, often with a tinge of pink. It is softer than the 
white substance and much more vascular. It is composed chiefly of cell-bodies 
and non-medullated processes. In some situations it is modified to form the 
gelatinous substance (Substantia gelatinosa), which is pale yellowish-gray and 
jelly-like. 

Ganglia are gray masses found on the dorsal roots of the spinal nerves and 
on the course of many nerves. They are commonly ovoid in form, but some 
are irregular in shape and branched. They vary greatly in size; some are micro- 
scopic, while others are several inches long. They are enclosed in a fibrous capsule. 
They are composed largely of the cell-bodies of neurones, but have connected with 
and passing through them nerve-fibers (processes) which extend peripherally and 
centrally. In origin and function the spinal ganglia belong properly to the central 
system, but it is customary to include them \\ith the peripheral part in gross ana- 
tomical descriptions. 

Nerves (Nervi) are conducting trunks composed of bundles of parallel nerve- 
fibers. They are enveloped in a fibro-elastic sheath, the epineurium, which contains 
the blood and lymph vessels. They are classified according to their central connec- 
tions as cranial or cerebral, spinal, and sympathetic. The groups of cells of which 
the nerve-fibers are processes are termed the nuclei of origin (Nuclei originis) or 
terminal nuclei (Nuclei terminales) of the nerves, according as the latter conduct 

' Limitations of space and the purpose of this work preclude consideration of the finer 
structure of the nervous system, for which ample literature is available. 

760 



THE MENINGES 761 

impulses in a peripheral or central direction.' On the same basis the nerve-fibers 
are designated efferent and afferent respectively. A bundle of fibers which passes 
from one nerve-trunk to another is called an anastomotic branch (Ramus anasto- 
moticus). In some situations the exchange of branches between adjacent nerves 
is so free as to constitute a nerve-plexus (Plexus nervorum). The term ramus 
communicans is properly restricted to branches which connect the ventral divisions 
of the spinal nerves ^-ith adjacent ganglia or nerves of the sympathetic system. 
The terminal twgs of the nerves are designated, according to their distribution, as 
muscular branches (Rami musculares), cutaneous nerves (Nervi cutanei), and 
articular nerves (Nervi articulares). The muscular branches are motor in function, 
the cutaneous and articular sensor^y, but all contain vasomotor fibers which control 
the caliber of the blood-vessels. 



THE MENINGES 

The central organs of the nervous system are enclosed in three meninges or 
membranes. From without inward these are: (1) the dura mater, (2) the arach- 
noidea, and (3) the pia mater. 

The Dura Mater 

The dura mater is a dense, resistant membrane of white fibrous tissue ; in the 
fresh state it is bluish-white in color. On account of the difference in its arrange- 
ment within the cranium from that in the spinal canal it is customary to describe 
it as consisting of two parts, cerebral and spinal; these portions are continuous with 
each other at the foramen magnum. 

The cerebral dura mater (Dura mater encephali) is adherent to the interior 
of the cranium, and may be regarded as forming an internal periosteum for the 
bones here as well as being an envelope of the brain. Its outer surface is connected 
with the bony wall of the cranial cavitj' by numerous fine fibrous strands and by 
blood-vessels; hence it appears rough in many places when separated from the wall. 
The degree of adhesion varies greatly at different points. It is most firmly attached 
at the various projections, e. g., the internal parietal crest, the tentorium osseum, 
the petrosal crest; also at the base and the foramen magnum. Before the sutures 
are closed the dura is connected A\dth the sutural ligaments and through them is 
continuous with the external periosteum. The cranial nerves receive sheaths from 
the dura, which is thus continuous without the cranium with the epineurium and 
periosteum. Along the roof and sides (except as noted above) the adhesion is 
relatively slight, and lymph spaces are said to exist between the dura and the bone. 
The internal surface of the dura is smooth and glistening, since it is lined by endo- 
thelium and is moistened by a fluid resembling lymph; it forms the outer boundary 
of the subdural space. In accordance ^vith its double fmiction the dura is composed 
of two layers, which are, however, intimately adherent to each other in most places 
in the adult. The venous sinuses are chamiels between the two layers and are lined 
by endothelium. They have been described ^\ith the other vessels. Two folds or 
septa given off from the imier surface of the dura project into the cranial cavity 
between the gross subdivisions of the brain. These are: (1) the falx cerebri; (2) 
the tentorium cerebelli. 

The fabc cerebri is a sickle-shaped median partition which is situated in the 
longitudinal fissure between the cerebral hemispheres. It is attached dorsally 
to the internal parietal crest, in front to the crista galli, and behind to the 
tentorium osseum. Its dorsal border is convex and separates into two layers 

' These cell-groups are the real origin or termination of a nerve. The term " apparent 
origin" is a convenient designation for the point at which a nerve is connected with the surface 
of the brain. 



762 THE NERVOUS SYSTEM 

which enclose the dorsal longitudinal sinus. Its ventral border is concave and 
lies over the corpus callosum. The falx is thick above, but much thinner below, 
and is in some places cribriform.' 

The tentorium cerebelli is a crescentic transverse fold which occupies the 
transverse fissure between the cerebellum and the cerebral hemispheres. It is 
attached dorsallj' to the tentorium osseum and laterally to the petrosal crest. Its 
ventral border is thin, concave, and free ; it forms the dorsal and lateral boundaries 
of an opening (Incisura tentorii) in which the mid-brain is situated. 

The diaphragm sellae is a thickening of the dura which roofs over the pitui- 
tary fossa; it covers the pituitary body and the cavernous and intercavernous 
sinuses. It is perforated centrally by an opening (Foramen diaphragmatis) for 
the infundibulum. 

The f.alx cerebelli, a sickle-shaped fold which projects into the median notch between the 
cerebellar hemispheres in man, is not present in the domesticated animals. There is instead 
merelj' a slight thickening of the dura. 

The spinal dura mater (Dura mater spinalis) forms a tube around the spinal 
cord from the foramen magnum to the second or third segment of the sacrum. It 
is separated from the periosteum of the spinal canal by a considerable epidural 
space (Cavum epidurale), which is occupied by fatty coimective tissue and veins. 
It is held in position chiefly by the sheaths which it furnishes to the roots of the 
spinal nerves, and in its anterior part by two ligaments; the latter connect it with 
the ventral atlanto-occipital membrane and with the dens of the axis. It is large 
in proportion to its contents, but its diameter is not uniform. It is largest in the 
atlas, small in the thoracic region, and becomes very small in its terminal part, 
where it encloses the delicate filum terminale of the spinal cord. 

The subdural space (Cavum subdurale) is the cavity between the inner surface 
of the dura mater and the arachnoidea. It is a mere capillary space which contains 
just sufficient fluid to moisten its surfaces; this fluid is usually regarded as lymph, 
which is replenished by filtration through the walls of the blood-vessels. The 
space is in communication with the lymph paths of the nerve sheaths. 

The Arachnoidea 

The arachnoidea is a very delicate and transparent membrane which is situated 
between the dura and pia mater. Its outer surface forms the inner wall of the sub- 
dural space and is covered by a layer of endothelium continuous v,nth that of the 
opposed surface of the dura mater. Between it and the pia mater is the subarach- 
noid space (Cavum subarachnoideale), which contains the cerebrospinal fluid. An 
inner surface can scarcely be said to exist, since deeply the membrane becomes a 
reticulum of fine fibers which traverse the subarachnoid space and are attached 
to the pia mater. The arachnoidea furnishes sheaths to the cerebral nerves from 
their superficial origins to a variable but usually short distance beyond the emer- 
gence from the sac. In the case of the optic nerve this sheath extends to the ej'eball. 

The cerebral arachnoidea (Arachnoidea encephali), except in the case of the 
great longitudinal and transverse fissures, does not dip into the sulci on the surface 
of the brain. On the summits of the gyri it is so closely attached to the pia mater 
that the two form practically a single membrane. Its outer part bridges over the 
sulci, and here the subarachnoid space is partially divided up by the loose arach- 
noid tissue into intercommunicating cavities. In certain situations the arach- 
noidea is separated from the pia by spaces of consideral)le depth and extent. These 
enlargements of the subarachnoid space are termed subarachnoid cisterns (Cisternse 
subarachnoidales) . In them the subarachnoid tissue does not form a close network, 

1 In the horse the posterior part of the falx cerebri does not extend to the corpus callosum, and 
the cerebral hemispheres are here in contact and adlierent to each other over a small area. In the 
Other animals the falx does not descend so far as in the horse. 



PIA MATER 763 

but consists of a relatively small number of long, thread-like strands which traverse 
the cavity. 

The chief cistemEe are: (1) the cistema magna, which is at the angle formed between the 
posterior face of the cerebellum and the dorsal surface of the medulla oblongata. It communi- 
cates with the fourth ventricle through lateral openings in the latter, and behind with the wide 
subarachnoid space of the spinal cord; (2) the cisterna pontis, on the ventral surface of the pons; 
(3) the cistema basalis, which lies at the base of the cerebrum and is divided by the optic chiasma 
into two parts (cistema chiasmatis, cistema interpeduncularis) ; (4) the cistema fossae lateralis, 
situated at the lower part of the lateral fissure and continuous with the cistema basalis. 

Along the dorsal border of the falx cerebri the arachnoidea bears bulbous 
excrescences, the arachnoid granulations.^ These are enclosed in thin evaginations 
of the dura mater and project into the dorsal longitudinal sinus or the parasinoidal 
sinuses along either side of it. In some cases they are sufficiently large to exert 
pressure on the bone and produce in it depressions of variable depth. 

The spinal arachnoidea (Arachnoidea spinalis) is continuous with that of the 
brain at the foramen magnum. It forms a relatively wide tube around the spinal 
cord, so that the latter (enclosed in the pia) is surrounded by a very considerable 
quantity of cerebrospinal fluid. The spinal subarachnoid space is traversed by 
fewer trabeculse than is the case in the cranium. It is partially subdivided by three 
imperfect septa. One of these, the septum dorsale, is median and dorsal. The 
other two, the ligamenta denticulata, are lateral and will be described with the pia 
mater. 

Pia Mater 

The pia mater is a delicate and very vascular membrane, which invests closely 
the surface of the brain and spinal cord and sends processes into their substance. 
It also furnishes sheaths to the nerves, which blend outside of the dural sac with the 
epineurium. 

The cerebral pia mater (Pia mater encephali) follows accurately all the in- 
ecjualities of the surface, dipping into all the fissures and sulci of the cerebrum, and 
into the larger fissures of the cerebellum. Its external surface, which forms the 
inner boundary of the subarachnoid space, is covered by a layer of endothelium. 
From its deep face numerous trabeculse are given off which penetrate into the sub- 
stance of the brain, forming a path for the blood-vessels, and concurring with the 
neuroglia in forming the supporting tissue of the nervous substance proper. The 
larger blood-vessels of the brain lie within the subarachnoid space, but the smaller 
vessels ramify in the pia, forming rich plexuses. The twigs which penetrate into 
the gray matter are enclosed in pial sheaths. They are end-arteries, i. e., constitute 
the entire supply of the district which they enter and do not anastomose with 
adjacent vessels. 

Important folds of the pia extend into two of the great fissures of the brain. 
One of these passes in at the transverse fissure between the cerebellum and 
the cerebral hemispheres, and is continued so as to overlie the third ventricle; it 
forms the tela chorioidea of that cavity. Another fold passes in at the fissure 
between the cerebellum and the medulla oblongata and forms the tela chorioidea 
of the fourth ventricle. They constitute paths for the deeper vessels and their 
edges contain vascular convolutions which are known as chorioid plexuses. They 
will receive further consideration more appropriatelj' later. 

The spinal pia mater (Pia mater spinalis) is thicker and denser than that of 
the brain. It has a strong outer layer of fibrous tissue, most of the fibers of which 
are longitudinal. The inner layer is vascular and adheres closely to the surface 
of the spinal cord, because numerous processes extend into the latter from it. It 
sends a fold into the median ventral fissure and also helps to form the median 
dorsal septum of the cord. Along the median ventral line it forms a band-like 

1 They are also known as Pacchionian bodies. 



764 NERVOUS SYSTEM OF THE HORSE 

thickening, the linea splendens, along which the ventral spinal artery runs. On 
each side the pia mater gives off a strong longitudinal band, the ligamentum den- 
ticulatum, which is connected externally with the dura mater. The inner or pial 
border extends in a line between the dorsal and ventral roots of the nerves. The 
outer or dural border is denticulated and to a large extent free. The denticulations 
are attached to the dura between the nerve-roots. 



NERVOUS SYSTEM OF THE HORSE 
The Spinal Cord 

The spinal cord (Medulla spinalis) is the part of the central nervous system 
which is situated in the vertebral canal. It extends from the foramen magnum to 
about the middle of the sacrum. Its average length is about 76 to 78 inches (ca. 
190-195 cm.), and its weight about 8)4 to 9 ounces (ca. 240-255 grams). 

It is approximately cylindrical, but more or less flattened dorso-ventrally. 
There is no natural line of demarcation between it and the medulla oblongata, but 
for descriptive purposes the division is usually assumed to be at the plane of the 
foramen magnum. Its posterior part tapers rapidly to a point, forming the conus 
medullaris. This is prolonged for a short distance by the slender filum terminale. 

Forty-two pairs of spinal nerves are connected with the sides of the spinal cord. 
They are classified as eight cervical, eighteen thoracic, six lumbar, five sacral, and 
five coccygeal. According to the attachments of these series of nerves the spinal 
cord is divided into cervical, thoracic, lumbar, and sacral parts. ^ 

In the embryo these divisions correspond primitivelj^ to the regions of the 
vertebral column, but later, through unequal growth of the cord and spine, the 
correspondence between the two is not at all exact in the anterior regions and is 
lost in the last two. The lumbar part of the cord in the horse ends at the junction 
of the fifth and sixth lumbar vertebrae, so that the roots of the last lumbar nerve 
must run backward the length of the last lumbar vertebra to reach the interverte- 
bral foramen through which it emerges. The conus medullaris reaches only to the 
anterior part of the sacral canal, so that the roots of the sacral and coccygeal nerves 
extend backward in the spinal canal for a considerable distance, forming a leash 
of bundles, in the center of which lie the conus medullaris and the filum terminale. 
This arrangement is expressively designated the cauda equina. 

Each pair of spinal nerves is attached by its root-fibers to a certain length of 
the cord, and the latter is, therefore, regarded as consisting of as many segments 
as there are pairs of nerves. It is to be noted, however, that there is no line of 
demarcation between the segments other than the intervals between the root-fibers 
of adjacent nerves. 

The segments are of different lengths; the longest are the third to the sixth cervical, which 
measure 11, 10, 10, and 8..5 cm. respectively. The spinal nerves are in general designated accord- 
ing to the vertebra! behind which they emerge from the vertebral canal. In the neck, however, 
there are eight pairs of nerves and only seven vertebra-; here the first nerve emerges through the 
intervertebral foramen of the atlas and the eighth between the last cervical and the first thoracic 
vertebrae. 

In the greater part of the thoracic region the spinal cord is fairly uniform in 
size, but there are two conspicuous enlargements which involve the segments with 
which the nerves of the limbs are connected. The cervical enlargement (Intumes- 
centia cervicalis) begins gradually in the fifth cervical vertebra and subsides in 

' In a horse about 16J^ hands high these parts measured 65 cm. (ca. 26 in.), 86 cm. (ca. 34.4 
in.), 27 cm. (ca. 10.8 in.), and 15 cm. (ca. 6 in.) respectively (Dexler). 



THE SPINAL COED 



7Q5 



the second thoracic. Its maximum transverse diameter is about an inch (ca. 25 
mm.) and its dorso-ventral nearly half an inch fca. 12 mm.). The Iximbar enlarge- 
ment (Intumescentia lumbaHs) is situated in the fourth and fifth lumbar vertebrae. 

It is a little narrower than the cervi- 
cal enlargement, and its dorso-ventral 
diameter is also slightly smaller. Be- 
hind this the cord tapers rapidly to 
form the conus medullaris. The tip 
of the latter is continued by a delicate 
glistening strand, the filiim terminale, 
which is composed largely of fibrous 
tissue continued from the pia mater, 
covered by arachnoid. 






Fig. 626. — Ventral View of Medulla Oblongata 
AND First and Secoxd Segments of Spinal 
Cord of Horse; the Membranes are Cut and 
Reflected. 

1, Lig. auspensorium arachnoideale ; 2, right cere- 
brospinal artery; 3, 5, digitations of lig. denticulatum; 
4. free border of lig. denticulatum; 6, middle spinal 
arter>-; 7, basilar artery; S, pons; 9, arachnoidea; 
10, dura mater; 11, 12, ventral root-bundles of first 
and second segments of spinal cord; T'/, N. abducens; 
IX, X, glosso-phar>'ngeus and vagus; XI, accessorj-, 
medullarj- part; ,Y7', accessorj-, spinal part; a, line 
between medulla oblongata and spinal cord. (Dexler, 
in Ellenberger-Baum, Anat. d. Haustiere.) 



Fig. 627. — Cauda EqtnNA. 
1, Dura and arachnoidea divided and reflected; Zt 
spina! cord; 3, nerve-roots. (From l.eisering'3 Atlas, re- 
duced.) 



The surface of the spinal cord is 
divided into two similar halves by a 
dorsal median groove and a ventral 
median fissure. On either side of the 
former is the dorso-lateral groove (Sul- 
cus dorsalis lateralis), at which the fibers 
of the dorsal nerve-roots enter the cord; 
it is faint except at the enlargements, and is represented by two grooves in the first 
cervical segment. The ventral root-fibers as they emerge from the cord do not 
form a continuous series, but arise from a zone (Area radicularis ventralis) 3 to 5 



766 



NERVOUS SYSTEM OF THE HORSE 



mm. in width, a little lateral to the ventral median fissure, and no groove is found 
here. In the greater part of the cervical region and the anterior part of the thoracic 
region there is a shallow dorsal intermediate groove (Sulcus intermedius dorsalis) a 
short distance lateral to the median groove. These grooves indicate the division 
of the white matter of the cord into columns to l)e described later. 

Examination of cross-sections of the spinal cord shows that it is a bilaterally 
symmetrical structure, incompletely divided into right and left halves by a ventral 
fissure and a dorsal septum. The ventral median fisstire (Fissura mediana ven- 
tralis) is narrow and penetrates nearly to the middle of the dorso-ventral diameter 
of the cord. It is occupied by a fold of pia mater. The dorsal median septum 
(Septum medianum dorsale) is a partition which descends from the dorsal median 
groove to about the middle of the cord. It apparently consists of condensed neu- 
roglia with an admixture of pial tissue. The two halves of the cord are connected 




Fig. 62S. — Ckosb-section of Spinal Cord in situ. Enlarged and in Part Schematic. 
1, Dorsal column; S, lateral column; S, ventral column; 4i doraal horn; 5, ventral horn; 6, gray commissure; 7, 
white commissure ; 5, central canal; 5, dorsal septum; iO, ventral fissure; i ^ , dorsal nerve-root ; / 5. ventral nerve-root. 
I3y spinal ganglion; 14, spinal nerve; 15, intervertebral foramen; 16, arch of vertebra; 17, epidural space; IS, dura 
mater (represented a little too thick); 19, ligamcntum denticulatum; 20, BO, longitudinal venous sinuses; £1, middle 
spinal artery; 22, body of vertebra. The subdural and subarachnoid spaces (black) are traversed by delicate trabec- 
ule. The outer part of the arachnoid and the pia mater are not shown. 



by commissures of gray and white matter. The gray commissure (Commissura 
grisea) is a transverse band of gray matter at the ventral end of the dorsal septum. 
It is divided into dorsal and ventral parts by the central canal of the cord. The 
white commissure (Commissura alba) is a bridge of white matter which connects 
the ventral columns of the cord over the dorsal end of the ventral median fissure, 
and constitutes a conducting path from one side to the other. 

The central canal of the spinal cord (Canalis centralis), the spinal vestige of the 
lumen of the embryonal neural tube, is a minute passage which tunnels the gray 
commissure. It opens at its anterior end into the posterior part of the fourth 
ventricle of the brain, and its terminal part in the conus meduUaris forms a slight 
dilatation, the ventriculus terminalis. It is lined by epithelium and is surrounded 
by a layer of modified neuroglia (Substantia grisea centralis). 

The gray matter of the spinal cord as seen in cross-sections resembles roughly 



THE SPINAL CORD 767 

a capital H, the cross-bar of the letter being formed by the gray commissure. 
Each lateral part is considered as consisting of dorsal and ventral gray columns 
(Columna grisea dorsalis, ventralis), which appear in cross-section as the so-called 
horns (Cornu dorsale, ventrale) . In the greater part of the cord the dorsal column 
or horn is elongated and narrow and tapers to a point which extends almost to the 
surface of the cord at the attachment of the dorsal root-fibers of the spinal nerves. 
Its apex or tip consists of gray matter which is lighter in color and less opaque 
than that of the rest of the horn, and is termed the substantia gelatinosa. The 
ventral column or horn is short, thick, and rounded, and is separated from the surface 
of the cord by a thick layer of white matter, through which the fibers of the ventral 
roots of the spinal nerves pass. From the middle of the cervical region to the 
lumbar region there is a medial projection of gray matter on the ventral part of the 
dorsal column; this is the nucleus dorsalis.' In the anterior part of the cord there 
is an outward projection of the gray matter at the base of the ventral horn; this 
is termed the lateral column or horn. The demarcation between the gray and 
white matter is in many places indistinct; this is especially the case laterally, 
where processes of gray matter extend into the white substance, producing what 
is kno\vn as the formatio reticularis. 

Cross-sections of the spinal cord present the following gross regional characters: (1) The 
cervical cord near the medulla is compressed dorso-ventrally. Its width is about IS mm. and 
its greatest thickness about 8 mm. It has dorsally a deep median sulcus and a distinct dorso- 
lateral sulcus. Lateral grooves are also present. The dorsal comua are strongly everted. Each 
has an expanded head, which comes very close to the surface of the cord, and has an extensive 
cap of substantia gelatinosa. The neck is distinct. The ventral cornua are short and blunt and 
diverge very little. The gray commissure is about in the middle of the section, and 2.5 mm. 
in length. According to Dexler, the column between the median and lateral grooves dorsally 
is the funiculus cuneatus, the funiculus gracilis being very small and not showing on the surface 
in this region. In the middle of the cervical region the diameters are about 16 mm. and 10 mm. 
respectively. The ventral surface is somewhat flattened. The dorsal cornua have pointed ends 
and turn decidedly outward. The ventral cornua are short and thick and are directed very slightly 
outward; their ends are about 4 mm. from the ventral surface. The gray commissure is just 
above the middle of the section and is about 2 mm. long. The cervical enlargement measures 
about 2.5 mm. transversely and 12 mm. vertically. The dorsal cornua are smaller than the ventral 
and have a large cap of substantia gelatinosa. The ventral cornua are short and thick, curve 
strongly outward, and are about 4 mm. from the ventral surface. Each bears a prominence on its 
medial side near the base. The gray commissure is considerably above the middle of the section 
and is about 4 mm. long. (2) In the middle of the thoracic region the cross-section is biconvex, 
the ventral surface being the more strongly curved. The transverse diameter is about 15 mm. 
and the dorso-ventral about 10 mm. The gray columns are close together, the gray commissure 
being only about 1 mm. in length, and lying considerably above the middle of the section. The 
dorsal cornua are short and have slightly enlarged ends. The ventral comua have a uniform diame- 
ter, turn very little outward, and end about 3 mm. from the ventral surface. (3) The lumbar enlarge- 
ment is much flattened, especially dorsally. The transverse diameter is about 22 mm. and the 
dorso-ventral 9 to 10 mm. The comua are very large. The ventral cornua are thick and rounded 
and turn sharply outward; they end about 2 mm. from the ventral surface. The dorsal cornua 
are smaller and shorter and do not diverge so strongly. The gray commissure is about in the 
middle of the section and is about 3 mm. long. In the third lumbar vertebra the cord is about 
3 mm. narrower and thicker, and both surfaces are about equally convex. The dorsal comua are 
smaller, considerably everted, and constricted in the middle. The ventral comua are very short 
and do not turn outward. (4) In the first sacral vertebra the cord is almost round and is 5 to 6 mm. 
in diameter; the cornua are relatively very large and the commissure has the form of a high inter- 
mediate mass. 

The ventral horn contains large cells, the axones of which emerge as the fibers of the ventral 
nerve-roots (Fila radicularia). The axones of many cells cross to the opposite side in the white 
commissure and pass out in a ventral root of that side, or enter the white matter and pass forward 
and backward, associating various segments of the cord. Some pass to the ventral horn of the 
opposite side at the same or at different levels. Others pass to the periphery of the cord, join 
the cerebellospinal fasciculus, and extend to the cerebellum. Scattered through the gray matter 
are many smaller cells with axones which pursue a short course and serve to connect different 
parts of the gray matter. 

The white matter of the spinal cord is divided into three pairs of columns. 
The dorsal columns (Funiculi dorsales) lie on either side of the dorsal median septum 
and extend outward to the dorso-lateral groove and the dorsal gray column. The 

' Also known as Clarke's column. 



768 NERVOUS SYSTEM OF THE HORSE 

ventral coliunns (Funiculi ventrales) are situated on either side between the median 
fissure and the ventral gray columns. The.v are connected above the fissure by 
the white commissure. The lateral columns (Funiculi laterales) are lateral to the 
gray columns on either side; their limits are indicated superficially by the dorso- 
lateral groove and the emergence of the ventral root-fibers. The intermediate 
groove (where present) indicates a subdivision of the dorsal column into two fasci- 
culi or tracts; the medial of these is the fasciculus gracilis; the lateral one is the 
fasciculus cuneatus.^ 

The amounts of gray and white matter vary greatly in different parts of the 
cord both absolutely and relatively. In cross-section the absolute areas of both are 
greatest in the enlargements. The relative area of gray matter is smallest in the 
thoracic region (except at its anterior end), and increases from the lumbar enlarge- 
ment backward. 

Investigations have shown that in man the columns of white matter are subdivided into 
fascicuh or tracts, wliich constitute definite conductmg paths of greater or less length. Our 
knowledge of the tracts in the domesticated animals is very limited, and it is quite unsafe to make 
inferences from the arrangement ill man. As evidence of this it may be noted that the ventral 
cerebrospinal or direct pyramidal tract of man cannot be recognized as such. 

The dorsal white columns consist essentially of two sets of axones. The afTerent or sensory 
axones which come from the cells of the spinal ganglia enter as the dorsal roots of the spinal nerves 
and divide into two branches in the vicinity of the dorsal gray column. The anterior branches 
form the direct sensory path to the brain and extend in the fasciculus cuneatus and fasciculus 
gracilis or corresponding tracts to nuclei in the medulla oblongata. The posterior branches 
extend backward for varying distances and give off numerous collaterals to cells of the gray column, 
thus forming part of the mechanism for the mediation of reflex action. Some collaterals cross 
in the white commissure to the opposite side. Many of these fibers are collected in the comma- 
shaped tract between the fasciculus gracilis and cuneatus. The second set of axones arises from 
the smaller cells of the gray column. They enter the white matter, divide into anterior and 
posterior branches, forming the fasciculi proprii or ground bundles of the cord. Some branches 
cross to the opposite side. The function of this set of axones is chiefly to associate various levels 
of the cord. 

The lateral columns contain some axones of the dorsal nerve-roots, which (in man) are 
grouped in the marginal tract of Lissauer, situated just dorsal to the apex of the dorsal horn. 
The cerebellospinal fasciculus (direct cerebellar tract of Flechsig) extends along the periphery 
of the lateral column. It contains the axones of the cells of the nucleus dorsalis (Clarke's column), 
which proceed to the medulla oblongata and enter the cerebellum by the restiform body. The 
rubrospinal tract (of Monakow) appears to take the place of the lateral cerebrospinal fasciculus or 
crossed pyramidal tract of man. It lies at the medial side of the cerebellospinal fasciculus. Its 
fibers arise in the nucleus ruber of the mid-bram, cross the median plane (decussation of Forel), 
and ppss backward in the tegmentum and medulla oblongata to the lateral colunm of the cord. 
It is a path for motor impulses coming from the cerebral cortex and the cerebellum. The lateral 
fasciculus proprius or groimd-bu. die is deeply situated at the side of the gray columns. The 
bulk of its fibers are axones of cells of the dorsal column which divide into anterior and posterior 
branches. They are intersegmental paths which associate different levels of the gray matter of 
the cord. The significance of the remaining fibers is not yet knomi. 

The ventral white columns do not contain a ventral cerebrospinal or direct pyramidal tract, 
as in man. There is a small tract (Fasciculus intraccmmissuralis ventralis) dorsal to the white 
commissure, which separates it from the rest of the ventral column. It extends to the middle of 
the thoracic region. It consists of intersegmental fibers, and contains in the anterior part of 
the cervical cord in the sheep and goat both crossed and direct pyramidal fibers. The descending 
cerebellospinal fasciculus extends from the cerebellum to the lumbar region. In the ceri-ical 
region it occupies a semilunar area which reaches almost to the surface ventro-laterally. Scattered 
fibers belonging to it lie also in the medial part of the ventral column. Posteriorly it diminishes 
in size and comes to occupy a position next to the ventral median fissure, corresponding to the 
sulco-marginal fasciculus of man (Dexler). 



The Brain 

The brain or encephalon is the part of the central nervous system that is 

situated in the cranial cavity. It is the enlarged and highly modified cephalic 

part of the primitive neural tube. It conforms in great part in size and shape to 

the cavity in which it lies. Its average weight without the dura mater is about 

' These are also known as the columns of Goll and of Burdach respectively. 



THE BRAIN 769 

23 ounces (ca. 650 gm.), and forms about y of 1 per cent, of the body-weight in a 
subject of medium size. 

It is desirable to examine the general external configuration of the brain before 
stutlying its various parts in detail.' 

When divested of its membranes and vessels (Fig. 629), its ventral surface or 
base presents the median brain stem (Caudex eneephali), which is continuous with 
the spinal cord without any natural line of demarcation; it divides in front into 
two branches, the cerebral peduncles, each of which disappears into the mass of 
the corresponding cerebral hemisphere. The brain stem consists of three parts. 
The medulla oblongata is the posterior part which extends forward as the direct 
continuation of the spinal cord. The pons is a transversely elongated mass which 
appears to turn up on either side into the cerebellum. The cerebral peduncles 
(Pedunculi cerebri) extend forward from the pons and diverge to plunge into the 
ventral part of the cerebral hemispheres. The area between them is the inter- 
peduncular fossa. It is largely covered by the hypophysis cerebri or pituitary 
body, a yellowish-brown, discoid structure, which is connected with the base of 
the cerebrum by a delicate tube called the infundibulum.- On drawing the pitu- 
itary body gently aside, the infundibulum is seen to be attached to a slight gray 
eminence, the tuber cinereum. Behind this is the mammillary body (Corpus 
mamillare), a well-marketl round prominence. The posterior part of the space 
is perforated by numerous openings for tlie passage of small arteries, and hence 
is termed the substantia perforata posterior. A large band of white matter, the 
optic tract (Tractus opticus), crosses the anterior end of the cerel^ral peduncle ob- 
liciuely, and unites \vith the opposite tract to constitute the optic chiasm or commis- 
sure (Chiasma opticmn), and form the anterior boundary of the interpeduncular 
fossa. Aljove and in front of the chiasm the hemispheres are separated by the 
median longitudinal fissure. In contact with the anterior extremity of each 
hemisphere is the olfactory bulb (Bulbus olfactorius), an oval enlargement which 
occupies the ethmoidal fossa of the cranium. This appears as a gray swelling 
on a wide flat band, the olfactory tract or peduncle (Tractus olfactorius), which 
is continued behind by two divergent bands, the olfactory striae. The medial 
stria (Stria medialis) disappears after a very short course on to the medial surface 
of the hemisphere. The lateral stria (Stria lateralis) is larger and longer; it runs 
backward, inclines at first outward and then curves medially and disappears on 
the concealed or tentorial surface of the hemispheres. It is separated from the 
lateral cerebral gyri by a distinct groove (Sulcus rhinalis). Along the medial side 
of the stria are two eminences. The anterior of these is the trigonum oUactorium, 
a gray elevation situated in the angle of divergence of the medial and lateral strise. 
Behind this is a depression, the fossa lateralis, which is continued across the lateral 
stria and sharply limits the second and much larger eminence, the piriform lobe. 

The superficial origins of most of the cranial nerves are visible on the base of 
the iDrain. 

The olfactory nerve-fibers join the convex surface of the olfactory bulb and give 
it a shaggy appearance in specimens which have l^een removed intact — a difficult 
proceeding. 

The second or optic nerves converge to the optic chiasm. 

The third or oculomotor nerve arises from the medial part of the cerebral 
peduncle. 

' The description given here is intended to present the chief facts in regard to the brain as 
they may be studied in the dissecting-room. The vessels and membranes, which must be exam- 
ined first, have been described. 

" Unless care is used in removing the brain, the infundibulum is likely to be torn and the 
hypophysis left in the cranium. In this case there is a small opening which communicates with 
the third ventricle. 
49 



770 



NERVOUS SYSTEM OF THE HORSE 



The fourth or trochlear nerve may be seen emerging between the pons and the 
cerebral hemisphere, Ijut its connection with the brain is not visible. 

The fifth or trigeminal nerve is connected with the lateral part of the pons. 




I» 



'^-■. \ 



w 



Fig. 629. — Base of Brain of Horse About Natural Size. 
Hardened in sHu. 

The sixth or abducent nerve arises just Ijehind tlie pons and lateral to the 
pyramid of the medulla. 

The seventh or facial and the eighth or acoustic nerves arise close together 
just behind the pons on the extremity of the corpus traiiezoideum. 



THE BRAIN 



771 



The ninth or glosso-pharyngeal, the tenth or vagus, and the eleventh or spinal 
accessory nerves are connected lay a linear series of roots with the lateral aspect of 
the ventral surface of the medulla. The spinal part- of the accessorj^ nerve comes 
forward along the edge of the medulla to join its medullary root. 

The twelfth or hypoglossal nerve arises from the posterior part of the medulla 
along the lateral edge of the pyramid. 

The parts that are visible when the brain is viewed from above are the cerebral 
hemispheres, the cerebellum, and part of the medulla oblongata. The cerebral 
hemispheres (HemisphEeria cerebri) form an ovoid mass, and are separated from 
each other by the median longitudinal fissure (Fissura longitudinalis cerebri), 

Liiiigiliiiliniil fixxiirc 



Trigemimil 
ncriv 



Sulcus rhinalis'^^ 
Optic nerve ^ 
Optic chiasma^^^ 
Tuber ciuereum -^^ 

Piriform lobe — 
Pituitary body 
Oridomotor neriv 
nsory root 



motor root 
CerclxUum ~^ 



Tubcrciilum faciale 

Glosso-pharyngeal ner 
Vagus ner re 
Accessory nerve {medullary root 



Fig. 630.— Li.ve D 

VI, Abducent 




Accessory nerve {spinal root) -' 
Hypoglossal nerve 



Olfactory bulb 

^^-^ Olfactory trad 

-- Medial stria 

, Lateral stria 

— Trigonum olfactorium 
~- Fossa lateralis 
Cerebral peduncle 
Tract us ped. transversiis 

- Interpeduncular fossa 

- Pons 

'■ — Corpus trapezoidcum 

Pyramid 

Medulla oblongata 

~"~~~ Chorioid plexus of fourth 

ventricle 
Median fissure and de- 
cussation of pyramids 
Spinal cord 
Fig. 629.) 



in which the falx cerebri is situated. Their surfaces are marked by thick ridges, 
the gyri cerebri, separated by sulci. The upturned ends of the olfactory bulbs 
are seen in front of the frontal poles of the hemispheres. The occipital poles of 
the hemispheres overlie the anterior part of the cerebellum, from which they are 
separated by the transverse fissure (Fissura transversa cerebri) and the tentorimn 
cerebelli contained in it. The cerebellum is a much smaller rounded mass which con- 
ceals the greater part of the medulla oblongata. Its surface is divided into a middle 
lobe, the vermis cerebelli, and two lateral hemispheres ( Hemisphffiria cerebelli). It 
is marketl by numerous gyri and narrow sidci wliich have in general a transverse direc- 
tion. The posterior third of the medulla oblongata is not covered by the cerebellmn. 

The brain is developed from the expanded cephaUc part of the neural tube of the embryo. 
The process comprises a series of thickenings, flexures, and unequal growth and expansion of 



772 



NERVOUS SYSTEM OF THE HORSE 



various parts of the tube. In the higher animals the result is that 'the tubular character of the 
brain is not very evident, since the lumen comes to consist of four irregular cavities, the cerebral 
ventricles, which are connected by narrow passages. The tube is first subdivided by two con- 
strictions into three brain vesicles, termed respectively the hind-brain or rhombencephalon, the 
mid-brain or mesencephalon, and the fore-brain or prosencephalon. The hind-brain gives rise to 
three secondary segments and the fore-bram to two. The annexed table indicates the origin of the 
principal structures of the fully developed brain from the primitive vesicles. It has become 
ciistomary to describe the brain with reference to its erabryological relations. 



Longitudinal 

iiasure Olfactory bull. 



Transverse fissure 




Frontal pole of hemisphere 



Cerebrum 



Occipital pole of 
hemisphere 



Medulla oblongata 



Fig. 631. — Brain • 
1, Entomarginal fiss 



■ Horse; Dorsal View, About ? Natural Siz: 
re; 2, marginal fissure; 3, ectomarginal fissure; 



Hardened in situ. 
, suprasylvian fissure. 



TABLE INDICATING THE DERIVATION OF THE PRINCIPAL PARTS OF THE 



Primary Segments. 



Rhombe ncephal o 
terior vesicle) . 



Mesencephalon 
vesicle) 



BRAIN 

Secondary Segments. Derivatives. 
Myelencephalon Medulla oblongata 

Metencephaion { c?^beiium :::::::::::::: : 

Anterior cerebellar pedunclei 



Isthmus rhombencephali . 



Anterior medullary velu 



M 



, , I Corpora quadrigemin 

epnaion -^ pprphrRl npHun^-lPS 



Cerebral peduncle; 

\ Optic thalami 

Diencephalon -j Hypothalamic tegmenta. . 

I Pineal body 

I Pituitary body 
Optic nerves and rptinse. . 
Cerebral hemispheres .... 
Olfactory tracts and bulb. 



Fourth ventricle 



I" Cerebral aqueduct 

I Posterior part of third 
t ventricle 

1 Anterior part of third 
ventricle. Lateral 
ventricles and olfac- 
tory continuations. 



THE RHOMBENCEPHALON 773 



THE RHOMBENCEPHALON 
The Medulla Oblongata 

The medulla oblongata (Figs. 629, 632, 635) lies on the basilar part of the 
occipital bone. It is quadrilateral in outline, but much wider in front than behind, 
and compressed dorso-ventrally. Its length, measured from the root of the first 
cervical nerve to the pons, is about two inches (ca. 5 cm.). 

Its ventral surface is convex in the transverse direction, and presents a ventral 
median fissure (Fissura mediana ventralis), which is continuous behind with the 
similar fissure of the spinal cord. The posterior part of the fissure is faintly marked, 
but in front it becomes deeper and ends in a small depression (Foramen caecum) 
behind the central part of a transverse band, the corpus trapezoideum. On either 
side of the fissure is a rounded tract, the pyramid (Pyramis), which is bounded 
laterally by a faint groove (Sulcus intermedius ventralis). The pyramids join 
the pons in front; behind they become narrower and disappear into the substance 
of the medulla, in which their fibers intercross, forming the decussation of the 
P5rramids (Decussatio p3a-amidum).' The superficial origin of the oculomotor 
nerve (N. oculomotorius) is just lateral to the anterior end of the pyramid. The 
corpus trapezoideum is a transverse band which extends across the surface imme- 
diately bchintl the pons. It is crossed by the pyramids, which cut off a small 
central part. The lateral part extends out to the roots of the seventh and eighth 
nerves on either side. Behind the lateral part of the corpus trajjezoitleum there 
is a variably developed roimded eminence, the tuberculimi faciale. The root- 
fibers of the hypoglossal nerve form an oblique linear series lateral to the posterior 
part of the p.\'ramid. 

The dorsal surface is largely concealed by the cerebellum and forms the greater 
part of the floor of the fourth ventricle. The dorsal median fissure (Fissura 
mediana dorsalis), the direct continuation of the corresponding groove of the spinal 
cord, extends forward to about the middle of the surface. Here the restiform 
bodies, which constitute the lips of the fissure, diverge to form the lateral lioun- 
daries of a triangular depression; this is the posterior part of the rhomboid fossa or 
floor of the fourth ventricle of the brain. The dorso-lateral groove winds outward 
and forward to the lateral aspect of the medulla, where it presents the roots of the 
glosso-pharyngeal, vagus, and accessory nerves. Lateral to it is a ilistinct oval 
eminence on tlie anterior part of the lateral column, termed the tuberculum cin- 
ereum. The central canal of the cord is continued in the posterior part of the 
mcLluUa, inclines dorsally, and opens in the posterior angle of the fourth ventricle. 
Hence it is customary to distinguish a closed and an open part of the medulla. 
The dorsal aspect of the latter, which is concealed at present, will be considered 
later in the description of the fourth ventricle. 

The lateral surface is narrow behind, wider and rounded in front. From it 
the root-fibers of the ninth, tenth, and eleventh cranial nerves arise in a linear 
series, and alongside of it the spinal part of the eleventh nerve passes forward to 
join the medullary root. Close inspection reveals the presence of striae which 
curve ventrally and backward from the surface of the restiform ])0(:i>- toward the 
hypoglossal root-fibers; these are the external arcuate fibers (Fibrte arcuatse 
externse). The recess between the lateral aspect of the medulla and the cerebellum 
is occupied by an irregular mass of villous projections of the pia mater, containing 
tufts of vessels ; this is the chorioid plexus of the fourth ventricle, and is the lateral 
edge of the tela chorioidea of the ventricle. On raising the chorioid plexus, it is 
seen that the tela chorioidea is attached to the dorsal aspect of the medulla, and 
reinforces here the wall of the fourth ventricle; also that the restiform body ter- 

' The decussation varies superficially in different specimens. In some there is a distinct 
superficial crossing of fibers so that the median fissure is practically effaced at this point. 



774 



NERVOUS SYSTEM OF THE HORSE 



minates in front by entering tlie base of tiie cerebellum, forming its posterior 
peduncle. 

In the medulla the fiber tracts of the spinal cord either terminate in the nuclei of the gray 
matter or undergo changes in their relative position, and new tracts appear. The gray matter 
is highly modified and forms masses which have no homologues in the cord. The central canal 
of the closed part of the medulla is surrounded by a thicker layer of gray matter than is the case 
in the spinal cord. As the medulla opens out this gray matter is natiu'ally spread in the floor of 
the fourth ventricle. The dorsal horns of sray matter become wide, s])read a|)art, and are broken 
up to a great extent in the formatio reticulans. Two cldiipialcd nm.s.-;i's of cells appear above the 
central gray matter; these are the nucleus gracilis and nucleus cuneatus, and in them the 
fasciculi of like name gradually end. In front of t hese are the terminal nuclei of the afferent or 
sensory cranial nerves and of the sensory portions of the mixed nerves. The ventral horns are 
succeeded by the nuclei of origin ot the efferent or motor cranial nerves and the motor root-fibers 
of the mixed nerves. Of the twelve pair.'i of cranial nerves, the last eight are connected with 
nuclei in the medulla and pons. The posterior olivary nucleus (Nucleus olivaris caudalis) is a 
conspicuous gray mass which lies dorsal to t he pyramid on each side. On cross-sections it appears 



Tra tisvcrse fissure 




Olfactory Olfactory 
bulb tract 



Fig. 632. — Brain of Horbe; Left View. 
1, Lateral fissure; 8, suprasylvian fissure; 5, presylvian fissure; 4. ectomarginal fissure; 5, S', sulcus rhinalis i 
terior et posterior; L. ;>., piriform lobe; B. p., middle peduncle of cerebellum (brachium pontia); P. c, choroid plej 
of fourth ventricle. Roman numerals indicate roots of crai 



as a wavy layer oi gray matter which is folded on itself so as to enclose a mass of white matter. 
It is about 2 cm. long in the horse, but is smaller in circumference than in man and hencje does 
not cause any very distinct external enlargement (olivary eminence), as in the latter. It is con- 
nected with the opposite side of the cerebellum by the cerebello-olivary fibers. At its medial side 
are two small icccssory olivary nuclei. The pyramidal tracts, which are small in ungulates, send 
most of tlicir tihcrs across to the opposite side in the posterior part of the medulla, forming the 
pyramidal decussation. Some fibers, however, continue in the ventral column of the same side 
of the cord, and others are connected with the nuclei of the motor nerve-roots. From the nu- 
cleus gracilis and nucleus cuneatus fibers arise which are traceable forward to the thalamus. 
These are the internal arcuate fibers (Fibrse arcuatie inteniEe), which curve across the median 
pl.ane ventral to the central gray matter and form with those ot the opposite side the decussation 
of the fillet (Decussatio lemniscorum). Beyond the decussation the fibers form an important 
longitudmal tract which extends forward in the mid-brain. This is the fillet or lemniscus, the 
chief continuation of the sensory conducting path from the dorsal roots of the spinal nerves. 
The external arcuate fibers (Fibrse arcuatse externEe), some of which were seen on the lateral 
aspect of the medulla, have a similar origin. Part of them (Fibra- dorsales) pa.ss directly to the 
dorsal aspect of the restiform body of the same side; others (Fibra- ventrales) cross to the opposite 
side, descend close to the ventral fissure, and then curve upward and forward to the restiform body. 
The decussation of the arcuate fibers forms the distinct median raphe seen on cross-sections of the 
medulla anterior to the pyramidal decussation. The restiform body, situated dorso-laterally, 
contains, in addition to the arcuate fibers, the cerebello-olivary fasciculus before mentioned, 



THE PONS 



775 



and the cerebellospinal fasciculus or direct cerebellar tract. The dorsal longitudinal fascic- 
ulus corresponds tn the \cn(n[l ground-bundle of the spinal cord, disphu-cd dmsally l>y tlir decus- 
sation of the i^yraniids and fillet. Li the posterior part of tlie medulla it is ncit niarkeil off from 
the fillet, along the dorsal edge of which it lies. From the level of the hypoglossal nucleus forward 
it is distinct and can be traced as a conspicuous tract in the ventral margm of the gray matter of the 
floor of the fourth ventricle and of the central gray matter of the mid-brain. Ventral to the resti- 
form body and related laterally to the external arcuate fibers there is a considerable bundle of 
longitudinal fibers, the spinal root (Tractus spinalis) of the fifth nerve; medial to it is the 
terminal nucleus of the sensory root of the nerve. 




Fig. 633. — Cross-section of Medulla Oblongata of Horse, Passing through Facial Nucleus. 
Cr, Corpus restiforme; D, dorsal longitudinal fasciculus; Fa, ascending part of facial nerve; L, fillet: iV"?", nucleus 
of facial nerve; iV5, triangular nucleus of of vestibular root of eighth nerve; .V5', spinal root of eighth nerve; Py, p>Ta- 
mid; /2a. raphe; fi7, radicular part of facial nerve; ff5, vestibular root of eighth nerve; Sj;, substantia gelatinosa; Ta, 
posterior end of tuberculum acusticum; T, spinal root of trigeminus. (EUenberger-Baum, Anat. d. Haustiere.) 



c 




Py h 



Fig. 634. — Cross-section of Medulla Oblongata of Horse; Section Passes through Middle of Corpus 

Thapezoideum. 
Cr, Corpus restiforme; D, dorsal longitudinal bundle; Fa, ascending part of facial nerve; Fa', emergent or de- 
scending part of facial nerve; L, fillet; Af. central white matter of cerebellum; N6, abducens nucleus; -VS, triangular 
nucleus; NS', nucleus of Deiters; NS", tuberculum acusticum; Oo, anterior olive; Py, pjTamid; R6, root of abducens 
nerve: R7, root of facial nerve; Re, cochlear nerve; Rv, vestibular nerve; Sg, substantia gelatinosa; T, corpus 
trapezoideum; Y, spinal root of trigeminus. (Ellenberger-Baum, .\nat. d. Haustiere.) 



The Pons 
The pons is that part of the brain stem which lies Ijetween the medulla and 
the cerebral peduncles; it is marked off from these ventrallv bv anterior and 



776 NERVOUS SYSTEM OF THE HORSE 

posterior grooves. Viewed ventrally, it is elongated transversely, convex in 
both directions, and presents a wide shallow median groove (Sulcus basilaris), 
which lodges the basilar artery. Laterally a large part of its mass curves dorsally 
and backward into the base of the cerebellum, forming the middle cerebellar 
peduncle (Brachium pontis). The superficial origin of the trigeminal (fifth) nerve 
is at the lateral limit of the ventral surface. Transverse striations indicate the 
course of superficial (ventral) fibers which connect the two sides of the cerebellum. 
The dorsal surface is blended on either side with the overlying anterior peduncles 
of the cerebellum; the central free portion forms the anterior part of the floor of 
the fourth ventricle, and will be considered in the account of that cavity. 

On cross-section the pons is seen to be composed of dorsal and ventral parts. The dorsal 
part (Pars dorsalis pontis) consists superficiaUy of a layer of gray matter covered by the epen- 
dyma of the fourth ventricle. Beneath this the median raphe of the medulla is continued into 
the pons, dividing it into similar halves. In the anterior part of the pons the fillet divides into 
a medial and a lateral part, the medial and lateral fillets (Lemniscus mediahs, lateralis); the latter 
arches outward to reach the outer side of the anterior cerebellar peduncle. The dorsal longitudinal 
fasciculus becomes sharply defined into a round bundle which Ues close to the raph(; under the 
gray matter of the floor of the fourth ventricle. In cross-section the formatio reticularis forms 
a large area below the superficial gray matter and the longitudinal bundles. Dorso-laterally is 
the large rounded section of the anterior cerebellar peduncle. Lower down is a large bundle, the 
sensory root of the fifth nerve. In fiont of this is tlie motor nucleus of tlie same nerve, lateral 
to which is its motor root. The basilar or ventral part of the pons (Pars basilaris pontis) is com- 
posed of transverse and longitudinal fil)('rs, and a large armiimt of gi-ay matter which is broken up 
into small masses (Nuclei pontis) by the intersection nf tlic filii'rs. Tlio transverse fibers are gath- 
ered laterally into a compact mass which tuiiis di)isally and barkward and enters the central white 
matter of the cerebellum, forming the middle cerebellar peduncle. Centrally the fibers are ar- 
ranged in bundles which intercross. The transverse fiber.s are chiefly of two kinds. Some arise 
from the Pm-kinje cells of the cerebellar cortex and pass either to the opposite side of the cere- 
bellum or turn at the raphe and run forward and backward in the brain stem. Others are axones 
of cells of the nuclei pontis, and pass to the hemisphe 3s of the cerebelhmi. The corpus trape- 
zoideum is mainly the central continuation of the cochlear division of the acoustic nerve. Above 
it is the small anterior olivary nucleus (Nucleus olivaris nasalis). The loniiitudinal fibers of the 
ventral part of the pons consist chiefly of the cerebrospinal or pyramidal fasciculi. These come 
from the ventral part (pes) of the cerebral peduncles and are situated laterally-, int(^rspersed among 
the deep transverse fibers in the anterior part of the pons. Towanl the jHisterior part the 
bundles inchne toward the median plane and become collected into a C(im]iact mass which appears 
superficially at the posterior border. Many fibers come from the cerebral I'ortcx and terminate 
in the nuclei of the gi'ay matter of the pons; they may be designated corticopontile fibers. 

The Cerebelhim 

The cerebellum is situated in the posterior fossa of the cranium, and is sep- 
arated from the cerebral hemispheres by the transverse fissure and the tentorium 
cerebelli which occupies it. It overlies the pons and the greater part of the medulla, 
from which it is separated by the fourth ventricle. Its average weight is about two 
ounces (ca. 60 gm.), or about 9 per cent, of the weight of the entire brain. Its 
shape is approximately globular but very irregular. It is sontewhat compressed 
dorso-ventrally and its transverse diameter is the greatest. 

The anterior surface faces dorsally and forward and is covered partially by 
the tentorium cerebelli. The posterior surface is almost vertical. The ventral 
surface or base lies over the fourth ventricle, anil is connected by three pairs of 
peduncles with the metlulla, pons, and mid-brain. 

It is customary to recognize three gross divisions of the cerebellum, viz., the 
median vermis and two lateral hemispheres. The vermis cerebelli is curved in a 
circular manner so that its two extremities are close together, or even in contact 
on the ventral surface. The anterior extremity is termed the lingula; it lies 
lietween the cerebellar peduncles and gives attachment to the anterior medullary 
velum (Velum medullare orale), a thin lamina which forms the anterior part of the 
roof of the foin-th ventricle. The posterior extremity, the nodulus, gives attach- 
ment to the posterior medullary velum (Velum medullare aborale) , which covers the 
posterior recess of the fourth ventricle. The hemispheres (Heraisphaeria cerebelli) 



THE CEREBELLUM 777 

are separated from the vermis l:)y two deep paramedian fissures. They lie in the 
lateral depressions of the cerebellar compartment of the cranium. 

In tracing the fissures from behind forward it will be noticed that they are nearly sagittal 
as far as the anterior sm-face, where they diverge widely, so that the vermis forms all of the fore 
part of the cerebellum. 

The surface of the cerebellum is further cut up into numerous gyri (cerebelli) 
by narrow and relatively deep sulci (cerebelli), many of which approach a trans- 
verse direction. Certain of the sulci are more pronounced than the others, and by 
means of them it is possible to define groups of gyri. Such groups are termed 
lobes, and have received specific names, derived chiefly from the systematic de- 
scriptions of the human cerebellum. 

The lobes of the vermis are readily distinguished on median section. Enumerated from 
the anterior to the posterior extremity they are: (1) lingula, (2) lobus centralis, (3) lobus ascendens, 
(4) lobus culminis, (5) lobus ch\i, (6) tuber vermis, (7) pyramis, (8) uvula, (9) nodulus. Each 
hemisphere is cut into laterally by two sulci which mark off two sagittal discoid masses, termed by 
Ziehen tabulations. The lateral tabulation consists of four or five lobules, the lowest of which 
is regarded as the flocculus. The medial part of the hemisphere is divided into three or four lobes. 
Martin proposes the term tractus for the sagittal masses; on this basis the vermis would become 
the tractus medianus, and the others tractus laterales (primus, secundus, etc.). In the absence 
of a satisfactoi-y morphological basis it seems undesirable to deal with the lobation of the cere- 
bellum in further detail. 

The cerebellar peduncles (Pedunculi cerebelli), three on each side, join the 
central white matter of the cerebellum at the base. The posterior peduncle is the 
restiform body of the medulla, a large rounded tract derived from the lateral and 
ventral columns of the cord. Near the middle of the medulla it inclines outward, 
forms the lateral wall of the fourth ventricle, and ends by entering the central white 
matter of the cerebellum. The mialle peduncle is formed, as previously seen, by 
the brachium pontis. The anterior peduncles (Brachia conjunctiva) pass forward 
on either side on the dorsal surface of the pons, forming the lateral boundary of the 
fore part of the fourth ventricle. They disappear under the corpora cjuadrigemina 
into the substance of the mid-brain. At the point of disappearance the trochlear 
(fourth) nerve emerges from the mid-brain. In some cases two or three bundles of 
fillers (Fila lateralia pontis) arise in the angle between the middle and anterior 
peduncle, curve obliquely forward and downwartl over the outer aspect of the 
latter, and spread out on the ventral face of the cerebral peduncle just in front of 
the pons. 

On sagittal section the cerebellum is seen to consist of a layer of gray cortical 
substance (Substantia corticalis) and the white medullary substance. The white 
matter consists of a large basal mass (Corpus medullare), which is joined by the 
peduncles and gives off primary laminae (Lamina medullares) to the lobules; 
from these secondary and tertiary laminge arise, the latter entering the gj^i. The 
arrangement on sagittal section is tree-like, hence the term "arbor meduUaris," 
which is applied to it.^ The central gray matter consists of groups of cells which 
form small nuclei embedded in the central white substance. 

The principal connections established by the peduncular fibers of the cerebellum are .as 
follows: The posterior jieduncle (Corpus restiforme) is composed of afferent and elToi-cnt fibers 
which connect the ccn'lx'llum with the medulla and spinal cord. The cerebello-spinal fascicu- 
lus or direct cerebellar tract, which arises from the cells of the nucleus dorsali.s (Clarke's colunui) 
of the cord, ends in tlie cortex of the vermis; many of its fibers cross to the opposite side. Nu- 
inerous arcuate fibers from the nucleus gracilis and nucleus cuneatus of the same and opposite 
sides e.st;ibli^h cDunections with cells of the cerebellar cortex. Olivo-cerebellar fibers (chiefly 
afferent) connect with the olivary nucleus of the same and of the opjiosife side of the medulla 
oblongata. The nucleo-cerebellar fasciculus comprises libers (lcri\'('il fioiii the nuclei of the 
fifth, eighth, and tenth cruiiial nerves (Edinger). The descending cerebello-spinal fasciculus 
consists of fibers wliich terminate in relation with cells of the ventral horns of the spinal cord. 
The chief facts concerning the middle peduncle have been mentioned in the description of the 
pons. The anterior peduncle is essentially an efferent tract, the fibers of which pass forward 

' A1.SO known as the "arbor vitae." 



778 



NERVOUS SYSTEM OF THE HORSE 



to the tPsmpiitum of the cerebral podunele. tlie liy]intlialamic region, and the thalamus. After 
tlic ])rihiii(li's disappear under thi> (-(jrpora (luadriKi'inina, they converge and many of their fibers 
intercross, forming the decussation of the anterior peduncles. A considerable number of fibers 
end in tlic nucleus ruber. Thence inipuUes are trausmitteLl in two directions: first, by thalamo- 
cortical fibers to the cerebral cortex; second, by the rubro-spinal tract through the brain stem 
and lateral cohmins of the cord to the ventral horn cells. The \'entro-lateral cerebellospinal 
fasciculus (Gowers' tract) is an ill-defined tract which connects the spinal cord with the cere- 
bellum. Its fibers appear to be axones of cells of the dorsal columns of the cord; they pass 
in the lateral column of the cord, become scattered in passing tlu'ough the reticular formation 
of the meduUa and pons, and enter the cerebelliuu by way of the anterior medullary velum. 

The Fourth Ventricle 
The fourth ventricle (Ventriculus qiiartus) is the cavity of the rhomljencepha- 
lon; it communicates with the central canal of the spinal cord behind and through 



Corpus callusum [section) Latirnl vcnlridp 



Plexus chorioideus 

Corpus quadrige milium 

anlerius 

Corpus quadrigeminum 
poslerius 



Tuberculaiii acusticuin 
Tirnia ventriculi quarti 



!,Colum. 
ulcus medi 



Fig. 635, 
IS of fornix (secti 



Scpliim pellucidum 

Nucleus caudatus 

Thalamus (anterior 
tubercle) 

Stria terminalis 



f'nrpiiti geniculatuyn 

biln-.dr 

us iirnirulatum tnediale 
nculus cerebri 

m medullare anterius 



Brachium conjunclivum 
Brachium pontis 



Corpus restiforme 

Calamus scriptorius 
Tiiberculuin cinereum 

Fissura mediana 



G.\NGLi.\ OF Horse; Dorsal View. 
remnant of hippocampus; 3, taenia thalami; 4, pineal body; o, eniinentia medialis; 




J limitans; V.III., third ventricle; VjV., fourth ventricle. Stumps of cranial i 



indicated by Roman numerals. 



the cerebral acjueduct with the third ventricle in front. It is somewhat rhomlioid 
in outline, elongated from before backward, and narrowest behind. It is lined 
completely by an epithelium (Ependyma) and contains a small amount of fluid. 
Its floor, the fossa rhomboidea, is formed by the medulla oblongata and pons 



THE FOURTH VENTRICLE 779 

and is marked by three longitudinal furrows which converge behind. It is widest 
and deepest a little in front of its middle. The posterior part narrows to a point at 
the opening of the central canal of the spinal cord, and on account of its appearance 
in man it has been termed the calamus scriptorius. The median sulcus (Sulcus 
medianus) extends the entire length of the floor and is deepest toward the ends. 
The limiting sulci (Sulci limitantes) begin on either side of the opening of the central 
canal and extend forward as the lateral limits of the rhomboid fossa. Just beyond 
the middle of the fossa they expand into a shallow depression, the anterior fovea 
(Fovea oralis). On either side of the median sulcus and margined laterally by the 
limiting sulcus is a slightly rounded column, the eminentia medialis. Opposite the 
fovea this presents an elongated prominence, the coUiculus facialis, so named be- 
cause it overlies the bend formed by the fibers of origin of the facial nerve. Lateral 
to the limiting sulcus is a long fusiform elevation, the area acustica, from which a 
band of fibers (Striae acusticae) winds over the anterior end of the restiform body to 
the superficial origin of the cochlear nerve. 

The lateral wall is formed by the restiform body and the anterior peduncle 
of the cerebellum. 

The roof (Tegmeu ventriculi quarti) is formed in its middle part by the vermis 




s r I 

Fig. 636. — ^Brain Stem and Basal Ganglia of Horse; Right View. 
F.a., External arcuate fibers; C.r., corpus restiforme; P, pyramid; T, corpus trapezoideum; B. p., middle pe- 
duncle of cerebellum; P. c, cerebral peduncle; .S, sulcus lateralis; T.^, tractus transversus; L, trigonum lemnisci; C.a., 
corpus quad, ant.; C.p., corpus quad, post.; B, commissure of C.p,; G, corpus geniculatum mediale; T.o., olfactory 
peduncle; 5.o., olfactory bulb. 

of the cerebellum, covered by the epithelium before mentioned. There is com- 
monly a dorsal recess (Fastigium) between the extremities of the vermis. The 
anterior part of the roof is formed by a thin lamina of white substance, the anterior 
medullary velum (Velum medullare anterius),i which extends backward from the 
corpora quadrigemina, and is attached on either side to the anterior peduncles of 
the cerebellum. Its anterior part is relatively thick and contains the decussation 
of the fibers of the trochlear nerves. Posteriorly it blends with the white matter 
of the cerebellum. A thin lamina of white matter, the posterior medullary velum 
(Velum medullare posterius), backetl bj- pia mater, completes the roof posteriorly 
After removal of the cerebellum the line of attachment (Taenia ventriculi quarti) to 
the medulla is seen; it begins centrally over the opening of the central canal, runs 
for\vard on the inner face of the restiform body, and turns outward behind the 
brachium pontis. The thick part which stretches over the posterior angle of the 
ventricle is termed the obex. The posterior part of the ventricle forms three 
recesses, of which two are lateral and the third median and posterior. The lateral 
recesses ( Recessus lateralis) communicate w\th the subarachnoid space by lateral 
apertures (Aperturse laterales). The layer of pia mater which actually forms the 
roof here is named the tela chorioidea of the fourth ventricle. It is triangular in 
outline and closely adherent to tlie velum. It forms three fringed masses which 
1 Formerly termed the valve of Vieussens. 



780 NERVOUS SYSTEM OF THE HORSE 

contain vascular convolutions and are designated the median and lateral chorioid 
plexuses of the fourth ventricle (Plexus chorioides ventriculi quarti) . They appear 
to lie within the ventricle, but are really excluded from the cavity by the epithelial 
lining, which they invaginate. 

THE MESENCEPHALON 

The mesencephalon or mid-brain connects the rhombencephalon with the 
fore-brain. In the undissectetl lirain it is covered dorsally by the cerebral hemi- 
spheres. It consists of a dorsal part, the corpora quadrigemina, and a larger 
ventral part, the cerebral peduncles, which are visible on the base of the brain. 
It is traversed longitudinally by a narrow canal, the cerebral aqueduct, which con- 
nects the fourth ventricle \\ith the third (Fig. 639). 

The corpora quadrigemina^ are four rounded eminences which lie under the 
posterior part of the cerebral hemispheres. They consist of two pairs, separated 
by a transverse groove. The anterior pair (Colliculi nasales) are larger and much 
higher than the posterior pair. They are gray in color, almost hemispherical, and 
are separated by a narrow furrow which leads forward to the subpineal fovea. 
A wide groove intervenes between them and the optic thalami. The posterior pair 
(Colliculi caudales) are relatively small and are paler than the anterior pair. They 
are marked by a wide median depression, and are limited l^ehind by a transverse 
furrow (Sulcus postquadrigeminus), at either side of which the trochlear (fourth) 
nerve emerges. Laterally each is prolonged to the medial geniculate body by a 
band of wliite matter termed the posterior peduncle (Brachium aborale).- 

The cerebral pediuicles (Pedunculi cerel^ri)^ appear on the base of the brain 
as two large, rope-like stalks which emerge from the pons close together and diverge 
as they extend forward to enter the cerebrum. At the point of disappearance the 
optic tract winds obliquely across the peduncle. About half an inch further back 
a small tract (Tractus peduncularis transversus) curves across the peduncles, and 
behind this, near the median line, is the superficial origin of the oculomotor nerve. 
The triangular depression between the diverging peduncles is the interpedimcular 
fossa (Fossa interpedmicularis). It is covered to a large extent by the hypophysis 
cerebri or pituitary body, a discoid brown mass which is connected with the base of 
the brain liy a hollow stalk, the infimdibulum. The posterior part of the fossa is 
pierced by numerous minute oijenings \\'hi('h transmit blood-vessels, and is therefore 
termed the substantia perforata posterior. The objects here belong to the dien- 
cephalon, and vAW be described later. The lateral aspect of the peduncle is marked 
by a groove (Sulcus lateralis mesencephali) which indicates the division into a 
dorsal part, the tegmentiun, and a ventral part, the basis pedvmculi; these are 
separated by a layer of dark gray matter, the substantia nigra. The triangular 
area (Trigonum lemnisci) above the lateral groove is faintly marked by fibers 
passing dorsally and backward to the anterior cerebellar peduncle; these belong 
to the fillet or lemniscus, an important tract that connects the thalamus and corpora 
quatlrigcmina with the sensory reception nuclei of the opposite side of the medulla. 

The aqueduct of the cerebrum (Aquaeductus cerebri)^ is the canal which extends 
through the mid-ljrain from the third to the fourth ventricle. It is largest beneath 
the posterior pair of corpora quadrigemina. It is surrounded by a layer of gray mat- 
ter (Stratum griseum centrale), in the ventral part of which are the nuclei of origin 

1 In the new nomenclature the term lamina quadrigemina is applied to the dorsal mass of 
tlie mid-brain, and tlie four eminences which it bears are tiie corpora quadrigemina. 

- In man a distinct superior brachium connects the superior pair with tlie hitcral geniculate 
body, but in the domesticated animals the union with the optic thalamus is too direct to allow of 
any definite arm being recognized. 

2 Also termed the crura cerebri. 

^ Also termed the aqueduct of Sylvius. 



THE DIENCEPHALON 781 

of the oculomotor and trochlear nerves, and laterally nuclei of the mesencephalic 
roots of the trigeminal nerves. 



THE DIENCEPHALON 

The diencephalon or inter-brain comprises the thalamus and a number of 
other structures grouped about the third ventricle, the cavity of this division of the 
brain.' To expose its dorsal aspect, the greater part of the cerebral hemispheres, 
the corpus callosum, the fornix, the hippocampus, and the tela chorioidea of the 
third ventricle must be removed (Fig. 635). 

The thalamus is the principal body in this part of the brain. It is a large 
ovoid mass placed obliquely across the dorsal face of each cerebral peduncle, so 
that the long axes of the two thalami would meet in front about at a right angle. 
Medially' they are fused to a large extent, and around the area of adhesion they 
are separated by a sagittal circular space, the third ventricle. The dorsal surface 
is convex, and is separated from the overlying hippocampus by the tela chorioidea. 
Laterally it is separated from the nucleus caudatus by an oblique groove in which 
there is a band of white matter termetl the stria terminalis. When the tela chori- 
oidea of the lateral ventricle has been detached from this band it leaves a torn edge, 
the taenia chorioidea. Medially it is bounded by a narrow white band, the stria 
meduUaris ; to this the tela chorioidea of the third ventricle is attached, and when 
the latter is removed in dissection, there remains a thin irregular edge termed the 
taenia thalami. The striae unite posteriorly and blend with the stalk of the pineal 
body. Near this point they present a small enlargement caused by the nucleus 
habenulse. Anteriorly there is a small eminence, the anterior tubercle of the 
thalamus (Tuberculum orale thalami) . The posterior part of the thalamus has the 
form of a rounded ridge which is continuous laterally with the optic tract.- Behind 
the point of origin of the tract, in the angle between the thalamus and the cerebral 
peduncle, is the medial geniculate body (Corpus geniculatum mediale), a well- 
defined oval prominence. 

The lateral surface is separated from the lenticular nucleus by the internal capsule, an 
important mass of white matter composed of fibers passing to and from the cerebral cortex. 
These fibers go to form a large part of the ventral portion (basis) of the cerebral peduncle. From 
the entire lateral surface of the thalamus fibers pass into the internal capsule and radiate to reach 
the cerebral cortex; similarly fibers coniing fniin the cortex converge in the internal capsule 
to enter the thalamus. This anangi'iiiciit is termed the thalamic radiation. Ventral to the 
thalamus proper is the hypothalamic tegmental region. This is the continuation of the tegmental 
part of the cerebral peduncle into the diencephalon. It contains the red nucleus (Nucleus ruber), 
an important ganglion on the course of the motor tracts. It receives numerous fibers from the 
cerebral cortex and the corpus striatum. From it fibers proceed to the thalamus and to the 
spinal cord; the fibers to the cord, which constitute the rubro-spinal tract (Tractus rubro-spinaUs), 
cross to the opposite side and extend back in the tegmentum to the lateral columns of the cord. 
Lateral to the red nucleus a conspicuous lenticuku' area of dark gray matter is visible on cross- 
sections of the hypothalamic region; this is the hypothalamic nucleus (Nucleus hypothalamicus 
Luysi), which consists of pigmented nerve-cells scattered through a dense network of fine medul- 
lated fibers, and is richly supphed with capillary blood-vessels. The two nuclei are connected 
by a transverse commissure (Commissura hypothalamica), which crosses the floor of the third 
ventricle above the mammiUary body. 

The pineal body or epiphysis cerebri (Corpus pineale) is a small ovoid or fusi- 
form red-brown mass situatetl in a dee]3 central depression between the thalami and 
corpora quadrigemina. It is variable in size, but is commonly about 10 to 12 
mm. long and 6 mm. wide. It is attached at the postero-superior quadrant of 
the third ventricle by a short stalk, in which is a small recess of that cavity. Its 

1 On a strictly embryological basis the optic part of the hypothalamus, comprising the 
anterior part of the third ventricle and the structures associated with it, belongs to the telen- 
cephalon, but wiU be considered here as a matter of convenience. 

- This backward projection of the thalamus is equivalent to the pulvinar and lateral genicu- 
late body of man, which are not superficially divided in the horse. 



782 NERVOUS SYSTEM OF THE HORSE 

base blends in front with the junction of the strise medullares of the thalamus. 
Immediately under the posterior part of the stalk is a short transverse band of white 
matter, the posterior commissure of the cerebrimi (Commissura aboralis cerebri). 

The pineal body is enclosed in a fibrous capsule from which numerous trabeculfe pass inward, 
dividing the organ into spaces occupied by round epithehal cells of the same origin as the epen- 
dyma of the ventricle. 

The mammillary body (Corpus mammillare) is a white, round elevation a little 
larger than a pea which projects ventrally at the anterior end of the median furrow 
of the interpeduncular fossa. While it is a single body in external form in the horse, 




Sulcus rhiniil 
Ventral horn of 
lateral ventricle 



Fig. 637. — Ckoss-section of Bhain of Hohsb, Natural Size. 
Section passes through posterior part of third ventricle and is viewed from behind. 1, Longitudinal fissure; S, 
hippocampus; 2', fimbria; S, septum pellucidum; 4, lateral ventricle; .5, thalamus; 6, habenula; 7, third ventricle; 
8. cerebral peduncle; S', hypothalmus; 9, mammillary body; 10, hypophysis or pituitary body; //, piriform lobe; 
IB, ventral end of hippocampus; tS, amygdaloid nucleus. Between the upper parts of the tjenije thalami is the chorioid 
plexus of the third ventricle, and above this are the internal cerebral veins. 

sections show that it is double in structure and contains a nucleus of gray matter 

on either side (Fig. 637). 

Three sets of fibers are connected with the mammillaiy body. The column of the 
fornix curves down in the lateral wall of the third ventricle to the body and many of the fornix 
fibers end in it. A bundle (Fasciculus thalamo-mammillaris) passes dorsally and backward 
from it into the anterior part of the thalamus, and a tract (Fasciculus pedunculo-mammillaris) 
extends back in the floor of the tliird ventricle to the tegmentum of the mid-brain. 

The hypophysis cerebri or pituitary body was mentioned as covering part of the 
interpeduncular fossa. It is oval in outline, flattened dorso-ventrally, and nearly an 
inch (ca. 2 cm.) in width. It is attached by a delicate tubular stalk, the infundibu- 
Itun, to the tuber cinereum, a small gray prominence situated between the optic 
chiasm in front and the mammillary body behind. A fibrous capsule, derived from 
the dura mater, encloses and is intimately adherent to it. 

The body consists of two parts which can be distinguished on sections by their color"(Fig. 639). 
The glandular lobe is brown in color and forms the external and greater part of the body. It is 



THE TELENCEPHALON 783 

glandular in character and there is good ground for the view that it is an organ of internal se- 
cretion. Besides the chief cells, which stain hghtly, it contains large, deeply staining chromophile 
cells. It arises as an outgrowth from t lie dorsal wall of the primitive mouth cavity. The cerebral 
lobe is pale and is connected with the infundibulum so as to form a rather flask-shaped arrange- 
ment. It is almost entirely enclosed by the glandular part. It arises as an outgrowth from the 
primitive diencephalon, but loses most of its earher nervous character. 

The optic chiasm and tracts form the anterior boundary of the interpeduncular 
fossa (Figs. 629, 636). The optic chiasm (Chiasma opticum) is formed by the 
convergence of the optic nerves and the crossing of the major part of tlie fibers of 
the nerve of one side to the tract of the opposite side. From the chiasm eacii optic 
tract (Tractus opticus) curves obUquely around the cerebral peduncle to the pos- 
terior part of the thalamus and the medial geniculate body; some fibers reach the 
anterior quadrigeminal body. 

All the fibers in the chiasm are not derived from the optic nerves. The posterior part 
contains fibers which pass from one tract to the other and are connected with the medial genicu- 
late bodies; this bundb is called the ventral commissure (Commissura ventraUs). Above it is 
the dorsal commissure (Commissura dorsalis), the fibers of which enter the hypothalamic body.' 

The third ventricle (Ventriculus tertius) is the narrow annular space between 
the thalami. It communicates by means of the cerebral aqueduct with the fourth 
ventricle behind, antl in front it is continuous with the lateral ventricle on each side 
through the interventricular foramen. Its floor is formed by the structures of the 
interpeduncular fossa, and to a small extent by the tegmentum of the cerebral 
peduncles. The roof is formed in the strict sense only by the ependyma, above 
which is a fold of pia mater, termed the tela chorioidea of the third ventricle.'- The 
roof is invaginated by the two delicate chorioid plexuses (Plexus chorioidei ventriculi 
tertii) which appear to lie within the ventricle, although they are excluded from the 
cavity by the epithelium. When the tela is removed, the delicate ependyma of the 
roof is torn away with it, leaving the line of attachment to the stria meilullaris to 
constitute the taenia thalami. The anterior wall is formed by the lamina terminalis, 
a thin layer of gro.y matter which extends from the optic chiasm dorsally to the 
corpus callosum. A distinct rounded band of white matter extends across its 
posterior face, bulging into the ventricle. This is the anterior commissure (Com- 
missura oralis) of the cerebrum; its fibers extend to the olfactory bulb and to the 
piriform lobe. A similar but more slender posterior commissure (Commissura 
aboralis) crosses the posterior wall above the entrance to the cerebral aqueduct; 
the connections of its fibers are not yet clearly known. The interventricular 
foramen' is situated on either side of the anterior part of the ventricle, and leads 
outward and slightly dorsally between the column of the fornix and the anterior 
tubercle of the thalamus (Fig. 639) . The cavity presents three recesses or diver- 
ticula, of which two are ventral and the third is posterior. The optic recess (Re- 
cessus opticus) lies above the optic chiasm. Just behind it is the infundibular 
recess (Recessus infundibuli), which extends through the infundibuhnn to the 
pituitary body. The pineal recess (Recessus pinealis) is in the stalk of the pineal 
body. 

THE TELENCEPHALON 
The telencephalon or end-brain comprises two principal parts, the cerebral 
hemispheres and the optic part of the hypothalamus. The latter has been con- 
sidered as a matter of convenience in the description of the diencephalon. 

The Cerebral Hemispheres 
The cerebral hemispheres (Hemisphseria) form the greater part of the fully 
developed brain. Viewed from above (Fig. 631) they form an ovoid mass, of 
' These are commonly termed Gudden's and Meynert's commissures respectively. 
^ Also commonly termed the velum interpositum. ' Also termed the foramen of Monro. 



784 NERVOUS SYSTEM OP THE HORSE 

which the Ijroader end is posterior, and the greatest transverse diameter is a httle 
behind the middle. The two hemispheres are separated by a deep median cleft, 
the longitudinal fissure of the cerebrum (Fissura longitudinalis cerebri), which is 
occupied by a siclde-shapcd fold of dura mater, the falx cerebri. In front the 
separation is complete, and it appears to be behind also, Ijut here the two hemi- 
spheres are attached to each other over a small area by the pia mater. When the 
hemispheres are gently drawn apart, it is seen that the fissure is interrupted in its 
middle part at a depth of a little more than an inch (ca. 3 cm.) by a white commis- 
sural mass, the corpus callosum ; this connects the hemispheres for al)out half of 
their length. The transverse fissure (Fissura transversa cerebri) separates the 
hemispheres from the ccrclDellum, and contains the tentorium cerebelli. 

The convex or dorso-lateral surface (Facies convexa cerebri) conforms closely 
to the cranial wall. The medial surface (Facies medialis cerebri) (Fig. 639) is flat 
and sagittal and Ijounds the longitudinal fissure ; to a large extent it is in contact with 
the falx cerebri, ]:)ut behind the great cerebral vein the two hemispheres are in 
contact and are attached to each other over a small area as noted above. In well- 




FlG. 638. — Left Cerebral Hemisphere of Horse; Lateral View. The Olfactort Bole is Cot Off. 

i, Lateral fissure (of Sylvius) : 5, 3, 4t middle, posterior, and anterior branches of /; J, presylvian fissure: 6, G', sulcus 

rhinalis, anterior et posterior; 7, suprasylvian fissure; t'l, ectomarginal fissure; 9, 9', ectosylvian fissure. 

hardened specimens there is usually an impression for the vein in front of the area 
of adhesion. The base or ventral surface (Basis cerebri) (Fig. 629) is irregular. 
Its anterior two-thirds is adaptetl to the cerebral fossa of the cranial floor. Cross- 
ing this area in front of the optic tract is a depression, the lateral fossa (Fossa 
lateralis), which leads outward to the lateral fissure (Fissura lateralis),' and lodges 
the middle cerebral artery. In front of the fossa there is a considerable rounded 
elevation knowai as the trigonum olfactorium. The trigonum and the medial part 
of the fossa are pierced by numerous openings for the passage of small blood-vessels 
and are equivalent to the substantia perforata anterior of man. Behind the lateral 
part of the fossa is the rounded anterior end of the piriform lobe (Lobus piriformis). 
Traced backward, the lobe curves dorso-medially over the optic tract and the 
thalamus to the tentorial aspect of the hemisphere; its continuation, the hippo- 
campus, forms jiart of the floor of the lateral ventricle, and will be examined later. 
The tentorial surface (Fig. 640) is flattened, faces medially and backward as well 
as ventrally, and rests largely on the tentorium cerebelli ; on its anterior ]3art there 
is a shallow depression adapted to the corpora quadrigemina and the pineal body. 
' Also commonly known as the fissure of Sylvius. 



THE CEEEBRAL HEMISPHERES 785 

The frontal pole or anterior extremity (exclusive of the olfactory bulb) is 
compressed laterally, and the occipital pole or posterior extremity forms a blunt 
point. 

The hemisphere comprises: (1) The pallium, which consists of an outer layer 
of gray matter, the cortex (Sulistantia corticalis), covering a large mass of white 
matter (Centrum semiovale) ; (2) the rhinencephalon or olfactory portion of the 
brain; (3) the corpus callosum and fornix, the great commissural white masses; 
(4) the lateral ventricle and certain important structures associated therewith. 

The pallium is throwm into numerous folds, the gyri cerebri, which are sep- 
arated by sulci or fissures of varying depth. The general pattern of the gyri and 
sulci is similar in normal brains of the same species, but the details are very variable 
and are never alike on the two hemispheres of the same brain. In the horse the 
arrangement is complicated by the existence of numerous short accessory fissures 
which cut into the gyri at right angles and tend to confuse the observer. The 
principal fissures and sulci of the convex surface (Figs. 631, 632, 638) are as follows i^ 

1. The lateral fissure (Fissura lateralis Sj'lvii) ascends on the lateral surface 
of the hemisphere as the continuation of the fossa lateralis in front of the piriform 
lobe. After crossing the lateral olfactory stria it divides into three branches; 
of these one passes dorsally, one runs obliquely forward and dorsally, and the third 
is directed dorsally and backward. It contains the middle cerebral artery. 

2. The suprasylvian fissure (F. suprasylvia)- is long and divides a large part 
of the convex surface of the hemisphere into dorsal and lateral portions. It begins 
on the dorso-medial border near its anterior end, and, inclining gradually downward, 
passes back to end on reaching the tentorial surface. It is usually continuous 
medially with the transverse fissure and in front with the presylvian fissure. 

3. The presylvian fissure (F. prsesylvia) is on the anterior part of the hemi- 
sphere, passes forward and ventro-laterally almost to the frontal pole, and then 
inclines backward to end at the groove which marks the dorsal limit of the rhinen- 
cephalon (Sulcus rhinalis). 

4. The marginal fissiu-e (F. marginalis) extends along the dorso-medial border. 
It begins a little in front of the middle of the border and turns around the occipital 
pole to end on its tentorial aspect. 

5. The entomarginal fissure (F. entomarginalis) lies medial to the dorso- 
medial l:)order. It does not extend quite as far forward as the marginal fissure, 
from which it is separated by a narrow gyrus. 

6. The ectomarginal fissure (F. ectomarginalis) lies about midway between the 
marginal fissure and tlie posterior part of the suprasylvian fissure. 

7. The sulcus rhinalis is a very distinct furrow on the ventral part of the 
lateral surface which marks off the olfactory part of the brain (rhinencephalon) from 
the rest of the hemisphere. It is undulating and is highest where it is crossed by 
the lateral fissure. 

Just above this point is a lobe which is homologous with the insula of man. When the 
overhanging gjTi which partly conceal it — forming the operculum — are removed, there are dis- 
closed several short, deeply placed gyri (GjTi breves). 

On the medial surface (Fig. 639) the main fissures and sulci are as follows: 
1. The calloso-marginal fissure (F. callosomarginalis) is extensive and well 
defined. It is approximately parallel to the dorso-medial border of the hemisphere, 
from which it is about half an inch distant. It begins in front a short distance 
below and in front of the genu of the corpus callosum, and forms a C-shaped curve, 
its posterior part extending on the tentorial surface to a point behind the depression 

1 The homologies and terminology of many fissures of the brain in the domesticated animals 
are still in a chaotic state. Only a few of the most important and constant ones are given here. 

2 Termed by Lesbre the parietal fissure and by M'Fadyean the great obUque fissure. 

60 



786 



NERVOUS SYSTEM OF THE HORSE 



for the corpora quadrigemina. It separates the marginal gyri above from the gyrus 
fornicatus, which extends down to the corpus callosum. 

2. The transverse fissure (F. transversa) begins a little behind the middle of 
the calloso-marginal fissure, passes obliquely dorsally and forward to the dorso- 
medial border — into which it cuts deeply — and usually joins the suprasylvian 
fissure. 1 

3. The sublimbic fissure (F. sublimbica) curves over the gyrus fornicatus a 
short distance above the corpus callosum. Its middle part is commonly indistinct, 
and it is often divided into anterior and posterior parts. 



Transverse Cnllosn-mnr- 
Gyrus fornicatus fissure ginal fissure 



Marginal fissure 



Entomarginal fissure 




Anterior com- ' 

nussure Lamina 



terminaiis optic u 



Aiiltri 
Ca-dral mclul- 
aqueduct lary 
velum 



Fig. 639. — Median Section of Brain of Hohse. 
The membranes and vessels are removed. C. Central white matter (corpus medullare) of cerebellum; P.c. cere- 
bral peduncle; C.q., corpora quadrigemina; P, pineal body; Th.. thalamus; V.III., third ventricle; r, optic recess; 
r', infundibular recess; Cm., mammillary body; s. subcallosal gyrus; A.p., area parolfactoria; G, genu of corpus 
callosum; S, splenium of same; F.i., interventricular foramen; B.o., olfactory bulb. The cerebral lobe of the 
hypophysis cerebri or pituitary body is distinguished by its lighter color. 



4. The callosal sulcus (Sulcus corporis callosi) separates the corpus callosum 
from the gyrus fornicatus. 

The hippocampus- is a gyrus which curves from the deep face of the piriform 
lobe around the thalamus and forms the posterior part of the floor of the lateral 
ventricle. It can be displayed by cutting away the brain stem up to the optic 
tract and the interventricular foramen. Viewed from below, the hippocampal 
gyrus is seen to form a semicircular curve from the apex of the piriform lobe to 
the angle of divergence of the crura of the fornix, /. e., to a point under the central 
part of the corpus callosum. It is separated deeply by the hippocampal fissure 
from the gyrus dentatus (Fig. 640). Along the concave margin of the latter is a 

' By some authors this is regarded as the homologue of the cruciate fissure of the dog, but it 
seems likely that the latter is represented by a short and inconstant sulcus situated further forward. 
^ Also termed the eornu Ammonis. 



THE CEREBRAL HEMISPHERES 



787 



band of white matter, termed the fimbria, which is the prolongation of the greater 
part of the crus of the fornix into this region. The ventricular surface of the 
hippocampus (Fig. 642) is covered with a thin layer of white matter, the alveus, 
which is also derived from the crus of the forni.x, and is therefore continuous with 
the fimbria. The two hippocampi are connected at their highest parts by trans- 
verse fibers which constitute the hippocampal commissure. 

The interval between the hippocampus and fimbria on the one hand, and the 
brain stem on the other, is a lateral continuation of the transverse fissure of the 
brain, and is occupied by a fold of pia mater, the tela chorioidea of the third ven- 
tricle. This fold is triangular in outline and its apex reaches to the interventricular 
foramen. Its base is continuous at the transverse fissure with the pia which covers 
the surface of the brain. Its middle part lies over the epithelial roof of the third 
ventricle, as has been seen (Fig. 637) . The lateral borders will be seen on the floor 



Intervenlricular foramen Transi'i'rse fissure 
Gyrus fornicat us I Calloso-marginal fissure 

Subhmbic fissure (ant. pari) \ _^^ — ^ _^ / Sublimbic fissure (post. parO 

Entomarginal fissure 

Marginal fissure 




Sulcus rhinalis anterior 



Ectotnarginal fissure 



Hippocampal fissu 



Sulcus rhinalis posterior 



Fig. 640. — Medio-ventral Aspect of Right Cerebral Hemisphere ( 
The olfactory bulb is cut off. T.ol.. Olfactory tiact; A.p., area parolfacto 
Tr.op., optic tract: Co., chiasma opticum; G.s., subcallosal gyrus; C.c, corpus calh 
fornix; F', fimbria; G.c, callosal gyrus; T, cut surface of thalamus; G.d., gyrus dentatus; L.p., pirifo 
G.h., hippocampal gyrus. 



Tr.O., trigonum olfactorium; 
a; S.p.. septum pellucidum: F, 



of the lateral ventricles, where they form thick, rounded bands containing convolu- 
tions of blood-vessels, known as the chorioid plexuses of the lateral ventricles (Fig. 
642). 

When the tela is pulled out, one may easily get the impression that the lateral ventricle 
communicates with the e.'cterior by means of the chorioid fissure. Such is not the case, since the 
chorioid plexus is covered by the epithelial lining of the ventricle, which has been torn away. 

The rhinencephalon or olfactory part of the brain comprises the olfactory 
bulb, tract, and striae, the trigonum olfactorium, the area parolfactoria, and the 
jjiriform lol:)e.' 

Th(> olfactory bulb (Bulbus olfactorius) is an oval enlargement which curves 
upwartl in front of the frontal pole of the hemisphere. Its convex superficial face 
fits into the ethmoidal fossa and receives numerous olfactory nerve-fibers through 
the cribriform plate; hence it is very difficult to remove the bulb intact. It con- 
tains a considerable cavity, the ventricle of the olfactory bulb (Ventriculus bulbi 

' From the morphological point of view other structures should be included, but in descriptive 
anatomy it is usual to Umit the application of the term to the parts enumerated above. 



788 



NERVOUS SYSTEM OF THE HORSE 



olfactorii) which is connected with the lateral ventricle by a small canal in the 
olfactory tract. The deep face is largely in contact with the frontal pole of the 
hemisphere and is connected with the olfactory tract. 

The gray matter of the bulb is external and is thickest on the convex anterior surface. The 
posterior part consists to a large extent of fibers wliich are the axones of the mitral cells of the 
deep layer of the gray substance and go to form the tract and stria;. 

The olfactory tract (Tractus olfactorius)' is a very short but wde band of 
white substance which arises in the olfactory bulb and extends back to be continued 
by the olfactory striae. It contains a canal which connects the ventricle of the 
bulb with the lateral ventricle. 

The olfactory striae (Striae olfactorii)- are two in number. The lateral stria 
(Stria lateralis) is much the largest and most distinct. It passes backward, upward, 
and outward, widens out and joins the piriform lobe. It is clearly defined dorsally 
by the sulcus rhinalis and is marked off from the trigonum olfactorium by the 
sulcus arcuatus. The medial stria (Stria medialis) is smaller, short, and not so 




Fig. 641. — Lateral View of Cast of Cavities of Brain of Horse. 
Bo, Cavity of olfactory buib. which communicates through the carial / with a lateral ventricle; Ca, anterior horn, 
Cm, body. Ci, ventral horn of lateral ventricle; M , interventricular foramen wbich connects lateral and third ventricles; 
Ep, suprapineal recess, below which is the small infrapineal recess (not visible): Ro, optic recess; Rh, infundibular 
and pituitarj- recess: .S, aqueduct: Fl, ridge corresponding to sulcus limitans; Rl, lateral recess, Rm, posterior 
recess of fourth ventricle: Cc, beginning of central canal of spinal cord. (Dexler.) 



well defined; it bends over to the parolfactory area on the medial face of the hemi- 
sphere below the genu of the corpus callosum.^ 

The trigonum olfactorium is the prominent gray area situated in the angle of 
divergence of the medial and lateral olfactory striae. It is bounded laterally by the 
lateral olfactory stria, from which it is defined by the sulcus arcuatus. It is con- 
tinuous with the area parolfactoria on the medial surface; behind the latter a band 
descends from the rostrum of the corpus callosum and is continuous below with the 
anterior perforated sulistance; it is termed the subcallosal gyrus (Gyrus sub- 
callosus). 

The piriform lobe (Lobus piriformis) is the well-marked prominence on the 
base lateral to the optic tract and cerebral peduncle, from which it is separated by a 
deep fissure. Its nipple-like apex lies behind the fossa lateralis and covers the 
optic tract. The external surface is marked by one or two sulci (lobi piriformis). 
The lobe contains a cavity, the ventral horn of the lateral ventricle. 

• Commonly termed the peduncle. - Commonly termed the tracts. 

' An intermediate or middle stria has been described; its presence cannot be demonstrated 
in the horse. 



THE CEREBRAL HEMISPHERES 



789 



The fibers of the olfactory striae go to the piriform lobe and hippocampus, the trigonum 
olfactorium, the area parolfactoria, the subcallosal gyrus, and part of the gyrus fornicatus. The 
central connections of the olfactory apparatus are complex and are not yet fully understood. The 
anterior cerebral commissui-e contains fibers which pass from the olfactory bulb of one side by 
way of the medial striae to the bulb of the opposite side; also fibers which cross in it from the 
medial striae of one side to the piriform lobe of the opposite side. Many fibers pass to the 
hippocampus by way of the septum pellucidum, fornix, and fimbria. Other fibers pass in the 
column of the fornix to the mammillary body and thence to the thalamus by the thalamo-mam- 
millary bundle. 

The corpus callosum is the great transverse commissure whicii connect.? the 
two cereljral hemispheres through about half of their length. On median section 




Olfactory bulb 



^_^--' Cortex cerebri 



'Corpus medullare 
- Caudate nucleus 

Chorioiil plexus 

Fornix 

■Hippocampus 



-Brain of Horse, 



WITH Lateral Ventricles Opened by Removal op Cpper Part of Cerebral 
Heuisphebes and Most of the Corpus Callosum. 



(Fig. 639) it is seen to be arched from before backward, white in color, and com- 
posed substantially of transverse fibers. The middle part or trimcus (Truncus 
corporis callosi) slopes downward and forward antl is thinner than the ends. The 
anterior thickened end, the genu, bends ventrally and backward and thins out to 
form the rostnun ; the latter is continuous with the lamina terrainalis. The pos- 
terior end, the spleniiun, also thick, lies at a consitlerably higher level than the 
genu. The dorsal surface is convex in its length, concave transversely; it forms 
the floor of the longitudinal fissure. It is covered by a thin layer of gray matter 
(Induseiun griseum), in which are strands of longitudinal fibers (Strise longitudi- 
nales) ; the latter are arranged in medial and lateral bundles (Stria medialis, striae 



790 



NERVOUS SYSTEM OF THE HORSE 



laterales).! The ventral surface has the reverse configuration, and presents trans- 
verse ridges and grooves. It forms the roof of the lateral ventricles, and the 
septum pellucidum is attached to it medially. The fibers of the corpus callosum 
(with the exception of the longitudinal stria;) run transversely and spread out 
laterally in all directions in tlie central white matter of the hemispheres to the cor- 
tex, forming the radiation of the corpus callostun (Radiatio corporis callosi) . 

The fornix is a bilateral structure composed of white fibers which arch chiefly 
over the thalamus and the third ventricle. It is described as consisting of a body, 
two columns, and two crura. The body (Corpus fornicis) is formed by the fusion of 
the two arches of which the fornix is composed. It is triangular and overlies the an- 
terior parts of the thalami and the third ventricle. The dorsal surface gives 




rnlerreiitricvlar foramen 
AnlerioT cominissure 



Optic Optic trad 

cli iasm 



Fig. 643. — Cross-section of Brain of Horse, A: 
Section passes through optic chiasm, and is viewed from in front. 
cidum; 3, columns of fornix; 
hemisphere; 7, caudate nuclei 



Natural Size. 

Longitudinal fissure; S, septum pellu- 
lateral ventricle; 5, chorioid plexus; 0, corpus medullare (central white matter) of 
c9, lenticular nucleus; 5, internal capsule; 70, external capsule; //, insula. 



attachment medially to tlie septum pellucidum, and on either side forms part of the 
floor of the lateral ventricle. The lateral border is related to the chorioid plexus of 
the lateral ventricle and forms the inner boundary of the interventricular foramen. 
The columns (Columnae fornicis) (Fig. 643)- are two slender round bundles which 
emerge from the body in front of the interventricular foramen and diverge 
slightly as they curve ventrally and backward to the mammillary body. 

From the mammillary body the greater part of these fornix fibers are continued to the 
thalamus by the thalamo-mammillary fasciculus (or bundle of Vicq d'Azyr). Others pass to 
the cerebral peduncle. A portion of the fibers cross to the opposite thalamus and cerebral 
peduncle. > 

The crura (Crura fornicis)^ are much larger bands which diverge widely from 

' It is generally beUeved that these constitute an olfactory path. 

' Also known as the anterior pillars. ' Also termed the posterior pillars. 



THE CEREBRAL HEMISPHERES 791 

the posterior angles of the body. Each curves outward and backward over the 
thalamus (from which it is separated by the tela chorioidea), and is chiefly continued 
as the fimbria along the concave border of the hippocampus. The crura give off 
fibers to form the alveus, a layer of white matter which covers the ventricular face 
of the hippocampi, and between them are transverse fibers which constitute the 
hippocampal commissure (Commissura hippocampi). 

The septum pellucidimi is the median partition between the two lateral ven- 
tricles. Its convex dorsal border blends with the corpus callosum and its concave 
ventral border joins the fornix. Its anterior part is received into the genu of the 
corpus callosum. Traced backward, it diminishes in height and the two edges meet 
at an acute angle at the spleniuin. 

The septum consists of two layers (Laminae septi pellucidi) which are in contact with each 
other. They consist of medullated nerve-fibers and gray matter. The latter exists in considerable 
amount in the thicker part of the septum adjacent to the columns of the fornix. Many of the 
fibers of the .septum pa.ss up through the corpus callosum to the gyrus fornicatus. Others are 
connected with the subcallosal gyrus and the parolfactory area. 




Fig. 644. — Sagittal Sectiom of Brain of Hor-se. 
Section is cut about 1.5 cm. to the right of the median plane. M, Medulla oblongata; P, pons; P.c. (above AT), 
chorioid plexus of fourth ventricle; Cm., central white matter (corpus medullare) of cerebellum and of cerebrum: 
P.c. (in front of P), cerebral peduncle; H, hippocampus: V, lateral ventricle; T, thalamus; JV.c, caudate nucleus; 
a., internal capsule; N.I., lenticular nucleus; B.o., olfactory bulb. 

The lateral ventricle (Ventriculus lateralis cerebri) is the irregular cavity in the 
interior of each cerebral hemisphere.^ Each communicates with the third ventricle 
through the interventricular foramen (Foramen interventriculare),- and by a small 
canal with the cavity of the olfactory bulb. It is usual to describe the ventricle 
as consisting of three parts, viz., the central part or body, and anterior and ventral 
horns. The central part (Pars centralis) extends back to the splenium of the corpus 
callosum. It opens into the third ventricle through the interventricular foramen, 
which is situated between the fornix and the anterior part of the thalamus. The 
anterior horn (Cornu orale) is the part- in front of the interventricular foramen; 
it communicates ventrally Avith the olfactory cavity. The ventral horn (Comu 
ventrale) curves downward and forward into the piriform lobe. The roof of the 
ventricle is formed bj^ the corpus callosum, and the medial wall is the septiun pellu- 
cidum. After removal of the roof the floor is seen to be formed chiefly by two bodies. 

' It is hardly possible to get an accurate idea of the shape of the ventricle except by studying 
a cast of it (Fig. 641). The size of the ventricles varies in different subjects, and it is common to 
find more or less disparity between the two ventricles of the same brain. 

2 Formerly termed the foramen of Monro. 



792 NERVOUS SYSTEM OF THE HORSE 

The anterior one is the caudate nucleus (Nucleus caudatus), a somewhat pear- 
shaped gray eminence, the long axis of which is directed obliquely upward, back- 
ward, and outward. Its anterior large end is termed the head (Caput nuclei 
caudati), and the posterior long tapering end the tail (Cauda nuclei caudati). The 
posterior bod.v, the hippocampus, is white on its ventricular surface, which is 
strongly convex. It curves outward and backward and then turns ventrall}' and 
forward to join the piriform lobe. The two liodies are separated l>y an obHcjue 
groove which is occupied l^y the chorioid plexus of the lateral ventricle (Plexus 
chorioideus ventriculi lateralis). This is the thickened edge of a fold of pia mater, 
the tela chorioidca of the third ventricle, which lies between the hippocampus and 
the thalamus. It contains convolutions of small blood-vessels, and in old sulDJects 
there are often calcareous concretions in it. The plexuses of the two sides are 
continuous through the interventricular foramen. On drawing the chorioid plexus 
backward, a narrow white band, the stria terminalis/ is seen along the margin of the 
caudate nucleus, where it bounds the intermediate groove. The plexus partially 
covers a wider white band which is blended with the white substance of the hippo- 
campus; this is the cms of the fornix and its continuation, the fimbria. 

The corpus striatum- is the great basal ganglion of the hemisphere. It is sit- 
uated in front of the thalamus and the cerebral peduncle, and its anterior rounded 
end appears on the base of the hemisphere at the trigonum olfactorium. It is 
composed of two masses of gray matter, the caudate antl lenticular nuclei, separated 
incompletely by tracts of white matter which are knowai collectively as the internal 
capsule. The caudate nucleus (Nucleus caudatus) is the dorso-medial and larger 
of tlie two gray masses; it was seen in the examination of the lateral ventricle. 
The lenticular nucleus (Nucleus lentiformis) lies ventro-laterally, over the frigonum 
olfactorium and the fossa lateralis. It is related externally to a layer of white 
matter termed the external capsule (Capsula externa), which separates it from a 
stratum of gray suljstance knowai as the claustrum. The two nuclei are fused in 
front, and further back they are connected by strands of gray matter which inter- 
sect the internal capsule. 

The amygdaloid nucleus (Nucleus amygdalte) (Fig. 637) is an ovoid mass of 
gray matter lateral to the ventral horn of the lateral ventricle and ventral to the 
posterior part of the lenticular nucleus. Some fibers of the stria terminalis are 
comiected with it. 

The internal capsule (Capsula interna) is a broad band of white matter situated 
between the thalamus antl caudate nucleus medially and the lenticular nucleus 
laterally. A sagittal section through the brain (Fig. 644) shows that it is in great 
part directly continuous with the basis or ventral part of the cerebral peduncle. 
It contains most of the so-called projection fibers of tlie hemisphere, which con- 
nect the cerebral cortex with nuclei of other and more posterior parts of the brain. 
When the fibers of the internal capsule are traced forward it is evident that they 
spread out in all directions to reach the cerebral cortex. This arrangement, in 
which the fillers of the corpus callosum participate, is termed the corona radiata. 

The internal capsule also contains fibers which connect the corpus striatum with the thala- 
mus. These are termed the thalamo-striate and strio-thalamic fibers respectively, according to 
the direction in which they conduct impulses. 

The fibers of the stria tcrminahs connect the amygdaloid nucleus with the septum pelluci- 
dum and trigonum olfactorium. It is therefore probably part of the complex connections be- 
tween the primary and secondary olfactory centers. 

Blood-vessels of the Brain. — The arteries which supply the brain are derived 
chiefly from the internal carotid and occipital arteries. The basilar artery, formed 
by the union of the right and left cerebral branches of the occipital artery, enters 

• Formerly termed the taenia semicircularis. 

- The term arose from the striated appearance of the mass in sections cut in certain planes, 
the gray matter being cut up into strands by tracts of white fibers. 



THE CRANIAL NERVES THE OPTIC NERVE 793 

the cranial cavity through the foramen magnum, and divides at the interpeduncular 
fossa into the two posterior cerebral arteries. These concur with branches of the 
internal carotid arteries in forming the remarkable arterial circle on the base of the 
cerebrum. From these emanate basal arteries which supply in general the brain 
stem and basal ganglion, and cortical arteries which in general run superficially and 
supply the cortical substance and medullary white substance. 

The veins enter the sinuses of the dura mater, and in the main are not satel- 
lites of the arteries. The sinuses communicate with the ophthalmic, dorsal and 
ventral cerebral, and spinal veins. 



The Cranial Nerves 

The cranial or cerebral nerves (Nn. cerebrales) comprise twelve pairs which 
are designated from befors* l)ackward numerically and by name. Their number, 
names, and functional characters are given in the subjoined table: 

I. Olfactory Sensory (Smell) 

II. Optic Sensory (Sight) 

III. Oculomotor Motor 

IV. Trochlear ' Motor 

V. Trigeminal Mixed 

VI. Abducent Motor 

VII. Facial Mixed 

VIII. Acoustic Sensory (Hearing and EquiUbration) 

IX. Glosso-pharyngeal Mixed 

X. Vagus Mixed 

XI. Spinal accessory Motor 

XII. Hypoglossal Motor 



THE OLFACTORY NERVE 
The olfactory nerve (N. olfactorius) is peculiar in that its fibers are not aggre- 
gated to form a trunk, but are coimectetl in small bundles with the olfactory bulb. 
They are non-medullated, and are the central processes of the olfactory cells which 
are situated in the olfactory region of the mucous membrane of the nasal cavity. 
This region is distinguished by its brown color and comprises the posterior part of 
the lateral mass of the ethmoid, a small adjacent area of the dorsal turbinate, and 
the corresponding surface of the septum nasi. The nerve-bundles are enclosed in 
sheaths derived from the membranes of the brain and pass through the foramina of 
the cribriform plate to join the convex surface of the olfactory bulb. Some 
fibers come from the vomero-nasal organ. 



THE OPTIC NERVE 
The optic nerve (N. opticus) is composed of fibers which are the central proc- 
esses of the ganglion cells of the retina. The fibers converge within the eyeball to 
the optic papilla, where they are collected into a round trunk, the optic nerve. The 
nerve thus formed pierces the chorioid and sclera, emerges from the posterior part 
of the eyeball, and passes backward and medially to the optic foramen. After 
traversing the latter it decussates with its fellow of the opposite side to form the 
optic chiasma. In the orbit the nerve is slightly flexuous and is embedded in the 
fat behind the eyeball and surrounded by the retractor oculi muscle. Its intraos- 
seous part is an inch or more (ca. 3 cm.) long. The sheath of the nerve is formed by 
prolongations of the membranes of the brain, and includes continuations of the 
subdural and subarachnoid spaces. 

The greater part of the fibers of the optic nerve cross in the chiasma to the tract of the oppo- 
site side. In the tract the fibers proceed to (1) the medial geniculate body, (2) the posterior 



794 



NERVOUS SYSTEM OF THE HORSE 



pai't of the thalamus, and (3) the ajiterior quadrigeminal body (indirectly). The fibers which 
go to the medial geniculate body appear to belong to Gudden's commissure and to be non-visual 
in function. The \dsual fibers, which come from the lateral part of the retina of the same side 
and the medial part of the retina of the opposite side, terminate about cells in the anterior quad- 
rigeminal body and the part of the thalamus which corresponds to the pulvinar and lateral genicu- 
late body of man. From the cells of the former fibers pass to the nuclei of the motor nerves of 
the eyeball, and complete the reflex arc. Fibers proceed from the cells of the thalamus to the 
visual area of the cortex in the occipital part of the hemisphere. 



THE OCULOMOTOR NERVE 

The oculomotor nerve (N. oculomotorius) arises by several radicles from the 
basal surface of the corcliral iieduncle, a little lateral to the interpeduncular furrow. 

It turns sharply outward and for- 
ward, crosses over the cavernous 
sinus, and continues above the 
maxillary nerve and in company 
with the ophthalmic nerve to the 
foramen orbitale. It emerges 
through the foramen with the lat- 
ter nerve and the abducens and 
divides into two branches. The 
dorsal branch is short and divides 
into two twigs which supply the 
rectus dorsalis and levator pal- 
pebrse superioris. The ventral 
branch (Figs. 563, 564) is larger 
and much longer. It supplies the 
motor fibers to the ciliary gan- 
glion (which lies directly on this 
branch in the horse) and short 
branches to the rectus medialis 
and rectus ventralis, and con- 
tinues forward on the latter to 
end in the ventral oblique mus- 
cle. 

The deep origin of the fibers of 
the oculomotor nerve is in the oculo- 
motor nucleus, situated in the gray mat^ 
ter of the floor of the cerebral aque- 
duct in the region of the anterior cor- 
pora quadrigemina. 




Cranial Cavity of Horse. 
nerves are shown on the left side 



and 



Fig. 645.— Floor 
The roots of the era 

designated by number: 7. Anterior cranial fossa; II, 
middle cranial fossa: ///, posterior cranial fossa; a, ethmoidal 
fossa; b, ethmoidal foramen; c, foramen for nasal branch of 
ophthalmic artery; d, orbital wing of sphenoid bone; e, optic 
groove; /, hypophyseal fossa; g, spheno-occipital crest; h, h', con- 
tour of hypophysis or pittiitary body: h'\ slight elevation repre- 
senting dorsum sellse; i, k, grooves for nerves and cavernous sinus; 
ly depression for piriform lobe of cerebrum; m, groove for middle 
meningeal artery; n, depression for pons; o, foramen lacerum an- 
terius: p, foramen lacerum posterius; q, incisura carotiea; g'.anci- 
sura ovalis; q", incisura spinosa; r, depression for medulla oblongata; 
s, hypoglossal foramen: t, internal acoustic meatus: u, foramen 
magnum; v, frontal sinus; w, zygomatic process of temporal bone; 
X, section of petrous temporal; y, section of occipital bone; z, crista 
galli; 1, 1', 1", dotted lines indicating position of olfactory striae 
and tract. (After EUenberger-Baum, Top. .\nat. d. Pferdes.) 



THE TROCHLEAR NERVE 
The trochlear nerve (N. tro- 
chlearis)' is the smallest of the 
cranial nerves. It arises from 
the anterior cerebellar peduncle 
just behind the corpora quadri- 
gemina, curves outward and for- 
ward, pierces the tentorium cere- 
belli, and passes forward along 
the lateral border of the maxillary 
nerve (Figs. 635, 636). It emerges from the cranium through a small foramen 
' Formerly termed the nervus patheticus. 



THE TRIGEMINAL NERVE 795 

immediately above the foramen orbitale or through the latter and passes forward 
along the medial wall of the orbit to end in the posterior part of the dorsal oblique 
muscle of the eyeball (Fig. 564). 

The fibers of the fourth nerve spring from a nucleus in the gray matter of the floor of the 
cerebral aqueduct behind the oculomotor nucleus. The fibers run backward in the tegmentum, 
then turn dorso-medially, and undergo total decussation with those of the opposite nerve in the 
anterior part of the anterior medullary velum. In addition to this peculiarity it is the only nerve 
which is connected with the dorsal aspect of the brain. 



THE TRIGEMINAL NERVE 

The trigeminal nerve (N. trigeminus)^ is the largest of the cranial scries. It 
is connected with the lateral part of the pons by a large sensory root and a smaller 
motor root (Fig. 629). 

The sensory root (Portio major) extends forward through a notch on the lower 
part of the petrosal crest and widens out to join the semilunar ganglion. 

The semilunar ganglion (Ganglion semilunare)- is a crescent-shaped mass of 
nerve-fibers and cells which overlies the antero-lateral part of the foramen lacerum 
basis cranii, antl is partly embedded in the dense fibrous tissue which occupies the 
foramen except where vessels and nerves pass through. Its long axis, which is 
about an inch (2.5 cm.) in length, is directed forward and medially and its convex 
anterior face gives rise to the ophthalmic, the maxillary, and the sensory part of 
the mandibular division of the nerve. The surface of the ganglion is irregularly 
striated. It is connected by filaments with the adjacent carotid plexus of the sym- 
pathetic, and sends delicate twigs to the dura mater. 

The fibers of the sensory root arise from the ganglion as axones of the gangUon cells, and the 
fibers of the nerves which extend peripherally from the ganglion are dendrites of the cells. The 
sensory root-fibers enter the tegmentum of the pons and divide into anterior and posterior branches, 
which terminate about the cells of the sensory nucleus of termination of the trigeminus. This 
nucleus extends from the pons to the sixth cervical segment of the spinal cord (Dexler). The 
posterior branches of the fibers are collected into a compact bundle, the spinal tract or root of the 
trigeminus, which lies lateral to the substantia gelatinosa in the medulla. The central connections 
of the sensory part of the trigeminus are very extensive. The most important paths are: (1) 
Axones of cells of the sensory nucleus and the substantia gelatinosa pass chiefly as arcuate fibers 
across the raphe to the thalamus, whence impulses are transmitted by thalamo-cortical fibers 
to the cerebral cortex. In ungulates a distinct tract extends from the anterior part of the sensory 
nucleus to the thalamus of the same side (Wallenberg). It is probable that collaterals of the 
arcuate fibers go to the motor nuclei of the fifth, seventh, ninth, and tenth cranial nerves. (2) 
Axones of cells of the sensory nucleus enter the posterior cerebellar peduncle of the same side 
and reach the cerebellar cortex. (3) Collaterals are distributed to the nuclei of origin of the 
hjfpoglossal and of the motor part of the trigeminal and facial nerves. 

The motor root (Portio minor) extends forward beneath the sensory root and 
the semilunar ganglion and is incorporated with the mandibular division of the 
nerve. Its fibers arise chiefly from the so-called masticatory nucleus, which is 
situated in the pons near the inner face of the sensory nucleus; a few of these fibers 
come from the nucleus of the opposite side and cross in the raphe. Other fibers, 
which constitute the mesencephalic root, arise from cells in the outer part of the 
central gray matter of the mid-brain. 

It is evident from the foregoing statements that the trigeminus has essentially 
the same arrangement as a typical spinal nerve. It divides into three branches. 

I. The ophthalmic nerve (N. ophthalmicus) (Figs. 563, 564, 565) is purely 
sensory antl is the smallest of the three branches of the trigeminus. It arises from 
the medial part of the front of the semilunar ganglion, passes forward along the outer 
side of the cavernous sinus, and is blended with the maxillary nerve for some dis- 
tance. It enters the foramen orbitale with the third and sixth nerves and divides 
into three branches. 

1. The lacrimal nerve (X. lacrimalis) runs forward on the rectus dorsalis and 

' Also known as the trifacial nerve. ^ Formerly termed the Gasserian ganglion. 



796 NERVOUS SYSTEM OF THE HORSE 

the levator palpebrse superioris and ramifies chiefly in the lacrimal gland and the 
upper eyelid. A branch (Ramus zygomatico-temporalis) exchanges twigs with the 
zygomatic branch of the maxillary nerve, perforates the periorbita, and emerges 
from the orbital fossa behind the supraorbital process; it forms a plexus with 
branches of the auriculo-palpebral and frontal nerves, and ramifies in the skin of 
the temporal region. 

2. The frontal nerve (N. frontalis), also termed the supraorljital, runs forward 
almost parallel with the dorsal oblique muscle, at first within, then outside of, the 
periorjjita. It passes through the supraorbital foramen with the artery of like 
name and ramifies in the skin of the forehead and upper eyelid, forming a plexus 
with the lacrimal and auriculo-palpebral nerves. It divides into three branches. 

3. The naso-ciliary nerve (N. nasociliaris), also termed the palpebro-nasal, 
runs forward along the medial side of the optic nerve between parts of the retractor 
muscle and divides into two branches. Of these, the ethmoidal nerve (N. ethmoid- 
alis) is the continuation of the parent trunk. It accompanies the ethmoidal 
artery through the foramen of like name into the cranial cavity and crosses the 
lower part of the ethmoidal fossa. Leaving the cranium through an opening in the 
cribi-iform plate close to the crista galli, it enters the nasal cavit.v and ramifies in 
the iiiucous membrane of the septum nasi and the dorsal turbinate. The infra- 
trochlear nerve (N. infratrochlearis) runs forward to the medial canthus and rami- 
fies in the skin in this region; it detaches twigs to the conjunctiva and caruncula 
lacrimalis, and a long branch which supplies the third eyelid and the lacrimal ducts 
and sac. The naso-ciliarj- nerve furnishes the sensory or long root (Radix longa) 
of the ciliary ganglion. 

The ciliary gangUon is placed on the ventral branch of the oculomotor nerve, 
close to its origin from the latter. It is usually not larger than a millet-seed, and 
is best found bv following the nerve to the ventral oblique muscle back to its origin. 
The ganglion receives — (a) sensory fibers from the naso-ciliary nerve; (6) motor 
fibers from the oculomotor nerve; and (c) sympathetic fibers from the spheno- 
palatine plexus. It detaches filaments which unite with t\\dgs from the ophthalmic 
and maxillary nerves and from the sphenopalatine ganglion to form the ciliary 
plexus. From the latter emanate five to eight delicate short ciUary nerves (Nn. 
ciliares breves), which pursue a somewhat flexuous course along the optic nerve, 
pierce the sclera near the entrance of that nerve, and run forward between the 
sclera and chorioidea to the circumference of the iris. Here the branches of ad- 
jacent nerves anastomose to form a circular plexus (Plexus gangliosus ciliaris), 
from which filaments go to the ciliary body, iris, and cornea. 

The circular fibers of the iris and the ciliary muscle are innervated by fibers derived from the 
oculomotor nerve, the radial fibers of the iris by the sympathetic. 

II. The maxillary nerve (N. maxillaris)' is purely sensory- and is much larger 
than the ophthalmic. It extends forward from the semilunar ganglion in the middle 
cranial fossa in the large groove on the root of the temporal wing of the sphenoid. 
It is related medially to the cavernous sinus and dorsally to the ophthalmic nerve, 
with which it is blended for some distance. It emerges through the foramen 
rotundum, passes forward in the pterygo-palatine fossa abov§ the internal maxillary 
artery and embedded in fat, and is continued in the infraorbital canal as the in- 
fraorbital nerve (Fig. 564). Its branches are as follows: 

1. The zygomatic nerve (N. zygomaticus s. subcutaneus malre), also termed 
the orbital branch, arises before the maxillary nerve reaches the pterygo-palatine 
fossa (Figs. 563, 564, 646). It pierces the periorbita and divides into two or three 
delicate branches which pass along the surface of the lateral straight muscle to 

1 This is also termed the superior maxillary branch. 



THE TRIGEMINAL NERVE 



797 



the lateral canthus and ramify chiefly in the lower lid and the adjacent skin. Anas- 
tomoses are formed with branches of the lacrimal nerve. 

2. The sphenopalatine nerve (N. sphenopalatinus) is given off in the pterygo- 
palatine fossa from the ventral border of the maxillary nerve (Fig. 564). It is 
broad and flat and forms a plexus in which several small sphenopalatine ganglia 




Fig. 646. — Dissection cfF Head of Horse. 
The maaseter and superficial muscles and the parotid gland are in great part removed, a, a. Levator labii superi- 
oiis proprius; 6, 6, levator nasolabialis; c, dilatator naris inferior; d, buccinator; e, common mass of buccinator and 
depressor labii inferioris; /, depressor labii inferioris; g, masseter; h, orbicularis ocuh; (', temporalis; k, occipito- 
hyoideus; k', occipito-mandibularis; I, sterno-cephalicus; I', tendon of same; iti, omo-hyoideus; n, crico-pharyngeus; 
o, mastoid tendon of brachiocephalicus; p, splenius; q, inferior buccal and labial glands; r, superior buccal glands; 
s, remnant of parotid gland; /, mandibular gland; u, anterior cervical lymph glands; v, probe passed into diverticulum 
nasi; w, cornu of alar cartilage; x, medial palpebral hgament; j/, wing of atlas; 2, scutiform cartilage of ear; i, lateral 
nasal nerve; 2, anterior nasal nerve; S, superior labial nerve; 4. anterior part of superior buccal nerve; 5, buccinator 
nerve; 6, 6', inferior alveolar nerve; 6", mental nerve — continuation of 6; 7, masseteric nerve; S, facial nerve (cut); 
5, superficial temporal nerve; i(>, anastomosis between P and 5; 11, internal auricular nerve; 7;?, posterior auricular 
nerve; 13, digastric nerve; 14, cervical branch of facial nerve (cut); 15, auriculo-palpebral nerve; 16, lacrimal nerve; 
17, frontal nerve; IS, infratrochlear nerve; 19, zygomatic nerve; 20, spinal accessory nerve; 21, ventral branch of 
spinal accessory nerve (to sterno-cephalicus); 22, ventral end branch of first cervical nerve; 23, thyro-laryngeal 
artery; 24, internal maxillary artery; 25, masseteric artery; 26, great (posterior) auricular artery; 27, external branch 
of -55; ^5, deep auricular artery; ^5, anterior auricular artery; 50, transverse facial artery; 57, facial artery; 55, inferior 
labial artery; 33, superior labial artery; 34, lateral nasal artery; 35, dorsal nasal artery; 36, angular artery of eye; 37, 
terminal branches of superior labial nerve; 38, branch of buccinator arters*; 39, buccinator vein; 40, vena refiexa; 42, 
jugular vein; 43, external maxillary vein; 44^ ventral cerebral vein; ^5, stump of great auricular vein; 46, ramus of 
mandible; -}''. facial crest; 4^, zygomatic arch; 4^, parotid duct. (After EUenberger-Baum, Top. Anat. d. Pferdes.) 



are interposed. It divides into posterior nasal, and greater and lesser palatine 
nerves. (1) The posterior nasal nerve (N. nasalis aboralis) passes through the 
sphenopalatine foramen, in which it bears one or more minute ganglia, enters the 
nasal cavity, and divides into medial and lateral branches (Figs. 565, 588). The 
medial branch (N. septi narium) runs forward in the submucous tissue of the lower 
part of the septum nasi, gives twdgs to the mucous membrane here and to the 
vomero-nasal organ, passes through the palatine fissure, and ramifies in the anterior 



798 NERVOUS SYSTEM OF THE HORSE 

part of the hard palate. The lateral branch (Ramus lateralis) ramifies in the 
mucous membrane of the ventral turl^inate and the middle and ventral meatus nasi. 
(2) The greater or anterior palatine nerve (N. palatinus major s. oralis) (Figs. 
563, 564) is the largest of the three branches. It runs forward in the palatine canal 
and groove and ramifies in the hard palate and gums. It also supplies twigs to the 
soft palate, and gives off branches which pass through the accessory palatine for- 
amina to supply the mucous membrane of the ventral meatus. 

The branches of the two nerves anastomose in the hard palate and form a plexus about the 
branches of the palatine arteries. 

(3) The lesser or posterior palatine nerve (N. palatinus minor s. aboralis), 
also termed the staphyline, is much the smallest of the three branches (Figs. 563, 
564). It passes downward and forward with the palatine vein in the groove at the 
medial side of the tuber maxillare and ramifies in the soft palate. 

The sphenopalatine ganglia and plexus (Fig. 647) lie on the perpendicular part of the palatine 
bone and the pterygoid process, under cover of the maxillary nerve. The afferent fibers of the 
plexus and ganglia come chiefly from the branches of the sphenopalatine nerve and the nerve of 
the pterygoid canal. Interspersed in these are several minute ganglia and one or more larger 
ones. The nerve of the pterygoid canal (N. canaUs pterygoidei)^ is formed by the union of sym- 
pathetic fibers -tv-ith the superficial petrosal branch of the facial nerve. It passes forward at first 
between the Eustachian tube and the sphenoid bone, enters the canal between the pterygoid bone 
and process, and joins the posterior part of the plexus. It is probable that it furnishes the motor 
fibers to the levator palati and palatinus muscles. Efferent filaments go to the periorbita and the 
ophthalmic vessels, and others accompany the branches of the maxillary nerve, around which they 
have a plexiform arrangement. 

3. The infraorbital nerve (N. infraorbitalis)^ is the continuation of the maxillary 
trimk. It traverses the infraorbital canal, emerges through the infraorbital fora- 
men, and divides into nasal and superior labial branches. Along its course it gives 
off maxillary alveolar or dental branches (Rami alveolares maxillae), which supply 
the teeth, alveolar periosteum, and gums. 

Small posterior alveolar branches (Rami alveolares maxilla' aborales) are given off in the 
pterygo-palatinc fossa, pass through small foraniinti in t he tuber maxillare, and supply the posterior 
molar teeth and the maxillary sinus. Tlic middle alveolar branches (Rami alveolares maxillae 
medii) are given off in the infraorbital canal, and (-(institute the chief nerve-supply to the cheek 
teeth and the maxillary sinus. The maxillary incisor branch I Ramus alveolaris maxilla; incisivus) 
runs forward in the incisor canal and su]i|ili('s brainlies to the canine and incisor teeth. The fore- 
going unite with each other to form the maxillary dental plexus (Plexus dentalis maxillce) from 
which the dental and gingival branches are given off. 

The external nasal branches (Rami nasales externi), two or three in number, 
accompany the levator labii superioris proprius and ramify in the dorsum nasi and 
the nasal diverticulum. 

The large anterior nasal brpich (Ramus nasalis oralis) gives branches to the 
upper lip and nostril, passes over the nasal process of the premaxilla under cover 
of the lateralis nasi, and ramifies in the mucous m.embrane of the nasal vestibule. 

The superior labial branch (Ramus labialis dorsalis) is the largest of the termi- 
nals of the infraorbital nerve. It passes downward and forward under cover of the 
levator nasolabialis and, after supplying the skin of the anterior part of the cheek, 
forms a rich terminal ramification in the skin and mucous membrane of the upper 
lip. It anastomoses vfith the superior buccal branch of the facial nerve. 

III. The mandibular nerve (N. mandibularis)' is formed by the union of two 
roots; of these, the large sensory root comes from the semilunar ganglion, and the 
small motor root is the pars minor of the trigeminus. It emerges from the cranium 
through the oval notch of the foramen lacerum, and passes between the temporal 
wing of the sphenoid bone and the muscular process of the petrous temporal. It 
then runs forward, downward, and a little outward, between the ventral surface of 

^ Also known as the Vidian nerve. ^ This is also called the superior dental nerve. 

' This is also termed the inferior maxillary branch. 



THE TRIGEMINAL NERVE 



799 



the pterygoideus medialis and the guttural pouch, and on reaching the lateral 
surface of the pterygoideus lateralis, it divides into two terminal branches — the 
inferior alveolar and lingual nerves. It gives off the following branches: 

1. The masseteric nerve (N. massetericus) (Figs. 562, 646) passes outward 
through the sigmoid notch of the mandible across the anterior surface of the tem- 
poro-mandibular articulation and enters the deep face of the masseter muscle, in 
which it ramifies. 

2. The deep temporal nerves (Nn. temporales profundi) (Fig. 562), two or 
three in number, arise from, or by a common trunk with, the masseteric. They 
supply the temporalis muscle. 

3. The buccinator nerve (N. buccinatorius) passes dowiiward and forward 
at first across the medial surface of the temporo-mandibular articulation, then 
through the anterior part of the lateral pterygoid muscle, then between the bucci- 




FiG. 647. — Deep Dissection of Base of Cranittm, Viewed from the Right and Below. 
The tympanic cavity is opened and the paramastoid process is sawn off. a, Occipital condyle; b, body of sphenoid; 
c, external acoustic meatus (part removed) ; d, malleus; e, incus; i, stump of ophthalmic nerve; ;?, stump of maxillary 
nerve; 5, sphenopalatine plexus; 4. nerve of pterygoid canal; 4', deep petrosal nerve; 4". branch to tympanic plexus; 
4'", superficial petrosal nerve; .5. superficial temporal nerve (cut off); 6, masseteric nerve (cut off); 7, mandibular 
nerve (raised); S, lingual nerve (cut off); 9, pterygoid nerve (cut); 10, nerve to tensor tympani; 11, otic ganglion; 
I ^, facial nerve; 73. stapedial nerve; ?4. chorda tympani; 75, glosso-pharyngeal nerve (cut) ; 7(?. tympanic nerve; 17, 
vagus (cut off); 18, auricular branch of vagus; 19, spinal accessory nerve (cut ofT) ; SO, hypoglossal nerve (cut off; 
SI, sympathetic nerve (cut off) ; 2^, internal carotid artery. (.4fter EUenberger, in Leisering's Atlas.) 



nator vein and the tuber maxillare (Fig. 646). It continues forward in the sub- 
mucous tissue of the cheek along the ventral border of the depressor labii inferioris 
and divides into branches which ramify in the mucous membrane and glands of the 
lips in the vicinity of the commissure. It supplies small branches to the lateral 
pterygoid and temporal muscles and detaches numerous collateral twigs to the 
mucous membrane of the cheek and to the buccal glands. It also communicates 
with the inferior buccal branch of the facial nerve. 

4. The pterygoid nerve (N. pterygoideus) arises in common with the preceding, 
passes downward and forward under cover of the parent trunk, and divides into 
branches which enter the posterior part of the pterygoideus medialis at the division 
between the two layers of the muscle (Fig. 647). 

The otic ganglion (G. oticum) is situated on the mandibular near the origin of 
the Ijuccinator nerve, and is related medially to the tensor palati and the Eustachian 
tube. It receives motor fibers from the pterygoid nerve and sensory fibers by the 



800 



NERVOUS SYSTEM OF THE HORSE 



small superficial petrosal nerve from the tympanic plexus, through which communi- 
cations are made wdth the facial and glosso-pharyngeal nerves. Sympathetic 
fibers are derived from the plexus on the internal maxillary artery. Efferent fila- 
ments go to the tensor palati, tensor tympani, and pterygoid muscles and to the 
Eustachian tube. 

The ganglion is small and somewhat difficult to find, and in many cases it is replaced by 
a number of minute ganglia interspersed in a fine plexus. 

5. The superficial temporal nerve (N. temporalis superficialis) (Figs. 562, 
646, 647) runs outward across the pterygoideus lateralis, passes between the parotid 
gland and the neck of the ramus of the mandible, turns around the latter, and di- 
vides into two branches. The transverse facial branch (Ramus transversus faciei) 
accompanies the transverse facial vessels and ramifies in the skin of the cheek. 
The larger ventral branch unites with the ventral buccal division of the facial nerve. 
Before its division the nerve gives off twigs to the guttural pouch, the parotid 
gland, the external ear, and the skin of the external acoustic meatus and the mem- 







The bone has been i 
cheek teeth and gums; i 
ing's Atlas.) 



3. 648. — Part of Branch of Lower Jaw of Horse; Medial View, 

moved to show the vessels and nerves. /, 1', Mandibular alveolar nerve; 2, 2, branches to 

, branch to canine and incisor teeth; 5, 3', alveolar artery; 4, satellite vein. (After Leiser- 



brana tympani. Branches from it concur with filaments from the cervical branch 
of the facial nerve in the formation of the auricular plexus. 

6. The mandibular alveolar nerve (N. alveolaris mandibulse) (Figs. 561, 562, 
646)^ arises with the lingual Ijy a common trunk which passes forward at first on 
the lateral pterygoid muscle, then inclines ventrally between the medial pterygoid 
and the ramus of the mandible. The lingual and alveolar separate at an acute 
angle, and the latter enters the mandibular foramen and courses in the canal 
within the ramus (Fig. 648). Emerging at the mental foramen, it terminates by 
dividing into six to eight inferior labial and mental branches, which ramify in the 
lower lip and chin. Before entering the bone, the nerve detaches the mylo-hyoid 
nerve (N. mylohyoideus), which runs downward and forward between the ramus 
and the mylo-hyoid muscle; it supplies that muscle, the anterior belly of the 
digastricus, and the skin of the anterior part of the mandibular space. The dental 
and gingival branches detached from the nerve within the mandible are arranged 
like the corresponding nerves of the upper jaw. 

7. The lingual nerve (N. lingualis) arises by a common trunk with the mandib- 
ular alveolar nerve (Figs. 561, 562). After separating from the latter it runs 

' Also termed the inferior dental nerve. 



THE ABDUCENT NERVE THE FACL\L NERVE 801 

downward and forward, lying at first between the ramus of the mandible and the 
medial pterygoid muscle, then on the medial face of the mylo-hyoid. On reaching 
the root of the tongue it divides into superficial and deep branches. The super- 
ficial branch (Ramus superficialis) runs forward on the stylo-glossus and accom- 
panies the mandibular duct on the deep face of the sublingual gland. It supplies 
the mucous membrane of the tongue and the floor of the mouth. At the root of the 
tongue it gives off a recurrent branch to the isthmus faucium, which communicates 
with the lingual branch of the glosso-pharyngeal nerve. The larger deep branch 
(Ramus profundus) turns around the lower edge of the stylo-glossus and hyo- 
glossus, passes upward and forward between the latter muscle and the genio- 
glossus, and continues forward on the latter to the tip of the tongue. At the turn 
it gives off one or more ascending branches which ramify on the deep face of the 
hyo-glossus. It gives branches to the mucous membrane and the fungiform papilte 
of the tongue, and anastomoses \\dth branches of the h;,^oglossal nerve and with 
the superficial branch. ISIinute ganglia occur on the finer branches of the lingual 
nerve. The chorda tympani branch of the facial joins the lingual nerve at the origin 
of the latter and is incorporated with it in its distribution to the tongue. 



THE ABDUCENT NERVE 
The abducent nerve (N. abducens) emerges from the brain behind the pons 
and just lateral to the pjT^amid (Fig. 629). It passes forward across the pons, 
pierces the dura mater, and accompanies the third and ophthalmic nerves, below 
which it emerges through the foramen orbitale. In the orbit it divides into two 
branches which innervate the rectus lateralis and the retractor muscle of the eye- 
ball. Within the cranium it receives filaments from the carotid plexus of the sym- 
pathetic. 

The fibers of the abducent ner\'e are axones of the large multipolar cells of the abducent 
nucleus which is situated beneath the eminentia teres of the floor of the fourth ventricle. The 
nucleus Ues w-ithin tlie loop formed by the fibers of origin of the facial nerve. It is connected 
with (a) the anterior oUve; (b) the oculomotor nucleus of the opposite side; (c) the motor area of 
the cerebral cortex by means of the pyi'amidal tract of the opposite side. 



THE FACIAL NERVE 

The facial nerve (N. facialis) has its superficial origin at the lateral part of the 
corpus trapezoideum, immediately behind the pons (Fig. 629). It passes outward 
in front of the eighth nerve and enters the internal acoustic meatus. At the bottom 
of the meatus the two nerves part company, the facial coursing in the facial canal 
of the petrous temporal bone. The canal and nerve are at first directed outward 
between the vestibule and the cochlea, then curve backward and ventrally in the 
posterior wall of the tympanum to end at the stylo-mastoid foramen. The bend 
formed by the nerve is called the knee (Geniculum n. facialis), and bears at its 
highest point the round geniculate ganglion (G. geniculi). 

The nerve consists of two parts, motor and sensorj'. The motor part constitutes the bulk 
of the nerve. Its deep origin is from the cells of the facial nucleus, wliich is situated in the meduUa 
above the facial tubercle. On leaving the nucleus the root-fibers pass dorso-mediaUy, incline for- 
ward close to the median plane, and then bend sharply downward to the point of emergence. The 
highest point of the bend is subjacent to the gray matter of the eminentia teres in the floor of the 
fourth ventricle, and the abducent nucleus lies in the concavity of the curve. The small sensory 
part (N. intermedins) consists of axones of cells of the geniculate ganglion, wliich is interposed on 
the facial nerve as it bends downward in the facial canal. The fibers of this part, after entering 
the medulla, pass to the nucleus of termination which it shares with the ninth and tenth nerves. 
The peripheral fibers from the geniculate ganglion constitute the chorda tympani. 

After its emergence through the stylo-mastoid foramen (Fig. 646) the nerve 
passes ventrally, forward, and outward on the guttural pouch under cover of the 
51 



802 NERVOUS SYSTEM OF THE HORSE 

parotid gland, and passes between the origin of the superficial temporal and 
internal maxillary arteries medially and the superficial temporal vein laterally. It 
then crosses the posterior border of the ramus of the mandible ventral to the trans- 
verse facial artery and about an inch and a half (ca. 3.5^ cm.) below the articu- 
lation of the jaw. Emerging from beneath the parotid gland upon the masseter 
muscle, it receives the ventral Ijranch of the superficial temporal nerve, and divides 
into dorsal and ventral buccal branches. The following collateral branches are 
given off, the first five being detached within the facial canal, and the others 
between the stylo-mastoid foramen and the border of the jaw. 

1. The great superficial petrosal nerve (N. petrosus superficialis major) arises 
from the geniculate ganglion.' It passes through the petrosal canal, contributing 
a filament to the tympanic plexus, receives the deep petrosal nerve from the carotid 
plexus of the sympathetic, emerges through the foramen lacerum, and is continued 
as the nerve of the pterygoid canal to the sphenojaalatine plexus and ganglia (Fig. 
647). 

2. A delicate branch (R. anastomoticus cum plexu tympanico) emerges from 
the geniculate ganglion and unites with a filament issuing from the tympanic plexus 
to form the small superficial petrosal nerve (N. petrosus superficialis minor) ; this 
ends in the otic ganglion. 

3. The stapedial nerve (N. stapedius) (Fig. 647) is a short filament detached 
from the facial nerve as it turns down in the facial canal. It innervates the stape- 
dius muscle. 

4. The chorda tympani (Fig. 647) is a small nerve which arises a little below the 
preceding and pursues a recurrent course in a small canal in the mastoid part of 
the temporal bone (Canaliculus chordae tympani), to reach the tympanic cavity. 
It traverses the latter, passing between the handle of the malleus and the long branch 
of the incus. Emerging through the petrotympanic fissure, the nerve passes down- 
ward and forward on the guttural pouch, crosses beneath the internal maxillary 
artery, and joins the lingual nerve. It sends twigs to the mandibular and sublingual 
glands, and through its incorporation with the lingual nerve furnishes fibers to the 
mucous membrane of the anterior two-thirds of the tongue which are believed to 
mediate the sense of taste. 

5. Anastomotic filaments unite with the auricular branch of the vagus near 
the stylomastoid foramen. 

6. The posterior auricular nerve (N. auricularis aboralis) arises from the 
facial at its emergence from the facial canal (Fig. 646). It runs upward and back- 
ward with the posterior auricular artery under cover of the parotid gland, and sup- 
plies the posterior and dorsal auricular muscles and the skin of the convex surface 
of the external ear. It anastomoses with branches of the first and second cervical 
nerves. 

7. The internal auricular nerve (N. auricularis internus) springs from the 
facial close to or in common with the preceding (Fig. 646). It ascends in the 
parotid gland just behind the styloiil process of the conchal cartilage, passes 
through an opening in the cartilage, and ramifies in the skin of the concave surface 
of the ear. 

8. The digastric branch (R. digastricus) (Fig. 646) arises from the facial below 
the auricular nerves and descends under cover of the parotid gland. Its branches 
innervate the posterior belly of the digastricus, the stylo-hyoideus, and the occipito- 
hyoideus. At its origin it gives off a small branch which forms a loop around the 
great auricular artery or its posterior liranch and rejoins the trunk. 

9. The auriculo-palpebral nerve (N. auriculopalpebralis) (Fig. 646) arises 
from the upper edge of the facial near the posterior border of the ramus. It ascends 

' Although this nerve sprmg.s directly from the ganghon, it contains motor as well as sensory 
fibers. 



THE ACOUSTIC NERVE 803 

in the parotid gland behind the superficial temporal artery, and terminates in 
anterior auricular and temporal branches. The small anterior auricular branches 
form with the frontal and lacrimal branches of the trigeminus the anterior auricular 
plexus. They innervate the anterior auricular and parotido-auricularis muscles. 
The temporal branch runs forward and inward over the temporal muscle to the 
medial canthus of the eye, forms a plexus with the terminal branches of the ophthal- 
mic nerve, and is distributed to the orbicularis oculi, corrugator supercilii, and 
levator nasolabialis. 

10. The cervical branch (R. colli) (Fig. 560) is small; it arises from the ventral 
border of the facial opposite to the preceding nerve. It passes obliquely through the 
parotid gland, emerging under cover of the parotido-auricularis, passes downward 
and backward on or near the jugular vein, and anastomoses with the cutaneous 
branches of the cervical nerves. It gives branches to the parotido-auricularis and 
the cervical cutaneous muscle. In its course along the neck the nerve is reinforced 
by twigs from the cutaneous branches of the second to the sixth cervical nerves. 

11. Small branches are detached to the guttural pouch and the parotid gland. 
The latter (Rami parotidei) concur with branches of the superficial temporal nerve 
in forming the parotid plexus. 

The facial nerve usually terminates after a short course on the surface of the 
masseter by dividing into two buccal branches (Fig. 560). 

1. The dorsal buccal nerve (N. buccalis dorsalis) passes forward on the upper 
part of the masseter, dips under the zygomaticus, and reaches the ventral border of 
the dilatator naris lateralis. It continues under cover of the last-named muscle 
and the levator nasolabialis in company with the superior labial artery and ramifies 
in the muscles of the upper lip and nostril. It gives collateral branches to the 
buccinator and anastomoses with the infraorbital and ventral buccal nerve. 

2. The ventral buccal nerve (N. buccalis ventralis) crosses the masseter 
obliquely and continues forwartl along the depressor labii inferioris. It is connected 
by variable anastomotic branches with the dorsal nerve. It gives collateral 
branches to the cutaneus, buccinator, and depressor labii inferioris, and ramifies 
in the muscles of the lower lip. 

The buccal nerves are subject to much variation in regard to their course, anastomoses, 
and relations to the sensory components derived from the superficial temporal nerve. Their 
distribution is constant. The point at which the branch of the superficial temporal nerve joins 
the facial is variable. 



THE ACOUSTIC NERVE 

The acoustic nerve (N. acusticus) is connected with the lateral aspect of the 
medulla just l^ehind and lateral to the facial (Fig. 629). It has two roots, vestib- 
ular and cochlear (Radix vestibularis, cochlearis). 

The acoustic nerve consists of two distinct parts which might well be regarded as separate 
nerves. The cochlear part mediates the sense of hearing, while the vestibular part is not auditory 
in function, but is concerned in the sense of the position of the body and the mechanism of 
equilibration. 

The nerve passes outward to the internal acoustic meatus, which it enters 
behind the facial nerve. In the meatus it divides into two nerves, of which the 
upper is the vestibular and the lower is the cochlear nerve. 

1. The vestibular nerve (N. vestibuli) is distributed to the utriculus, the saccu- 
lus, and to the ampullae of the semicircular ducts of the internal ear. In the 
internal acoustic meatus the nerve is connected Isy filaments with the geniculate 
ganglion of the facial nerve. At the bottom of the meatus it bears the vestibular 
ganglion (G. vestibulare), from the cells of which the fibers of the nerve arise. 

2. The cochlear nerve (N. cochlea?) detaches a filament to the sacculus, passes 



804 NERVOUS SYSTEM OF THE HORSE 

through the lamina cribrosa to the labyrinth, and is distributed to the organ of 
Corti in the cochlea. 

The fibers of the vestibular nerve arise from the vestibular ganglion as central processes 
(axones) of the bipolar cells of the ganglion. The peripheral processes (dendrites) of the cells 
form arborizations about the deep ends of the hair-cells of the macute and crista; acusticae of the 
utriculus, sacculus, and semicircular ducts. The fibers enter the medulla, pass between the 
restiform body and the spinal tract of the trigeminus, and spread out to end in the vestibular 
nucleus in the floor of the fourth ventricle. Among the central connections of the vestibular 
nerve are: (1) fibers which connect its nucleus with centers in the cerebellum (chiefly of the oppo- 
site side); (2) the vestibulo-spinal tract, which conveys impulses to the motor cells of the ventral 
columns of the spinal cord; (3) fibers which connect the nucleus with those of the abducent nerve 
of the same side, the third and fourth nerves, and the motor part of the trigeminus of both sides. 

The fibers of the cochlear nerve are the central processes of the bipolar cells of the spiral 
ganglion of the cochlea. The periphei'al processes of these cells end in relation to the hair-cells 
of the organ of Corti. Some of the nerve-fibers enter the ventral cochlear nucleus in the meduUa 
close to the superficial origin of the nerve; others end in the dorsal nucleus of the tuberculum 
acusticum at the lateral angle of the floor of the foui'th ventricle. From the ventral nucleus 
fibers pass in the corpus trapezoideum to the anterior olivary nucleus of the same and of the 
opposite side. Thence tracts pass to the nuclei of the motor nerves of the eye, and through the 
lateral fillet to the posterior quadrigeminal body and the medial geniculate body. The axones 
of the cells of the dorsal nucleus pass largely (as the strise acustics) over the restiform body and 
across the floor of the fourth ventricle toward the median plane. They then turn ventrally, 
cross to the oppcsite side, and are continued by the lateral fillet. From the mid-brain a tract 
proceeds to the cortex of the temporal lobe of the hemisphere. 



THE GLOSSO-PHARYNGEAL NERVE 
The glosso-pharyngeal nerve (N. glossopharjoigeus) is attached to the anterior 
part of the lateral aspect of the medulla by several filaments (Fig. 629). The root- 
bundles enter the furrow ventral to the restiform body; they are separated by a 
shorti interval from the origin of the facial nerve, but are not marked off behind from 
the roots of the vagus. The bundles converge laterally to form a nerve which per- 
forates the dura mater and emerges through the foramen lacerum posterius just 
in front of the tenth nerve (Fig. 647). As it issues from the cranium the nerve 
bears a considerable ovoid gray enlargement, the petrous ganglion (G. petrosmn)."^ 
It then curves do\vnward and forward over the guttural pouch and behind the great 
comu of the hyoid bone, crosses the deep face of the external carotid artery, and 
divides into pharjTigeal and lingual branches (Fig. 562). The collateral branches 
are as follows: 

1. The tympanic nerve (N. tympanicus) (Fig. 647) arises from the petrous 
ganglion and passes upward between the petrous and tympanic parts of the temporal 
bone to reach the cavity of the tympanum. Here it breaks up into branches to 
form, along with branches from the carotid plexus of the sympathetic, the tympanic 
plexus. From the plexus branches pass to the mucous membrane of the tympanum 
and the Eustachian tube. The continuation of the nerve issues from the plexus 
and unites with a filament from the geniculate ganglion of the facial to form the 
small superficial petrosal nerve; this runs forward and ends in the otic ganglion. 

Filaments also connect the petrous ganglion with the jugular ganglion of the vagus nerve 
and with the anterior cervical ganglion of the sympathetic. 

2. A considerable branch Tuns backward on the guttural pouch, contributes 
filaments to the pharyngeal plexus, and concurs with twigs from the vagus and the 
sympathetic in forming the carotid plexus on the terminal part of the carotid 
artery and on its chief branches. In this plexus is the small ganglion intercaroticum. 

3. The very small nerve to the stylo-pharyngeus muscle (N. stylopharyngeus) 
arises from the dorsal border of the nerve. 

The pharyngeal branch (R. pharyngeus) (Fig. 562) is the smaller of the two 
terminal branches. It runs forward across the deep face of the great comu of the 

' This ganglion appears to be equivalent to the jugular or superior and petrous ganglia of man. 



THE VAGUS NERVE 805 

hyoid bone and concurs with the pharyngeal branches of the vagus and with sym- 
pathetic filaments in forming the pharyngeal plexus; from this branches pass to 
the muscles and mucous membrane of the pharynx. 

The lingual branch (R. lingualis) is the continuation of the trunk (Fig. 562). 
It runs along the posterior border of the great cornu of the hyoid bone in front of 
the external maxillary artery, and dips under the hyo-glossus muscle. It gives 
collateral branches to the soft palate, isthmus faucium, and tonsil, and ends in 
the mucous membrane of the posterior part of the tongue, where it supplies gusta- 
tory fibers to the vallate papillae. A considerable branch unites ^\ath a twig from 
the lingual nerve. 

The glosso-pharyngeal is a mixed nerve, containing; both motor and sensory fibers. The 
latter constitute the bulk of the nerve and inclutle those which mediate the special sense of taste. 
They are processes of the cells of the petrous gangUon. The central processes of the ganglion 
cells enter the medulla, pass dorso-medially through the formatio reticularis, and end in the 
nucleus of termination in the floor of the fourth ventricle. The motor fibers arise from dorsal and 
ventral efferent nuclei in the medulla. The glosso-pharyngeal shares these nuclei with the vagus 
and has practically the same central connections as that nerve {q. v.). 



THE VAGUS NERVE 
The vagus (N. vagus)' is the longest and most widely distributed of the 
cranial nerves; it is also remarkable for the connections which it forms with 
adjacent nerves and with the sympathetic. It is attached to the lateral aspect of the 
medulla by several filaments which are in series with those of the ninth nerve in 
front and the eleventh nerve behind (Fig. 629). The bundles converge to form a 
trunk which passes outward, pierces the dura mater, and emerges from the cranium 
through the foramen lacerum posterius (Fig. 647). In the foramen the nerve bears 
on its lateral aspect the elongated flattened jugular ganglion (G. juguJare). 

The gangUon communicates with — (a) the tympanic nerve, (b) The petrous ganglion of the 
glosso-pharyngeal nerve, (c) the spinal accessory, and (</) the hJ^50glossal. It also gives off the 
auricular branch ( R. auricularis), wliich runs forward below the petrous gangUon and passes through 
a siiuill canal in tlie petrous temporal bone to gain the facial canal. Here it gives filaments to the 
facial and emerges with that nerve through the stylo-mastoid foramen. It ascends beliind the 
external acoustic meatus, dips under the deep auricular muscles, and passes through a foramen 
in the conchal cartilage to ramify in the integument which lines the meatus and the adjacent 
part of the ear. It may be noted that many fibers of the vagus pass over the medial face of the 
ganglion withimt entering it. 

A ganglion nodosum in the form of a compact mass is not present in the horse. It appears 
to be represented by masses of ganglion ceUs in the nerve trunk which begin in front of the origin 
of the pharyngeal branch and continue a considerable distance behind the origin of the anterior 
laryngeal nerve. 

Beyond the ganglion the vagus runs backward and downward with the spinal 
accessory in a fold of the g-uttural pouch (Fig. 562). Then the two nerves separate, 
allowing the hj^poglossal to pass between them, and the vagus descends ^vith the 
internal carotid artery and crosses the medial face of the origin of the occipital 
artery. Here it is joined by the cervical trunk of the STOipathetic, and the two 
nerves continue along the dorsal aspect of the common carotid artery in a common 
sheath (Fig. 558).- At the root of the neck the vagus separates from the sym- 
pathetic, and from this point backward the relations of the right and left vagi differ 
somewiiat and must be described separately. 

The right vagus nerve (Fig. 554) enters the thorax in the angle of divergence of 
the right brachial artery and the truncus bicaroticus. It then passes backward and 
slightly upward, crossing obliquely the lateral surface of the brachiocephalic artery 
and the right face of the trachea. Reaching the dorsal surface of the latter near 
the bifurcation, it divides into dorsal and ventral branches. 

' Also commonly termed the pneumogastric nerve. 
2 There is formed thus a vago-sympathetic trunk. 



sot) 



NERVOUS SYSTEM OF THE HORSE 



The left vagus nerve (Fig. 553) enters the thorax on the lateral or the ventral 
face of the oesophagus, crosses obliquely under the left brachial artery, and passes 
back on the lateral surface of that vessel in company with a large cardiac nerve.' 
Separating from the latter, the vagus continues backward on the left face of the 



lAg. nuchcB 
Splenius 



Nuchal fat 



Branch of occipital artery 
Complexits 



Complexus tendon 



Rectus capitis 
dorsalis minor 



Rectus capitis 
dorsalis nmjor 




Spina 

accessory 

nerre 

(dorsa. 

branch) 

Brach io- 

cephaliciu, 

Vagus 



External max- 
illary vein 



Sterno-cephalicjis 
Omo-hyoideus and sterno-hyoideits 



Spinal accessory 
nerve (dorsal 
branch) 
Rectus capitis 
ventralis nuijor 

Jugular vein 

Thyro-laryngeal 

artery 

Anterior cervical 

lymph 



Thyroid gland 
Sterno-thyroideus 



Fig. 649. — Cross-section of Neck of Hor.se, Passing through Posterior Part of Atlas. 

The head and neck were extended. /, Doraal arch of atlas; 2, dens of axis; .3, ligament of dens; i, vertebral 

sinuses: 5, dura mater; 6, spinal cord; 7, vertebral artery; 8, wing of atlas; 9, atlanto-axial joint cavity: 10, 

oesophagus; 11,11, recurrent nerves; 12, 12, ventral branches of spinal accessory nerves. By an oversight the obliquua 

cap. post, (above wing of atlas) is unmarked; also the parotid gland between the jugular and external maxillary vein. 



aorta, inclines to the upper surface of tlic left bronchus, and divides into dorsal and 
ventral branches. 

The dorsal and ventral branches unite with the corresponding branches of the 
opposite nerve, thus forming dorsal and ventral oesophageal trunks (Truncus 

' In some cases the left vagus passes back below the junction of the jugular veins and the 
termination of the left brachial vein. It then runs backward and somewhat dorsaUy across the 
left face of the anterior vena cava to reach its usual position. 



THE VAGUS NERVE 807 

cesophageus dorsalis, ventralis). These run backward in the posterior mediastinum, 
dorsal and ventral to the oesophagus respectively, and enter the abdominal cavity- 
through the hiatus cesophageus; they supply branches to the oesophagus and 
anastomose with each other. The dorsal trunk receives the major part of its fibers 
from the right vagus. After entering the abdomen it passes to the left of the 
cardia, and divides into gastric and coeliac branches; the former gives branches to 
the visceral surface of the stomach, forming the posterior gastric plexus; the latter 
ends in the right coeliaco-mesenteric ganglion and the anterior interganglionic cord. 
The smaller ventral trunk passes to the lesser curvature of the stomach and ramifies 
on the parietal surface of the stomach; it forms here the anterior gastric plexus 
from which branches are supplied also to the first part of the duodenum and to the 
liver and pancreas.' 

The collateral branches of the vagus are as follows: 

1. The pharyngeal branch (R. pharyngeus) is given off in relation to the 
anterior cervical ganglion, turns around the internal carotid artery, and runs 
ventrally and forward on the guttural pouch to the dorsal wall of the pharynx 
(Fig. 562). Here its branches concur with the pharyngeal branch of the glosso- 
pharyngeal nerve and with filaments from the spinal accessory and the sympathetic 
in forming the pharyngeal plexus. This supplies the muscles of the pharynx and 
of the soft palate (except the tensor palati), delicate filaments to the anterior 
cervical ganglion of the sympathetic, and a larger branch which passes along the 
side of the oesophagus and ramifies in its cervical part. 

According to Ellenberger and Baum, the pharyngeal plexus receives filaments also from the 
digastric, anterior laryngeal, hypoglossal, and first cervical nerves. The branches of the plexus 
form secondary intermuscular and submucous plexuses, in which there are numerous minute 
ganglia. 

2. The anterior (or superior) laryngeal nerve (N. laryngeus cranialis) is larger 
than the preceding and arises a little behind it (Fig. 562). It crosses the deep face 
of the origin of the external carotid artery, runs do^vnward and forward over the 
lateral wall of the pharynx behind the hypoglossal nerve, and passes through the 
foramen below the anterior cornu of the thyroid cartilage. Its terminal branches 
ramify in the mucous membrane of the larynx, the floor of the pharynx, and the 
entrance to the oesophagus; they anastomose with those of the recurrent. At 
its origin the nerve gives off its small external branch (R. externus) ; this descends 
to the crico-thyroid muscle, which it supplies, and sends filaments to the crico- 
pharyngeus also. It often arises from the vagus just below the anterior laryngeal 
and may come from the pharyngeal branch. 

At the point of origin of the anterior laryngeal nerve there is a plexiform widening which is 
regarded by some authors as the homologue of the ganglion nodosum of man; it often contains 
minute ganglia. From it a filament arises which, after a short course, rejoins the vagus or enters 
the sympathetic trunk. Stimulation of its central end causes a reduction of the blood-pressure, 
and it is therefore termed the depressor nerve (N. depressor). On reaching the heart it passes 
between the aorta and the pulmonary artery and is distributed to the myocardium. 

3. The recurrent nerve (N. recurrens), also termed the inferior or posterior 
laryngeal nerve, differs on the two sides in its point of origin and in the first part of 
its course. The right nerve (Fig. 554) is given off opposite the second rib, turns 
around the dorso-cervical artery from without inward, runs forward on the ventral 
part of the lateral surface of the trachea, and ascends in the neck on the ventral 
face of the common carotid artery. The left nerve (Fig. 553) arises from the vagus 
where the latter begins to cross the aortic arch. It passes back over the ligamentum 
arteriosum, winds around the concavity of the aortic arch from without inward, 

' It will be noted that the formation of the ventral oesophageal trunk usually occurs at the 
root of the lungs, while the union of the dorsal branches of the two vagi generally occurs nearer the 
hiatus cesophageus. 



808 NERVOUS SYSTEM OF THE HORSE 

runs forward on the ventral part of the left face of the trachea, and continues in the 
neck in a position similar to the right nerve. 

It is worthy of note that the left nerve passes beneath the bronchial lymph glands as it 
winds around the aorta; also that in the next part of its course it lies between the left surface of 
the trachea and the deep face of the aorta, and is then related to lymph glands which lie along 
the ventral aspect of the trachea. The left recm-rent is often incorporated in part of its course 
in the anterior mediastinum with a deep cardiac nerve. Fiu-ther, the left nerve lies at first ven- 
tral to, and then upon, the oesophagus in the neck. The right recurrent is given off from, or in 
common with, a considerable trtink which connects the vagus with the first thoracic ganglion 
of the sympathetic. The arrangement here is commonly more or less plexiform, and from it 
one or two cardiac nerves arise. 

The terminal part of each nerve (Fig. 649) lies on the dorsal surface of the 
trachea, in relation to the oesophagus medially and the carotid artery dorsally.' It 
passes between the crico-arytenoideus dorsalis and the crico-pharjTigeus, and 
enters the larynx at the medial side of the lamina of the thyroid cartilage. Before 
entering it gives branches to the crico-arytenoideus dorsalis and arytenoideus 
transversus, and afterward supplies the internal muscles of the larjTix. It also 
communicates bj^ delicate filaments with branches of the anterior laryngeal nerve. ^ 
Collateral branches are given off to the cardiac plexus (Rami cardiaci), to the 
trachea (Rr. tracheales), to the oesophagus (Rr. oesophagei), and to the posterior 
cervical ganglion of the sjninpathetic. 

4. Cardiac branches (Rr. cardiaci), usually two or three in number, are given 
off from each vagus wdthin the thorax (Figs. 553, 554). These concur with the 
cardiac branches of the s>mipathetic and recurrent nerves to form the cardiac 
plexus, which imiervates the heart and great vessels. 

5. Small tracheal and oesophageal branches (Rr. tracheales et oesophagei) 
are given off from both vagi in the thorax. These concur wath branches from the 
recurrent nerves and the posterior cervical and anterior thoracic ganglia of the 
sympathetic in forming the posterior tracheal and oesophageal plexuses, from 
which twigs go to the trachea, oesophagus, heart, and large vessels. 

6. Bronchial branches (Rr. bronchiales) are detached at the roots of the lungs 
and unite with s>^llpathetic filaments in forming the pulmonary plexuses. From 
the latter numerous branches proceed in a plexiform manner along the bronchi 
and vessels into the substance of the lungs. 

The v.agus and glosso-phar3Tigeal nerves are so closely associated in origin and central 
connect ion.s tliat they may be described together in this respect. 

The sensory fibers arise from the petrous and jugular ganglia, and their central parts enter 
the lateral aspect of the meduDa and divide into anterior and posterior branches Uke the fibers of 
the dorsal roots of the spinal nerves. Most of the fibers end in arborizations about the cells of the 
vago-glosso-pharyngeal nucleus of termination, which consists of two parts. Of these, the dorsal 
sensory nucleus (Nucleus ala? cineroa') is situated in the posterior pai't of the floor of the fourth 
ventricle and in the adjacent part of tlie i-ldscd portion of the medulla near the median plane. 
The other part is termed tlie nucleus of the solitary tract, and is so named because its cells are 
grouped about the bundle (Tractus solitarius) formed by the posterior divisions of the afferent 
nerve-fibers. It ends about the level of the pyramidal decussation. The secondary central con- 
nections are similar to those of the sensory part of the trigeminus. 

The motor fibers (and those of the medullary part of the accessory) arise from the dorsal 
motor nucleus and the ventral motor nucleus. The cells of the former lie in groups aloiig the 
ventro-medial side of the dorsal sensory nucleus. The latter, also termed the nucleus ambiguus, 
is situated more deeply in the lateral part of the formatio reticularis. 



THE SPINAL ACCESSORY NERVE 
The spinal accessory nerve (N. accessorius) is purely motor. It consists of 
two parts which differ in origin and function. 

' The nerve lies here about a finger's breadth above the thyroid gland. If, liowever, the 
gland is enlarged it may come in contact with the nerve. The same is true in regard to the rela- 
tion to the anterior cervical lymph glands. 

2 The recurrent nerves innervate all the intrinsic muscles of the larynx except the crico- 
thyroid. 



THE SPINAL ACCESSORY NERVE 



809 



The medullary part arises from the lateral aspect of the medulla by several 
rootlets which are behind and in series wth those of the vagus (Fig. 629). The 
Spinal part arises from the cervical part of the spinal cord by a series of fasciculi 
which emerge between the dorsal and ventral roots. The bundles unite to form 
a trunk which is very small at its origin at the fifth segment of the cord, but 
increases in size when traced toward the brain, since it continually receives accessions 
of fibers. It passes through the foramen magnum and joins the medullary part. 




omo-hyoide 



Fig. 650. — Neck of Hobse, After Removal of Part of CuTANEns and Tbapezius. 
chiocephalicus: b, anterior superficial pectoral muscle; r, cervical eutaneus: d, sterno-cephaIi( 
/, sterno-thyro-hyoideus; g, trachea; h, h', h'\ tendoas of s 



, brachiocephalicus, and longissin 



: I, anterior deep pectoral muscle; m, rhomboideus cervicalis 
borders of which are indicated by dotted lines; p, parotid gland 
, spine of scapula; I, external maxillary vein; 2, S, jugular vein 
?rvical artery; 6, cephalic vein; 7-11. ventral branches of second to 
ond cervical nerve; /.3, cervical branch of facial nerve: 74. terminal 

branches of dorsal divisions of cervical nerves; 15, dorsal branch of spinal accessory nerve. (After Ellenberger-Baum, 

Top. Anat. d. Pferdes.) 



atlantis; i, trapezius cervicalis; k, supraspinati 
n, serratus cervicis; o, splenius, upper and lowe 
g, parotido-auricularis muscle; r, wing of atlas; 
4, carotid artery: 3, descending branch of inferior 
seventh cervical nerves; 13, cutaneous branch of si 



The trunk thus formed sends its medullary fibers to the vagus and glosso-pharyngeal 
nerves and emerges through the foramen lacerum posterius. It then runs backward 
and downward with the vagus in a fold of the guttural pouch, separates from that 
nerve, crosses the deep face of the mandibular gland and the occipital artery, and 
divides in the recessus atlantis into dorsal and ventral branches. 

It is connected by anastomotic branches wdth the vagus and hypoglossal nerves and the 
anterior cervical ganghon of the sympathetic, and contributes a branch to the pharyngeal plexus. 



810 NERVOUS SYSTEM OF THE HORSE 

The dorsal branch (R. dorsalis) (Figs. 558, 649, 650) receives a twig from the 
second and third cervical nerves and turns around the atlantal tendon of the splenius 
under cover of the brachiocephalicus. It then passes obliquely through the latter 
muscle and continues backward on the cervical part of the serratus, inclines upward 
across the anterior deep pectoral and the supraspinatus, and enters the deep face 
of the trapezius, in which it ramifies. 

The ventral branch (R. ventralis) (Fig. 561) is smaller and much shorter. It 
passes downward and backward under cover of the cervical angle of the parotid 
gland and enters the deep face of the sterno-cephalicus muscle at the junction of the 
muscular substance with the tendon of insertion. It usually crosses over the 
carotid artery just behind the lateral lobe of the thyroid gland. 

The fibers of the spinal part of the accessory arise from the ventro-lateral cells of the ventral 
gray column of the cord as far back as the fifth cervical segment. The fibers of the medullary 
part come chiefiy from the nucleus ambiguus in common with the motor fibers of the vagus. 

THE HYPOGLOSSAL NERVE 

The hypoglossal nerve (N. hypoglossus) is purely motor; it innervates the 
muscles of the tongue and the genio-hyoideus (Fig. 562). Its root-fibers arise from 
the ventral face of the medulla in linear series about 3 to 4 mm. lateral to the poste- 
rior half of the pyramid (Fig. 629). The filaments converge to three or four bundles 
which perforate the dura mater and unite to form the trunk. The latter emerges 
through the hypoglossal foramen (Fig. 647) and runs downward and backward 
between the guttural pouch and the capsule of the atlanto-occipital articulation 
for a distance of a little less than an inch (ca. 2 cm.). It then passes between the 
vagus and accessory nerves, turns downward and forward, crosses the lateral face 
of the external carotid artery, and continues over the pharynx parallel with the 
great cornu of the hyoid bone and behind the external maxillary artery. It then 
crosses beneath the artery, runs forward on the lateral face of the hyo-glossus muscle, 
and divides into its terminal branches (Rami linguales). The smaller branch 
supplies the stylo-glossus, hyo-glossus, and lingualis. The larger branch passes 
upward and forward between the hyo-glossus and genio-glossus, ramifies on the latter, 
and supplies the remaining muscles and the genio-hyoideus. Anastomoses occur 
with branches of the lingual nerve. 

In the first part of its course the nerve communicates with the anterior cervical 
ganglion and Math the ventral branch of the first cervical nerve, and gives filaments 
to the pharyngeal branch of the vagus and the pharjmgeal plexus. 

The fibers of the nerve arise from the hypoglossal nucleus, an elongated group of large multi- 
polar cells situated chiefly under the posterior part of the floor of the fourth ventricle, close to the 
median plane. The two nuclei are connected by commissural fibers. The other central connec- 
tions include: (o) communications by the medial longitudinal fasciculus with the nuclei of ter- 
mination of other cranial nerves; (6) cortico-nuclear fibers which come from the cortex by way of 
the internal capsule and the pyramids and go largely to the nucleus of the opposite side; "(c) fibers 
which join the dorsal longitudinal bundle of Schlitz, a tract which underlies the floor of the fourth 
ventricle and is traceable forward below the cerebral aqueduct. 



THE SPINAL NERVES 

The spinal nerves (Nervi spinales) are arranged in pairs, of which there are 
usually forty-two in the horse. They are designated according to their relations to 
the vertebral column as cervical (8), thoracic (18), lumbar (6), sacral (5), and 
coccygeal (5). Each nerve is connected with the spinal cord by two roots, dorsal 
and ventral (Fig. 628). 

The dorsal root (Radix dorsalis) is the larger of the two. Its fibers (Fila 
radicularia) spread out in fan shape and join the cord in a linear series along the 
dorso-lateral groove. The fibers converge laterally to form a compact bundle, on 



THE SPINAL NERVES 



811 



which there is a gray nodular enlargement, the spinal ganglion (Ganglion spinale). 
Beyond the ganglion the dorsal root joins the ventral root to constitute the nerve. 
The ganglia are external to the dura mater, and are situated in the intervertebral 
foramina, except in the case of the sacral and coccygeal nerves, the ganglia of which 
lie within the vertebral canal. Those of the coccygeal nerves are intradural. 

The ganglia vary greatly in size ; that of the first cervical nerve is scarcely as large as a hemp- 
seed, while that of the eighth cervical is about 2 cm. long and 1 cm. wide. On the large roots 
connected with the cervical and lumbar enlargement of the cord there are multiple gangha of 
varying sizes interposed in the course of the root-bundles. The fibers of the dorsal roots arise 
from the cells of the spinal ganglia; connected with each ganglion cell there is a process which 
bifurcates, giving rise to a fiber wliich enters the spinal cord and another which passes into the nerve. 

The ventral root (Radix ventralis) contains fewer fibers than the dorsal root, 
except in the case of the first cervical nerve. It arises from the ventral surface of 
the spinal cord (Fig. 626) by means of numerous small bundles of fibers which do 
not form a linear series, but emerge from the cord over an area three to five 
millimeters in width (ventral root zone). The fibers are processes of the 
large cells of the ventral gray 

columns of the spinal cord. Spinal branch of intercostal artery 

There is no ganglion on the 
ventral root. 

In the cervical, thoracic, and 
anterior lumbar regions the bundles 
of both roots pass through separate 
openings in linear series in the dura 
mater before uniting into a root 
proper. Further back the bundles 
of each root unite within the diu-a. 
In the anterior part of the cervical 
region and in the thoracic part of the 
cord there are intervals of varying 
length between adjacent roots, but in 
some places the fibers of adjacent 
roots overlap and an exchange of 
fibers may be observed . M any of the 
roots are directed almost straight out^ 
ward or inchne slightly backward, but 
the posterior lumbar, sacral, and coc- 
cygeal roots and nerves run backward 
to reach the foramina, tlirough which 
they emerge. The distance thus to 
be traversed increases from before 
backward, so that these nerves form 
a tapering sheaf around the conus 
medullaris and filum terminale in the last lumbar vertebra and the sacrum, wliich is known as the 
Cauda equina. 

The size of the spinal nerves varies greatly. The largest are connected with 
the cervical and lumbar enlargements. 

In, or immediately after its emergence from, the intervertebral foramen each 
spinal nerve gives off a small meningeal branch (Ramus meningeus). This is 
joined by a bundle of fibers from the ramus comnmnicans and enters the vertebral 
canal, in which it is distributed. Each nerve then divides into two primary 
branches, dorsal and ventral (Ramus dorsalis, ventralis). The dorsal branches 
are smaller than the ventral, except in the cervical region. They arc distributed 
chiefiy to the muscles and skin of the dorsal part of the body. The ventral branches 
supply in general the muscles and skin of the ventral parts of the body, including 
the limbs. Each nerve or its ventral branch is connected with an adjacent ganglion 
of the sympathetic system by at least one small short branch known as a ramus 
communicans. Many nerves have two and some have three such rami. A nerve 
may be connected with two ganglia, and a ganglion may be connected with two 
nerves. 




Spinal ganglion 

Dura mater 
Lig. denticulatum 

Dorsal root butidles 



Dorsal longitudinal ligament 



Conjugal ligament 



-Vertebral Canal Opened by Sawing off t 
(After Schmaltz, Atlas d. Anat. d. Pferdes.) 



812 NERVOUS SYSTEM OF THE HORSE 

The dorsal root is sensory or afferent, i. e., it conveys impulses to the central system. Its 
fibers are axones of the cells of the spinal ganglion. The ventral root is motor or efferent, and 
conveys impulses toward the periphery. Its fibers are axones of the large cells in the ventral 
gray columns of the spinal cord. The common trunk or nerve formed by the union of the two 
roots contains both kinds of fibers, as tlo also their primary di\isions. In addition to these fibers, 
which are distributed to the skeletal muscles and the skin, the spinal nerves contain fibers derived 
from the sympathetic system through the rami communicantes; these go to the glands and 
unstriped muscle and are designated secretory and vasomotor fibers. 



THE CERVICAL NERVES 

The cervical nerves (Ncrvi cervicales) (Figs. 556, 558, 650, 655) number eight 
pairs. The first of these emerges through the intervertebral foramen of the atlas, 
the second through that of the axis, and the eighth between the last cervical and 
the first thoracic vertebra. 

The dorsal branches are distributed to the dorso-lateral muscles and skin of 
the neck. They divide usually into lateral and medial branches. The medial 
branches (Rami mediales) run in general across the multifidus and the lamellar part 
of the ligamentum nuchae to the skin of the dorsal border of the neck; they supply 
the deep lateral muscles and the skin. The lateral branches (Rami laterales) are 
chiefly muscular in their distribution. The dorsal branches of the third to the 
sixth nerves are connected by anastomotic branches to form the dorsal cervical 
plexus. 

The ventral branches arc smaller than the dorsal ones — an exception to the 
general rule. Thej' increase in size from first to last. They supply in general the 
muscles and skin over the lateral and ventral aspect of the vertebrae, but the last 
three enter into the formation of the brachial plexus, and the two or three preceding 
the last give off the roots of the phrenic nerve. An irregular ventral cervical plexus 
is formed by anastomoses established between the ventral branches. The follo^ving 
special features may be noted: 

The first cervical nerve emerges through the intervertebral foramen of the 
atlas. Its dorsal branch (N. occipitalis) passes dorso-laterally between the obliqui 
capitis and the recti capitis dorsales and supplies branches to these muscles, the 
scutularis and posterior auricular muscles, and the skin of the poll. The ventral 
branch descends through the alar foramen of the atlas, crosses over the ventral 
straight muscles and the carotid artery under cover of the parotid gland, and divides 
into two branches. The anterior branch enters the omo-hyoideus muscle. The 
posterior branch passes do\vnward and backward under cover of that muscle, unites 
with a branch of the ventral division of the second cervical nerve, and continues its 
course on the ventro-lateral surface of the trachea to enter the sterno-thyro-hyoideus 
behind the intermediate tendon. In the recessus atlantis the ventral branch is 
connected by one or more twigs with the anterior cervical ganglion of the sym- 
pathetic, and a little lower with the hypoglossal nerve. It also sends branches to 
the ventral straight muscles of th© head and the thyro-hyoideus. Below the atlas 
the ventral branch is crossed superficially by the spinal accessory nerve, the occi- 
pital artery, and the ventral cerebral vein. 

The second cervical nerve is larger than the first. It emerges from the verte- 
bral canal through the intervertebral foramen of the anterior part of the arch of the 
axis. Its dorsal branch ascends between the complexus and the ligamentum 
nuchse and ramifies in the skin of the poll. The ventral branch gives off muscular 
branches to the rectus capitis ventralis major, and anastomotic branches to the 
spinal accessory and the ventral divisions of the first and third cervical nerves; 
one of these crosses over the carotid artery and concurs in the formation of the nerve 
to the sterno-thyro-hyoideus mentioned above. The ventral branch then becomes 
superficial by passing between the two parts of the brachiocephalicus, and divides 
into posterior auricular and cutaneous branches. The posterior auricular nerve 



PHRENIC NERVE 813 

passes upward and forward on the parotid gland parallel -with the posterior border 
of the parotido-aiiricularis to ramify on the convex face of the external ear. The 
cutaneous nerve of the neck (N. cutaneus colli) crosses the brachiocephaliciis muscle 
and turns backward along the course of the jugular vein. On the lower part of 
the parotid gland it is connected liy a twig with the cervical cutaneous branch of 
the facial nerve. It gives off twigs to the subcutaneous muscles and the skin of 
the parotid and larj-ngeal regions, and a long branch which passes forward in the 
mandibular space. 

The third cervical nerve leaves the vertebral canal through the foramen be- 
tween the second and third cervical vertebriE. Its dorsal branch emerges between 
two bundles of the intertransversalis muscle, accompanied by a branch of the verte- 
bral artery, turns dorsally on the multifidus, and divides into several branches which 
radiate on the deep face of the complexus. It gives branches to these muscles and 
to the skin, and a twig which joins the corresponding branch of the fourth nerve. 
The ventral branch emerges through the intertransversalis below the bundle above 
which the dorsal branch appears. It gives branches to the longissimus capitis et 
atlantis, rectus capitis ventralis major, longus colli, splenius, and brachiocephalicus. 
It also gives off a large cutaneous nerve which passes out between the two parts of 
the brachiocephalicus and divides into several divergent branches. 

The fourth antl fifth cervical nerves are distributed in general like the third. 
Their dorsal branches are united liy anastomotic twigs with each other and with 
those of the third and sixth nerves to form the dorsal cervical plexus. The ventral 
branch of the fifth nerve often contributes a small twig to the phrenic nerve. 

The sixth cervical nerve has a smaller dorsal branch than the fifth. Its 
ventral branch is larger and goes in part to the brachial plexus; it supplies twigs 
to the intcrtransversales, the longus colli, the brachiocephalicus, and the cervical 
parts of the serratus and rhomboideus, furnishes a root of the phrenic nerve, and 
gives off several considerable subcutaneous branches. One of the latter ramifies 
on the thick part of the cervical cutaneus, to which it gives branches; another and 
larger branch (N. supraclavicularis) sends twigs to the skin over the shoulder joint, 
and descends to the skin over the superficial pectoral muscles (Fig. 590). 

The seventh and eighth cervical nerves have small dorsal branches, which 
ascend between the longissimus and multifidus, giving twigs to these muscles, the 
spinalis and semispinalis, the rhomboideus, and the skin. Their ventral branches 
are very large and go almost entirely to the brachial plexus; that of the seventh 
nerve contributes the posterior root of the phrenic nerve. 

Phrenic Nerve 
The phrenic nerve (N. phrenicus) (Figs. 553, 554, 558), the motor nerve to the 
diaphragm, is formed by the union of two or three roots which run obliquely down- 
ward and backward over the superficial face of the scalenus muscle. The chief 
roots come from the ventral branches of the sixth and seventh cervical nerves. The 
root derived from the fifth nerve is small and inconstant. The root from the 
seventh cervical comes by way of the brachial plexus. The nerve crosses the ventral 
border of the scalenus a fingerbreadth in front of the first rib, passes through the 
angle of divergence of the inferior cervical and brachial arteries, and enters the 
thorax by passing between the latter vessel and the anterior vena cava. Beyond 
this the course of the nerve is not the same on both sides. The right nerve courses 
backward and somewhat downward over the right face of the anterior vena cava, 
crosses the pericardium, and continues along the posterior vena cava to the dia- 
phragm. In the latter part of its course it is enclosed in a special fold of the right 
pleura and inclines gradually to the ventral face of the vein. The left nerve, in 
part with the vagus, runs its entire course in the mediastinum. In the anterior 
mediastinum it lies along the lateral face of the brachiocephalic artery ventral to 



814 NERVOUS SYSTEM OF THE HORSE 

the left vagus and a cardiac nerve, and crosses over the dorso-cervical vein. It 
then parts company with the vagus, passes over the upper part of the pericardium, 
and runs backward in the posterior mediastinum to reach the tendinous center of 
the diaphragm considerably to the left of the median plane. Each nerve is usually 
connected near its origin with the first thoracic ganglion of the sympathetic by a 
ramus communicans, and each terminates by dividing into several branches which 
are distributed to the corresponding part of the diaphragm. 

The Brachial Plexus 
The brachial plexus (Plexus brachialis) (Fig. 558) results from anastomoses 
established between the ventral branches of the last three cervical and first two 
thoracic nerves. It appears as a thick, wide band between the two parts of the 
scalenus muscle, and is covered by the anterior deep pectoral and subscapularis 
muscles. Each of the three chief roots, i. e., those from the last two cervical and the 
first thoracic nerve, is connected with the sympathetic by a ramus communicans. 

The root, derived from the sixth cervical nerve is very small, while the ventral branches of 
the seventh and eighth cervical nerves go ahnost entirely to the plexus. The first thoracic nerve 
furnishes the largest root; its whole ventral brancli goes to the plexus with the exceptiod of its 
small first intercostal branch. The root from the second thoracic nerve is small, since most of its 
ventral branch goes to form the second intercostal nerve. 

The branches emanating from the plexus go for the most part to the thoracic 
limb, but some are distrilsuted on the chest-wall. The names of the branches, and 
their arrangement so far as they can be conveniently examined before removal of 
the foreliml), are as follows:^ 

1. The large suprascapular nerve (N. suprascapularis) arises from the anterior 
part of the plexus, passes ventro-laterally, and disappears between the supraspinatus 
and subscapularis muscles. 

2. The much smaller subscapular nerves (Nn. subscapulares), usually two 
primary trunks, arise close behind the suprascapular, run backward a short dis- 
tance, and divide into several branches which enter the distal third of the subscap- 
ularis muscle. 

3. The anterior thoracic or pectoral nerves (Nn. pectorales craniales), three or 
four in number, arise from the anterior part of the plexus and from the loop formed 
by the musculo-cutaneous and median nerves. One enters the anterior deep 
pectoral muscle. Another passes between the divisions of the deep pectoral to 
supply the superficial pectoral and brachiocephalicus, giving a twig usually to the 
posterior deep muscle. The latter receives one or two other nerves. 

4. The musculo-cutaneous nerve (N. musculocutaneus) arises from the ante- 
rior part of the plexus and descends over the lateral face of the brachial artery, 
below which it is connected Ijy a large but short branch with the median nerve, 
thus forming a loop in which the artery lies.^ One or two branches to the pectoral 
muscles are given off from the nerve or the loop. 

5. The median nerve (N. medianus) is usually the largest branch of the bra- 
chial plexus. It tlescends over the insertion of the scalenus, crosses the medial 
face of the brachial artery, and reaches the anterior border of that vessel. It is 
easily recognized by its large size and the loop which it forms with the musculo- 
cutaneous nerve. 

6. The ulnar nerve (N. ulnaris) arises with the median by a short common 

' In order to examine the plexus and the origins of its chief branches conveniently and with 
as little disturbance of relation as possible, the subject should be suspended in imitation of the 
natm-al position and the foreUmb abducted as much as is necessary. In doing this some disturb- 
ance of the position and relations of the nerves and vessels takes place. The brachial vessels are 
drawn away from the chest-wall so that their lateral surface now faces forward, and the nerves 
are similarly affected. 

' The loop may be absent or double. 



SUPKASCAPULAR NEBVE — MUSCULO-CUTANEOUS NERVE 815 

trunk. It descends behind the brachial artery and is accompanied a short distance 
by the radial nerve, from which it can be distinguished by its smaller size. 

7. The radial nerve (N. radialis) arises from the posterior part of the plexus 
and is sometimes the largest branch. It descends with the ulnar nerve over the 
medial face of the origin of the subscapular artery and the lower part of the teres 
major and dips into the interstice between that muscle and the long and 
medial heads of the triceps. 

8. The axillary nerve (N. axillaris) arises behind the musculo-cutaneous. It 
passes downward and backward on the medial face of the subscapularis and dis- 
appears between that muscle and the subscapular artery. 

9. The long thoracic nerve (N. thoracalis longus) is wide and thin. It arises 
from the anterior end of the plexus, gives off (usually) three branches to the ser- 
ratus ventralis at the junction of its cervical and thoracic parts, and passes back- 
ward across the surface of the serratus thoracis, to which it is distributed. The 
branches which enter the muscle are given off both upward and downward in fairly 
regular fashion. 

10. The thoraco-dorsal nerve (N. thoracodorsalis) passes upward and back- 
ward across the subscapularis nmscle to ramify in the latissimus dorsi. 

11. The external thoracic nerve (N. thoracalis lateralis) arises by a common 
trunk ^vith the ulnar. It passes backward and ventrally across the medial surface of 
the humeral tendon of the cutaneus muscle, and continues backward in company with 
the external thoracic vein. Its terminal branches ramify in the cutaneus and the 
skin of the abdominal wall as far back as the flank. It gives collateral branches 
to the deep pectoral muscle and others which anastomose with perforating branches 
of intercostal nerves. A branch from it, accompanied by a large perforating inter- 
costal branch, winds around the ventral border of the latissimus dorsi and ramifies 
in the cutaneus on the lateral surface of the arm. 

The term posterior thoracic or pectoral nerves (Nn. pectorales caudales) may be used to 
include 9, 10, and 11. 

Suprascapular Nerve 
The suprascapular nerve (Fig. 566), short but large, is usually derived chiefly, 
if not exclusively, from the sixth and seventh cervical components of the brachial 
plexus. It passes between the supraspinatus and subscapularis muscles and turns 
around the distal fourth of the anterior border of the scapula to reach the supra- 
spinous fossa. It gives branches to the supraspinatus and continues backward 
and upward into the inf raspinous fossa, and terminates in several branches which 
innervate the infraspinatus. 

The direct relation of this nerve to the scapula renders it liable to injury, the result 'of which 
may be paralysis and atrophy of the muscles supplied by it. There is, however, a small tendinous 
band which extends over the nerve as it turns around the edge of the scapula. 

MUSCULO-CUTANEOUS NeRVE 

The musculo-cutaneous nerve (Fig. .566) arises close behind the suprascapular, 
and is derived chiefly from the part of the brachial plexus which is supplied by the 
seventh and eighth cervical nerves. It descends across the lateral surface of the 
brachial artery, below which a great part of the nerve unites with the median to 
form the loop previously mentioned. It gives off a branch which enters the proxi- 
mal part of the belly of the coraco-brachialis, passes downward and forward in 
company with the anterior circumflex vessels between the two parts of that muscle 
or between the muscle and the bone, and divides into branches which enter the biceps 
brachii. It contributes one of the nerves to the pectoral muscles. In some cases 
this nerve sends a branch to join the cutaneous branch of the median. 



816 



NERVOUS SYSTEM OP THE HOKSE 



Axillary Nerve 
The axillary nerve (Figs. 566, 652)^ derives its fibers chiefly from the eighth 
cervical root of the brachial plexus. It runs downward and backward across 
the distal part of the subscapularis, and, in company 
with the posterior circumflex artery, dips in between that 
muscle and the subscapular artery at the level of the 
shoulder joint. Continuing outward in the interval between 
the teres minor and the long and lateral heads of the triceps, 
it reaches the deep face of the deltoid and divides into several 
divergent branches. The muscular branches supply the teres 
major, capsularis, teres minor, deltoid, and brachiocephali- 
cus. The cutaneous branch (N. cutaneus brachii lateralis) 
runs downward and a little forward across the lateral head 
of the triceps and ramifies on the fascia on the front of the 
forearm and on the superficial pectoral muscle. 

Radlal Nerve 
The radial nerve- (Figs. 566, 568, 652) is sometimes the 
largest branch of the brachial plexus. Its fibers are derived 
chiefly from the first thoracic root of the plexus. It passes 
do■^^'nward and backward over the medial surface of the origin 
of the subscapular artery and the distal part of the teres 
major. In this part of its course it is related in front to the 
ulnar nerve, which separates it from the brachial vein.^ It 
detaches a branch to the tensor fasciae antibrachii, passes out- 
ward in the interval between the teres major and the long 
and medial heads of the triceps, and gains the musculo-spiral 
groove of the humerus. Accompanied by a branch of the 
deep brachial artery, it runs obliquely downward and outward 
in the groove, covered laterally by the lateral head of the tri- 
ceps and the extensor carpi radialis, and reaches the flexion 
surface of the elbow joint. In this part of its course it gives 
off muscular branches to the three heads of the triceps and 
to the anconeus, and a cutaneous nerve (N. cutaneus anti- 
brachii dorsalis); branches of the latter emerge below or 
through the lateral head of the triceps and ramify on the 
dorso-lateral surface of the forearm. At the elbow the nerve 
descends with the anterior radial vessels on the joint capsule, 
between the brachialis and extensor carpi radialis, and sup- 
plies branches to the extensor carpi and the common extensor 
of the digit and (inconstantly) to the brachialis. Below the 
elbow joint the nerve detaches a large branch which passes 
back between the lateral extensor and the radius to the ulnaris 
lateralis, and terminates by small branches which descend on 
the radius to enter the radial and ulnar heads of the common 
and lateral extensors of the digit, and the oblique extensor of 
the carpus. Thus the radial nerve innervates the extensors 
of the elbow, carpal, and digital joints, and supplies also 
the lateral flexor of the carpus.^ 

' Also termed the circumflex nerve. 

^ This is also known as the museulo-spiral nerve. 

' The relative positions of the vessels and nerves here are variable ; not rarely the ulnar nerve 
passes between the subscapular artery and vein. 

■• Morphologically the last-named muscle belongs to the extensor group. In man and in 
many animals it is an extensor in function. 

( 




Fig. 652. — C utaneous 
Nerves of Right 

FORELIMB OF HoRSE; 

Lateral Face. 

a, Cutaneous branch 
of axillarj'' nerve ; b, cu- 
taneous branches of radial 
nerve; c, posterior cutane- 
ous branch of ulnar nerve ; 
d, cutaneous branch of me- 
dian nerve ; e, superficial 
branch of ulnar nerve; /, 
lateral volar nerve; s, anas- 
tomotic branch connecting 
medial and lateral volar 
nerves; 1, lateral head of 
triceps: 2, extensor carpi 
radialis; 3, common ex- 
tensor; 4i ulnaris lateralis. 
{After EUenberger, in Leis- 
ering's Atlas.) 



ULNAR NERVE 



817 



Ulnar Nerve 
The ulnar nerve (Figs. 566, 567, 568, 652) arises with the median from the 
thoracic components of the brachial plexus. It descends between the brachial 
arterj' and vein, accompanied for a short distance by the radial nerve. It then 
crosses the vein and continues behind the latter along the anterior border of the 
tensor fasciae antibrachii and dips under that muscle near the elbow. Here it is 
joined by the ulnar vessels and passes downward and backward over the medial 
epicondyle of the humerus. In the forearm it crosses obliquely the deep face of the 
ulnar head of the flexor carpi ulnaris and descends under the deep fascia with the 



Extensor carpi radialis 



Intermuscular septum 



Common extensor of digit 



Intermuscular septn 

Lateral extensor of digit 
Intermuscular septum 



Ulruiris hilerulis 
Deep digital flexor 
{humeral head) 



Superficial digital ficxor — -^ 
Deep digital flexor (ulnnr head) 




Accessory cephalic vein 

Vein 

Cephalic rein 
Mediid ligament of elbow 

Median nerve 
Median reins 
Median artery 

Flexor carpi radialis 



Flexor carpi ulnaris 



Ulnxir vein Ulnar nerve 
Ulnar artery 

Fig. 653. — Cross-section of Forearm of Horse about Three Inches (ca. 8 cm.) below the El 
The deep fascia is designated by red line. N, A, V, Interosseous vessels and nerve. 



vessels, at first on the ulnar head of the deep ficxor, and then Ijetween the middle 
and lateral flexors of the carpus. Near the level of the accessory carpal bone it 
divides into two terminal branches, suix-rficial and deep. It gives off two principal 
collateral branches. The cutaneous branch (Ramus cutaneus volaris) is detached 
just before the nerve passes under the tensor fasciae antibrachii; it runs downward 
and backward on that muscle under cover of the posterior superficial pectoral, 
becomes superficial Ijelow the elbow, and ramifies on the posterior surface and both 
sides of the forearm. The muscular branches, which are given off at the elbow, 
supply the superficial digital flexor, the ulnar head of the deep flexor, and the flexor 
carpi ulnaris. Of the two terminals, the superficial branch (Ramus superficialis) 
emerges between the tendons of insertion of the lateral and middle flexors of the 
carpus and ramifies on the dorso-lateral aspect of the carpus and metacarpus. The 
deep branch (Ramus profundus), after a verv short course, unites under cover of 
.52 



818 



NERVOUS SYSTEM OF THE HORSE 



tlie tendon of the ulnaris lateralis with the lateral branch of the median nei-ve to 
form the lateral volar nerve. 

Median Nerve 
The median nerve (Figs. 566, 567, 572, 652, 653) derives its fillers chiefly from 
the eighth cervical and first thoracic roots of the brachial plexus. It is usually the 
largest branch, and it accompanies the chief arterial trunks to the distal part of the 
limb. It descends over the medial face of the brachial artery, which it crosses 
obliquely, and continues do^vn the arm in front of the arterJ^ Near its origin it is 



Medial metacarpal vein 

Volar nerre 

Digital artery 



Dorsal digital branch 
Volar digital branch 



Coronary plexus 




Distal end of lateral small meta- 
carpal bone 

Large metacarpal hone 

Suspensory ligament 

Superficial flexor tendon 

Posterior annular ligament of 
fetlock 



Extensor branch of suspensory 

ligament 

Oblique or middle distal 

sesamoidean ligament 

Volar ligameid of pastern joint 

Proximal annular ligament of digit 

Deep flexor tendon 

Distal annular ligament of digit 



Fig. G54. — Dissection of Distal Part of Right Fore Limb of Horse; Volar Surface. 

I, Cartilage of third phalanx; ^, 3, 4, ligaments from first phalanx to distal sesamoid, bulb of heel and cartilage of third 

phalanx. (After Schmaltz, Atlas d. Anat. d. Pferdes.) 



joined by a large branch with the musculo-cutaneous nerve, thus forming a loop in 
which the artery appears to be suspended. Near the elbow it usually crosses 
obliquely over the median artery and lies behind it on the medial ligament. 
Below the joint it again crosses the artery and lies behind the radius and the 
lower part of the long medial ligament. 

At the elbow the nerve is covered by the posterior superficial pectoral muscle and is crossed 
by the large obUque connection between the cephalic and brachial veins. The variable and often 
plexiform venous arrangement renders approach to the nerve here undesirable. It can be reached 
best by an incision just behind the lov/er part of the long medial ligament; here the nerve 
lies under the deep fascia in the furrow between the radius and the anterior border of the flexor 
carpi radialis, overlapped by the latter. Not uncommonly the nerve retains its position in front 
of the artery at the elbow; in other cases it lies upon the artery, and rarely it crosses the deep face 
of the artery. 



MEDIAN NERVE 819 

Passing beneath the medial flexor of the carpus, the nerve continues down- 
ward in the forearm with the median vessels, and divides at a variable distance 
above the carpus into two branches; these are the medial volar nerve, and the 
lateral branch, which unites Avith the ulnar to form the corresponding lateral volar 
nerve. 

At the proximal part of the forearm the nerve runs almost straight downward along the 
posterior border of the long medial ligament, while the artery here incUnes somewhat backward. 
Thus the nerve is superficial to the artery for a short, distance, then lies in front of the latter to 
about the middle of the region, where it inclines a little backward and arrives at the interval 
between the radial and ulnar flexors of the carpus. The division may occur about the middle of 
the region or even higher, but commonly takes place in the distal third or fourth. 

The collateral branches are as follows: 

1. The musculo-cutaneous branch is in reality the continuation of the nerve of 
that name. It is given off al)out the middle of the arm, passes beneath the lower 
part of the laiceps, and divides into muscular and cutaneous branches. The mus- 
cular branch enters the brachialis. The cutaneous branch emerges between the 
brachiocephalicus and the biceps and divides into two branches; these descend 
on the fascia of the forearm with the cephalic vein and its accessory, and ramify 
on the front and medial face of the forearm, carpus, and metacarpus. 

2. Muscular branches to the radial flexor of the carpus and the humeral head 
of the deep flexor of the digit are given off just as the nerve passes under the first 
named muscle. 

3. The small interosseous nerve passes through the interosseous space and 
is distributed chiefly to the periosteum, but in some cases twigs may go to the 
exten.sor muscles. 

The volar or metacarpal nerves,^ medial and lateral, are the continuations 
of the median and ulnar nerves in the distal part of the limb. 

The medial volar nerve (N. volaris medialis) arises as the medial terminal 
branch of the median nerve at a variable distance above the carpus (Fig. 567). 
It descentls through the carpal canal along the medial border of the superficial 
flexor tendon, and lies at first in front of the common digital artery. It then passes 
behind the artery to the distal third of the metacarpus, where it lies behind the vein, 
the artery here becoming deeper in position. In addition to cutaneous twigs, the 
nerve gives off near the middle of the metacarpus a considerable anastomotic 
branch which winds obliquely over the flexor tendons and joins the lateral nerve 
below the middle of the metacarpus (Fig. 572) . Near the fetlock the nerve divides 
into two digital branches. * 

1. The dorsal (or anterior) digital branch (Ramus dorsalis) descends at first 
between the digital artery and vein, then crosses over the vein and ramifies in the 
skin and the corium of the hoof on the dorsal face of the digit. 

2. The volar (or posterior) digital branch (Ramus volaris) is the direct con- 
tinuation of the trunk. It descends behind the digital artery, which it accompanies 
in its ramification. A middle digital branch is sometimes described as descending 
behind the vein. In some cases this branch is distinct, but usually there are instead 
several small twigs derived from the volar branch, which cross very obliquely 
over the artery and anastomose in a variable manner with each other and A\ith the 
dorsal branch. 

The lateral volar nerve (N. volaris lateralis) is formed by the union of the 
lateral terminal branch of the median ^\^th the deep branch of the ulnar nerve 
(Fig. 567). It descends with the lateral volar metacarpal artery in the texture of 
the posterior annular ligament of the carpus. In the metacarpus it descends along 
the lateral border of the deep flexor tendon behind the lateral metacarpal vein, and 
is accompanied by a small artery from the volar subcarpal arch. Toward the 

' In veterinary works these are frequently termed plantar nerves, which is an unfortunate 
misnomer. 



820 NERVOUS SYSTEM OF THE HORSE 

distal end of the metacarpus it is joined by the oblique branch from the medial 
nerve, and beyond this is arranged like the latter. Below the carpus it detaches a 
deep branch to the suspensory ligament and the interossei, and also supplies twigs 
to the skin.i 

THE THORACIC NERVES 

The thoracic nerves (Nn. thoracales) number eighteen on either side in the 
horse. They are designated numerically according to the vertebra behind which 
they emerge. Most of them are arranged in a very similar manner and therefore 
do not require separate description. Each divides into a dorsal and a ventral 
branch, the latter being the larger. 

The dorsal branches (Rami dorsales) emerge behind the levatores costarum 
and divide into medial and lateral branches. The medial l^ranches ascend on the 
multifidus and supply the dorsal spinal muscles. The lateral branches run outward 
under the longissimus dorsi and emerge between that muscle and the longissimus 
costarum; after giving twigs to these muscles they pass through the latissimus 
dorsi and the lumbo-dorsal fascia and ramify as dorsal cutaneous nerves under the 
skin of the back (Fig. 655). In the region of the withers they give branches to the 
serratus dorsalis and rhomboideus, and their cutaneous terminals pass through 
these muscles and the dorso-scapular ligament to supply the skin over the liga- 
mentum nuchae and the scapular cartilage. 

The ventral branches or intercostal nerves (Nn. intercostales) are much larger 
than the preceding, and are connected with the sympathetic by rami communi- 
cantes. The first goes almost entirely to the brachial plexus, but sends a small 
branch downward in the first intercostal space, which is expended in the muscle 
there without reaching the lower end of the space. The second ventral branch 
furnishes a considerable root to the brachial plexus, but its intercostal continuation 
is typical. The intercostal nerves (Fig. 273) descend in the intercostal spaces 
with the vessels of like name, at first between the intercostal muscles, and lower clown 
chiefly between the pleura antl the internal intercostal muscle. In the anterior 
spaces the artery lies along the posterior border of the rib, with the nerve in front 
of it; further back the nerve lies behind the border of the rib, with the artery in 
front of it. They supply the intercostal muscles, give off lateral perforating branches, 
and terminate in the following manner: The second to the sixth inclusive emerge 
through the spaces between the costal cartilages and concur in supplying the pectoral 
muscles. The second to the eighth give branches to the transversus thoracis. 
The succeeding ones give branches to the diaphragm, pass between the transverse 
and internal, oblique abdominal muscles, give twigs to these, and end in the rectus 
abdominis.- There are three series of cutaneous nerves given off by the intercostal 
nerves. The dorsal nerves emerge through the serratus ventralis and the external 
intercostals about parallel with the digitations of the external oblique. The middle 
ones perforate the origin of the latter muscle. The Ventral ones appear through 
the abdominal tunic. They supply branches to the abdominal muscles, the cu- 
taneus, and the skin. Some of the anterior ones anastomose with the posterior 
thoracic branches of the brachial plexus. The posterior three supply in part the 
skin of the flank. The ventral branch of the last thoracic nerve runs outward 
behind the last rib across the dorsal surface of the psoas major and divides into 
superficial and deep branches. The superficial branch passes over the superficial 
face of the transversus abdominis, perforates the obliquus externus, and ramifies 
under the skin of the flank (Fig. 657) . The deep branch descends on the deep face 
of the internal oblique to the rectus abdominis, in which it ends. 

' Anastomoses are established between the digital branches, and the areas innervated by 
them are not well defined, but really overlap each other. In certain diseased conditions, however, 
in which the lesions are confined to the volar structures, relief from pain may be afforded by sec- 
tion of the volar branches only. 



822 



NERVOUS SYSTEM OF THE HORSE 



THE LUMBAR NERVES 

There are six pairs of lumbar nerves (Nn. luml:)ales) in the horse, the last of 
which emerge between the last lumbar vertelira and the sacrum. The anterior two 
or three are about the same size as the thoracic nerves, but the others are much 
larger. 

Their dorsal branches are small in comparison with the ventral ones. They 
are distributed to the muscles and skin of the loins and croup in a fashion similar 
to those of the thoracic nerves. 

The ventral branches are connected with the sympathetic by small rami 
communicantes, and give branches to the sublumbar muscles. Those of the first 
two nerves are arranged in a manner analogous to the corresponding branch of the 
last thoracic nerve. 

The ventral branch of the first lumbar nerve is termed the ilio-hypogastric 
nerve (N. iliohypogastricus). It passes outward between the quadratus luni- 



Cnira of diaphragm: 

Diaphragm 

Last thoracic 
neri' 

Ilio-hypogastric 
nerve 
IHo-inguinal nerve — f 

External spermatic I.. 

nerve 
External cutaneou: 
nerve 




Spla7ichnic nerve 
Last intercostal arteries 
First lumbar arteries 



Attachments of psoas major 
Body of vertebra 
External spermatic nerve 
Trunk of lumbar arteries 



Sixth lumbar artery 



Sympathetic 
trunks 

Insertion of quad- 
ratus lumhorum 

Anterior part of I, 
lumbosacral plexus [' '. 

Obturator nerve — 
Femoral nerve 

Fig. 656. — Lumbar Nerves of Horse; Ventral View. (After St-hmaltz, Atlas d. Anat. d. Pferdes.) 



- Ventral sacro-iliac 
ligament 



borum and the psoas major, and divides at the lateral border of the latter into a 
superficial and deep branch. The superficial or cutaneous branch passes over the 
dorsal edge of the internal oblique, ilescends between that muscle and the external 
oblique, perforates the latter, and runs doAvnward and backward and ramifies 
under the skin of the posterior part of the flank and the lateral surface of the thigh. 
It gives branches to the transversus and obliquus externus abdominis. The deep 
(or muscular) branch is smaller; it runs downward and backward beneath the 
peritoneum to the lateral border of the rectus abdominis, gives branches to the 
internal oblique, and terminates in the rectus abtlominis. 

The ventral branch of the second lumbar nerve is usually connected by an 
anastomotic branch with that of the tliirtl nerve. It gives off a large branch to the 
psoas major and is continued as the ilio-inguinal nerve (N. ilioinguinalis). This 
divides like the ilio-hypogastric into superficial and deep branches. Its superfi- 
cial branch perforates the external ol)lique muscle a little in front of the point of 
the hip, rims do^vnward on the front of the thigh and the lateral surface of the 
stifle, and gives off cutaneous branches. The deep branch runs behind and parallel 
with that of the ilio-hypogastricus and detaches branches to the abdominal muscles. 



THE LUMBAR NERVES 



823 



It joins a branch of the external spermatic nerve, and the trunk so formed de- 
scends the inguinal canal, to be distributed to the external genital organs and the 
surrounding skin in the inguinal region. 

The ventral branch of the third lumbar nerve is connected Ijy a small anasto- 
motic branch with the second nerve antl furnishes a root of the lumbo-sacral plexus. 
It gives off a branch to the psoas muscles, the external spermatic nerve, and 
is continued as the lateral 
cutaneous nerve. The ex- 
ternal spermatic nerve (N. 
spermaticus externus) pa.sses 
backward in the substance of 
the psoas minor and divides 
into two branches. One of 
these, the muscular branch, 
emerges in front of the circum- 
flex iliac vessels and goes to the 
cremaster and internal ol^lique 
muscles. The other, the in- 
guinal branch, emerges behind 
the vessels just mentioned. It 
then runs lateral to and parallel 
with the external iliac artery 
and descends in the metlial 
part of the inguinal canal. It 
emerges at the external ring 
with the external pudic artery 
and ramifies in the exiernal 
genital organs and the skin of 
the inguinal region. The lat- 
eral cutaneous nerve of the 
thigh (N. cutaneus femoris 
lateralis) runs backward in 
the substance of the psoas 
muscles and emerges at the 
lateral border of the psoas 
minor. It then passes outward 
and backward on the iliac fas- 
cia and accompanies the pos- 
terior branch of the circumflex 
iliac artery. With this vessel 
it perforates the abdominal 
wall by passing between the 
external oblique and the iliacus 
a short distance below the 
point of the hip, descends on 

the medial face of the tensor fasciae lata (near its anterior border), and ramifies 
subcutaneously in the region of the stifle. 

The origin and disposition of some of the foregoing nerves are variable. In some cases the 
ilio-inguinal nerve ends in the psoas major, and appears then to be absent. The mode of formation 
of the inguinal nerves is inconstant. 

The ventral branches of the fourth, fifth, and sixth lumbar nerves concur in 
the formation of the lumbo-sacral plexus. 




Fig. 657. — Superfici.\l Nerves of Pel- 
vic Limb .\nd Posterior Part of 
Trunk of Horse. 

a, Cutaneous branches of sixteenth 
venteenth thoracic nerves; b, cuta- 
branches of lumbar nerves: c, cu- 
taneous branches of sacral 
cutaneous branches of coccygeal nerves; 
e, /, ff, cutaneous branches of last thoracic 
and first and second lumbar 
end of lateral cutaneous nerve of thigh; 
h, posterior cutaneous nerve of tliigh; i, i, 
cutaneous branches of great sciatic nerve-, 
A-, posterior cutaneous nerve of the leg; 
/, superficial peroneal nerve; m, terminal 
part of deep peroneal nerve; n, lateral plantar nerve; /, obliquus ab- 
dominis externus; 2, tensor f.-isci3e latse; 3, gluteus superficialig; 4, 
biceps femoris; o, semitendinosus; 6, common extensor; 7, lateral ex- 
ten.sor; 5, flexor tendons; 9, great metatarsal arterj'. (After EUen- 
berger, in Leisering's Atlas.) 



824 NERVOUS SYSTEM OF THE HORSE 

LUMBO-SACRAL PLEXUS 

This plexus (Fig. 576) results substantially from the union of the ventral 
branches of the last three lumbar and the first two sacral nerves, but it derives a 
small root from the third lumbar nerve also. The anterior part of the plexus lies 
in front of the internal iliac artery, between the lumbar transverse processes and the 
psoas minor. It supplies branches to the ilio-psoas (designated by Girard the 
iliaco-muscular nerves). The posterior part lies partly upon and partly in the 
texture of the sacro-sciatic ligament. From the plexus are derived the nerves of the 
pelvic limb, which are now to be described. 

Femoral Nerve 

The femoral nerve (N. femoralis)' is derived chiefly from the fourth and fifth 
lumbar nerves, but commonly, if not always, receives a fasciculus from the third 
nerve also (Fig. 656). It is the larger of the two nerves which are given off from 
the anterior part of the lumbo-sacral plexus. It runs ventrally and backward, at 
first between the psoas major and minor, then crosses the deep face of the tendon 
of insertion of the latter, and descends under cover of the sartorius over the termi- 
nal part of the ilio-psoas. It gives off the saphenous nerve, arid divides into several 
terminal branches which dip into the interstice between the rectus femoris and the 
vastus medialis (Fig. 575). These branches are accompanied by the anterior 
femoral vessels and innervate the quadriceps femoris. A collateral branch is given 
off to the ilio-psoas. 

The saphenous nerve (N. saphenus) (Figs. 575, 576, 582) is given off as the 
femoral crosses the terminal part of the ilio-psoas. It gives off a branch which 
enters the deep face of the sartorius, and descends with the femoral vessels in the 
femoral canal. About the middle of the thigh it divides into several branches 
which emerge from between the sartorius and gracilis, perforate the deep fascia, and 
ramify on the medial surface and the front of the limb as far downward as the hock. 
The longer posterior branches accompany the saphenous vessels, while the anterior 
branches deviate forward toward the stifle and the anterior surface of the leg. 

Obturator Nerve 
The obturator nerve (N. obturatorius) is derived chiefly from the ventral 
branches of tlie fourth and fifth lumbar nerves, but may receive fibers from the 
third or the sixth (Fig. 656). It runs do^vnward antl backward, at first above 
and then upon the external iliac vein, inclines inward across the obturator vein, and 
passes through the anterior part of the obturator foramen (Fig. 576) . It continues 
do^vnward through the obturator externus, and divides into several branches which 
innervate the obturator externus, pectineus, adductor, and gracilis muscles (Fig. 
581). 

Anterior Gluteal Nerve 

The anterior gluteal nerve (N. gluta^us cranialis) is derived chiefly from the 
last lumbar and first sacral nerves, but commonly has a fifth lumbar root. It 
divides into four or five branches which emerge through the greater sciatic 
foramen with the divisions of the anterior gluteal artery and supply the glutei, 
tensor fascia lata\ and capsularis (Fig. 658). The nerve to the tensor fasciie latse 
and the anterior part of the superficial gluteus passes between the deep part of the 
gluteus medius and the gluteus profundus, and is accompanied on the iliacus by 
branches of the lateral circumflex vessels. 

Posterior Gluteal Nerve 
The posterior gluteal nerve (X. glut;eus caudalis) is derived mainly from the 
sacral roots of the lumbo-sacral plexus (Figs. 576, 658). It divides into two trunks 
' Also termed the anterior crural nerve. 



GREAT SCIATIC NERVE 



825 



which emerge above the great sciatic nerve. The dorsal nerve passes backward 
on the upper part of the sacro-sciatic Hgament and divides into branches which 
enter the biceps femoris; it supplies a laranch to the posterior part of the middle 
gluteus, and a nerve which turns around the posterior border of the latter and enters 
the posterior head of the superficial gluteus. The ventral nerve runs do\vnward 
and backward on the sacro-sciatic ligament and divides into the posterior cutaneous 
nerve of the thigh (N. cutaneus femoris caudalis) and muscular branches which 
supply the semitendinosus. The former passes through the liiceps femoris, emerges 
between that muscle and the semitendinosus at or a little below the level of the tuber 
ischii, and ramifies subcutaneously on the lateral and posterior surfaces of the hip 
and thigh (Fig. 657). The deep part of the nerve is connected by filaments with 
the pudic nerve. 

Great Sciatic Nerve 
The great sciatic nerve (N. ischiadicus) (Figs. 574, 580, 658), the largest in 
the body, is ilerived chiefly from the sixth lumbar and first sacral roots of the lumbo- 



Sacral spines 



Coccygeal 
lertebrce 



Lateral <!acro- / 
iliac ligament \ 




Tuhu 
isch ii 

Lesser Geyntl- Anastomosis^ 
sciatic lus between ob- 

foramen turator and 

internal pudic 
veins 



Iliaeo-femoral or lateral circumflex vessels 



Pubic tubercle 



"Obturator artery 
Obturator internus 
^Obturator vein 



Fig. 658. — Vessels and Nerves on Pelvic Wall of 



Nervua ischiadicus 



= great sciatic nerve: n. glut. inf.= 
Schmaltz, Atla 



posterior gluteal nerv 
1 d. Anat. d. Pferdes.) 



Horse. 

1. pudendus —pudic nerve. (Afte; 



sacral plexus, but usually has a fifth lumbar root and may receive a fasciculus from 
the second sacral nerve. It emerges through the greater sciatic foramen as a 
broad flat band which is blended at first with the posterior gluteal nerve and 
passes do^vnward antl backward on the lower part of the sacro-sciatic ligament and 
on the origin of the deep gluteus muscle. It turns downward in the hollow between 



826 NERVOUS SYSTEM OF THE HORSE 

the trochanter major and the tuber ischii over the gemellus, the tendon of the 
obturator internus, and the quadratus femoris. In its descent in the thigh it lies 
between the biceps femoris lateralh' and the adductor, semimembranosus, and 
semitendinosus medially, and is continued between the two heads of the gastroc- 
nemius as the tibial nerve. Its chief branches are as follows: 

1. In the pelvic part of its course the sciatic nerve supplies small muscular 
branches to the obturator internus, gemellus, and quadratus femoris; the branch 
to the obturator internus reaches the muscle by passing through the anterior end 
of the lesser sciatic foramen. 

These very small nerves arise from the upper border or deep face of the great sciatic, about 
half way between the two sciatic foramina. The nerve to the obtui'ator internus Ues along the 
dorsal margin of the sciatic and divides into branches for both heads of the muscle. The nerves 
to the gemellus and quadratus femoris commonly arise from the deep face of the sciatic by a com- 
mon trunk which passes back between the latter and the sacro-sciatio hgament to the posterior 
border of the gluteus profundus, where it divides. 

2. As the sciatic nerve turns down behind the hip joint it gives off a large 
muscular branch (Ramus muscularis proximalis), which divides to supplj^ the 
semimembranosus and the short heads of the biceps femoris and semitendinosus. 

3. The posterior cutaneous nerve of the leg or external saphenous nerve (N. 
cutaneus sura; caudalis) is detached from the sciatic about the middle of the thigh. 
It receives a fasciculus from the peroneal nerve and descends with the recurrent 
tarsal vein on the lateral face of the gastrocnemius to the distal third of the leg. 
Here it perforates the deep fascia and ramifies under the skin on the lateral surface 
of the tarsus and metatarsus (Fig. 657). 

4. The peroneal nerve (N. peronajus) (Figs. 580, 585, 659)^ is a large trunk 
which arises from the great sciatic nerve very shortly after the latter emerges from 
the pelvic cavity. It descends with the parent trunk to the origin of the gastroc- 
nemius; here the peroneal nerve deviates outward and forward across the lateral 
face of the gastrocnemius under cover of the biceps femoris, and divides at the 
origin of the lateral extensor muscle into superficial and deep branches. The 
collateral branches include one to the biceps femoris, the reinforcing fasciculus 
detached about the mitldle of the thigh to the posterior cutaneous nerve, and, 
lower down, the lateral cutaneous nerve of the leg (Ramus cutaneus surse later- 
alis).^ The latter emerges between the middle and posterior divisions of the 
biceps femoris at the level of the stifle joint and ramifies under the skin. The 
superficial peroneal nerve (N. peronsus superficialis)^ furnishes branches to the 
lateral extensor, and descends in the furrow between that muscle and the long 
extensor, perforates the deep fascia of the leg, and ramifies imder the skin on the 
front and the lateral face of the tarsus and metatarsus. The deep peroneal nerve 
(N. peronaeus profundus)* is the direct continuation in point of size of the peroneal 
trunk. It dips in between the lateral and long extensors of the digit, gives branches 
to these muscles and the tibialis anterior, and descends in front of the intermuscular 
septum which separates the two muscles first named. It continues downward 
behind the tendon of the long extensor and divides on the front of the hock into 
medial and lateral branches. The medial branch (Ramus medialis) passes do^vn 
under the skin on the anterior face of the metatarsus and supplies the cutaneous 
fibers of this region. The lateral branch (Ramus lateralis) furnishes a twig to the 
extensor brevis muscle and descends with the great metatarsal artery. It supplies 
the skin on the lateral face of the metatarsus and the fetlock. 

In the greater part of its course in the leg the deep peroneal nerve is separated from the 
anterior tibial vessels by the tibiaUs anterior. It should be noted that the lateral one of the two 

' Also known as the external pophteal nerve. 
^ Also termed the peroneal cutaneous nerve. 
' Also termed the musculo-cutaneous nerve. 
■* Also termed the anterior tibial nerve. 



TIBIAL NERVE 



827 



veins which almost always accompany the artery here is usually very large, and the layer of muscle 
whioli intervenes between it and the nerve is often exceedingly tliin. In the distal part of the leg 
tlie nerve is in direct contact witli the vein, and on the front of the lioclv it Ues behind the vessels. 
In very exceptional cases the nerve lies for a variable distance in the middle of the leg in the lateral 
part of the tibialis anterior. 

Tibial Nerve 

The tibial nerve (N. tibialis)' is the direct continuation of the great sciatic 

nerve (Figs. 576, 580, 583, 584, 659). It passes clown between the two heads of the 

gastrocnemius, and accompanies the recurrent tibial vessels to the distal third of 

the leg, where it divides into the two plantar nerves. In the proximal third of the 



Long digital extensor 

Anterior tibial vessels "■ 

Deep peroneal nerve \ /// 
Superficial peroneal 
nerve 
Intermuscular septum 
Fibrous band 

Lateral extensor 
Intermuscular septum 



Deep head of deep 
flexor {flex, hall, 



Tibialis posterior 
N. cutaneus surce 
Recurrent tarsal vein 
and artery 

Soleus 




Tibialis anterior 



Saphenous vein' 
Saphenous artery 



Posterior tibial vessels 

Tendon of long digital 
flexor 

Recurrent tibial vein 

Recurrent tibial artery 

Tibial nerve 

Tarsal tendon of biceps femoris 
and semitendinosus 

Superficial flexor tendon 



Gastrocnemius tendon 

Fig. 659. — Cross-section of Dist.^l Third of Left Leg of Horse. 

The deep fascia is shown by red line. 



leg it lies along the medial side of the superficial flexor under cover of the mctlial 
head of the gastrocnemius; lower down it is covered by the common deep fascia 
and is situated in the space between the deep flexor and the medial border of the 
tendo calcaneus (Achillis). 

At the usual point of election for tibial neurectomy, ('. c, about a handbreadth above the 
level of the tuber calcis, the nerve hes in areolar tissue and fat in a fascial compartment formed by 
the special fascia of the deep flexor in front and by the common fascia and the tarsal tendon of the 
semitendinosus and biceps femoris behind and medially. 

At its origin the tibial nerve gives off a muscular branch (Ramus muscularis 
distalis), the divisions of which pass between the two heads of the gastrocnemius 
' Also termed the posterior tibial nerve. 



828 NERVOUS SYSTEM OF THE HORSE 

and radiate to supply that muscle, the popliteus, the soleus, and the flexors of the 
digit. Small cutaneous twigs are also detached along the course of the nerve. 

Plantar Nerves 
The plantar nerves, medial and lateral (N. plantaris medialis, lateralis), 
result from the bifurcation of the tibial nerve in the distal part of the leg (Figs. 
583, 584) . They continue at first in the same direction and relations as the parent 
trunk, in direct apposition and enclosed in a common sheath. At the hock they 
diverge at a very acute angle and descend in the tarsal canal behind the deep flexor 
tendon in company with the plantar arteries. The medial plantar nerve supplies 
cutaneous nerves to the medial aspect of the tarsus and metatarsus, descends along 
the medial border of the flexor tendons behind the superficial plantar metatarsal 
vessels, and is otherwise arranged like the corresponding volar nerve of the fore- 
limb. The lateral plantar nerve deviates outward between the two flexor tendons 
to reach their lateral border. It supplies a branch to the suspensory ligament, and 
in its further course resembles the corresponding nerve of the fore limb. 

In so-called "tibial" neurectomy the operator really cuts the two plantar nerves which have 
not yet separated. The anastomotic branch between the two plantar nerves is smaller and more 
distal thnn that which connects the corresponding nerves of the fore limb, and is absent in 30 per 
cent, of the cases according to Rudert. 

Sacral Nerves 

Five pairs of sacral nerves (Nn. sacrales) are present in the horse. 

The small dorsal branches emerge through the dorsal sacral foramina and the 
space between the sacrum and the first coccygeal vertebra, and ramify in the 
muscles and skin of the sacral region and the adjacent part of the tail (Fig. 657). 
The fifth anastomoses with the dorsal branch of the first coccygeal nerve. 

The ventral branches leave the vertebral canal through the ventral sacral 
foramina and the interval between the sacrum and first coccygeal vertebra. They 
are connected with the sympathetic by rami communicantes, and contribute 
branches to the pelvic plexus. The first and second are the largest, and unite Avith 
each other and with those of the last three lumbar nerves to form the lumbo-sacral 
plexus. The third and fourth are connected with each other, and the majority of 
their fibers go to form the pudic and posterior hsemorrhoidal nerves. 

The pudic nerve (N. pudcndus) (Figs. 576, 580, 658) passes downward and 
backward partly embedded in the sacro-sciatic ligament, then accompanies the 
internal pudic artery to the ischial arch, turns around the latter, parting company 
with the artery, and pursues a flexuous course along the dorsum penis as the nervus 
dorsalis penis and ramifies in the glans penis and the penile layer of the prepuce. 
Within the pelvis it anastomoses with the posterior hsemorrhoidal nerve, and gives 
branches to the bladder and urethra, the terminal part of the rectum, and the skin 
and muscles of the anus (Fig. 577). It also supplies the nerve to the ischio-caverno- 
sus muscle and numerous branches to the corpus cavernosum of the penis and 
urethra. In the female it terminates in the clitoris and vulva (Fig. 578). 

The posterior haemorrhoidal nerve (N. hsemorrhoidalis caudalis) passes down- 
ward and backward above the ]3udic nerve, with which it anastomoses. It gives 
twigs to the terminal part of the rectum, the sphincter ani ex-ternus, and the sur- 
rounding skin (Fig. 577). In the female it supplies twigs to the vulva also (Fig. 
578). 

The ventral branch of the fifth nerve is small. It gives twigs to the sacro- 
coccygeus ventralis lateralis and the skin of the root of the tail and joins the first 
coccygeal nerve. 



THE SYMPATHETIC NERVOUS SYSTEM 829 



Coccygeal Nerves 
The coccygeal nerves (Nn. coccygei) commonlj' number five pairs. Their 
dorsal and ventral branches anastomose to form respectively two trunks on either 
side, which extend to the tip of the tail and supply its muscular and cutaneous 
nerves. The dorsal trunk runs with the dorso-lateral artery between the sacro- 
coccygeus dorsalis and intertransversales muscles (Fig. 579). The ventral trunk 
accompanies the ventro-lateral artery below the intertransversales. 



The Sympathetic Nervous System' 

The sympathetic nervous system (Systema nervorum sympathicum) is that 
part of the nervous sj'stem which serves (1) to transmit stimuli to the heart muscle, 
unstriped muscle, and glands; (2) to conduct impulses from the viscera to the cere- 
brospinal system. 

Many of the fibers are derived from the cerebrospinal system and are rearranged and dis- 
tributed in the sympathetic system. Numerous sympathetic fibers are contributed to the cerebro- 
spinal nerves, through which they are distributed to the unstriped muscular tissue and glands, 
as vasomotor, pilomotor, and secretory nerves. The sympathetic, Uke the cerebrospinal system, 
consists of neurones, each of which comprises the cell-body, an axone, and numerous branched 
dendrites. The cell-bodies are aggregated into ganglia, some of which are large and more or less 
constant in position and form, while others are microscopic and are scattered in an irregular man- 
ner through the peripheral part of the system. Simple visceral reflexes may be mediated by sym- 
pathetic nem-ones alone. 

In descriptive anatomy the sympathetic system is regarded as consisting of 
(1) a chain of ganglia extending along each side of the vertebral column antl con- 
nected by association fibers to form the sympathetic trunk ; (2) central branches 
to and from the cerebrospinal nerves; (3) peripheral branches, which form plexuses 
(Plexus sympathici) with each other and the cerebrospinal nerves ; (4) the peripheral 
ganglia which are interposed in the plexuses (Ganglia plexuum sympathicorum). 

The sympathetic trunk (Truncus sympathicus) extends on either side from 
the base of the cranium to the tail. In it are interposed, at intervals of varying 
regularity, the ganglia of the sympathetic trunk (Ganglia trunci sympathici). 
These are connected with the cerebrospinal nerves by central branches, the rami 
commimicantes. 

Two kinds of rami communicantes occur. Of these, one type consists largely of mcchillated 
fibers derived from the spinal nerves and ganglia; they have therefore a white appearance, and 
are termed white rami. They contain both efferent and afferent fibers. The efferent splanch- 
nic fibers are derived fruiii the \-entral roots of the spinal nerves and terminate in great part 
about tlie cells of the nearest symi)athetic ganghon; others end in more distant or in peripheral 
gangUa. The afferent splanchnic fibers are chiefly peripheral processes of the cells of the spinal 
ganglia, but some are sympathetic fibers which enter the spinal nerve-trunk and terminate about 
cells of the spinal gangUon. The gray rami consist mainly of non-meduUated fibers derived from 
the sympathetic gangha directly or through the trunk, which proceed centraUy to the spinal 
nerves and are ilisti-iJKited along tlie somatic divisions of the latter to imstriped muscle and glands 
as vasomotor, pilomotor, and secretory fibers. Some go to the membranes of the spinal cord, 
and a few terminate about cells of the .spinal gangha as sensory sympathetic fibers. 

Similar but more complex and irregular communications which exist between 
the sympathetic system and the cranial nerves — with the exception of the first 
and second — have been referred to in the accounts of the nerves. 

It is convenient for descriptive purposes to divide the sympathetic system into 
cephalic, cervical, thoracic, abdominal, and pelvic parts. 

1. The cephalic part (Pars cephalica systematis sympathici) comprises the 
otic, sphenopalatine, and ciliary ganglia, which may be regarded as homologues of 
the ganglia of the trunk of other regions. It also includes three plexuses formed by 

1 The special statements of this description refer to the system of the horse. A few important 
differential features wiU be mentioned in the account of the nervous system of the other animals. 



830 



NERVOUS SYSTEM OF THE HORSE 



branches derived from the anterior cervical ganglion. The ganglion gives off two 
or three filaments which sul)divide to form the internal carotid plexus (Plexus 
caroticus internus) around the artery of like name. The cavernous plexus (Plexus 
cavernosus) surrounds the artery within the cavernous sinus and communicates 
with that of the opposite side. The external carotid plexus (Plexus caroticus 
externus) is formed around the homonymous artery, and filaments from it go to the 
vessel and its branches and to the salivary glands. 

2. The cervical part (Pars cervicalis s. sympathici) includes two ganglia and 
the trunk which connects them. 

The anterior or superior cervical ganglion (G. cervicale craniale) lies on the 
guttural pouch beloAV the occipito-atlantal articulation (Fig. 562). It is reddish- 
gray in color, fusiform, and about an inch (ca. 2-3 cm.) in length. It is connected 
by rami communicantes with the last four cranial and first cervical nerves, sends 
branches to form the plexuses mentioned above, and contributes to the pharyngeal 
plexus. 

The cervical trunk of the sympathetic connects the anterior and posterior 




Fig. 660. — Right Cervico-thoracic Ganglion and 
Reuated Structures of Horse. 
G, G', Ganglia: 5, sympathetic trunk; V, vagus; 
R, recurrent nerve; N.c, cardiac nerves, C.VIII, T.I., 
rami communicantes from eighth cervical and first thor- 
acic nerves; -V.(r., nervustransversarius; r.ft., brachio- 
cephalic trunk; A.d.c, dorso-cervical artery; A.b.d., 
right brachial arterj^; A.c.c., common carotid artery. 




Fig. 661. — Left Cervico-thoracic Ganglion and 
Related Structures of Horse. 
G, G', Ganglia; S, sympathetic trunk; V, vagus; 
R, recurrent nerve; C.VII. C.VIII. T.I, rami com- 
municantes from last two cervical and first thoracic 
nerves; N.tr., nervus transversarius; N.c.^ cardiac 
nerves. 



cervical ganglia. On leaving the former it is associated in a common sheath with 
the vagus along the dorsal face of the common carotid artery. At the root of the 
neck it separates from the vagus and joins the posterior cervical ganglion. 

The posterior or inferior cervical ganglion (G. cervicale caudale) is situated 
under cover of the first rib and the insertion of the scalenus (Figs. 660, 661). On 
the right side it lies upon the longus colli and the trachea, on the left side upon the 
same muscle and the oesophagus. It is flattened, very irregular and variable in 
outline, and is blended more or less with the first thoracic ganglion,^ so that the two 
may be considered together as the ganglion stellatum. This receives at its antero- 
dorsal angle the nervus transversarius, which accompanies the vertebral artery 
in the canalis transversarius; it is a trunk formed by the rami communicantes of 
the cervical nerves except the first and last. Large rami connect Avith the last 
cervical and first and second thoracic nerves. Filaments also connect with the 
vagus. From the ventral part of the ganglion proceed the cardiac nerves now to 
be describeil. 

' In some cases there exists a more or less distinct middle cervical ganglion wWch receives 
the filaments from the vagus and is connected with the posterior cervical ganglion liy a trunk. It 
occurs oftenest on the right side and gives off one or two cardiac nerves. 



THE SYMPATHETIC NERVOUS SYSTEM 831 

The cardiac nerves (Nn. cardiaci) are formed by branches from the posterior 
cervical and first thoracic gangHa, together with twigs from the sympathetic trunks 
and the vagi. They form the cardiac plexus (P. cardiacus) on the ventral face of the 
trachea with each other and with branches of the vagus and recurrent nerves. 
They are subject to considerable variation, but their general arrangement may be 
stated as follows: 

(a) On the right side there are usually two cardiac nerves. Of these one 
passes back ^\^th the vagus in the angle between the right brachial artery and the 
bicarotid trunk, pierces the pericardium, crosses the aortic arch, and divides into 
branches which are mingled with those of the left nerves. The second crosses 
obliquely over the right face of the trachea and joins the vagus, where the latter 
gives off the right recurrent nerve; a small plexus is formed here, from which two 
or three cardiac branches are detached. These pass back beneath the trachea and 
ramify on the atria and ventricles. 

(6) On the left side there are commonly three cardiac nerves. One of these is 
distributed to the great vessels in the anterior mediastinum. The largest passes 
back at first ■with the vagus beneath the arch of the left brachial artery, inclines 
downward, perforates the pericardium, and divides into two branches. One 
branch passes beneath the bifurcation of the pulmonary artery and is distributed 
to the left atrium. The larger branch dips in between the aorta and the pulmonary 
artery, gives twigs to these vessels, and ramifies on the ventricles, especially along 
the course of the right coronary artery. The third nerve crosses the deep face of 
the left brachial artery, passes back below the trachea, and unites with filaments 
of a right cardiac nerve. It passes around the aorta and ramifies chiefly along the 
course of the left coronary artery on the left face of the ventricles. 

3. The thoracic part (Pars thoracalis systematis sympathici) extends back- 
ward ventral to the costo- vertebral joints from the posterior cervical ganglion to the 
crura of the diaphragm, and passes between the latter and the psoas minor to be con- 
tinued by the abdominal part. 

The trunk is concealed in the first part of its course by the subcostal vessels 
and the lateral border of the longus colli, but further back it is visible under the 
pleura. 

The ganglia are arranged segmentally at each intercostal space and partly on 
the heads of the ribs. They are flattened and are small and fusiform, with the 
exception of the first. This (G. thoracale primum) is extensive, irregularly quadri- 
lateral in outline, and is united with the posterior cervical ganglion, as previously 
mentioned. The ganglia are connected with the thoracic nerves by white and gray 
rami communicantes. Distinct ganglia may be absent at two or three spaces 
succeeding the first, and here the trunk is thickened and contains ganglion cells. 

The visceral branches comprise aortic, cardiac, pulmonary, and oesophageal 
branches, antl the splanchnic nerves. The aortic branches ramify on the thoracic 
aorta, forming around that vessel the thoracic aortic plexus (P. aorticus thoracalis). 
The cardiac branches concur mth those of the vagus in forming tlie cardiac plexus 
(P. cardiacus). From this branches go to form the coronary plexuses (P. coronarii) 
along the course of the vessels of like name. The pulmonary branches join with 
corresponding branches of the vagus and filaments from the cardiac plexus in 
forming the pulmonary plexus (P. pulmonalis) at the root of the limg. Branches 
of the plexus, on which are minute ganglia, ramify with the bronchi in the substance 
of the lung.' The oesophageal branches join with those of the vagus in the forma- 
tion of the oesophageal plexus (P. oesophageus). 

The great splanchnic nerve (N. splanchnicus major) arises by a series of roots 
derived from the sixth or seventh to the fourteenth or fifteenth thoracic ganglia 

' The right and left plexuses communicate with each other, so that both lungs receive fibers 
from both vagi. 



832 NERVOUS SYSTEM OF THE HORSE 

inclusive. It extends along the bodies of the vertebrae medio-ventral to the thoracic 
trunk, then crosses the latter ventrally, passes back between the crus of the dia- 
phragm and the lateral border of the psoas minor, and joins the coeliaco-mesenteric 
ganglion. It is small at its origin, but becomes considerably larger than the sym- 
pathetic trunk. Near its termination it may present a small splanchnic ganglion, 
from which and from the nerve filaments go to the aorta, the oesophagus, and the 
vertebriae. The fibers of the nerve are derived chiefly from the spinal cord; hence 
its white appearance as compared with the sympathetic trunk. 

The small splanchnic nerve (N. splanchnicus minor) is formed bj' roots derived 
from the last two or three thoracic ganglia. It runs back with the great splanchnic 
nerve, but ends in the cceliac or in the renal and adrenal plexuses. 

The splanchnic nerves are quite variable. The greater splanchnic is often blended more or 
less with the sympathetic trunk and may be separate only in tlie posterior part of the thorax. 
The lesser splanchnic may be included in the gi-eater, and thus appear to be absent. Its roots 
communicate by filaments with the gi'eat splanchnic. 

4. The abdominal part of the sympathetic trunk (Pars abdominalis systematis 
sympathici) lies along the medial border of the psoas minor, above the aorta on the 
left side and the posterior vena cava on the right (Fig. 656). The trunk is smaller 
than the thoracic part, and presents usually six small fusiform limibar ganglia (G. 
lumbalia), which are connected by rami communicantes with the ventral divisions 
of the lumbar nerves. Visceral branches go to the aortic and pelvic plexuses 
and to the coeliaco-mesenteric ganglion. 

5. The pelvic and caudal part of the sympathetic trunk (Pars pelvina et cau- 
dalis systematis sympathici) begins at the last lumbar ganglion and extends along 
the pelvic surface of the sacrum metlial to the emergence of the ventral branches 
of the sacral nerves (Fig. 576). At the third or fourth segment of the sacrum the 
trunk divides into medial and lateral branches. The medial branch inclines to the 
median plane and unites with the opposite branch. At the junction there is often 
found the small coccygeal ganglion (G. impar), which lies on the coccygeal artery 
at the joint between the first and second coccygeal vertebrae. A filament from the 
ganglion accompanies the artery. The lateral branch communicates with the last 
two sacral nerves and joins the ventral coccygeal nerves. Sacral ganglia (G. 
sacralia) occur near each of the first three sacral foramina, and are connected by 
gray rami communicantes with the ventral branches of the sacral nerves. The 
visceral branches are distributed through the pelvic plexus. They supply motor 
fibers to the longitudinal, and inhibitory fibers to the circular, muscular coat of the 
rectum; motor fibers to the bladder and uterus; and the vaso-dilator fibers (Nn. 
erigentes) to the penis. 

According to von Schumacher, minute segmental coccygeal ganglia occur along the caudal 
branches of tlie sympathetic trunk. The lateral branch is regarded by van der Broek as an 
aggregate of rami communicantes. 

THE ABDOMINAL AND PELVIC PLEXUSES 
The chief plexuses which distribute nerves to the viscera and vessels of the 
abdominal and pelvic cavities are two in number, the cceliac and the pelvic. From 
them fibers proceed to form numerous subsidiary plexuses which are named accord- 
ing to the organs which they supply or the vessels which they enlace. 

The cceliac plexus (Fig. 575)' is situated on the dorsal wall of the abdominal 
cavity, in relation to the aorta and the origin of its chief visceral branches. It is 
formed by the splanchnic nerves, branches of the vagi, and filaments from the 
anterior lumbar ganglia of the sympathetic. It contains the coeliaco-mesenteric 
ganglia. From the cceliac plexus and its ganglia subsidiary plexuses are continued 
upon the branches of the aorta. 

'■ Also known as the solar plexus. ' < 



THE ABDOMINAL AND PELVIC PLEXUSES 833 

The coeliaco-mesenteric ganglia (G. coeliaco-mesenterica)^ are two in number, 
right and left. They are situated on each side of the aorta, in relation to the origin 
of the coehac and anterior mesenteric arteries. The right ganghon is concealed by 
the posterior vena cava ; it is irregularly quadrilateral and is about two inches (4- 
6 cm.) in length. The left ganglion is largely covered by the left adrenal; it is 
narrower than the right one and is three or four inches (ca. 8-10 cm.) long. The 
two ganglia are united by irregular connecting branches in front of and behind the 
anterior mesenteric artery.^ Each receives the great splanchnic nerve of its own 
side and branches from the dorsal oesophageal continuation of the vagus nerves. 
Branches from the ganglia and the cords which connect them pass back to the 
posterior mesenteric ganglion which is situated at the origin of the posterior mesen- 
teric artery. 

The following unpaired plexuses proceed from the coeliac plexus and coeliaco- 
mesenteric ganglia: 

1. The abdominal aortic plexus (P. aorticus abdominalis) occurs along the 
abdominal aorta. It is connected with the renal plexuses and behind with the 
pelvic plexus. It receives filaments from some of the sympathetic lumbar ganglia. 

2. The gastric plexus (P. gastricus) enlaces the gastric artery and divides like 
the artery into two parts, forming the anterior and posterior gastric plexuses. 
These receive branches of the vagus nerves. 

3. The hepatic plexus (P. hepaticus) is formed by several nerves of consider- 
able size which accompany the hepatic artery and the portal vein. It receives 
fibers from the left vagus, ramifies in the liver, and gives off branches which 
accompany the collateral branches of the hepatic artery and supply the areas in 
which these vessels are distributed. 

4. The splenic plexus (P. lienalis) resembles the preceding in its arrangement. 
In addition to its terminal branches to the spleen it gives collateral twigs to the 
pancreas and the left part of the greater curvature of the stomach. 

5. The anterior mesenteric plexus (P. mesentericus cranialis) is formed 
mainly by branches from the posterior part of the coeliaco-mesenteric ganglia; it 
is continuous with the coeliac plexus in front and the posterior mesenteric behind. 
It surrounds the anterior mesenteric trunk and its branches, and supplies the viscera 
to which these vessels are distributed. 

The posterior mesenteric ganglion (G. mesentericum caudale) is unpaired; it 
is irregularly stellate, and is situated on the origin of the posterior mesenteric 
artery. It is connected with the coeliaco-mesenteric ganglia by anastomosing 
branches which concur in the formation of the aortic plexus. Two or more pairs 
of nerves proceed from it posteriorly. One of these, the internal spermatic nerve 
(N. spermaticus internus) , accompanies the spermatic artery to the spermatic cord 
and testicle in the male; in the female it goes to the ovary, uterine tubes, and 
adjacent part of the uterine horn. These concur in the formation of the spermatic 
and utero-ovarian plexuses. The other branches from the ganglion pass back to 
the pelvis ventral to the great vessels and concur in the formation of the pelvic 
plexuses. 

The posterior mesenteric plexus (P. mesentericus caudalis) accompanies the 
artery of like name in its distribution. 

The secondary plexuses which accompany the branches of the mesenteric arteries give off 
branches which form two fine peripheral plexuses in the wall of the intestine. One of these, the 
myenteric plexus (P. myentericus), or plexus of Auerbach, lies between the layers of the mus- 
cvdar coat, and is provided with microscopic gangha. The other is in the submucous tissue, and 
is therefore termed the submucous plexus (P. submucosus) or plexus of Meissner. 

' It has been customary to designate these in veterinary works as the semilunar or coeliac 
ganglia, but in the horse they evidently include the anterior mesenteric ganglia as well. 

^ A good preparation of the ganglia in the horse is often difficult to obtain on account of 
aneurysm of the artery and the formation of a quantity of connective tissue about it. 
53 



834 THE NERVOUS SYSTEM OF THE OX 

The following paired plexuses are derived mainly from branches of the coeliac 
and aortic plexuses: 

1. The renal plexuses (P. renales) proceed largely from the coeliaco-mesenteric 
ganglia, but receive fibers also from the small splanchnic nerves. They enlace the 
renal arteries and supply the kidneys. Minute renal ganglia occur on the course 
of the nerves along the renal vessels. 

2. The adrenal plexuses (P. suprarenales) are formed by a relatively very 
large number of fine fibers derived in great part directly from the coeliaco-mesen- 
teric ganglia. Numerous minute ganglia occur in their meshes. 

3a. The spermatic plexuses (P. spermatid) proceed from the aortic plexus 
and branches from tlie posterior mesenteric ganglion. Each accompanies the 
corresponding (internal) spermatic artery to the testicle. 

3b. The utero-ovarian plexuses (P. ovarici) are the homologues in the female 
of the preceding. They accompany the utero-ovarian arteries to the ovary and the 
cornua of the uterus. 

The pelvic plexuses (P. hypogastrici) are the pelvic continuations of the aortic 
and posterior mesenteric plexuses. Two or more nerves proceed from the posterior 
mesenteric ganglion and enter the pelvic cavity ventral to the large vessels, anasto- 
mose with each other and with branches from the sacral nerves — especially the 
third -and fourth — and ramify on the pelvic viscera. The peripheral plexuses 
derived therefrom are named according to the organs which they supply; the chief 
of these are the hasmorrhoidal, vesical, utero-vaginal, prostatic, cavernous (of the 
penis or clitoris) (P. hsemorrhoidalis, vesicalis, uterovaginalis, cavernosus penis s. 
clitoridis, etc.). Others enlace the arteries (P. iliacus, femoralis, etc.). 



THE NERVOUS SYSTEM OF THE OXi 

The spinal cord resembles that of the horse Ln conformation and structure. 
In cattle of mediiun size its length is about 165 to 170 cm. (ca. 65-67 inches), and 
its weight about 240 to 250 grams (ca. 8 ounces). 

In a cow 140 cm. in height Dcxler found the weight of the cord (including the intradural 
nerve-roots) to be 260 gm. and the length 102 cm. The lengths of the regions were: cervical 41 
cm., thoracic 72 cm., lumbar 32 cm., sacral 7 cm. 

The brain has an average weight of about 500 grams (ca. 16-17 ounces). 
Its differences in general form are correlated with those noted in the consideration 
of the cranial cavity. 

The medulla oblongata is short, wide, and thick. Its ventral face is strongly 
convex. The j^yramids are narrow, short, and close together in front. Near the 
decussation there is a well-defined oval prominence on either side which indicates 
the position of the posterior olive. The corpus trapezoideum is large; it has no 
central part between the pyramids. The external arcuate fibers are distinct. The 
restiform bodies are short and thick and diverge more strongly than in the horse. 
The floor of the fourth ventricle is only about two-thirds as long as in the horse. 
The area acustica is a well-marked oval prominence lateral to the middle part of 
the limiting sulcus. The tuberculum acusticum at the origin of the acoustic nerve 
is very large. The anterior fovea is distinct. The posterior recess of the fourth 
ventricle communicates through a median aperture (Apertura mediana)- with the 
subarachnoid space. 

1 Only the most salient differences as compared with the horse will be mentioned. 
^ Also known as the foramen of Magendie. 



THE NERVOUS SYSTEM OF THE OX 



835 



The pons is smaller, both transversely and longitudinally, than that of the 
horse. It is strongly convex and has a distinct central depression. 

The cerebellum is smaller and more angular in form than in the horse. The 
vermis is large and has a distinct depression on its anterior face for the posterior 
corpora quatlrigemina. The hemispheres are relatively small and are not clearly 
divided into tal)ulations. The anterior peduncles are very short.. 

The cerebral peduncles are short. A small eminence in the interpeduncular 



Longitudinal 
fissure 



Frontal pole 




Transivrse fissure 



1, Lateral; 2, sOprasyl 



, Glj2. — BuAiN- OF Ox; Dorsal View, 
oronal; 4, transverse; J, marginal; 0, entomarginal; 7, ectomarginal. S, 
Marginal or sagittal pole. 



fossa is caused by the presence of the interpeduncular ganglion. The medial gen- 
iculate body is prominent. The pineal body is long and fusiform, and is often 
pigmented in spots. The third ventricle forms two considerable recesses in rela- 
tion to the pineal body: one (R. pinealis) extends up into the body; the other 
(R. suprapinealis) is a long tubular prolongation in front of it. 

The optic tracts cross the cerebral peduncles almost at a right angle. 

The hypophysis or pituitary body is situated in a deep fossa and is surrounded 



836 



THE NERVOUS SYSTEM OF THE OX 



by a plexus of vessels. It is much narrower and thicker than that of the horse. 
The infiindibulum is relatively long and slopes dowiiward and backward. 

The cerebral hemispheres are shorter, higher, and relatively wider than in the 
horse. The frontal poles are small, the occipital, large. The length from pole to 
pole is about the same as the greatest transverse diameter of the two hemispheres. 



Longitudinal fissure 




Fig. 663.— Base of Brain of Ox. 
1, Olfactory bulb; S, S', olfactory striEe; 3, trigonum olfactorium; 4i foaaa lateralis; S. piriform lobe; 6, optic 
chiasma; 7, optic tract; 8, tuber cinereum; 5, cerebral peduncle; 10, pons; II, corpus trapezoideum; 12, pyramid: 
13, cerebellum; 14, chorioid plexus of fourth ventricle; C.I., first cervical nerve roots. The stumps of the cranial nerves 
are designated by Roman numerals. The hypophysis has been removed and its contour is indicated by dotted line. 
The central black area is the infundibular recess of the third ventricle opened up when the infundibulum is torn off. 



Viewed from the side, the dorsal surface is strongly convex. The highest point of 
the dorso-medial border is a little in front of its middle and forms a marked promi- 
nence termed the sagittal or marginal pole (Polus sagittalis s. prominentia mar- 
ginalis dorsalis). Anterior to this the Ijorder drops abruptly, being cut into by the 
deep transverse fissure. The arachnoid on the basal and anterior parts of the 
hemispheres is usually pigmented. The corpus callosxmi extends through a little 



THE NERVOUS SYSTEM OF THE OX 



837 



more than a third of the length of the hemisphere. The pattern of the fissures 
and gyri of the pallium is somewhat simpler than in the horse. 

1. The lateral fissure (of Sylvius) is very deep. Its middle branch extends almost ver- 
tically upward on the middle of the lateral surface of the hemisphere, and is separated by a gyrus 
of variable width from the suprasylvian fissure. The anterior branch runs forward about parallel 
with the sulcus rhinalis anterior, from which it is separated by the short gyri of the insula. The 
latter are covered to a small extent only by the overhanging gjTi (operculum). The posterior 
branch may run back a distance of only about 1.5 cm. and end in T-shaped manner, or it may 
join the sulcus rhinalis posterior. 

2. The suprasylvian fissure is deep and very distinct. It extends in an undulating manner 
from the lateral sm-face of the occipital pole to the lateral side of the sagittal pole. Here it may 



nrginal pole 




Cere- 
hfdlutn 



Olfactory Olfactory 
Jnfundibulum tract bulb 



Hypophysis or pituitary body 



Corpus Pons 
Medulla trap?- 
oblongata zoideum 

Fig. 664.— Brain op O.x; Right View. 
Fissures: /.Lateral; ^. 5, suprasylvian : 5. coronal; 4. transverse; o, ectoraarginal; 5, diagonal; ?■, posterior ecto- 
sylvian; 8, presylvian; 9, 9', rhinal {anterior and posterior); P.ch., chorioid plexus of fourth ventricle; P.c. cerebral 
peduncle; L.p., piriform lobe; /.insula. Stumps of cranial nerves are designated by Roman numerals. 



be interrupted or may be continued by the coronal fissure, which descends to the frontal pole 
and divides into two short branches. 

3. The diagonal fissure (S. diagonaUs) begins in front of the stem of the lateral fissure and 
runs upwai'd and forward. Its form is very variable. 

4. The transverse fissure cuts obhquely into the dorsal border in front of the sagittal pole. 
It is short and dcrp ami commonly communicates with the suprasylvian and coronal fissures, but 
may be separated fi-Diu the former. 

.5. The marginal fissure is distinct. It extends from the sagittal pole to the occipital pole. 
It is flexuous and di'\i:itc.s outward somewhat in its posterior two-thirds. 

6. The entomarginal fissure lies medial and parallel to the posterior part of the preceding. 

7. The ectomarginal fissure is lateral and parallel to the marginal fissure. It does not ex- 
tend so far in either tlircction as the latter, and is often more or less broken up by annectant gyri. 

8. The sulcus rhinalis is more open than in the horse, since it is not overlapped by the gyri 
above it. 

9. The calloso-marginal fissure is flexuous and not so regular as in the horse. It is often 
interrupted at or near the level of the genu of the corpus oaUosum, in which case the genual fissure 
continues it downward. 

10. The cruciate fissure is faint and is confined to the medial surface. It lies about one centi- 
meter in front of the transverse fissure, and commonly joins the calloso-marginal fissure below. 



838 



THE NERVOUS SYSTEM OF THE OX 



11. Short and variable fissui-es occur in front of and behind the middle branch of the lateral 
fissure (F. ectosylvia anterior, posterior). 

The olfactory bulb is much smaller than in the horse. The lateral olfactory 
stria is large, the medial one small and not distinct. 

The cranial nerves have in general the same superficial origin as in the horse. 
The more important differences in other respects are as follows: 

The oculoniotor nerve is larger than in the horse. It emerges with the fourth, 
sixth, ophthalmic and maxillary nerves through the foramen orbito-rotundum. 

The trigeminal nerve presents the following differences in its distribution: 



Cerebellii 




Olfactory 
Optic ficrve bulb 

I nfundibulum 

Hypophysis 

Pons Cerebral 
peduncle 

Fig. 665. — Sagittal Section of Brain of Ox. 
V.IV. Fourth ventricle; P.c, choroid plexuses; t'.m., anterior medullary velum; A.c, cerebral aqueduct; Cg., 
corpora quadrigemina; C.p., posterior commissure; C.pin., pineal body; V.c.i., great cerebral vein; T, thalamus; 
v. ///.. third ventricle (arrow points to interventricular foramen); Co., anterior commissure: L.^, lamina terminaUs; 
Co., chiasma opticum. Fissures: /, callosal: ^. calloso-marginal; 5, splenial: .J, transverse; 5, entomarginal. 



The internal branch of the lacrimal nerve supplies twigs to the mucous mem- 
brane of the frontal sinus; tlic large outer branch runs backward and supplies the 
corium of the horn. The frontal nerve emerges from the orbit below the supraor- 
bital process. The naso-ciliary nerve is large and sends filaments to the ocular 
muscles. The ciliary ganglion is somewhat larger than in the horse, and is con- 
nected with the lower division of the oculomotor nerve by several short filaments. 
In consequence of the absence of the canine and upper incisor teeth the correspond- 
ing branch of the infraorbital nerve is naturally wanting. The mandibular nerve 
emerges through the foramen ovale. The superficial temporal nerve giv(>s off a 
large branch which joins the superior buccal division of the facial on the masseter, 
about half-way between the zygomatic arch antl the angle of the jaw. The otic 
ganglion is larger than in the horse. According to Moussu the buccinator nerve 
furnishes excito-secretory twigs to the parotid and inferior buccal glands. 



THE NERVOUS SYSTEM OF THE OX 



839 



The facial nerve diviflcs into its two terminal branches before reaching the 
border of the jaw. The superior buccal nerve is the larger of the two; it crosses 
the masseter much lower than in the horse. The relatively small inferior buccal 
nerve runs beneath the parotid or in the gland substance parallel with the border 
of the lower jaw, crosses under the insertion of the sterno-cephalicus, and runs for- 
ward along the depressor labii inferioris. At the point where it crosses the facial 




Fig. 666. — Superficial Nerves of Head of Ox. 
Nerves: a. Facial; a', a", a'", superior buccal and primary branches; b. deep auricular; c, posterior auricular: 
d, d', d", auriculo-palpebral and primary branches; e, parotid plexus; /, digastric; o, s'. inferior buccal; g", anasto- 
mosis between g and a'; h, superficial temporal; i, k, I, branches of infraorbital; m, buccinator; m', branch of m to 
zygomaticua and malaris muscles; m", branch of m to parotid gland; n, branches of infratrochlear; o, frontal; p, p', 
p", lacrimal; g. dorsal branch of accessory: r, auricular branch of second cervical ; /■', r", branches of r; s, cutaneous 
branch of second cervical; s', anastomotic branch connecting s and t; t, t' , t", third cervical and branches; u, zygo- 
matic. Muscles: 1, Frontalis (part removed) ; 3. levator nasolabialis (part removed); 3. origin of levator labii 
superioris proprius; 4> malaris; 6, 5', stumps of zygomaticus; 6, buccinator; 7, masseter; S, sterno-cephalicus; 10, 
cleido-mastoideus; 11, 11', cleido-occipitalis; 12, zygomatico-aaricularis; 13, fronto-scutularis; H, scuto-auricularia 
superficialis superior; IB, scuto-auricularis superficialis accessorius; IB, cervico-scutularis; 17, 17', stumps of parot- 
ido-auricularis. 18, 18', Remnants of parotid gland; 19, 19', mandibular gland; 9, jugular vein; SO, facial vein. 
(After Schachtschabel.) 



superior nerve. 



vein and parotid duct it gives off an anastomotic branch to the 
The auriculo-palpebral nerve is large. 

The vagus bears — in addition to the relatively large jugular ganglion — a 
ganglion nodosum at the point of origin of the anterior laryngeal nervo. The 
trunk is large. The pharyngeal branch is large and anastomoses with the anterior 
and external laryngeal nerves. The latter commonly arises directly from the trunk. 
The dorsal oesophageal trunk communicates with the splanchnic nerve, contri- 
butes twigs to the hepatic plexus, and ramifies chiefly on the right surface of the 



840 



THE NERVOUS SYSTEM OF THE OX 



rumen and the adjacent surface of the abomasum. The ventral oesophageal tnink 
goes to the left surface of the rumen; it supplies branches to the hepatic plexus 
and to all the divisions of the stomach. 

The spinal accessory nerve presents two special features. The part which 
joins the jugular ganglion bears a small ganglion. The ventral branch supplies 
both parts of the sterno-cephalicus. 

The hypoglossal nerve is large. It is connected with the ventral division of 
the first cervical nerve by a Isranch of considerable size, and detaches a long branch 
which runs backward along the carotid artery. 




Median nerve- 



' Ulnar nerve 



A nastomotic 
branch 



667. — Nerves of Distal Part of Right Fore- 
limb OF Ox; Dorsal View (Schematic). 
p, Dorsal digital nerves. 



Fig. 668. — Nerves of Distal Part • 

limb of Ox; Volar View (Sch 

p, Volar digital nerves. 



Right Fore- 



The spinal nerves resemble those of the horse in origin and general arrange- 
ment. The thoracic nerves number thirteen pairs. The more important differ- 
ences in the limb-plexuses and their branches are as follows: 

The brachial plexus is formed by the ventral branches of the last three cervical 
and first thoracic nerves; the second thoracic nerve usually furnishes no root, but 
the ventral branch of the sixth cervical goes almost entirely to the plexus after 
giving off the nerve to the rhomboideus and the serratus cervicis. 

The differences in the nerves above the elbow are not of sufficient moment 
to receive notice in this brief account, but below this point there are naturally 



THE NERVOUS SYSTEM OF THE OX 841 

important special features correlated chiefly with the arrangement of the 
digits. 

The radial nerve is continued below the elbow by a large cutaneous branch 
(N. cutaneus antibrachii dorsalis) which emerges at the lower border of tlie lateral 
head of the triceps and descends on the dorsal aspect of the limb. It commu- 
nicates above the carpus %vith the lateral cutaneous branch of the median nerve and 
termmates in three dorsal digital nerves; two of these descend along the axial 
or interdigital side of the dorsal surface of the chief digits, and the third along the 
medial (abaxial) side of the medial chief digit. 

The ulnar nerve divides at a variable distance down the forearm into two 
branches. The dorsal (or superficial) branch emerges between the tendons of the 
ulnaris lateralis and flexor carpi ulnaris, and is continued as the lateral dorsal 
digital nerve on the lateral chief digit. The volar (or deep) branch desccntls along 
the superficial digital flexor, gives a branch to the suspensory ligament below the 
carpus, and unites with the lateral branch of the median nerve to form the lateral 
volar digital nerve (N. digitalis lateralis digiti IV). 

The median nerve is much larger than the ulnar. It passes beneath the prona- 
tor teres, descends the forearm as in the horse, and divides in the distal part of the 
metacarpus into two branches. The medial branch gives twigs to the medial small 
digit and is continued on the medial side of the volar surface of the medial chief tligit 
as the medial volar digital nerve (N. digitalis medialis digiti III) ; it also concurs 
with the lateral branch in forming the two digital nerves which descend along the 
interdigital aspect of the chief digits. The lateral branch is larger. It bifurcates, 
and one division unites vnth the twig from the medial branch to form a common 
digital trunk. From the latter two digital nerves proceed as mentioned above; 
these are the lateral and medial volar digital nerves of the medial and lateral 
chief digits respectively (N. digitalis volaris lateralis digiti III, medialis digiti IV). 
The other division unites with the volar branch of the ulnar nerve to form the 
lateral volar digital nerve of the lateral chief digit (N. digitalis lateralis digiti IV). 

The lumbo-sacral plexus and its branches to the pelvis and thigh present no 
very striking special features. 

The superficial peroneal nerve is much larger than in the horse. After crossing 
beneath the peroneus longus it passes down on the front of the tarsus and meta- 
tarsus and divides into three branches. The medial and lateral branches descend 
as the medial and lateral dorsal digital nerves on the chief digits. The larger 
middle branch joins a branch of the deep peroneal nerve in the interdigital space, 
and from this union proceed the dorsal digital nerves which descend on the opposed 
surfaces of the chief digits. 

The deep peroneal nerve descends in the leg as in the horse, and continues 
down the dorsal groove of the metatarsus with the dorsal metatarsal artery. It 
gives collateral branches to the anterior muscles of the leg and to the extensor 
digitalis brevis. Its terminal branches concur with branches from the superficial 
peroneal nerve in the formation of the two axial dorsal digital nerves (N. dig. dors, 
lat. dig. Ill et dig. dors. med. dig. IV pedis), and with a branch of the medial 
plantar nerve in the formation of corresponding plantar digital nerves. 

The tibial nerve divides at the back of the hock into medial and lateral plantar 
nerves. The medial plantar nerve descends between the superficial flexor tendon 
and the suspensorj^ ligament and tlivides into two branches; the medial branch 
descends as the medial plantar digital nerve (N. dig. plant, med. dig. Ill) along the 
medial side of the flexor tendons of the medial chief digit; the lateral branch turns 
around the flexor tendons to reach the interdigital space, where it concurs with a 
branch of the deep peroneal nerve in the formation of two axial plantar digital 
nerves (N. dig. plant, lat. dig. Ill et dig. plant, med. dig. IV), which descend on 
the opposed surfaces of the chief digits. The lateral plantar nerve descends along 



842 



THE NERVOUS SYSTEM OF THE OX 



the lateral border of the flexor tendons, gives a branch to the suspensory ligament 
and to the lateral small digit, and continues along the lateral face of the lateral 
digit as the lateral plantar digital nerve (N. dig. plant, lat. dig. IV). 

The sympathetic system closely resembles that of the horse in its general 
arrangement, and only a few differential features will receive attention. The 
anterior cervical ganglion is closer to the cranial base and is thicker than in the 
horse; its branches to the carotid and cavernous plexuses are large, and no con- 
nection is formed with the spinal accessory nerve. The cervical trunk is smaller 



Superficial peroneal - 
nerve ■ 
Deep peroneal nerve . 
Saphenous nerve 



r 



Tibial nerve 



Lateral plantar 
nerve 




Fig. 669. — Nerves of Distal Part of Right Hind 

Limb of Ox; Dorsal View (Schematic). 

p, Dorsal digital nerves. 



Fig. 670. — Nerves of Distal Part of Right Hind 

Limb of Ox; Plantar View (Schematic). 

p, Plantar digital nerves. 



than in the horse, and arises by two or three bundles from the anterior cervical 
ganglion behind its middle. The posterior cervical ganglion is distinctly separable 
from the first thoracic; the latter is large. There are thirteen pairs of thoracic 
ganglia. The great splanchnic nerve begins at the fifth or sixth thoracic ganglion 
and receives branches from the .succeeding ones; it is commonly difficult to dis- 
tinguish clearly from the thoracic trunk. The small splanchnic nerve is repre- 
sented apparently by filaments which go from tlic first lumljar ganglion to the 
adrenal plexus and the cceliac ganglion. The cceliac ganglion is rounded and lies 
on the cceliac artery. The anterior mesenteric ganglion is longer and is closely 



THE NERVOUS SYSTEM OF THE PIG 



843 



related to the anterior mesenteric artery. The two are connected by gangliated 
cords, and are similarly connected with the ganglia of the opposite side, so that the 
arrangement is plexiform. The coeliac plexus is more complex than that of the 
horse in correlation with the compound character of the stomach. The posterior 
mesenteric ganglion is small and is situated behind the artery of like name. It 
receives fibers from the last three or four lumbar ganglia and two fasciculi from the 
anterior mesenteric ganglia. The pelvic viscera receive branches from the posterior 
mesenteric ganglion and from the 



sacral ganglia; the latter number 
five pairs, and the right and left 
trunJcs are connected here by trans- 
verse anastomoses. The coccygeal 
trunks unite at a single fourth coc- 
cygeal ganglion, then separate, and 
reunite at the sixth coccygeal gan- 
glion. 



Longitudinal fis-ture Frontal pole 



OF 




THE NERVOUS SYSTEM 
THE PIG 

The spinal cord weighs about 
one and a half ounces (ca. 42 gm.). 
It is almost circular in cross-section, 
except at the enlargements, where 
it is somewhat flattened dorso-ven- 
trally. The conus medullaris ex- 
tends to the anterior part of the 
third sacral segment. The epidural 
space is occupied by a large quan- 
tity of fat. 

The brain in adults of medium 
size weighs about four to four and 
a half ounces (ca. 125 gm.). When 
viewed from above, the cerebrum 
has an elongated oval form. The 
hemispheres are widest at the pos- 
terior third. The occipital pole is 
larger than the frontal pole. The 
medulla oblongata is relatively 
broad. The cuneate tubercle is very 
large and is limited laterally by a 

groove. The corpus trapezoideum is very wide laterally. The pons is less promi- 
nent than in the ox. The cerebellum is very wide and short. Its anterior face is 
flattened and presents a depression for the corpora quadrigemina. The vermis is 
large. The hemisi:)heres consist of a large medial part and a small lateral part. 
The cerebral peduncles are very short. The posterior corpora quadrigemina are 
wide apart, rounded, and relatively large. The medial geniculate body is promi- 
nent. The cerebral hemispheres are somewhat bean-shaped in lateral profile, the 
convex border being dorsal. The arrangement of the gjTi and sulci is simpler than 
in the horse or ox. 

The principal fissures are as follows: 

1. The lateral fissure (of Sylvius) begins at the sulcus rhinalis and runs upward and 
somewhat backward on the depressed part of the lateral surface of the hemisphere; it appears 



Cerebellum 



Medulln oblongata 



Fig. 671. — Brain of Pig; Dorsal View. 

33: 1, Lateral, 3. suprasylvian, with anterior {£') 



and do 



1 (£") branches: 5, diagonal; 4> coronal; 3, presyl- 
vian; 6, marginal; 7, ectomarginal ; 5, entomarginal; 9, cruciate. 
Two different arrangements of the coronal and cruciate fissures 
are seen on the two sides. 



844 THE NERVOUS SYSTEM OF THE PIG 

unbranched on superficial examination, but when the gyrus which almost completely conceals the 
insula is raised, an anterior lirancli is exposed which forms the dorsal boundary of the insula. 

2. The suprasylvian fissure pursues a curved course approximately parallel with the 
dorso-medial border of the hemisphere. Its posterior end is separated by a short interval from 
the sulcus rhinalis posterior. From its highest point a branch proceeds obliquely upward and 
forward, crosses the dorso-medial border, and joins the cruciate fissure. 

3. The diagonal fissure crosses the anterior part of the lateral surface. It is directed 
obliquely downward and backward. 

4. The coronal fissure is constant and deep. It is directed upward and medially oyer 
the frontal pole, continues backward near the dorso-medial border, and often ends by passing 
obliquely over the border to the medial surface of the hemisphere. It is usually continuous in 
front with the presylvian fissure. 

5. The presylvian fissure begins — apparently as a branch of the sulcus rhinalis anterior — 
about 2 cm. in front of the lateral fissure, and carves over the lateral aspect of the frontal pole. 

6. The marginal fissure begins l)ehind the cruciate fissure close to the dorso-medial 
border and extends in a gentle curve backward to the occipital pole. 



nsmrse fissure 




Cerebellum 



Olfactory biilh 

Medulla oblongata Spinal cord 

Fio. fi72. — Brain of Pig; Left View. 
?', sulcus rhinalis (anterior et posterior); S. lateral; S, suprasylvian; .J, ectomarginal ; 5, coronal. Stumps 
of cranial nerves indicated by Roman numerals. 

7. The ectomarginal fissure lies above and nearly parallel to the posterior part of the 
suprasylvian fis.sure. 

8. The entomarginal fissure lies along the posterior part of the dorso-medial border. 

9. The calloso-marginal fissure consists of two separate parts. The more extensive pos- 
terior part is termed the splenial fissure. It extends from the tentorial aspect of the hemi- 
sphere in a direction parallel willi the corpus callosum nearly to the middle of the medial 
surface; it is continucil by tlic cruciate fi.ssure and may be also connected with the corona! fis.<*ure 
by a brand] wliiili ixissis oMiquely upward and forward. The anterior part, the genual fissure, 
lies about midway lutween the anterior part of the corpus callosum and the dorso-medial Ixmler. 

10. Tlic cruciate fissure runs obliquely upward and forward from the anterior end of the 
splenial fissure on tlie inner surface of the hemisphere, cuts obliquely into the dorso-medial margin 
about its middle, and usually joins the dorsal branch of the suprasylvian fissure. 

11. The sulcus rhinalis extends in an undulating manner along the entire lower part 
of the lateral surface of the hemisphere and forms the upper limit of the rhinencephalon. 

The olfactory bulbs are very large and the tracts extremely broad and sliort. 

Tlie trigoniini olfactorium is so prominent as to suggest the designation tuberculum 

olf actor ium. 

The cranial nerves present tlie following special fcattiros: 

The third, fourth, sixth, and the ophthalmic and maxillary divisions of the 

fifth nerve emerge together as in the ox. 



THE NERVOUS SYSTEM OF THE PIG 



845 



The lacrimal nerve resembles that of the horse, the frontal that of the ox. 
The naso-ciliary nerve is relatively large and sends numerous filaments to the ocular 
muscles. The maxillary nerve has a very short course in the pterygo-palatine 
fossa. The infraorbital nerve is large in correlation with the development of the 
snout, which receives numerous branches. The mandibular nerve emerges through 
the foramen lacerum anterius. The superficial temporal nerve is small ; according 
to Moussu it furnishes the excito-secretory fibers to the upper part of the parotid 
gland, while those going to the lower part are derived from the mylo-hyoid nerve. 

The inferior buccal nerve passes downiward and forward under cover of the 
parotid gland and accompanies the parotid duct, with which it turns around the 
lower border of the jaw in front of the masseter. 

The vagus bears a jugular ganglion and a ganglion nodosum ; the latter occurs 



Ulnar nerve 
(dorsal branch) — ' 




Ulnar nerve 
'Dorsal branch 



^^Deep branch 




Fig. 673. — Nehves of Distal Part of Right Fore- 
limb OF Pig; Dors.4L View (Schematic). 
c. Dorsal common digital nerves; p, dorsal proper 
digital nerves. 



Fig. 674. — Nerves of Distal Part of Right Fore- 
limb OF Pig; Volar View (Schematic). 
p. Volar proper digital nerves. 



at the point of origin of the anterior laryngeal nerve, and may be as large as a small 
pea. Proximal to this the vagus is easily divided into two strands, one of which is 
the accessory component. The cesophageal trunks form a posterior oesophageal 
plexus, as in man, from which two nerves issue. The ventral nerve is small and 
ramifies on the parietal surface of the stomach. The dorsal nerve is much larger; 
it gives branches to the stomach, crosses the lesser curvature of that organ, and 
joins the cceliac plexus. 

The hjrpoglossal nerve may present a small dorsal root, on which there is a 
minute hypoglossal ganglion. 

The spinal nerves number on each side eight in the cervical region, fourteen 
(commonly) in the thoracic, seven in the lumbar, and four in the sacral. Some 
of the special features of the nerves of the limbs are as follows: 



846 



THK NERVOUS SYSTEM OF THE PIG 



The brachial plexus is derived from the same nerves as in the ox, but the root 
furnished by the sixth cervical is relatively smaller. The plexus consists of two 
parts, the upper of which emerges above the scalenus, the lower between the two 
parts of that muscle. The more important differences in the nerves emanating 
from the plexus from the arrangement in the ox occur in the distal part of the limb. 
The cutaneous branch of the radial nerve divides at the carpus into branches which 
concur with the dorsal branch of the ulnar nerve in supplying the dorsal digital 
nerves, two for each digit. The volar digital nerves, also two for each digit, are 
formed by the terminal branches of the median nerve and the volar or deep branch 
of the ulnar nerve. The formation and arrangement of the digital nerves are 
indicated in the annexed schematic figures. 

The lumbo-sacral plexus is derived from the ventral branches of the last three 



Deep peroneal 
nerve 

Superficial 
peroneal nerve 



. Saphenous 

nerve 




Tibial nerve 



Medial jihintar 

nerve 




Fig. 675. — Nerves of Dist.\l Part of Right Hixd 

Limb of Pig; Dors.4l View (Sche.matic). 

p. Dorsal proper digital nerves. 



Fig. 676. — Nerves of Distal Part of Right Hind 
Limb of Pig; Plantar View (Schematic). 
p, Plantar proper digital i 



lumbar and first sacral nerves. The distribution of the branches of the plexus 
differs chiefly in the distal part of the limb. The superficial peroneal nerve is 
large and terminates by forming the greater part of the dorsal digital nerves. 
The latter, two for each digit, are also in part formed by the terminal Ijranches of 
the deep peroneal nerve. 

The tibial nerve divides at the tarsus into medial and lateral plantar nerves. 
The latter divide to form the plantar digital nerves, two for each digit. In addi- 
tion, the lateral plantar nerve supplies a branch to the dorsal aspect of the lateral 
(fifth) digit. The arrangement of the digital nerves is indicated by the aimexed 
schematic figures. 

The sympathetic system of the pig has received very little attention from 
anatomists. The anterior cervical gangUon is long and fusiform. It gives off 



THE NERVOUS SYSTEM OF THE DOG 847 

filaments which join the vagus near the ganghon nodosmn. The cervical trunk is 
short and relatively larger than in the ox; it is enclosed in a common sheath with 
the vagus in the neck and separates from that nerve to join the middle cervical 
ganglion at the thoracic inlet. 



THE NERVOUS SYSTEM OF THE DOG 

The spinal cord is almost circular in cross-section except at the well-marked 
cervical and lumbar enlargements, where it is compressed dorso-ventrally. The 
conus medullaris lies over the junction of the sixth and seventh lumbar vertebrte. 
The length of the cord of a rather large dog was found to be about fifteen inches 
(ca. 38 cm.) ; of this, the cervical part was about four and a half inches (ca. 11 cm.), 
the thoracic a little less than seven inches (17.4 cm.), the lumbar a little less than 
three inches (ca. 7 cm.), and the sacro-coccygeal about an inch (ca. 2.6 cm.) 
(Flatau-Jacobson) . 

The brain weighs about two to two and a half ounces (ca. 60-70 gm.) in dogs 
of medimn size, but there is, of course, a wide range of weight in the different breeds. 
Thus in small terriers the weight is about an ounce (ca. 30 gm.) or even less, while 
in very large dogs it may exceed five ounces (ca. 150 gm.). It corresponds much 
more closely with the external form of the cranium in size and general form than in 
the animals previously described; this is specially true of the small breeds, in which 
the bony crests and frontal sinuses are little developed. 

The medulla oblongata is broad and thick. Its ventral surface is strongly 
convex from side to side. The pyramids are large and prominent and are Ihnited 
by a distinct median fissure and lateral grooves. The median fissure ends at a 
small depression, the foramen caecum, just behind the pons. The olivary eminence 
is a well-defined oval elevation situated between the pyramid and the superficial 
origin of the hypoglossal nerve. The external arcuate fibers form a wide band 
which crosses the lateral surface obliquely upward and forward, and obscures 
the facial tubercle and the groove which limits the restiform body laterally. The 
cuneate tubercle is distinct. The rhomboid fossa is deep and narrow. The 
fourth ventricle communicates with the subarachnoid space on each side through 
a lateral aperture. 

The pons is relatively small, and in correlation with this fact the corpus trape- 
zoideum is \ery wide; it is divided by the pyramids into two lateral parts. The 
cerebellum is very broad, but is low and also compressed from before backvv'ard. 
Rather more than half of it is overlapped by the cerebral hemispheres. The an- 
terior surface is accurately adapted to the concave tentorial surfaces of the hemi- 
spheres and to the posterior corpora quadrigemina and their commissure. The 
posterior surface is almost vertical and is convex centrally and flattened laterally. 
The vermis is prominent and in general well defined, although it is cormected in its 
middle part with the hemispheres. The latter are three-sided and consist of four 
lobules. The small lobule lateral to the origins of the facial and acoustic nerves 
is the flocculus. Lateral to this, and separated from it by a deep fissure, is the 
paraflocculus; this is divided into dorsal and ventral parts by a sagittal fissure. 
The anterior peduncles are very short. 

The posterior corpora quadrigemina are large, very •n-ide apart, and prominent, 
and are connected by a curved commissure. The medial geniculate body is large 
and distinct. In the deep interjieduncular fossa are two small bands which indi- 
cate the course of the fasciculi retroflcxi, tracts which connect the habenular and 
interpeduncular ganglia. The mammillary body is double. The tuber cinereimi 
is relatively large. The hypophysis or pituitary body is circular and rather small. 



848 



THE NERVOUS SYSTEM OF THE DOG 



Optic nerve 

Optic chiasm 

Optic tract 

Hypophysis 

Cerebral peduncle 
Pons 

Facial nerve 

Acoustic nerve 

Flocculus 

Chorioid plexus of fourth 
ventricle 




Olfactory bulb 



Olfactory tract 
- Sulcus rhinuLs 

Fossa lateralis 
Piriform lobe 
Oculomotor nerve 



Trochlear nerve 

Trigeminal nerve 
Abducent nerve 
Corpus trapezoideum 
Glosso-pharyngeal nerve 
Vagus nerve 

Accessory nerve 



Spinal cord Median fissure Pyramid 

Fig. 678.— Key to Fig. 677. 



THE NERVOUS SYSTEM OF THE DOG 



849 



The cerebral hemispheres are very broad behind and diminish in width an- 
teriorly; there is a sudden narrowing at the frontal poles, which are flattened 
laterally. The tentorial surfaces are concave and form a deep cavity which re- 
ceives the anterior part of the cerebellum. The arrangement of the fissures and 
gyri is simpler than in the animals previously examined. 

The chief fissures arc as follows: 

1. The lateral fissure extends upward and backward from the sulcus rhinalis a little behind 
the middle of the lateral siu-face of the hemisphere. 

2. The ectosylvian fissure has approximately the shape of an inverted U, and curves over 
the lateral fissm'e. It is regarded as consisting 
of three parts — anterior, middle, and posterior 
(F. ectosylvia anterior, media, posterior). 

3. The suprasylvian fissure Ues above and 
approximately concentric with the preceding. It 
also consists of three parts — anterior, middle, 
and posterior. 

4. The ectomarginal or collateral fissure 
runs forward on the dorsal aspect of the hemi- 
sphere almost parallel with the dorso-medial bor- 
der. A little in front of tlie middle of the surface 
it gives off a short ansate fissure (F. ansata) 
which runs obliquely mediaDy and forward. It 
is usually continued anteriorly by the coronal 
fissure, and may be in contmuity posteriorly 
with the medilateral (or post-liHeral) fissure. 



Longitudinal Jist:ure 



Olfactory bulb 
Frontal pole 





FiQ. 679. — Brain Stem of Dog; Dorsal View. 

o, Spinal cord; b, dorsal median groove; c, c', funicu- 
lus gracilis; c", clava; d, d', funiculus cuneatua; d", tuber- 
culum cuneatum; c, funiculus lateralis: e', tuberculum cin- 
ereum; /. medulla oblongata; /, //. Ill, fovese of floor of 
fourth ventricle (fossa rhomboidea) ; g, limiting groove; h, 
median fissure; i, eminentia medialis; k, ala cinera; I, I', 
pons; m, posterior peduncle, and n, middle peduncle, of cere- 
bellum (cut); o, anterior peduncle of cerebellum; p, p', cor- 
pora quadrigemina, anterior and posterior; q, q', peduncles 
(brachia) of corpora quadrigemina; r, thalamus: s, massa 
intermedia; i, stria meduUaris; u, anterior tubercle of 
thalamus: v, pulvinar; w, corpus geniculatum laterale; x, 
corpus geniculatum mediale. (.\fter Ellenberger, in Leiser- 
ing's Atlas.) 



Fig. 680. — Brain of Dog; Dorsal View. 
Fissures: 1, Lateral; 2, ectosylvian; 5, supraayl- 
i; i, ectomarginal (or collateral); 4't ansate; 5, 
, ectolateral; 7, entomarginal; 8, presylvian 
(or orbital): 9, cruciate; 10, medilateral (separated 
from entomarginal on right side, but connected with it 
on left hemisphere) ; 11,{. prorese. 



5. The coronal fissure is usually the 
continuation of the ectomarginal. It runs 
forward and downward, curving around the 
cruciate fissure, and ends behind the middle 
of the presylvian fissure. 

6. The ectolateral fissure hes between 
the posterior part, of the ectomarginal fissure 
and the suprasylvian fi.ssure. 

7. The entomarginal fissure lies between the anterior part of the ectomarginal fissure and 
the dorso-medi:d bdidir. It is often indistinct :ind not rarely absent. 

S. The presylvian fissure — sometimes termed the orbital — begins at the sulcus rhinalis, 
a little in front of its middle, and curves over the anterior third of the lateral surface of the hemi- 
sphere in front of the coronal fissm'e. 
54 




850 THE NERVOUS SYSTEM OF THE DOG 

9. The cruciate fissure is tlie deepest and most characteristic. It cuts deeply into the an- 
terior third of till' dorsD-iiicdial border and runs ahnost straiglit outward. It is continuous on the 
medial surface of tlie hemisphere with the caUoso-piarginal or splenial fissure. 

10. The sulcus rhinalis is continued on the tentorial 
surface of the hemisphere tiy the occipito-temporal fissure. 
Anteriorly it is jirolonfied as the olfactory fissure, wliich 
is concealed by the olfactory Inilb and tract. . 

11. The calloso-marginal fissure usually consists of 
two parts, splenial and jienual. The splenial fissure is 
parallel with the splenium and middle part of the corpus 
callosum on the medial surface of the hemisphere. It is 
continuous in front with the cruciate fissure and runs for- 
ward and outward across the tentorial surface to join the 
occipito-temporal or calcarine fissure. It gives ofT from 

pjg ggj Right < I i;i HI, VI iifmisphere its highest part the short accessory cruciate fissure. The 

OF Dog- Medial View genual fissufe is approximately parallel with the genu of 

' " „ , ^lie corpus callostmi. 

J Corpu.s callosum; / , genu; / splen- j.3 rj,^^ suprasplenial fissure runs almost parallel 

mm of corpus callosum; a, genua fissure; ^^^y^ ^^^ posterior part of tlie calloso-inarsinal fissure on 

b. splemal fissure; c. suprasplemal fissure; jj^g ^^^^^ ^„j tentorial surfaces of tlie hemisphere. 
d, hippocampal fissure; e, sulcus corporis jg rpj^^ occipito-temporal or calcarine fissure is the 

callosi; /, postsplenial fissure; g. lesser continuation on the tentorial sm-face of the hemisphere of 

cruciate fissure; A, cruciate fissure. (After the splenial fissure 

Ellenberger, in Leisering's Atlas.) '^ J4 y^^ - hippocampal fissure forms the medial 

boundary of the piriform lobe. 

The olfactory bulb is large and is compressed laterally; its anterior end pro- 
jects beyond the frontal pole of the hemisphere. The tract is short and is also 
flattened laterally. Both contain a narrow cavity which communicates with the 
lateral ventricle. The piriform lobe is large and rounded. 

The cranial nerves present the following special features which are worthy of 
notice: 

The ophthalmic nerve gives off frontal, long ciliary, ethmoidal, and infratro- 
chlear branches. The lacrimal nerve arises from the ophthalmic at its origin ;' its 
recurrent branch emerges at tlic orl)ital ligament and concurs ^\^th the zygomatic 
and frontal nerves in the formation of the anterior auricular plexus. The frontal 
nerve emerges from the orbit in front of the upper end of the orbital ligament, 
ramifies in the upper lid and the adjacent skin of the forehead, and sends branches 
backward to the anterior auricular plexus. The long ciliary nerve accompanies 
the optic nerve and divides into several branches which pierce the posterior part of 
the sclera. The ethmoidal nerve gives off internal nasal branches and ends in the 
muzzle. The infratrochlear nerve runs forward between the medial straight and 
the superior oblique muscles of the eye and ramifies on the face in the vicinity of 
the medial canthus. 

The maxillary nerve emerges through the foramen rotundum and gives off 
five branches. The lacrimal nerve emerges from the orbit lateral to the frontal; 
its branches concur with the frontal and auriculo-palpebral nerves in the formation 
of the anterior auricular plexus. The zygomatic nerve emerges through an opening 
in the upper part of the orlntal ligament antl ramifies in the lower lid and on the 
adjacent surface of the face. The infraorbital nerves, two in number, divide within 
the infraorbital canal and after their emergence upon the face, thus forming seven 
or eight external nasal and superior labial branches. The sphenopalatine nerve 
gives off lesser and greater palatine and posterior nasal nerves. 

The mandibular nerve passes out through the foramen ovale. The superficial 
temporal nerve tlivides into auricular, temporal, and malar branches; the last- 
named crosses the masseter and ramifies with the buccal nerves. The mylo-hyoid 
nerve is given off from the mandibular nerve almost immediately after the latter 
emerges from the cranium; it innervates the mylo-hyoideus and occipito-mandib- 
ularis and gives off a branch which turns around the lower jaw, joins the inferior 

' The origin of the lacrimal nerve is such that EUenberger-Baum and Martin describe it 
as a branch of the maxillary nerve. 



THE NERVOUS SYSTEM OF THE DOG 



851 



buccal nerve, and ramifies on the lateral surface of the face. The inferior alveolar 
nerve arises by a common trunk with the mylo-hyoid; it gives off dental branches 
and terminates in mental and inferior labial branches. The lingual nerve supplies 
vaso-dilator and excito-secretory filaments to the mandibular and sublingual 
salivary glands; these fibers are derived from the chorda tympani. 

The facial nerve divides near the posterior border of the jaw into four branches. 
The upper branch is the auriculo-palpebral nerve, which divides after a very short 
course into anterior auricular and zygomatic branches. The latter curves upward 
and forward across the zygomatic arch toward the eye, and divides into branches 
which supply the eyelids and nasal region and concur \vith the frontal anfl lacrimal 
nerves in forming the anterior auricular plexus. The superior buccal nerve ac- 
companies the parotid duct across the masseter. The inferior buccal nerve runs 
forward along the lower border of the masseter and the mandible. The two nerves 




Fig. 682. — Deep Dissection of Head of Dog, Showing Especially Trigeminal and Hypoglossal Nerves. 
a, Hypoglossal nerve; b, cervical branch of a; c, mandibular division of trigeminus; d, lingual nerve; e, nerve to 
mandibular gland; /, deep temporal nerve; g, pterygoid nerve; h, buccinator nerve (cut); i, inferior alveolar nerve; 
k, staphyline branch of lingual nerve; I, chorda tympani; m, mylo-hyoid nerve; n, sphenopalatine nerve; o, lesser 
palatine nerve; p, great palatine nerve; q, infraorbital nerves; r, n. subcutaneua malse; s, branch of oculomotor nerve 
to inferior oblique muscle; f, lacrimal nerve; u, frontal nerve; if, trochlear nerve; li', abducens nerve; i, carotid artery; 
^, lingual artery; ^, internal maxillary artery; 4. m. Ihyro-pharyngeus; o, m. hyo-pharjmgeus; <?, m. thyrb-hyoideus; 
7, m. sterno-hyoideus; 8, m. hyo-glossus; 5, m. genio-hy oideus ; W, m. genio-glossus; 11, m. stylo-glossus; 12, m. 
pterygoideus medialis; 13, outhne of mandibular gland (dotted) ; 14, atlas; 15, bulla oasea; 16, zygomatic arch (dotted); 
17, m. rectus ocuh inferior; 18, m. obliquus oculi inferior. (Ellenberger-Baum, Anat. d. Hundes.) 



ramify on the cheek and anastomose with each other and the infraorbital nerves 
to form a plexus from which branches go to the muscles of the lips and nostrils. 
The cervical branch runs dowmward and backward over the mandibular gland 
and ramifies in the cervical cutaneus muscle; it communicates with the inferior 
buccal nerve and sends twigs to the parotido-auricularis muscle and the mandibular 
space. 

The vagus bears a jugular ganglion and a ganglion nodosiun. The former is 
situated on the nerve just before the emergence of the latter from the cranium. The 
latter is situated near the anterior cervical ganglion on the rectus capitis ventralis 
major and dorsal to the internal carotid artery; it is fusiform and may be about half 
an inch (ca. 1-1.5 cm.) long in a large dog. In its course in the neck the nerve is 
inclosed with the sympathetic trunk in a common sheath and is related ventrally 



852 



THE NERVOUS SYSTEM OF THE DOG 



to the common carotid artery. The two nerves separate after entering the thorax 
(Figs. 613, 614). The right vagus crosses obliquely over the right face of the, 
trachea and divides a short distance behind the bifurcation of the latter into dorsal 
and ventral branches. The left vagus crosses the lateral surface of the aortic arch 
and divides similarly. By the union of the dorsal and ventral divisions of the two 
nerves there are formed dorsal and ventral oesophageal trunks. The dorsal tnink 
concurs with branches of the coeliac plexus in forming the posterior gastric plexus 
on the visceral surface of the stomach. The ventral trunk ramifies on the parietal 
surface of the stomach, forming the anterior gastric plexus, from which a consider- 
able branch passes along the lesser curvature to the pylorus. Some special features 
of the collateral branches are : Two pharyngeal branches are present. The anterior 
pharjmgeal branch arises from the vagus above the ganglion nodosum. It passes 
under the deep face of the carotid artery and descends on the lateral surface of the 
pharynx to end in the erico-thyroid muscle. It furnishes a root of the inferior pharyn- 
geal branch, and communicates with the pharyngeal branch of the ninth and with the 




Fig. 683. — Nerves of Face of Dog. Parotid Glawd is Removed. 
Nerves: a, Facial; (). posterior auricular; c, internat auricular; d, digastric; e, inferior buccal; /, cervical branch 
of facial; g, auriculo-palpebral; h, superior buccal; i, temporal branch; k, k' , k" , zygomatic branch; I, auriculo-tem- 
poral; m, malar branch of /,• n, buccinator; o, mylo-hyoid branch; p, subcutaneus malse; g, lacrimal; r, frontal; s, 
infratrochlear; t, infraorbital. 1, Paramastoid process; 2, occipito-mandibularis ; S, base of concha; 4t masseter; 
6, zygomaticus; G, scutularia; 7, zygomatic arch; 5, maxilla. (EUenberger-Baum, Anat. d. Hundes.) 



anterior laryngeal and hypoglossal nerves. The posterior pharyngeal branch is 
formed by the union of roots derived from the anterior pharyngeal nerve and the 
ganglion nodosum, together with filaments from the anterior cervical ganglion. 
It crosses the sitle of the pharynx behind the anterior phar^mgeal and ramifies on 
the posterior constrictor of the pharynx and the origin of the oesophagus. It 
contributes filaments to the pharyngeal plexus, communicates with the recurrent 
nerve, and supplies twigs to the thyroid gland. The pharyngeal plexus is formed 
on the lateral surface of the pharynx by branches of the pharyngeal nerves and the 
communications above described; branches from it imiervate the muscles and 
mucous membrane of the pharynx. The anterior laryngeal nerve arises from the 
ganglion nodosum and descends over the side of the pluirjaix, crossing beneath the 
carotid arter^y and the anterior laryngeal nerve. It passes through the thyroid 
notch and ramifies in the mucous membrane of the larynx. It communicates with 
the anterior cervical ganglion and the anterior pharyngeal branch of the vagus, antl 
gives twigs to the hyo-pharjTigeus muscle. Immediately after its entrance into the 
larynx it gives off a large branch which, instead of uniting with the recurrent as in the 



THE NERVOUS SYSTEM OF THE DOG 853 

other animals, has a pecuHar arrangement. It runs back near the dorsal border of the 
th.vroid cartilage, gives a branch to the crico-arytenoideus dorsalis as it passes over 
that muscle, and continues along the trachea medial to the recurrent nerve. At the 
thoracic inlet it communicates with the posterior cervical ganglion and continues 
backward to unite with the vagus at or near the point of origin of the recurrent 
nerve. Its collateral filaments supply the trachea and concur with the posterior 
pharyngeal branch in forming a plexus on the cervical part of the oesophagus which 
innervates that tube.' The recurrent nerves present no remarkable special features. 
The depressor nerve is a very delicate filament which arises usually from the an- 
terior laryngeal nerve and is incorporated in the vago-sympathetic trunk to the 
thorax. Here the nerve separates from the ventral border of the vago-sympathetic 
trunk. The right nerve passes backward between the anterior vena cava and the 
trachea, inclines to the left, and reaches the medial surface of the aortic arch. The 
left nerve passes backward ventral to the vagus and across the lateral (left) face 
of the aortic arch. Both nerves give filaments to the cardiac nerves and to the 
aorta and pulmonary artery. Their terminal branches pass between these vessels 
and enter the wall of the heart. The pulmonary and posterior oesophageal plexuses 
are highly developed. 

The hypoglossal nerve gives off a long branch (R. descendens) which runs 
downward and backward across the pharynx and larynx, communicates with the 
ventral branch of the first cervical nerve, and supplies the thyro-hyoid, sterno- 
hyoid, and sterno-thyroid muscles. 

The spinal nerves number thirty-six or thirty-seven on either side, and com- 
prise eight cervical, thirteen thoracic, seven lumbar, and five or six coccygeal. 

The brachial plexus (Fig. 616) is derived from the ventral branches of the last 
four cervical and first thoracic nerves; the root supplied by the fifth cervical nerve 
is very small. The roots unite at the ventral border of the scalenus. The more 
important special features in the arrangement of the nerves which emanate from 
the plexus arc as follows: 

The musculo-cutaneous nerve passes between the coraco-brachialis and the 
brachial artery and descends in the arm in front of the artery. At the shoulder 
joint it gives off branches to the biceps and coraco-l:)rachialis, and in the distal third 
of the arm is coimected with the median nerve by an oblique branch. It terminates 
near the elbow by dividing into a branch for the brachialis and a small cutaneous 
nerve which passes down over the medial face of the elbow and, inclining a little 
forward, descends over the deep fascia of the forearm to the carpus. 

The radial nerve descends behind the ulnar nerve, gives brandies to the 
extensors of the elbow, dips in between the medial head of the triceps and the 
accessory head of the anconeus, winds arounil the arm, and divides between the 
brachialis and the lateral head of the triceps into two branches. The deep branch 
(R. profundus) sujjplies the extensor and supinator muscles on the forearm. The 
superficial branch (R. superficialis) emerges upon the flexor surface of. the cll)ow 
and divides into two branches which terminate by supplying two dorsal digital 
nerves to each digit, except the fifth, which receives its lateral dorsal nerve from the 
ulnar. The medial branch descends along the medial side of the cephalic vein to the 
carpus, where it divides into dorsal nerves for the first digit and the medial side of 
the second. The lateral branch is much larger. It descends on the middle of the 
front of the forearm and supplies the remaining dorsal digital nerves except that to 
the lateral side of the fifth digit. 

The ulnar nerve is as large as or larger than the median, with which it is united 
for some distance. At the distal third of the arm it separates from the median 
and passes over the medial epicondyle of the humerus. At the proximal part of 

1 Lcsbre terms this the tracheo-cEsophageal branch, and considers that it must be regarded 
as an accessory or internal recurrent nerve. 



854 



THE NERVOUS SYSTEM OF THE DOG 



the forearm it gives off the dorsal branch (R. dorsalis), which supplies cutaneous 
twigs to the dorso-lateral surface of the distal part of the forearm and carpus and 
terminates as the lateral dorsal digital nerve of the fifth digit. Descending under 
cover of the flexor carpi ulnaris, the ulnar inclines medially under the tendon of 
insertion of that muscle and di\ndes into superficial and deep branches. The 
superficial branch (R. superficialis) tlcscends along the lateral border of the flexor 
tenilons, gives off the lateral volar digital nerve of the fifth digit (N. dig. vol. lat. dig. 
V), and a branch (N. met. vol. R") which descends in the space between the fourth 
and fifth metacarpal bones and unites with the deep Ijranch. The deep branch 
(R. profundus) descends in the carpal canal and divides under the deep flexor 



Branches of tv ' 
radial nerve 




Median nerve -- 




Fig. 684. — Nekves of Distal Part of Right Fore- 
limb OF Dog; Dorsal View (Schematic). 
p, Dorsal proper digital nervea. 



Fig. 685. — Nerves of Distal Part of Right Fore- 
limb OF Dog; Volar View (Schematic), 
p, Volar proper digital nerves. 



tendon into its terminal branches. The smaller of these supi^h' the volar meta- 
carpal muscles. The larger terminals are the three volar common digital nerves 
(Nn. dig. col. comm. II, III, IV), which descend along the second, third, and fourth 
intermetacarpal spaces, subcUvide, and concur with the volar" metacarpal branches 
of the median nerve in forming the volar proper digital nerves (Nn. dig. vol. proprii). 
The median nerve descends behind the tirachial artery, passes over the metlial 
epicondyle of the humerus, then under the pronator teres, and continues in the 
forearm under cover of the flexor carpi radialis. It gives branches below the elbow 
to the flexor and pronator muscles, and lower dowia a volar branch to the skin on 
the medial and volar aspect of the carpus, and terminates between the superficial 
and deep flexor tendons by dividing into three volar metacarpal nerves (N. met. vol. 



THE NERVOUS SYSTEM OF THE DOG 



855 



I, II, III). These descend in the first, second, and third intermetacarpal spaces 
and unite with the volar common digital nerves in forming volar proper digital 
nerves. The arrangement of the digital nerves is indicated in the annexed sche- 
matic figures. 

The lumbo-sacral plexus is formed from the ventral branches of the last five 
lumbar and first sacral nerves. The more important special facts in regard to the 
nerves of the pelvic limb are as follows : 

The saphenous nerve (Fig. 621) is relatively large, and, in fact, might be 
consideretl as the continuation of the femoral nerve. It descends at first in front 
of the femoral artery, then passes over the lower part of the medial surface of the 
thigh with the saphenous artery, continues ilown the leg with the dorsal branch of 



Superficial 

peroneal nerve 




Medial plantar 
nerve 




Plantar 
common 
-''Z digital 
nerves 



Fig. 686. — Nerves of Dist.\l Pabt of Right Hind 
Limb of Dog, Dorsal View (Schematic). 
p, Dorsal proper digital i 



Fig. 6S7. — Nerves of Distal Part op Right Hind 

Limb of Dog, Plantar Vie^v (Schematic). 

p. Plantar proper digital nerves. 



that vessel, and anastomoses with branches of the superficial peroneal nerve. It 
supplies cutaneous twigs from the stifle to the metatarsus. 

The common peroneal nerve separates from the tibial above the origin of the 
gastrocnemius, runs tlo\\Tiward and forward across the lateral head of that muscle, 
passes between the deep flexor of the digit and the peroneus longus, and divides into 
superficial and deep branches. The superficial peroneal nerve descends the leg 
along the peroneus tertius and longus, gives off a dorsal branch to the first digit (N. 
cutaneus dorsalis medialis), and divides at the proximal part of the metatarsus into 
three dorsal common digital nerves (Nn. dig. pedis dors. comm. II, III, IV). These 
descend with the superficial dorsal metatarsal arteries and concur with branches 
of the deep peroneal nerve in forming dorsal proper digital nerves (Nn. dig. ped. 
prop, dorsales). The deep peroneal nerve passes tlo\\^l the leg with the anterior 



856 THE NERVOUS SYSTEM OF THE DOG 

tibial vessels. It gives twigs to the liock joint and the extensor brevis muscle, and 
divides into three dorsal metatarsal nerves (Nn. met. dors. II, III, IV); these 
descend Math the corresponding arteries along the intermetatarsal spaces and unite 
with the dorsal common digital nerves in supplying the dorsal proper digital nerves. 

The tibial nerve divides at the tarsus into two plantar branches. The medial 
plantar nerve descends along the medial border of the superficial flexor tendon and 
divitles near the middle of the metatarsus into two branches. Of these, the medial 
branch constitutes the first plantar common digital nerve (N. dig. comm. plant. I). 
The lateral branch descends on the superficial flexor tendon and divides into three 
plantar metatarsal nerves (Nn. met. plant. II, III, IV), which unite with the 
plantar common digital nerves. The lateral plantar nerve passes down between 
the flexor tendons, sends twigs to the muscles on the plantar surface of the metatar- 
sus, and divides into three plantar common digital nerves (Nn. dig. comm. plant. II, 
III, IV). These descend with the deep plantar metatarsal arteries in the second, 
third, and fourth intermetatarsal spaces, receive the plantar metatarsal nerves, 
and divide into plantar proper digital nerves, which pass down the opposed surfaces 
of the second to the fifth digits. 

The sympathetic system presents few special features worthy of mention. 
The anterior cervical ganglion is situated behind the bulla ossea in close relation 
to the internal carotid artery and the ganglion nodosum of the vagus. It is fusi- 
form and is a little less than half an inch (ca. 1 cm.) long in a dog of medium size. 
It forms connections directly or through the carotid plexus with the last seven 
cranial and first cervical nerves. The cervical trunk unites with the vagus so in- 
timately as to form a vago-sympathetic trunk. The posterior cervical ganglion 
is situated at the point where the sympathetic trunk separates from the vagus 
(Figs. 613, 614). It is usually distinct from the first thoracic ganglion, which is 
stellate and lies on the longus colli opposite the first space. The two are connected 
bj^ filaments which cross each side of the brachial artery, forming the ansa sub- 
clavia. Two or three cardiac nerves proceed from these ganglia on the left side; 
they pass to the lateral surface of the aortic arch, where they ramify and concur 
with the nerves of the right side in the formation of the cardiac plexus. On the 
right side one or two cardiac nerves appear to come from the vagus and one from 
the first thoracic ganglion. They ramify on the right side of the trachea and vnih 
those of the right side form the cardiac plexus at the base of the heart. From the 
plexus branches go to the heart, pericardium, and pulmonary artery. The greater 
splanchnic nerve separates from the posterior part of the thoracic trunk, most often 
from the twelfth ganglion. It passes into the abdomen between the diaphragm 
and the psoas minor and joins a small adrenal ganglion close to the cceliac ganglion. 
The lesser splanchnic nerve arises from the last thoracic and first lumbar ganglia. 
It may be ilivided into two or three strands which go to the adrenal plexus. 

The cceliac and anterior mesenteric ganglia are separate. The former is 
elongated and lies along the posterior face of the origin of the cceliac artery. The 
latter is smaller and rounded and is in contact with the origin of the anterior mesen- 
teric artery. On the left side the two ganglia are connected by a trunk which is 
ganglionic in character. The cceliac, anterior mesenteric, and subsidiary plexuses 
enlace the corresponding arteries. There is a small elongated posterior mesenteric 
ganglion in relation to the origin of tlie posterior mesenteric artery. The posterior 
mesenteric plexus inclutles left colic, anterior haemorrhoidal, and spermatic plexuses. 
The lumbar trunk is deeply placed at the metlial siile of the psoas minor. It has 
seven ganglia, which are very small, with the exception of the last. There is a well- 
developed aortic plexus. The sacral tnmks are close to the middle sacral artery 
and have each three ganglia when this part is fully developed. The caudal trunks 
lie on each side of the coccygeal artery ; the number and arrangement of the visible 
ganglia are variable. The pelvic plexus is well developed and contains minute 
ganglia. 



/ESTHESIOLOGY 
THE SENSE ORGANS AND COMMON INTEGUMENT 

The organs of the senses (Organa sensuum) receive external stimuli and con- 
duct impulses to the brain which result in sensations of sight, hearing, taste, smell, 
and touch. They consist essentially of specially differentiated cells (neuro-epithe- 
lium) and a conduction path which is simple in the more generalized sense organs, 
elaborate in those which are highly specialized — the eye and the ear. 



THE SENSE ORGANS AND SKIN OF THE HORSE 
The Eye 

The eye or organ of vision (Organon visus) in the broader sense of the term 
comprises the eyeball or globe of the eye, the optic nerve, and certain accessory 
organs associated therewith. The accessory organs (Organa oculi accessoria) are the 
orbital fascise and muscles, the 

Upper eyelid 
Third eyelid 
Ciiruncula , 
lacrinuili? \ 
Medial 
canthtts^. 



eyelids and conjunctiva, and 
the lacrimal apparatus. These 
structures will be considered in 
the order in which they may be 
most conveniently examined, 
taking the horse as a type. The 
bony walls of the orbit have 
been described in connection 
\vith the skull; the periorbita, 
a fibrous membrane which en- 
closes the eyeball together with 
its muscles, vessels, and nerves, 
may be appropriately included 
in the account of the fascise. 




Lower eyelid 

Fig. 6SS. — Left Eye of Horse. 
9, Zygomatic arch; 10, supraorbital depression: IS, supraorbital proc- 
ess; S7, facial crest. (After Ellenberger-Baum, Anat. fiir Kiinstler.) 



THE EYELIDS AND CONJUNC- 
TIVA 

The eyelids, upper and 
lower (Palpebra superior et in- 
ferior), are movable folds of 
integument situated in front 

of the eyeball. When closed, they cover the entrance to the orbit and the 
anterior surface of the eyeball. The upper lid is much more extensive and 
more movable than the lower one, and its free edge is more concave. The 
interval between the lids is termed the palpebral fissure (Rima palpebrarum). 
When the eye is closed, it is an obliciue slit about two inches (ca. 5 cm.) 
in length; when open, it is biconvex in outline. The ends of the fissure are 
the angles or canthi, and are distinguished as medial or nasal, and lateral or 

857 



858 



THE SENSE ORGANS AND SKIN OF THE HORSE 



temporal (Angnlus oculi medialis, lateralis). The lateral angle is rounded when the 
eye is open, liut the medial angle is narrowed and produced to form a 3-shaped 
hay or recess, termed the lacrimal lake ( Lacus lacrimalis) . In this there is a rounded 
pigmented prominence kno^\^l as the lacrimal caruncle (Caruncula lacrimalis); it 
is about the size of a small pea, and is covered with modified skin, connected with 
that of the medial commissure, from which project a number of hairs provided with 
sebaceous glands. The lids unite on either side and form the commissures, medial 

and lateral (Commissura paliiebrariun 
medialis, lateralis). The anterior sur- 
face of the lids (Fades anterior palpe- 
brarum) is convex and is covered with 
very short hair. A considerable num- 
ber of tactile hairs are scattered over 
the lower part, of the lower lid, but on 
the upper liil they are very scanty. 
The infrapalpeljral depression (Sulcus 
infrapalpebralis) indicates somewhat 
indistinctly the limit of the lower lid. 
The upper lid is marked by two fur- 
rows when raised. The posterior sur- 
face (Fades posterior palpebrarum) is 
adapted to the free surface of the eye- 
ball and is covered by the palpebral 
conjunctiva. The free border of the 
lid is smooth and usuallj' black. It 
has a well-tlefinetl posterior margin 
(Limbus palpebralis posterior), along 
which the ducts of the tarsal glands 
open. The anterior margin (Limbus 
palpebralis anterior) bears stiff hairs 
termed the cilia (eyelashes). On the 
upper lid the cilia are long and num- 
erous except at its medial third, where 
they are very small or absent. On 
the lower lid the cilia are often scarcely 
distinguishable from the ordinary hairs; 
in other cases they may be clearly seen 
except near the lateral canthus, and 
are much finer and shorter than those 
of the upper lid. The edge of each lid 
is pierced near the medial angle by a 
minute, slit-like opening, the pxmctum 
lacrimale, which is the entrance to 
the lacrimal duct. 
The skin of the eyelids is thin and freely movable, except near the free edge, 
where it is more firmly attached. The underlying subcutaneous tissue is destitute 
of fat. The muscular layer consists chiefly of the elliptical bundles of the orbicu- 
laris oculi, with which are associated fibers of the corrugator supercilii in the upper 
lid and the malaris in the lower lid. At the medial side there is a fibrous band, the 
palpebral ligament, which is attached to the lacrimal tubercle and furnishes origin 
to some fibers of the orbicularis. At the medial commissure a bundle detached 
from the orliicularls passes inward behind the lacrimal sac, and is known as the pars 
lacrimalis (or Horner's muscle). At the lateral side an indistinct palpebral raph^ 
occurs where fibers of the orbicularis decussate. The fibrous layer is thicker and 




■ Eve 



'7 3 

Fig. 689. — Vertical Section of Anterior Part 
OF Horse, with Lids Half Closed. 
/, Tarsal gland of upper lid; 2, palpebral conjunctiva; 
3, fornix conjunctivse; 4. levator palpebrae superioria; 5, 
orbicularis oculi; 6, cornea; 7, anterior chamber; S, iris; 
0, 9', granula iridis; 10, posterior chamber; 11, ciliary proc- 
ess; IS, ciliary muscle; 13, ciliary zone or suspensory 
lig. of lens; 14> chorioid; 15, sclera; 16, lens; 17, root of 
tactile hair. (After Bayer, Augenheilkunde.) 



THE CONJUNCTIVA 859 

denser along the free edge of the hd, forming here the tarsus. The tarsus furnishes 
insertion to a layer of unstriped muscle known as the tarsal muscle. The tarsal 
glands (Glandulte tarsales)' are partly embedded in the deep face of the tarsus, and 
are visible when the lid is everted if the conjunctiva is not too strongly pigmented. 
They are arranged in a linear series, close together, and with their long axes per- 
pendicular to the free edge of each lid. In the upper lid they number forty-five to 
fifty; in the lower, thirty to thirty-five. Each consists of a tubular duct beset 
v,ith numerous alveoli, in which a fatty sul:)stance, the palpebral sebum, is secreted. 
The palpebral conjunctiva lines the internal surface of the eyelids. 

The conjunctiva is the mucous membrane which lines the lids as palpebral 
conjunctiva (C. palpebrarum), and is reflected upon the anterior part of the eyeball 
as bulbar conjunctiva (C. bulbi); the line of reflection is termed the fornix con- 
junctivae. The palpebral part is closely adherent to the tarsus, but is loosely at- 
tached further back. It is papillated and is covered with stratified cylindrical 
epithelium in which many goblet-cells are present. In the fornix and its vicinity 
there are tubular glands. Near the medial angle there are numerous lymph nodules. 
The conjunctiva of the lateral part of the upper lid is pierced near the fornix by the 
orifices of the excretory ducts of the lacrimal gland — twelve to sixteen in number. 



fT5jr:ii.4aj 





Fig. 690. — Piece of Upper Eyelid; Inner Surface. Fig. 691. — Cartilage of Third Eyelid of Horse; 

;, Cilia; e. limbus palp, posterior; 3, tarsal glands. Conve.x Surface. 

(Aiter Ellenberger, in Leisering's Atlas.) /, Gland; S, fat surrounding deep part of cartilage. 

(After Ellenberger, in Leisering's Atlas.) 

The bulbar conjunctiva is loosely attached to the anterior part of the sclera and is 
pigmented in the vicinity of the corneo-scleral junction. On the cornea it is repre- 
sented by a stratified epithelium. 

When the lids are in apposition, the conjunctiva (including the epitheliuni of the cornea) 
encloses a capillary space between the lids and the eyeball, and constitutes what is known as the 
conjunctival sac. 

The third eyelid (Palpebra tertia) is situated at the medial angle of the eye. 
It consists of a semilunar fold of the conjunctiva, known as the membrana nictitans, 
which covers and partly encloses a curved plate of hyaline cartilage. Its marginal 
part is thin and usually more or less pigmented. The cartilage has an elongated 
quadrilateral outline. The part of it which lies in the membrana is wide and thin. 
The deep part is narrower and thicker and is embedded in fat at the inner side of the 
eyeball. Numerous minute lymph nodules occur in the membrana nictitans, and 
the deep part of the cartilage is surrounded by a gland which resembles the lacrimal 
gland in structure (Glandula superficialis palpebrse tertiae). 

Ordinarily the third eyelid extends very little over the medial end of the 
cornea, but when the eyeball is strongly retracted, the membrana is protruded over 
it so as to measure about an inch (ca. 2-3 cm.) in its middle. This effect results 
from the pressure of the eyeball and its muscles on the fat which surrounds the deep 
part of the cartilage. 

Vessels and Nerves. — The arteries which chiefly supply the eyelids and con- 
1 Also known as the Meibomian glands. 



860 THE SENSE ORGANS AND SKIN OF THE HORSE 

junctiva are branches of the ophthahnic and facial arteries, and the Islood is drained 
away by corresponding veins. The sensory nerves are branches of the ophthahnic 
and maxillary divisions of the trigeminus. The motor nerves to the orbicularis 
oculi, corrugator supercilii, and malaris come from the facial nerve; the levator 
palpebrse superioris is innervated by the oculomotor nerve and the unstriped 
muscle of the lids by the sympathetic. 



THE LACRIMAL APPARATUS 

The lacrimal apparatus (Apparatus lacrimalis) comprises: (1) the lacrimal 
gland, which secretes the clear lacrimal fluid; (2) the excretory ducts of the gland; 
(3) the two lacrimal ducts or canaliculi, lacrimal sac, and naso-lacrimal duct, which 
receive the fluid and convey it to the nostril. 

The lacrimal gland (Glandula lacrimalis) is situated between the supraorbital 
process and the dorso-lateral surface of the eyeball (Fig. 563). It is flattened, oval 
in outline, and measures about two inches (ca. 5 cm.) transversely and an inch or 
more (2.5-3 cm.) in the sagittal direction. Its superficial face is convex and is 
related to the concave lower surface of the .supraorbital process. The deep face is 
concave in adaptation to the eyeball, from which it is separated by the periorbita. 
The excretory ducts (Ductuli excretorii) are very small and are twelve to sixteen 
in number; they open into the lateral part of the conjunctival sac along a line a 
little in front of the fornix conjunctiva superior. In appearance and structure the 
gland resembles the parotid. It receives its blood-supply chiefly from the lacrimal 
artery. The sensory nerve is the lacrimal, and the secretory fibers are derived 
from the sjTnpathetic. 

The puncta lacrimalia are the entrances to the two lacrimal ducts. Each is a 
fine, slit-like opening (about 2 mm. long), situated close behind the free edge of the 
lid and about a third of an inch (ca. 8 mm.) from the medial canthus. The lacri- 
mal ducts (Ductus lacrimales), upper and lower, begin at the puncta and converge 
at the medial commissure to open into the lacrimal sac. The latter (Saccus lacri- 
malis) may ])e regarded as the dilated origin of the naso-lacrimal duct. It occupies 
the funnci-like origin of the bony lacrimal canal, which is termed the fossa of the 
lacrimal sac, and leads to the naso-lacrimal duct (Ductus nasolacrimalis), which 
passes forward and a little downward along the outer wall of the frontal sinus and 
the nasal cavity and opens near the lower commissure of the nostril. Its length 
is about ten to twelve inches (ca. 25-30 cm.). In the first part- of its course it is 
enclosed in the osseous lacrimal canal ; further f onvard it lies in the lacrimal groove 
of the maxilla, covered at first by a plate of cartilage and then by the mucous mem- 
brane of the middle meatus (Fig. 59). The terminal part (Fig. 452) lies in the 
ventral turbinate fold and opens on the skin of the floor of the nostril near the tran- 
sition to mucous membrane. Accessory openings may occur a little further back. 

The first part of the duct, about 6 to 7 mm. in diameter, extends in a gentle curve, convex 
dorsally, from the medial commissure toward a point just above the level of the infraorbital fora- 
men. The second part (isthmus) is narrower (ca. 3-4 mm.); it extends forward and a little 
ventrally about to a transverse plane throuRh the first cheek tooth and lies in the groove above 
the ventral turbinate crest. Beyond this the duct inclines upwai'd and widens very consider- 
ably, crosses the nasal process of the i)rciiiaxilhi obUquelv, and contracts at its termination. The 
mucous membrane may present valvular folds, the most distinct of which is situated at the 
origin. 

THE PERIORBITA 

The periorbita' is a conical fibrous membrane which encloses the eyeball with 

its muscles, vessels, nerves, etc. Its apex is attached around the ojitic and orbital 

foramina, and its base is in part attached to the bony rim of the orbit, in part con- 

'■ Also known as the ocular sheath. 



THE ORBITAL FASCIA AND OCULAR MUSCLES 861 

tinuous with the fibrous layer of the hds. Its medial part, which is in contact with 
the orbital wall, is thin; incorporated with it beneath the root of the supraorbital 
process is the bar of cartilage around which the superior oblique muscle is reflected. 
The lateral part is thicker, and is strengthened by an elastic band which is attached 
to the pterygoid crest and furnishes origin to the thin, unstriped orbital muscle. A 
quantity of fat (Corpus adiposum extraorbitale) lies about the periorbita, and within 
it is the intraorbital adipose tissue (Corpus adiposum intraorbitale) which fills the 
interstices between the eyeball, muscles, etc. 



THE ORBITAL FASCLE AND OCULAR MUSCLES (Figs. 563, 564, 692) 

The straight muscles of the eyeball and the oblique muscles in parti are enclosed 
in fibrous sheaths (Fasciae musculares), formed by superficial and deep layers of 
fascia, which are united by intermuscular septa in the interstices between the 
muscles. The superficial fascia is thin; it Ijlends in front with the fibrous layer of 
the eyelids and is attached behind around the optic foramen. The deep fascia 
consists anteriorly of two layers, one of which is continuous with the fibrous tissue 
of the lids, while the other is attached at the corneo-scleral junction. 

The posterior part of the eyeball is covered by the fascia buibi, so that between 
them a lymph space (Spatium interfasciale) is enclosed which communicates with 
the subdural space along the course of the optic nerve. 

The levator palpebrae superioris muscle' is a thin band about half an inch in 
width which lies above the rectus dorsaUs. It is narrow at its origin above and 
behind the ethmoidal foramen and ends by an expanded tendon in the upper lid. 
Its action is to raise the upper lid. 

The muscles of the eyeball (Mm. oculi) are seven in number — four straight, 
two oblique, and a retractor. 

The straight muscles (Mm. recti) are designated according to their positions as 
rectus dorsalis s. superior, rectus ventralis s. inferior, rectus medialis, and rectus 
lateralis. They are all band-like, arise close together around the optic foramen, 
and diverge as they pass forward to the eyeball. On reaching the latter they end 
in thin tendons which are inserted into the sclera in front of the equator of the eye- 
ball. 

The retractor oculi surrounds the optic nerve, and is incompletely divided into 
four parts which alternate with the recti. They arise around the optic nerve and 
are inserted into the sclera behind the recti. 

The obliquus dorsalis s. superior is the longest and narrowest of the ocular mus- 
cles. It arises near the ethmoidal foramen and passes forward medial to the rectus 
medialis. Under the root of the supraorbital process it is reflected almost at a 
right angle around a cartilaginous pulley (trochlea), which is attached to the 
anterior part of the inner wall of the orbit, a bursa being interposed here. The 
muscle is then directed outward and somewhat forward, and ends in a thin tendon 
which passes between the rectus dorsalis and the eyeball, and is inserted into the 
sclera between the dorsal and lateral recti, al^out half an inch behind the margin 
of the cornea. 

The obliquus ventralis s. inferior is wide and much shorter than the recti. 
It arises from the medial wall of the orbit in the small depression (Fossa muscularis) 
behind the lacrimal fossa. It curves arountl the rectus ventralis and is inserted 
into the sclera near and partly lieneath the rectus lateralis. 

Actions. — The dorsal and ventral recti rotate the eyeball about a transverse 
axis, moving the vertex of the cornea upward and downward respectively.^ Simi- 

' Thi.s belongs to the upper eyelid, but is mentioned here on account of its position and the 
fact that in dissection it must be dealt with before the niu.<^cles of tlie eyeball. 

- These terms are used with reference to the a.xis of the eyeball, not that of the head. 



862 



THE SENSE ORGANS AND SKIN OF THE HORSE 



larly the medial and lateral recti rotate the eyeball about a vertical axis, turning 
the vertex of the cornea inward and outward respectively. The oblique muscles 
rotate the eyel^all about a longitudinal axis; the dorsal oblique raises the lateral 
end of the pupil, while the ventral oblique lowers it. The retractor as a whole 
draws the eyeball backward, and its parts may separately reinforce the correspond- 
ing, recti. Also the four recti acting together will retract the eyeball. 

The actual movements of the eyeball are by no means so simple as might be inferred from 
the foregoing general statements. Practically all movements are produced by the coordinated 
actions of several muscles, involving combinations which are quite complex and difficult to analyze 
accm'ately. Further compUcation is caused by the fact that the recti are not inserted at equal 




;}T-?;r<Jji!i'*,y" ' 



Fig. fi92. — Vertical Axial Seption of Orbit of Horse. 
a, Eyelids; 6, fascia buibi; r, c'. retractor oculi; d, rectus ventralis; e, obliqluus ventralis (in cross-section); /, 
rectus dorsalis; g, levator palpebrae superioris; h, obliquus dorsalis (in cross-section); i, lacrimal gland; k, k\ peri- 
orbita; /, superficial fascia; m, deep fascia; n, skin; o, retrobulbar fat; p, exlraorbital fat; q, temporalis muscle; r, 
supraorbital process; s, cranial wall; I, cornea: 2, sclera; 3, chorioidea; 4i ciliary muscle; 5, iris; G, granula iridis; 
7, retina; 7', optic papilla; 5, optic nerve; S, crystalline lens: /(?, capsule of lens; i J, ciliary zone; i:^, posterior cham- 
ber; i5, anterior chamber: /.{. conjunctiva buIbi; i5, vitreous body, (.\fter Ellenberger, in Leisering's .\tlas.) 



distances from the equator and the axes of rotation of the oblique muscles do not correspond to 
the longitudinal axis of the eyeball. 

Nerve-supply. — The oculomotor nerve supplies the foregoing muscles, with 
the exception of the rectus lateralis and oliliquus dorsalis, which are innervated by 
the abducens and trochlearis respectively. 



THE EYEBALL 

The eyeball (Bulbus oculi) is situated in the anterior part of the orlsital cavity. 
It is protect eil in front by the eyelids and conjunctiva, and in its middle by the 
complete orbital ring, and is related behind to the fascia bulbi, fat, and ocular 
muscles. 

It has the form approximately of an oblate spheroid, but is composed of the 
segments of two spheres of different sizes. The anterior transparent segment, 
which is formed by the cornea, has a radius of curvature of about 17 mm., and the 



THE FIBROUS TUNIC 



863 



posterior opaque, scleral segment one of about 25 mm. The anterior segment 
therefore projects more strongly, and the junction of the two segments is marked 
externall.y by a broad, shallow groove, the sulcus sclerae. The central points of 
the anterior and jjosterior curvatures of the eyeball are termed respectively the 
anterior and posterior poles (Polus anterior, posterior), and the line connecting the 
poles is the external optic axis (Axis oculi externa).' The angle of divergence of the 
optic axes is about 137 degrees. The equator (^Equator) is an imaginary line drawn 
around the eyeball midway between its poles, and meridians (Meridiani) are lines 
drawn around it through the poles. 

The average transverse diameter of the eyeball is about 5 cm., the vertical about 4. .5 cm., 
and the axial about 4.2.5 cm. The distance from the anterior pole to the point of entrance of the 
optic nerve is about 3 cm. 

The eyeball consists of three concentric tunics or coats, within which three 
refractive media are enclosed. 

The Fibrous Tunic 
The fibrous tunic (Tunica fibrosa oculi) is the external coat and is composed 
of a posterior opaque part, the sclera, and a transparent anterior part, the cornea. 
1. The sclera- is a dense fibrous 

Li^ns seen through cornea 
Corneoscleral ', 



junction 




" - Cornea 



membrane which forms about four- 
fifths of the fibrous tunic. Thickest 
in the vicinity of the posterior pole 
(ca. 2 mm.), it thins at the equator 
(ca. 0.4 mm.), and increases in thick- 
ness toward the junction witli the 
cornea (ca. 1.3 mm.). It is in gen- 
eral white, but may have a bluish 
tinge in its thinnest parts. Its ex- 
ternal surface furnishes insertion to 
the ocular muscles and is covered by 
the conjunctiva sclerse in its anterior 
part. The episcleral tissue, which is 
richly supplied with vessels and 
nerves, attaches the conjunctiva 
to the sclera; it is abundant and 
loosely meshed except at the junc- 
tion with the cornea. The inner 
surface is attached to the chorioid 
coat by a layer of delicate, pig- 
mented connective tissue, the 
lamina fusca. The anterior bor- 
der, which is oval, the long axis 

being transverse, is continuous with the cornea. The transition from the opaque 
scleral tissue to the transparent corneal substance occurs in such manner that the 
sclera appears to form a groove (Rima cornealis), into which the cornea fits some- 
what as a watch-glass in the case. Near the corneo-scleral junction there is a 
circular venous plexus, the plexus s. sinus venosus sclerae.^ The optic nerve 
passes through the posterior part of the sclera a little below and lateral to the 
posterior pole. The opening for the nerve is crossed by interlacing fibrous strands, 
forming the lamina cribrosa sclerae. The sclera consists of interlacing bundles of 
white fibrous tissue, associated with which there are a few elastic fibers. The 

' The term internal optic axis (Axis oculi externa) is appUed to a coincident line from the 
posterior surface of the cornea to the anterior surface of the retina. 

' Also termed the sclerotic coat, and popularly known as the "white of the eye." 
^ Formerly termed the canal of Schlemm. 



Fia. 693. — Left Eyeball of Horse, in situ, After Removal 
OF Upper and Lower Lids. 
9, Zygomatic arch; 1^, supraorbital process; 10, orbital 
fat; 37, facial crest. (.\fter EIlenberger-Bauin, .\nat. fiir 
KUnstler.) 



864 



THE SENSE ORGAN'S AND SKIN OF THE HORSE 



bundles are arranged chiefly in meridional and equatorial layers. The verj' limited 
blood-supply is derived from the ciliary arteries, and the veins open into the venae 
vorticosse and ciliary veins. The lymphatics are represented by intercommunicat- 
ing cell spaces. The nerves are derived from the ciliary nerves. 

2. The cornea forms the anterior fifth of the fibrous tunic. It is transparent, 
colorless, and non-vascular, ^'iewed from in front it is oval in outline, the long 
axis being transverse and the broad end medial; it appears more xiearly circular 
when viewed from behind. Its anterior surface (Fades anterior) is convex and is 
more strongly curved than the sclera: its central part is termed the vertex comeae. 
The posterior surface ( Facies posterior) is concave ; it forms the anterior boundary' 
of the anterior chaml^er, and is in contact with the aqueous humor. The margin 
(Limbus cornese) joins the sclera; the latter overlaps the cornea more in front than 
behind, and more above and below than at the sides, thus explaining the apparent 



Sclera 



Optic nerve - 

Optic papilla 
Retrobulbar fat 



Rectus oculi inferior 




Reflection of conjunctiva 



Granula iridis 



Anterior chamber 



Ciliary processes 



Fig. 694. — Vertical Sectton op Etebai.i, op Horse. ABorrr 3. 
The contour of the co'Stalline lens is dotted. 



difference in outline of the two surfaces. The cornea is thinnest at the vertex. 
The cornea consists, from before backward, of the following layers: (1) The epi- 
thelium comeae is continuous with that of the conjunctiva sclerae, and is of the 
stratified squamous type. (2) The lamina limitans anterior is merely a condensa- 
tion of the next layer. (3) The substantia propria forms the bulk of the cornea 
and is composed of interlacing bundles of connective tissue, arranged in part in 
lamellae disposed parallel with the surface. In the amorphous cement substance 
between the lamellae are flattened connective-tissue cells, the corneal corpuscles. 
These have branching processes which unite with those of other cells, thus form- 
ing a protoplasmic network.' (4) The lamina elastica posterior- is a thin and 

'According to Piersol, the system of spaces and canaliculi in the substantia propria is com- 
pletely filled by the ceUs and their processes, upon which the nutrition of the cornea largely de- 
pends. The lamina elastica anterior (Bowman's membrane), formerly described as a distinct 
layer between the corneal epithehum and the substantia propria, does not exist as such, but there 
is'a condensation of the superficial part of the latter, which Rollett termed the anterior limiting 
layer; it is not elastic. 

2 Also known as the membrane of Descemet or Demoiu's 



THE VASCULAR TUNIC 865 

practically homogeneous membrane which is less intimately attached to the sub- 
stantia propria than the anterior lamina. It is clear, glistening, and elastic. At 
the periphery the lamina divides into three sets of fibers. The anterior fibers join 
the sclera, the middle give attachment to the ciliary muscle, while the posterior 
pass into the iris and form the ligamentum pectinatum iridis. (5) The endothelium 
of the anterior chamber (Endothelium camerse anterioris) consists of a layer of 
flattened polygonal cells, and is reflected on to the anterior surface of the iris. The 
cornea is non-vascular except at its periphery, where the terminal twigs of the vessels 
of the sclera and conjunctiva form loops. The nerves are derived from the ciliary 
nerves. They form a plexus around the periphery (Plexus amiularis), from which 
fibers pass into the substantia propria, become non-medullated, and form the funda- 
mental or stroma plexus. From this perforating branches go through the anterior 
limiting layer and form a subepithelial plexus, from which filaments pass between 
the epithelial cells. Other branches from the plexuses in the substantia propria 
end as fibrils which are in close relation with the corneal corpuscles. 

The Vascular Tunic 

The vascular tunic (Tunica vasculosa oculi) lies internal to the fibrous coat; 
it comprises three parts — the chorioid, the ciliary body, and the iris. 

1. The chorioid (Chorioidea) is a thin membrane which lies between the sclera 
and retina. It is in general rather loosely attached to 
the sclera by the lamina fusca, but is intimately adherent 
at the point of entrance of the optic nerve and less closely 
in places where the ciliary vessels and nerves pass through. 
The inner surface is in contact with the layer of pigmented 
cells of the retina, which adhere so closely to the chorioid 
that they were formerly regarded as a part of the latter. 
The general color of the chorioid is dark bro^\^l, but an 
extensive semilunar area a little above the level of the 
optic papilla has a remarkable metallic luster, and is 
termed the tapetum of the chorioid (Tapetum chorioidese) . 
The appearance here varies in different individuals, but j-iq 695.— Tapetom of Horse. 
the prevailing colors in most cases are iridescent blue a, Optic papilla; 6, lower bor- 
and green in various nuances shading into yellow. Pos- d«'' °f tapetum. (After EUen- 
teriorly the chorioid is perforated by the optic nerve, ^"^"- '" l^'^^""^'^ ^tias.) 
and anteriorly it is continuous with the ciliary body. 

The chorioid consists of four layers, which from without inward are as follows: 
(1) The lamina suprachorioidea consists of interlacing fine lamellse of fibrous tissue, 
each containing a network of elastic tissue. Among these are large, branched, pig- 
mented, connective-tissue cells. The spaces between the lamellae are lined with 
endothelium, and form a system of lymph-clefts which together form the pericho- 
rioid space (Spatium perichorioideale). (2) The lamina vasculosa is the outer part 
of the proper tissue of the chorioid. It contains the larger blood-vessels, which 
are supported by areolar tissue. (3) The lamina choriocapillaris consists of an 
extremely rich network of capillaries embedded in an almost homogeneous matrix. 
Between it and the lamina vasculosa is a layer of fibro-elastic tissue, the tapetum 
fibrosum, which causes the metallic luster mentioned above. (4) The lamina 
basalis is very thin and transparent. It is composed of an inner homogeneous part 
and an outer elastic part. 

2. The ciliary body (Corpus ciliare), the middle part of the vascular coat, con- 
nects the chorioid with the periphery of the iris. In meridional section it has the 
form of a narrow triangle, the base of which is next to the iris. On its inner side 
are the ciliary processes and on its outer side is the ciliary muscle. It consists of 
three parts — the ciliary ring, ciliary processes, and ciliary muscle. The ciliary 

65 




866 



THE SENSE ORGANS AND SKIN OF THE HORSE 



ring (Orbiculus ciliaris) is the posterior zone, which is distinguished from the cho- 
rioid mainly by its greater thiclcness and the absence of the chorio-capillaris. Its 
inner face presents numerous fine meridional ridges, by the union of which the 
ciliary processes are formed. The ciliary processes (Processus ciliares), more than 
a hundred in numlier, form a circle of ratiial fokls which surround the lens and fur- 
nish attachment to the zonula ciliaris (or suspensory ligament of the lens). They 
are small at their origin on the ciliary ring and become much thicker and higher 
toward their central ends. The width of the circle formed by them is narrower 
at the medial side than elsewhere. Their bases extend forward to the peri- 
phery of the iris, and their central 
ends are close to the margin of 
the lens. They bear numerous 
secondary folds (Plicae ciliares). 
Their inner surface is covered by a 
continuation of the lamina basalis 
of the chorioid, on which there are 
two layers of epithelial cells which 
constitute the pars ciliaris retinse. 
They consist of a rich network of 
tortuous vessels supported in pig- 
mented connective tissue. The cil- 
iary muscle (M. ciliaris) (Figs. 689, 
692, 696) constitutes the outer part 
of the ciliary body, and lies between 
the sclera and the ciliary processes. 
It forms a circular band of unstriped 
muscle, the fibers of which are for 
the most part directed meridionally. 
They arise from the inner surface of 
the sclera and from the ligamen- 
tum pectinatum iridis close to the 
corneo-scleral junction, and run 
backward along the sclera to be 
inserted into the ciliary processes 
and ring. When the muscle con- 
tracts, it pulls the processes and 
ring forward, thus slackening the 
ciliary zone of the lens, and allowing the latter to become more convex. This is 
the mechanism of accommodation for near objects. 

In man the muscle has the form of a prismatic ring which is triangular in meridional section, 
the base being directed toward the periphery of the iris. It consists chiefly of meridional fibers, 
but a ring of circular fibers forms the inner angle of its base. In the horse the muscle is much 
less developed, and has the form of a flat band; it does not contain distinctly circular fibers, but 
the arrangement is rendered more or less plexiform by the existence of oblique and equatorial fibers. 

3. The iris (Figs. 689, 694, 696) is a muscular diaphragm placed in front of the 
lens, and is visible through the cornea. It is pierceil centrally by an elliptical 
opening, the pupil (Pupilla), which varies in size during life and determines the 
amount of light admitted to act on the retina. In strong light the vertical diameter 
of the pupil is v(>ry short, but the opening is almost circular when the pupil is fully 
dilated. The ciliary border (Margo ciliaris) is continuous with the ciliary body 
and is connected with the corneo-scleral junction by strands of connective tissue 
which con-stitute the ligamentum pectinatum iridis. The bundles of the ligament 
interlace and enclose spaces (Spatia anguli iridis) which arc lined with endothelium 
and communicate with the anterior chamber. The pupillary border (]\Iargo 




Fig. 696. — Vascui 



Horse; Front 






The cornea is removed and the sclera is reflected 
1, Sclera; 1', lamina fusca; 2, chorioidea; 2', ciliary veins; 5, 
ciliary muscle; 4' ins; 5, 5', granula iridis; 6, pupil, through 
which the lens is visible. (After Ellenberger. in Leisering's 
Atlas.) 



THE VASCULAR TUNIC 867 

pupillaris) surrounds the pupil. Its upper part bears in its middle several black 
masses of variable size, termed the granula iridis'; similar, but much smaller, 
projections may be seen on the lower margin of the pupil. The anterior surface 
(Facies anterior) is usually dark bro\vn in color; it presents fine folds (Plica> iridis), 
some of which are concentric with the pupil, others radial; they fade out near the 
pupil. 2 The smooth, narrow, central part is termed the annulus iridis minor, while 
the much broader plicated part is the annulus iridis major. The posterior surface 
(Facies posterior) is usually black; the color is caused by a layer of pigmented 
cells which is regarded as part of the retina. It presents numerous fine radial lines 
except at the pupillary margin. Its central part is in contact with the anterior 
surface of the lens, but peripherally the two are separated by a narrow space 
termed the posterior chamber. The iris consists chiefly of the stroma iridis, a 
delicate framework of connective tissue which supports numerous blood-vessels, 
and contains branched pigmented cells. The muscular tissue is unstriped and 
consists of a sphincter and a dilator of the pupil. The sphincter pupillae lies in 
the posterior part around the pupil, with which the fibers are largel.y concentric. 
The dilatator pupillae consists of fibers which radiate from the sphincter to the 
ciliary border. The anterior surface of the iris is covered by a continuation of the 
endothelium of the cornea. Beneath this is a condensation of the stroma, in which 
the cells are close together and are full of pigmented granules.' There appear to 
be minute clefts here by which the lymph-spaces of the stroma communicate with 
the anterior chamber. 

The arteries of the vascular tunic come from the ciliary branches of the oph- 
thalmic artery. The arteries of the chorioidea are derived chiefly from the short 
posterior ciliary arteries. These (four to six in number) perforate the sclera around 
the posterior pole, run forward in the lamina vasculosa, and form the rich capillary 
network of the choriocapillaris. The two long ciliary arteries perforate the sclera 
obliquely near the optic nerve; they run forward in the lamina suprachorioidea in 
the horizontal meridian, one on the medial, the other on the lateral side of the 
eyeball. On reaching the ciliary body each divides into two diverging branches; 
the subdivisions of these unite with each other and with twigs of the anterior ciliary 
arteries, thus forming near the periphery of the iris the circulus arteriosus major. 
From this branches go to the ciliary muscle and processes and to the iris. The 
branches in the iris run toward the pupillary margin, and by anastomotic branches 
form an incomplete circulus arteriosus minor. The two anterior ciliary arteries, 
dorsal and ventral, form an episcleral plexus around the corneo-scleral junction, 
and give off branches which perforate the sclera. These supply twigs to the ciliary 
muscle and recurrent branches to the chorioid, and assist in forming the circulus 
arteriosus major. The blood is carried away from the vascular tunic chiefly by four 
or five venous trunks, the venae vorticosae, which are formed by the convergence in 
whorls of numerous veins from the chorioid, the ciliary body, and the iris. The 
venae vorticosae perforate the sclera about at the ecjuator and join the veins of the 
ocular muscles. 

The nerves come from the long and short ciliary nerves. They form a plexus 
in the lamina suprachorioidea, which contains ganglion cells, and sends numerous 
non-medullated fibers chiefly to the blood-vessels of the chorioid. At the ciliary 
muscle a second plexus (P. gangliosus ciliaris) is formed, which supplies the muscle 
and sends fibers to the iris. The sphincter pupillae is supplied by fibers derived 
from the oculomotor nerve, while the dilatator pupillae is innervated by the sym- 
pathetic. 



• Also known as corpora nigra. 
' Some of these folds are permar 
of the iris. 
^ In albinos the pigment is absent here, as elsewhere, and the iris is pink in color. 



' Some of these folds are permanent, while others are temporary, i. e., produced by contrac- 
tion of the iris. 



»bS THE SENSE ORGANS AND SKIN OF THE HORSE 

THE RETINA 

The retina or nervous tunic of the eyeball is a delicate membrane which extends 
from the entrance of the optic nerve to the margin of the pupil. It consists of 
three parts. The large posterior part, which alone contains the nervous elements, 
including the special neuro-epithelium and the optic nerve-fibers, is termed the 
pars optica retinae. It extends forward to the ciliary body, where it terminates at 
an almost regular circular line called the era ciliaris retinae.' Here the retina 
rapidly loses its nervous elements, becomes much thinner, and is continued over the 
ciliary body and the jjosterior surface of the iris Ity two layers of epithelial cells as 
the pars ciliaris retinae ; the inner stratum is non-pigmented, while the outer layer 
is a direct continuation of the stratum pigmenti of the pars optica. The pars 
iridica retinae is a layer of pigmented cells which covers the posterior surface of the 
iris. In the dead subject the pars optica is an opaque, gray, soft membrane which 





e: 5. 

Fig. 697. — I.nneh Surface of Anterior Part of Fig. 698. — Fundus Oculi, Seen on Equatorial Sec- 
Eyeball OF Horse (Equatorial Section). tion of Eyeball of Horse. 
i, Sclera; 2, chorioidea; S, retina (drawn away I, Sclera; 2, chorioidea; 3, retina (loosened); 
from chorioidea); 4, ciliary processes; 5, crystalline 4, tapetum; .5, optic papilla: 6, optic nerve. (After 
lens, tiirough which the pupil (G) is seen. (After EUenberger, in Leisering's Atlas.) 
Ellenberger, in Leisering's Atlas.) 

can be stripped off the chorioid, leaving most of its outer pigmented layer on the 
latter. During life it is transparent, except as to its pigmented epithelium, and the 
reddish appearance of the fundus as viewed by the ophthalmoscope is caused by 
the blood in the network of the choriocapillaris. The entrance of the optic nerve 
forms a sharply defined, oval, light area, the optic papilla (Papilla nervi optici), 
situated about 15 mm. ventral to the horizontal meritlian and 3 to 4 mm. lateral 
to the vertical meridian. The central part of the papilla is slightly depressed 
(Excavatio papillae n. optici). 

The transverse diameter of the papilla is about 6 to 7 mm., and the vertical about 4 to 5 mm. 
It is commonly situated a little below the margin of the tapetum, but the latter may extend down 
somewhat on either side of the papilla. The lower margin is often indented a little. In inspec- 
tion of the fundus with the ophthalmoscope numerous fine branches of the arteria centralis retinae 
are seen radiating from the periphery of the papilla. 

The optic nerve fibers converge from all parts of the pars optica to the papilla, 
where they collect into bundles which traverse the lamina cribrosa of the chorioidea 
and sclera, and constitute the optic nerve. The area centralis retinae is a round 
spot, 2 to 3 mm. in diameter, situated dorso-lateral to the ojitic jiapilla; it corre- 

1 In man the line is finely serrated and is termed the ora serrata. 



EEFEACTIVE MEDIA OF THE EYEBALL 869 

sponds to the macula lutea of man, which is histologically more highly differen- 
tiated than the rest of the retina and is the area of most acute vision. 

The structure of the retina is very complex. It consists of nervous elements 
which are supported in a peculiar sustentacular tissue, and are covered externally 
by a layer of pigmented epithelium (Stratum pigmenti retinae). The nervous ele- 
ments comprise a highly specialized neuro-epithelium, the rods and cones; ganglion- 
cells, the axones of which form the optic nerve; and intermediate neurones. Ten 
layers may be recognized in sections microscopically.' 

The arteries of the retina are derived from the arteria centralis retinae and 
anastomotic branches from the short ciliary arteries. The arteria centralis enters 
the optic nerve a short distance behind the eyeball and runs in the axis of the nerve. 
It divides two or three millimeters before reaching the papilla, and gives off thirty to 
forty branches which radiate in the posterior part of the retina and divide dichoto- 
mously into end-arteries in the layer of nerve fibers. The veins accompany the 
arteries except in the capillary plexuses; their walls consist merely of a layer of 
endothelial cells, around which are a lymph-channel and sheath.^ 

CHAMBERS OF THE EYE AND AQUEOUS HUMOR 
The anterior chamber of the eye (Camera oculi anterior) is enclosed in front by 
the cornea and liehind by the iris and lens (Figs. 689, 692, 694). It communicates 
through the pupil with the posterior chamber of the eye (Camera oculi posterior) ; 
this is a small annular space, triangular in cross-section, which is bounded in front 
by the iris, behind by the peripheral part of the lens and its ligaments, and externally 
by the ciliary processes. The chambers are filled by the aqueous humor (Humor 
aqueus), a clear fluid which consists of about 98 per cent, of water, with a little 
sodium chlorid and traces of albumin and extractives. It is carrieil off chiefly 
through the spaces in the zonula ciliaris (or suspensory ligament of the lens) into 
the plexus venosus sclerse. 



REFRACTIVE MEDIA OF THE EYEBALL 

The vitreous body (Corpus vitreum) is a semifluid, transparent substance 
situated between the crystalline lens and the retina. In front it presents a deep 
cavity, the fossa hyaloidea, which fits the posterior surface of the lens. It 
consists of a framework of delicate fibrils, the vitreous stroma (Stroma vitreum), 
the meshes of which are filled by the fluid vitreous humor (Humor vitrcus). The 
surface is covered by a condensation of the stroma known as the hyaloid membrane 
(Membrana hyaloidea). 

The crystalline lens (Lens crystallina) is a biconvex, transparent body which 
is situated in front of the vitreous body and in partial contact with the posterior 
surface of the iris. Its periphery, the equator of the lens (.Equator lentis), is 
almost circular and is closely surrounded by the ciliary processes. The anterior 
surface (Facies anterior) is convex; it is bathed by the aqueous humor and is in 
contact with the iris to an extent which varies with the state of the j^upil. The 
posterior surface (Facies posterior) is much more strongly curved than the anterior. 
It rests in the fossa of the vitreous body (Fossa hyaloidea). The central points of 
the surfaces are the anterior and posterior poles (Polus anterior et posterior lentis), 
and the line which connects them is the axis of the lens (Axis lentis). 

The transverse diameter of the lens is about 2 cm., the vertical diameter is slightly smaller, 
and the axis measures about 13 mm. The radius of curvature of the anterior surface is 13.5 mm., 

' For the minute structure of the retina reference must be made to histological works. 
^ Martin states that in the horse a capillary plexus does not exist, but that the arteries com- 
municate with the veins by closely wound loops. 



870 THE SENSE ORGANS AND SKIN OF THE HORSE 

and of the posterior surface, 9.5 to 10 mm. But the curvatures of its surfaces — especially that of 
the anterior — vary during Ufe according as the eye is accommodated for near or far vision. 

The zonula ciliaris or suspensory ligament of the lens (Fig. 689) consists of 
delicate fibers (Fibr£e zonulares) which pass in a meridional direction from the 
ciliary processes to the capsule of the equator of the lens. Many fibers cross each 
other, and the spaces between the fibers (Spatia zonularia) are filled with aqueous 
humor; they communicate with each other and with the posterior chamber. 

The substance of the lens (Substantia lentis) is enclosed by a structureless, 
highly elastic memljrane, the capsule of the lens (Capsula lentis), and consists of a 
softer cortical substance (Substantia corticalis), and a dense central part, the 
nucleus of the lens (Nucleus lentis) . The capsule is thickest on the anterior surface, 
and here it is lined by a layer of fiat polygonal cells, the epithelium of the lens 
(Epithelium lentis). The lens substance, when hardened, is seen to consist of con- 
centric laminae arranged somewhat like the layers of an onion, and united by an 
amorphous cement substance. The laminae consists of lens fibers (Fibrse lentis), 
hexagonal in section, and of very different lengths. Faint lines radiate from the 
poles and indicate the edges of layers of cement substance which unite the groups 
of lens fibers. These lines, the radii lentis, are three in number in the foetus and 
new-born, and form with each other angles of 120 degrees. On the anterior surface 
one is directed upward from the pole and the other two diverge downward ; on the 
posterior surface one is directed downward and the others diverge upward. The 
developed lens has neither vessels nor nerves. 

In the foetus the lens is nearly globular, and is soft and pink in color. During part of foetal 
life it is surrounded by a vascular network, the tunica vasculosa lentis. This is derived chiefly 
from a temporary vessel, the hyaloid artery, which is a continuation forward of the arteria cen- 
tralis retinae through the hyaloid canal that traverses the vitreous body. In old age the lens tends 
to lose its elasticity and transparency; it also becomes flatter and the nucleus especially grows 
denser. 



The Ear 

The ear or organ of hearing (Organon auditus) consists of three natural divi- 
sions — external, middle, and internal. 



THE EXTERNAL EAR 

The external ear (Auris externa) comprises — (1) the auricula, a funnel-like 
organ which collects the sound waves, together with its muscles; and (2) the 
external acoustic meatus, which conveys these waves to the tympanic membrane, 
the partition which separates the canal from the cavity of the middle ear. 

The auricula or pinna is attached by its base around the external acoustic 
process in such a manner as to be freely movable. In the following description it 
will be assumed that the opening is directed outward and that the long axis is 
practically vertical. It has two surfaces, two borders, a base, and an apex. The 
convex surface or dorsum (Dorsum auriculse) faces medially and is widest in its 
middle part; its lower part is almost circular in curvature, while above it narrows 
and flattens. The concave surface (Scapha) is the reverse of the dorsum; it 
presents several ridges which subside toward the apex. The anterior border is 
sinuous; it is largely convex, but becomes concave near the apex. It divides below 
into two diverging parts (Crura helicis). The posterior border is convex. The 
apex is flattened, pointed, and curved a little forward. The base is strongly convex. 
It is attached to the external acoustic process of the petrous temporal bone, and 
around this there is a quantity of fat. The parotid gland overlaps it below and 
laterally. The structure of the external ear comprises a framework of cartilages 



THE EXTERNAL EAR 



871 



(which are chiefly elastic), the integument, and a compHcated arrangement of 
muscles. 

The concha! or auricular cartilage (Cartilago auriculae) determines the shape 
of the ear; its form can b(> made out in a general way without dissection, except 
below, where it is concealed by the nuiscles and the parotid gland. The l)asal part 
is coiled so as to form a tube, which encloses the cavity of the concha (Cavum con- 
chse). This part is funnel-shaped and curves outward and a little backward. Its 
medial siu'face is strongly convex, forming a prominence termed the eminentia 
conchae. The lowest part of the medial margin bears a narrow, pointed prolongation, 
the styloid process. This process is about an inch long and projects downward 
over the annular cartilage; the guttural pouch is attached to its free end. Behind 
its base there is a foramen through which the auricular branch of the vagus passes. 

The basal part of the posterior border is cut into by a notch, which separates two irregular 
quadrilateral plates. The upper plate (Tragus) is overlapped by the anterior border, and is sep- 
arated from the adjacent part of the posterior border (Antitragus) by a notch (Incisura inter- 
tragica). The lower plate is curved to form a half ring and partly overlaps the anterior border and 
the annular cartilage. Behind the notch there is a foramen, which transmits the internal auricular 
artery and internal aui-icular branch of the facial nerve. 

The annular cartilage (Cartilago annularis) is a quadrilateral plate, curved to 
form about three-fourths of a ring; its 
ends are a little less than half an inch (ca. 
1 cm.) apart medially and are united by 
elastic tissue. It embraces the external 
acoustic process and forms with the lower 
part of the conchal cartilage the carti- 
laginous part of the external acoustic 
meatus. 

The scutiform cartilage (Cartilago 
scutiformis s. Scutulum) is an irregular 
quadrilateral plate which lies on the tem- 
poral muscle in front of the base of the 
conchal cartilage. Its superficial face is 
slightly convex from side to side and 
its deep face is correspondingly concave. 
The anterior end is thin and rounded ; the 
posterior part or base is wider and thicker, 
and its medial angle is prolonged by a 
pointed process half an inch or more in 
length. The cartilage moves very freely 
over the underlying parts. 

The external acoustic meatus leads 
from the cavum conchte to the tympanic 
membrane. It does not continue the 
general direction of the cavity of the 
concha, but extends medially, downward, 
and slightly forward. It consists of a cartilaginous part (Meatus acusticus ex- 
ternus cartilagineus) which is formed by the lower part of the conchal cartilage 
and the annular cartilage, and an osseous part formed by the external acoustic 
process of the temporal bone. These are united by elastic membranes to form a 
complete tube. Its caliber diminishes medially, so that the lumen of the inner end 
is about half of that of the outer end. 

The skin on the convex surface of the concha presents no special features; it 
is attached to the cartilage by a considerable amount of subcutaneous tissue except 
at the apex. The integument which lines the concave surface is intimately ad- 




FiG. 699. — Conchal and Annular Cartilages of 
Ear of Horse, External View. 
/, Base of concha; 2, posterior border, S, anterior 
border of conclia; 4> intertragic notch; 5, eminentia 
conchge; 6, styloid process: 7, annular cartilage; 9, 
zygomatic arch. (After Ellenberger-Baum, Anat. fiir 
Kunstler.) 



872 THE SENSE ORGANS AND SKIN OF THE HORSE 

herent to the cartilage and is relatively dark in color. There are three or four 
cutaneous ridges which run about parallel with the borders of the conchal cartilage, 
but do not extend to the apex or the cavum conchee. The upper and marginal 
parts and the ridges are covered with long hairs, but the skin between the ridges 
and below is thin, covered sparsely with very fine hairs, and supplied with numerous 
sebaceous glands. In the external acoustic meatus the skin becomes thinner; in 
the cartilaginous part it is supplied with numerous large, coiled, cerviminous glands 
(Glandula> ceruminosae) , and is sparsely covered with very fine hairs; in the osseous 
part the glands are small and few or absent and there are no hairs. 



THE AURICULAR MUSCLES 

The auricular muscles may be subdivided into two sets, viz., (o) extrinsic 
muscles, which arise on the head and adjacent part of the neck, and move the ex- 
ternal ear as a whole, and (6) intrinsic muscles, which are confined to the auricula. 
In this connection the scutiform cartilage may be regardetl as a sesamoid cartilage 
intercalated in the course of some of the muscles. 

The extrinsic muscles are as follows: 

1. The scutularis is a thin muscular sheet situated subcutaneously over the 
temporalis muscle. Its fillers arise from the zygomatic arch and the frontal and 
parietal crests, and converge to the scutiform cartilage. It consists of three parts: 

(a) The fronto-scutularis comprises temporal and frontal parts, which arise 
from the zygomatic arch and the frontal crest, anil are inserted into the lateral and 
anterior borders of the scutiform cartilage respectively. 

{b) The interscutularis arises from the parietal crest, over which it is in part 
continuous with the muscle of the opposite side. Its fibers converge to the medial 
border of the scutiform cartilage. 

(c) The cervico-scutularis is not well defined from the preceding muscle. It 
arises from the nuchal crest and is inserted into the medial border of the scutiform 
cartilage. 

2. The anterior auricular muscles (Mm. auriculares orales) are four in number : 

(a) The zygomatico-auricularis arises from the zygomatic arch and the parotid 
fascia, and is inserted into the outer face of the base of the conchal cartilage partly 
under, partly al)ove, the insertion of the parotido-auricularis. 

(b) The scutulo-auricularis superficialis inferior arises on the lateral part of 
the superficial face of the scutiform cartilage and ends on the base of the conchal 
cartilage with the preceding muscle. 

(c) The scutulo-auricularis superficialis medius arises from the posterior part 
of the deep surface of the scutiform cartilage and is inserted into the dorsum of the 
conchal cartilage, close to the lower part of its anterior border, antl above and behind 
the preceding muscle. It receives a slip from the cervico-scutularis. 

(d) The scutulo-auricularis superficialis superior is a thin slip which is de- 
tached from the interscutularis over the medial border of the scutiform cartilage. 
It ends on the anterior aspect of the lower part of the dorsum of the conchal car- 
tilage. 

3. The dorsal auricular muscles (Mm. auriculares dorsales) are two in 
number. 

(a) The scutulo-auricularis superficialis accessorius is a narrow band which is 
largely covered by the preceding muscle. It arises from the posterior prolongation 
and the adjacent part of the superficial face of the scutiform cartilage, and is 
inserted into the convex surface of the conchal cartilage medial to the preceding 
muscle, the two crossing each other at an acute angle. 

(6) The parieto-auricularis is flat and triangular; it arises from the parietal 
crest under cover of the cervico-scutularis, runs outward and a little backward, 



THE AURICULAR MUSCLES 



873 



and is inserted by a flat tendon into the lower part of the convex surface of the 
concha under cover of the cervico-auricularis superficialis. 

4. The posterior auricular muscles (Mm. auriculares aborales) are three in 
number: 

(a) The cervico-auricularis superficialis is a thin triangular sheet. It is wide 
at its origin from the nuchal crest and the adjacent part of the ligamentum nuchae, 
and becomes narrower as it passes outward to be inserted into the medial side of 
the convex surface of the concha. 

(b) The cervico-auricularis profundus major arises from the ligamentum 
nuchse, partly beneath and partly behind the preceding muscle. It is directed 
outward and is inserted into the postero-lateral aspect of the base of the ear, partly 
under cover of the parotido-auricularis. 

(c) The cervico-auricularis profundus minor arises under the preceding 




Fig. 700. — External Eah of Horse and its Muscles; Lateral View. 
The cervico-auricularis superficialis has been removed, i, Posterior border; 3, anterior border of auricula; 8, 
scutiform cartilage; 9, zygomatic arch; n, parotido-auricularis; o, zygomatico-auricularis ; o', acutulo-auricularis 
superficialis inferior; o", scutulo-auricularis superficialis medius et superior; p, interscutularis ; p', fronto-scutularis 
(pars temporalis) ; 9, cervico-auricularis profundus major; s, anterior oblique muscle of head; (, splenius; j/, tendon of 
brachiocephalicus; x, wing of atlas. (After EUenberger-Baum, Anat. fur Kunstler.) 



muscle and passes downwartl and outward to be inserted into the lowest part of 
the convex surface of the concha, partly under cover of the parotid gland. 

5. The parotido-auricularis (s. M. auricularis inferior) is a ribbon-like muscle 
which lies on the parotid gland. It is thin and wde at its origin from the fascia on 
the lower part of the parotid gland, and becomes somewhat narrower and thicker 
as it ascends. It is inserted into the conchal cartilage just below the angle of junc- 
tion of its borders. 

6. The deep aitticular or rotator muscles (M. auricularis profuntli s. rotatores 
auriculce), two in number, are situated under the scutiform cartilage and the base 
of the concha and cross each other. 

(a) The scutulo-auricularis profundus major is the strongest of the auricular 
muscles. It is flat and is aljout an inc'li witle. It arises from the deep face of the 



874 



THE SENSE ORGANS AND SKIN OF THE HORSE 



sc'utiform cartilage and passes backwarfl to end on and below the most prominent 
part of the base of the concha (eminentia conchfe). 

(b) The scutulo-auricularis profundus minor lies between the base of the con- 
cha and the preceding muscle, and is best seen when the latter is cut and reflected. 
It is flat and about an inch in length. It arises from the posterior part of the deep 
face of the scutiform cartilage and from the cervico-scutularis, and passes do^vn- 
ward, backward, and outward to be inserted into the base of the concha under 
cover of the preceding muscle. 

7. The tragicus (or mastoido-auricularis) is a very small muscle which arises 
from the temporal bone just behind the external acoustic process and from the an- 




FiG. 701. — Muscles of Exterk.^l Ear of Horse; Dohs.vl View. 
On the right side parts of the superficial muscles have been removed and the scutiform cartilage turned back to 
display the deeper muscles, a, Frontal part; a', temporal part of fronto-scutularis; b, interscutularis; c, cervico- 
scutularis; d, e, scutulo-auricularis superficiaUs superior and medius; /, zygoma tico-auricularis; g, scutulo-auricularis 
superficialis accessorius; o, cervico-auricularis superficiaUs; q, scutulo-auricularis superficiaUs inferior; t, scutiform 
cartilage; u, parieto-auricularis; v, cervico-auricularis profundus major; u\ cervico-auricularis prof, minor; x, x' ^ 
scutulo-auricularis prof, major et minor; y, temporahs. (EUenberger-Baum, Anat. d. Haustiere.) 



nular cartilage; it passes upward to be inserted into the lower part of the anterior 
border of the conchal cartilage. 

The intrinsic muscles are very small and of little importance. They are as 
follows : 

1. The antitragicus consists of a few bundles which are attached to the conchal 
cartilage behind th(> junction of its two borders, and are partially blended with the 
insertion of the ]3arotido-auricularis. 

2. The helicis is a small muscle attached in a position opposite to the preceding 
on the anterior border of the conchal cartilage; it extends also into the depression 
between the two divisions of the border. It is in part continuous with the insertion 
of the parotido-auricularis. 



THE MIDDLE EAR 875 

3. The verticalis auriculae^ is a thin stratum of muscular and tendinous fibers 
which extends upward on the convex surface of the concha from the eminentia 
conchoe. 

Actions. — The base of the concha is rounded and rests in a pad of fat (Corpus 
adiposum auriculae), so that the movements of the external ear resemble those of 
a ball-and-socket joint. It is noticeable that movements about the longitudinal 
and transverse axes are accompanied by rotation. When the ear is vertical or 
drawn forward ("pricked up"), the opening is usually directed forward ; conversely, 
when the ears are "laid back," the opening faces backward. These movements 
evidently result from the coordinated actions of several muscles which are very 
complex and caimot be discussed in detail here. The scutularis acting as a whole 
fixes the scutiform cartilage, so that the muscles which arise on the latter act 
efficiently on the concha. The anterior auricular muscles in general erect the ear 
and turn the opening forward. The interscutularis concurs in this action, causing 
adduction and a symmetrical position of the ears; it also acts directly on the 
conchal cartilage, since the scutulo-auricularis superficialis superior is in reality a 
conchal insertion of the interscutularis. The scutulo-auricularis superficialis 
accessorius draws the concha forward and turns the opening outward. The parieto- 
auricularis adducts the concha and inclines it forward. The cervico-auricularis 
superficialis is chiefly an adductor of the conchal cartilage, and directs the opening 
outward. The cervico-auricularis profundus major turns the opening outward and, 
acting with the parotido-auricularis, inclines the ear toward the poll. The cervico- 
auricularis profundus minor tends to direct the opening downward and outward. 
The parotido-auricularis draws the ear downward and backward, and acts with the 
cervico-auricularis profundus major in "laying back the ears." The scutulo- 
auricularis profundus major chiefly rotates the concha so that the opening is turned 
backward. The scutulo-auricularis profundus minor assists in rotating the ear 
so that the opening is directed forward. The tragicus shortens the external acoustic 
meatus. The actions of the intrinsic muscles are inappreciable. 

Vessels and Nerves. — The arteries of the external ear are derived from the 
anterior auricular branch of the superficial temporal, the posterior or great auricular 
branch of the internal maxillary, and the anterior branch of the occipital artery. 
The veins go chiefly to the jugular and superficial temporal veins. The nerves 
to the muscles come from the auricular and auriculo-palpebral branches of the 
facial nerve and from the first and second cervical nerves. The sensory nerves are 
supplied by the superficial temporal branch of the mandibular nerve and the 
auricular branch of the vagus. 

THE MIDDLE EAR 

The middle ear (Auris media) comprises the tympanic cavity and its contents, 
the auditive or Eustachian tubes, and two remarkable diverticula of the latter, 
which are termed tlie guttural pouches. 

The tympanic cavity (Cavum tympani) is a space in the tj-mpanic and petrous 
parts of the temporal bone situated between the membrana tympani and the in- 
ternal ear. It is an air-cavity, which is lined by mucous membrane, and communi- 
cates with the pharynx and the guttural pouches by the auditive or Eustachian 
tubes. It contains a chain of auditory ossicles by which the vibrations of the 
membrana tympani are transmitted to the internal ear. 

The cavity consists of: (1) A main part or atrium, which lies immediately to 
the medial side of the membrana tympani; (2) the recessus epitympanicus, situated 
above the level of the membrane and containing the upper part of the malleus 

' Ellenberger and Baum regard tliia as the homologue of the transversus and obliquus 
auriculte of man. 



876 



THE SENSE ORGANS AND SKIN OF THE HORSE 



antl the greater part of tlie incus; (3) a relatively large ventral recess in the bulla 
ossea. 

The lateral, membranous wall (Paries membranacea) is formed largely by the 
thin membrana tympani, which closes the medial end of the external acoustic 
meatus, and thus forms the septum lietween the external and middle parts of the ear. 
The membrane is an oval disc, which slopes ventro-mcdially at an angle of about 
30 degrees with the lower wall of the external acoustic meatus. The circumference 
is attached in a groove (Sulcus tympanicus) in the thin ring of bone (Annulus 
tympanicus) which almost completely surrounds it. The handle of the malleus 
(the outermost of the auditory ossicles) is attached to the inner surface of the 
membrane and draws the central part inward, producing a slight concavity of the 
outer surface. The periphery is thickened, forming the annulus fibrosus. The 
membrana tympani consists of three layers. The external cutaneous layer (Stratum 
cutaneum) is a prolongation of the lining of the external acoustic meatus. The 





Fig. 702. — Right Petrous Temporal Bone of Horse; 
Antero-medial View. 

), External acoustic meatus; 2, annulus tym- 
panicus; 5, laminse radiating from 2; It, membrana 
tympani; 5, malleus; G, incus; 7, stapes; S, fenestra 
cochleae (s. rotundum); 9, facial canal; It, It", semi- 
circular canals; tV , vestibule; t2, cochlea. (After 
Ellenbergcr, in Leisering's Atlas.) 



Fig. 703. — Right Additort Ossicles and Mem- 
brana Tympani, Enlarged a.\d Viewed from 
Inner Side and Below. 

1, Malleus; 2, incus; 2' , 2", short and long proc- 
esses of 2; 3, stapes: -J, tensor tympani; o, ligament 
attaching long process of malleus; 6, stapedius muscle; 
7, fenestra cochleae (s. rotundum). (.\fter EUenberger, 
in Leisering's Atlas.) 



middle fibrous layer or membrana propria includes two chief sets of fibers; the 
external layer (Stratum radiatum) consists of fibers which radiate from the handle 
of the malleus, while the internal layer (Stratum circulare) is composed of circular 
fibers which are best developed peripherally. There are also branched or tlendritic 
fibers in part of the membrane. The internal mucous layer (Stratum mucosum) 
is a part of the general mucous membrane which lines the tympanic cavity. 

The medial, labyrinthine wall of the tympanic cavity (Paries labyrinthica) 
separates it from the internal ear; it presents a numlier of special features. The 
promontory (Promontorimn) is a distinct eminence near the center which corre- 
sponds to the first coil of the cochlea, and is marked by a faint groove for the super- 
ficial petrosal nerve. Above this is the fenestra vestibuli, a reniforni opening which 
is closed by the foot-plate of the stapes and its aimular ligament. The fenestra 
cochleae is situated below and behind the preceding; it is an irregularly oval 
opening and is closed by a thin membrane (Membrana tjanpani secundaria), 
which separates the tympanic cavity from the scala tympani of the cochlea. 

The anterior, tubal wall (Paries tubaria) is narrow, and is pierced by the slit- 



THE MIDDLE EAR 



877 



like tympanic opening of the auditive tube. Above this and incompletely separated 
from it by a thin plate of Ijone is the semicanal for the tensor tympani muscle. 

The tegmental wall or roof (Paries tegmentalis) is crossed in its medial part by 
the facial nerve; here the facial canal is more or less deficient ventrally, and the 
nerve is covered bj' the mucous membrane of the tympanum. 

The posterior, mastoid wall (Paries mastoidea) presents nothing of importance; 
a tympanic antrum and mastoid cells, such as are found behind the tympanic 
cavity proper in man antl many animals, are not present in the horse. 

The tympanic wall or floor (Paries tympanica) is concave and thin. It is 
crossed by delicate curved ridges, which radiate from the greater part of the annulus 
tympanicus. 

The auditory ossicles (Ossicula auditus) form a chain which extends from the 
outer to the inner wall of the cavity. They are named, from without inward, the 
malleus, the incus, the os lenticulare, and the stapes. The first is attached to the 
inner surface of the tympanic membrane and the last is fixed in the fenestra ves- 
tibuli. 

The malleus or hammer, the largest of the ossicles, consists of a head, neck, 
handle, and two processes. The head (Capitulum mallei) is situated in the epi- 





FiG. 704. — Auditory Ossicles and Membrana 
Tympani; Medial View, Enlarged. 
1, Annulus tympanicus; S, membrana tym- 
pani: 3, malleus: 4. incus; o, stapes. (After 
EUenberger, in Leisering's Atlas.) 



Fig. 705. — Right .Auditory Ossicles, Enlarged as In- 
dicated BY Lines Giving thmr Actual Length. 
a. Malleus: 1, Iiead; :S, neck; 5, handle; 4, long proc- 
ess; 5, muscular process, b. Incus: /, body; ^, short 
branch: 3, long branch; c, os lenticulare. c. Stapes: 1, 
head; ^, cms; ;5, base; 4, attachment of stapedius. (After 
EUenberger, in Leisering's Atlas.) 



tympanic recess. It is smooth and convex above and in front, and presents on 
its postero-medial aspect a concave facet for articulation with the body of the 
incus. The neck (CoUum mallei) is the constricted part below the head; its medial 
surface is crossed by the chorda tympani nerve. The handle (Manubrium mallei) 
is directed do%vnward, inward, and a little forwartl from the neck, and is attached 
along its entire length to the membrana tympani. On its medial surface, near the 
upper end, there is a slight projection to which the tendon of the tensor t>nnpani 
muscle is attached. The long process (Processus longus) is a pointed spicule which 
projects forward from the neck towaril the petro-tympanic fissure. The short 
process (Processus brevis) is a slight projection of the lateral side of the neck, and 
is attached to the upper part of the membrana tympani. 

The incus or anvil is situated chiefly in the epitympanic recess. It may be 
said to resemble in miniature a human bicuspid tooth with two divergent roots, and 
consists of a body and two processes. The body (Corpus incudis) articulates with 
the head of the hammer. The long process (Crus longum) projects downward 
from the botly and then curves inwartl; its extremity has attached to it a small 
nodule of bone, the os lenticulare, which articulates with the head of the stapes. 
The short process (Crus breve) projects chiefly backward, and is attached to the 
wall of the recess by a small ligament. 



878 THE SENSE ORGANS AND SKIN OF THE HORSE 

The stapes or stirrup consists of a head, two crura, and a base. The head 
(Capitulum stapedis) is directed outward and articulates with the os lenticulare. 
The crura, anterior and posterior (Crus anterius, posterius), are directed inward 
from the head, and join the ends of the base. The base or foot-plate (Basis stapedis) 
occupies the fenestra vestibuli, to which it is attached. The space between the 
crura and the base is closed by a membrane. 

The articulations and ligaments of the auditory ossicles comprise: (1) A 
diarthrodial joint lietween the head of the malleus and the body of the incus (Articu- 
latio incudomalleolaris), enclosed by a capsule. (2) An enarthrosis between the os 
lenticulare and the head of the stapes (Articulatio incudostapedia), also surrounded 
by a capsule. (3) The base of the stapes is attached to the margin of the fenestra 
vestibuli by a ring of elastic fibers (Lig. annulare baseos stapedis). (4) Small 
ligaments attach the head of the malleus and the short crus of the incus to the roof 
of the epitympanic recess. (5) The axial ligament (of Helmholtz) attaches the 
neck of the malleus to a small projection (Spina tympanica anterior) above and in 
front of the annulus tympanicus. 

The muscles of the auditory ossicles are two in number, viz., the tensor tym- 
pani and the stapedius. The tensor tympani arises from the upper wall of the 
osseous Eustachian tube, and ends in a delicate tendon which bends outward and 
is inserted into the handle of the malleus near its upper end. When it contracts, 
it draws the hantlle of the malleus inward and tenses the membrana tympani; it 
probably also rotates the malleus around its long axis. It is innervated by the 
motor part of the trigeminus through the otic ganglion. The stapedius arises from 
a small prominence (Eminentia pyramidalis) of the posterior wall of the tympanum, 
runs forward on the facial nerve, and is inserted into the neck of the stapes. Its 
action is to draw the head of the stapes backward and rotate the anterior end of the 
base outward, thus tensing the annular ligament. It is innervated by the facial 
nerve. 

The tympanic mucous membrane (Tunica mucosa tympanica) is continuous 
with that of the pliarynx and the guttural pouch through the auditive or Eustachian 
tube. It is thin, closely united with the underlying periosteum, and is reflected 
over the ossicles, ligaments, and muscles, the chorda tympani, and the facial nerve 
in the open part of the facial canal. It contains minute lymph nodules and small 
mucous glands (Glandulse tympanicse). The epithelium is in general columnar 
ciliated, but over the membrana tympani, ossicles, and promontory it is flattened. 

The artery of the tympanum is the stylo-mastoid, a small vessel which arises 
from the posterior auricular l:)ranch of the internal maxillary artery. It enters the 
tympanum through the stylo-mastoid foramen, and forms a circle around the tym- 
panic membrane. The nerves of the mucous membrane come from the tympanic 
plexus. 

The Auditive or Eustachian Tube 
The auditive or Eustachian tube (Tuba auditiva) extends from the tympanic 
cavity to the pharynx; it transmits air to the former and equalizes the pressure 
on the two surfaces of the membrana tympani. It is directed forward, downward, 
and slightly inward, and is four to five inches (ca. 10 to 12 cm.) in length. Its 
posterior extremity lies at the medial side of the root of the muscular process of 
the petrous temporal, and communicates with the anterior part of the tympanic 
cavity by the small, slit-like tympanic opening (Ostium tympanicum tubse auditivte). 
For a distance of about a quarter of an inch (ca. 6-7 mm.) in front of this opening 
it is a complete tube, with a curved lumen which is little more than a capillary space. 
Further forward it has the form of a plate which widens anteriorly and is curved to 
enclose a narrow groove that opens ventrally into an extensive diverticulum termed 
the guttural pouch. The pharyngeal opening (Ostium pharyngeum tubse audit- 



THE GUTTURAL POUCHES 879 

tivse) is situated on the postero-superior part of the lateral wall of the pharynx, just 
below the level of the posterior nares (Fig. 349). It is a slit, about two inches 
(ca. 5 cm.) in length, which slopes downward and backward. It is bounded medi- 
ally by the thin free edge of the tube, from the lower part of which a fold of mucous 
membrane (Plica salpingo-pharyngea) extends in the same direction on the lateral 
wall of the pharynx for a distance of a little more than an inch usually. The outer 
boundary of the opening is the lateral wall of the pharjaix. The basis of the tube 
is a plate of fibro-cartilage (Cartilago tubs auditivse) which is firmly attached 
dorsally to the fibrous tissue which closes the foramen lacerum, the temporal wing 
of the sphenoid, and the pterygoid bone.' On cross-section the cartilage is seen 
to consist — except at its ends — of two laminiB which are continuous with each 
other above (Fig. 348). The medial lamina (Lamina medialis) gradually widens 
toward the pharjmgeal end, where it forms a broad valvular flap; this is convex 
medially, and its thin anterior edge forms the basis of the inner margin of the pharyn- 
geal opening. Behind this the lamina has a thick free edge which projects ventrally 
from the roof of the guttural pouch. The lateral lamina (Lamina lateralis) is 
narrow and thin, and is related laterally to the levator and tensor palati muscles, 
which are in part attached to it; it does not extend to the pharyngeal end of the 
tube. The mucous membrane of the tube is continuous behind with that of the 
tympanum and in front with that of the pharynx. On either side it is reflected to 
form a large diverticulum, the guttural pouch. It is covered with ciliated epi- 
thelium, and contains mucous glands and lymph nodules. 

The pharyngeal opening appears to be closed ordinarily. Vermeulen states that it opens 
during deglutition, and that this action is apparently produced by the part of the palato-pharyn- 
geus muscle wliich is attached to tlie flap-like expanded part of the tube. 

The Guttural Pouches 
The guttural pouches, right and left (Figs. 349, 706), are large mucous sacs, 
each of which is a ventral diverticulum of the Eustachian tube (Diverticulum 
tubae auditivae) ; they are not present in the domesticated animals other than the 
equidse. They are situated between the base of the cranium and the atlas dorsally 
and the pharjmx ventrally. Medially they are in apposition in part, but are to 
some extent separated by the intervening ventral straight muscles of the head. 
The anterior end is a small cul-de-sac which lies below the bodj' of the presphenoid, 
between the Eustachian tube and the median recess of the pharynx. The posterior 
end lies near or below the atlantal attachment of the longus colli. The pouch 
is related dorsally to the base of the cranium, the atlanto-occipital joint capsule, 
and the ventral straight muscles. Ventrally it lies on the pharjux and the origin 
of the oesophagus. Laterally the relations are numerous and complex. They 
comprise the pterygoid, levator palati, tensor palati, stylo-hyoideus, occipito- 
hyoideus, occipito-mandibularis, and digastricus muscles; the parotid and mandib- 
ular salivary glands; the external carotid, internal maxillarj^ and external maxil- 
lary arteries; the internal maxillary and jugular veins; the pharj-ngeal lymph 
glands; the glosso-pharyngeal, hypoglossal, and anterior larjTigeal nerves. The 
vagus, accessory, and sympathetic nerves, the anterior cervical ganglion, the in- 
ternal carotid artery, and the ventral cerebral vein are situated in a fold of the 
dorsal part of the pouch. The pouch is reflected aromid the dorsal border of the 
great cornu of the hyoid bone so as to clothe both surfaces of the dorsal part of the 
latter. It thus forms an outer compartment, which extends backward lateral to 
the great cornu and the occipito-hyoideus muscle; this compartment is related 
laterally to the parotid gland, the articulation of the jaw, the ascending part of the 
internal maxillary artery, the superficial temporal artery, and the facial nerve; dor- 

' There is, strictly speaking, no osseous part of the tube such as occurs in man. In the horse 
the cartilage e3rtends to the tympanic orifice. 



880 



THE SENSE ORGANS AND SKIN OF THE HORSE 



sally it covers the mandil^ular nerve and its chief branches, and is attached to the 
styloid process of the conchal cartilage. 

Each pouch communicates with the pharynx through the pharyngeal orifice 
of the Eustachian tube, and is in direct continuity with the mucous membrane of 
the latter. 

The average capacity of each pouch is about ten fluidounces (ca. 300 c.c.) ; of 
this, the lateral compartment is about one-third. 



/ muscle 




Scutiform cartila^ 
posterior i^rocess 



Conchal cartilage 

Brachioceiihalicus 
tendon 

Nerves IX, X, XI 



'ciilral cerebral vein 
iili'nial carotid artery 
iilliiral pouch 

Occipito-liyoideus 

muscle 

gular vein 



Int. maxillary artery 
Ext. maxillary artery 

Parapharyngeal lymph 

'ands 
Occipito-mandibularis 
muscle 
Sterno-cephalicus tendon 

Mandibular gland 

Thyroid cartilage 

maxillary vein 



Onio-hyoidci + sterno-hyoidei 
Fig. 706. — Cross-section of He.id of Horse. 
The section passes through the base of the external ear and just behind the posterior border of the mandible. /, 
Rectus capitis ventralis minor; 2, rectus capitis ventralis major; S, medial walls of guttural pouches in apposition; 
4, ^, arytenoid cartilage, upper piece being apex; 5, posterior pillar of soft palate ; 6', false vocal cord; 7, lateral ventricle 
of larynx; 5, true vocal cord; .9, vocal muscle; iO, thyro-hyoideus muscle. The cavity in which the number 5 is placed 
is the pharynx, which was left unmarked by an oversight. 



The pouch is a delicate mucous membrane which is in general rather loosely 
attached to the surrounding structures. It is lined with ciliated epithelium and is 
supplied with glands which are chiefly mucous in type. 

It is worthy of note that tlie pharyngeal orifice of the EiLstachian tube is at such a level as 
to provide (in the ordinary position of the head) only an overflow outlet for the escape of fluid 
which may accumulate in the pouch. The exixmded part of the tube forms with the wall of the 
pharynx a sort of vestibule, at tlie posterior part of which is the opening of the guttural pouch. 



THE INTERNAL EAR THE OSSEOUS LABYRINTH 881 

This opening is only about an incli (ca. 2.5 cm.) long. The two pouches are often unequal in size, 
and variations in regard to the distance which they extend backward are not uncommon. In one 
case, for instance, a small aged horse, the right pouch extended along the cesophagus about five 
inches (ca. 12 cm.) beliind the ventral tubercle of the atlas, and the left one a little more than two 
inches (ca. 6 cm.). No pathological changes \v<tc api^arent, and the condition was not recognizable 
externally. Cases of extreme size — so-called t>-mpanites — of the pouches occur, and are apparently 
congenital defects. In a case in a yearling colt, the head of which was 24 inches long, the left 
pouch extended about 12 inches (ca. 30 cm.) behind the tubercle of the atlas, and had a capacity 
of six quarts. The anterior end formed a cul-de-sac about two inches (ca. 5 cm.) long between the 
Eustachian tube and levator palati medially and the lateral pterygoid muscle laterally. 

THE INTERNAL EAR 
The internal ear or labyrinth (Auris interna s. Laljyrinthus) consists of two 
parts, viz.: (1) A complex meml)ranous sac, which supports the auditory cells and 
the peripheral ramifications of the auditory nerve; (2) a series of cavities in the 
petrous temporal lione, which encloses the membranous part. The first is called 
the membranous labyrinth, and contains a fluid, the endolymph. The second is 
the osseous labyrinth. The two are separated by the perilymphatic space, wliich is 
occupied JDy a fluid termed the perilymph. 

The Osseous Labyrinth 
The osseous labyrinth (Labyrinthus osseus) (Fig. 702) is excavated in the 
petrous temporal bone medial to the tympanic cavity. It consists of three divisions : 
(1) a middle part, the vestibule ; (2) an anterior one, the cochlea ; and (3) a pos- 
terior one, the semicircular canals. 

1. The vestibule (Ve.stiVjuluni) is the central part of the osseous labyrinth, 
and communicates in front with the cochlea, behind with the semicircular canals. 
It is a small, irregularly ovoid cavity, which is about 5 to 6 mm. in lengtli. Its 
lateral wall separates it from the tympanic cavity, and in it is the fenestra vestibuli, 
which is occupied by the base of the stapes. The medial wall corresponds to the 
fundus of tlie internal acoustic meatus. It is crossed by an oblique ridge, the 
crista vestibuli, which separates two recesses. The anterior and smaller of these is 
the recessus sphdericus, which lodges the saccule of the membranous labyrinth. 
In its lower part there are about a dozen minute foramina which transmit filaments 
of the vestibular nerve to the saccule. The posterior and larger depression is the 
recessus ellipticus, which lodges the utricle of the membranous labyrinth. The 
crista vestitnili divides below into two divergent branches, which include between 
them the small recessus cochlearis ; this is perforated by small foramina, through 
which nerve-bundles reach the ductus cochlearis. Similar foramina in the recessus 
ellipticus and the crista vestiliuli transmit nerve filaments to the utricle and the 
ampullse of the dorsal and lateral semicircular ducts. The anterior wall is pierced 
by an opening which leads into the scala vestibuli of the cochlea. The posterior part 
of the vestibule presents the four openings of the semicircular canals. The inner 
opening of the aquaeductus vestibuli is a small slit behind the lower part of the 
crista vestibuli. The aquaeductus passes backward in the petrous temporal bone, 
and opens on the medial surface of the latter near the middle of its posterior border; 
it contains the ductus endoh-mphaticus. 

2. The osseous semicircular canals (Canales semicirculares ossei), three in 
number, are situated behind and above the vestibule. They are at right angles to 
each other, and are designated according to their positions as dorsal, posterior, 
and lateral. They communicate with the vestibule Ijy four openings only, since 
the inner end of the dorsal and the upper end of the posterior canal unite to form a 
common canal (Crus commune), and the ampullate ends of the dorsal and lateral 
canals have a common orifice. Each canal forms about two-thirds of a circle, 
one end of which is enlarged and termed the ampulla. The dorsal canal (Canalis 
semicircularis dorsalis) is nearly vertical and is placed obliquely vnth regard to a 

56 



882 THE SENSE ORGANS AND SKIN OF THE HORSE 

sagittal plane, so that its outer limb is further forward then than the inner one. The 
antero-lateral end is the ampulla and opens into the vestibule with that of the lateral 
canal. The opposite non-dilated end joins the adjacent end of the posterior canal 
to form the crus commune, which opens into the dorso-medial part of the vestibule. 
The posterior canal (Canalis semicircularis posterior) is also nearly vertical. Its 
ampulla is ventral, and opens into the vestibule directly, while the non-dilated 
end joins that of the dorsal canal. The lateral canal (Canalis semicircularis lateralis) 
is nearly horizontal. Its ampulla is external and opens into the vestibule with that 
of the dorsal canal. 

3. The cochlea is the anterior part of the bony labyrinth. It has the form of a 
short blunt cone, the base of which (Basis cochleae) corresponds to the anterior 
part of the fundus of the internal acoustic meatus, while the apex or cupola (Cupola) 
is directed outward, forward, and downward. It measures aljout 7 mm. across the 
base and about 4 mm. from base to apex. It consists of a spiral canal (Canalis 
spiralis cochleae) , which forms two and a half turns around a central column termed 
the modiolus. The modiolus diminishes rapidly in diameter from base to apex. 
Its base (Basis modioli) corresponds to the area cochleae of the fundus of the internal 
acoustic meatus, and its apex extends nearly to the cupola. Projecting from the 
modiolus like the thread of a screw is a thin plate of bone, the lamina spiralis ossea. 
This begins between the two fenestrae and ends near the cupola as a hook-like 
process (Hamulus laminae spiralis). The lamina extends about half-way to the 
periphery of the cochlea and partly divides the cavity into two passages; of these, 
the upper one is termed the scala vestibuli, and the lower the scala t3rmpani. The 
membrana basilaris extends from the free margin of the lamina to the lateral wall 
of the cochlea and completes the septum between the two scalae, but they com- 
municate through the opening at the cupola (Helicotrema). The modiolus is 
traversed by an axial canal which transmits the nerves to the apical coil, and by a 
spiral canal (Canalis spiralis modioli), which follows the attached border of the 
lamina spiralis, and contains the spiral ganglion and vein. Close to the beginning 
of the scala tympani is the inner orifice of the aquaeductus cochleae, a small canal 
which opens behind the internal acoustic meatus, and establishes a communication 
between the scala tympani and the subarachnoid space. 

The internal acoustic meatus has been described in part (vide Osteology). 
The fundus of the meatus is divided by a ridge (Crista transversa) into upper and 
lower parts. The anterior part of the upper depression (Area n. facialis) presents 
the internal opening of the facial canal; antl the posterior part (Area vestibularis 
superior) is perforated by foramina for the passage of nerves to the utricle and 
the ampullffi of the dorsal and lateral semicircular ducts. The anterior part of 
the inferior depression (Area cochleae) presents a central foramen and a spiral tract 
of minute foramina (Tractus spiralis foraminosus) for the passage of nerves to the 
cochlea. Behind these is an area of small openings which transmit nerves to the 
saccule (Area vestibularis inferior) , and the foramen singulare for the passage of a 
nerve to the ampulla of the posterior semicircular duct. 

The Membranous Labyrinth 

The membranous labyrinth (Labyrinthus membranaceus) lies within, but 
does not fill, the osseous labyrinth. It is attached to the latter by delicate tra- 
beculse which traverse the perilymphatic space. It conforms more or less closely 
to the bony labyrinth, but consists of four divisions, since the vestibule contains 
two membranous sacs — the utricle and saccule. 

1. The utricle (Utri cuius), the larger of the two sacs, lies in the postero- 
superior part of the vestibule, largely in the recessus ellipticus. It receives the 
openings of the semicircular ducts, and the small ductus utriculo-saccularis leads 
from its lower part to the ductus endolymphaticus. 



THE MEMBRANOUS LABYRINTH 



883 



2. The saccule (Sacculus) is situated in the recessus sphsericus of the vestibule. 
From its lower part the ductus reuniens proceeds to open into the ductus cochlearis, 
a little in front of the blind end of the latter. A second narrow tube, the ductus 
endol3miphaticus, passes from the posterior part of the saccule, and is joined by the 
ductus utriculo-saccularis; it then traverses the aquseductus vestibuli, and ter- 
minates under the dura mater on the posterior part of the medial surface of the 
petrous temporal bone in a dilated blind end, the saccus endolymphaticus. 

3. The semicircular ducts (Ductus semicirculares)' correspond in general to 
the osseous canals already described, but it may be noted that while the ampulliE of 
the ducts nearly fill those of the osseous canals, the other parts of the ducts only 
occupy about one-fourth of the bony cavities. 

4. The cochlear duct (Ductus cochlearis) is a spiral tube situated within the 
cochlea. It begins by a }:)lind end (Caecum vestibulare) in the cochlear recess of 
the vestibule, and ends by a second blind end (Ctecum cupulare) , which is attached 
to the cupola of the cochlea. The vestibular part is connected with the saccule 
by the ductus reuniens. The duct is triangular in cross-section, and it is usual to 
regard it as having three walls. The vestilnilar wall or roof, which separates the 
cochlear duct from the scala vestil^uli, is formed by the very delicate membrana 
vestibularis (of Reissner), which extends obliquely from the lamina spiralis ossea 




Fig. 



707.— Le 



Membranous Labyrinth (En- 
larged). 
1, Cochlea; 2, fenestra vestibuli; 5, fenestra coch- 
lese; 4. ductus endolymphaticus; 5, dorsal, G, lateral, 7, 
ventral, duct. (After EUenberger, in Leisering's At- 
las.) 




Fig. 70S. — Schematic Sectional View of Labyrinth 
(Enlarged). 
?, 5, 5, Dorsal, lateral, and ventral ducts; 4t 
utricle; 5, saccule; 6, cochlea; 7, acoustic nerve. 
(.4fter EUenberger, in Leisering's Atlas.) 



to the outer wall of the cochlea. The tympanic wall or floor intervenes between 
the cochlear duct and the scala tympani; it is formed by the periosteum of the mar- 
ginal part of the lamina spiralis and the membrana basilaris, which stretches be- 
tween the free edge of the lamina and the outer wall of the cochlea. The outer 
wall consists of th(> filjrous lining of the cochlea, which is greatly thickened to form 
the ligamentum spirale cochleae. 

Structure.- — The membranous labyrinth consists in general of an outer thin 
fibrous la>'er, a middle transparent tunic, and an internal epithelium, composed of 
flattened cells. But in certain situations special and remarkable structures occur, 
among which are the following: (1) The maculae acousticae appear as small whitish 
thickenings of the imicr walls of the saccule and utricle. The epithelium here 
consists of two kintls of cells, viz., supporting cells and hair cells. The latter are 
flask-shaped and are surrounded by the fusiform supporting cells. The free end 
of each hair cell bears a stiff, hair-like process composed of a bundle of cilia. Fibers 
of the saccular and utricular branches of the vestibular nerve form arborizations 
about the basal parts of the hair cells. Adherent to the surface of the maculse 

' Ako termed tlie membranous semicircular canals. 

" For the finer structure reference is to be made to the histological literature. 



884 THE SENSE ORGANS AND SKIN OF THE HORSE 

are fine crystals of lime salts, embedded in a mucoitl substance, and termed otoconia. 
(2) The cristae acusticae are linear thickenings of the wall of each ampulla of the 
semicircular ducts. Their structure is similar to that of the maculae. (3) The 
spiral organ of Corti (Organon spirale) is an epithelial elevation which is situated 
upon the inner part of the membrana basilaris, and extends the entire length of the 
ductus cochlearis. It is very complicated in structure, but consists essentially of 
remarkable supporting cells and hair cells. Fibers of the cochlear nerve ramify 
about the Isasal parts of the hair cells. 

Vessels and Nerves. — The artery of the internal ear is the internal auditory 
artery, a very small vessel which usually arises from the posterior cerebellar artery, 
and enters the internal acoustic meatus. The veins go to the ventral petrosal 
sinus. The vestibular nerve is distributed to the utricle, saccule, and semi- 
circular ducts, and mediates equilibration. The cochlear nerve gives a branch 
to the saccule and enters the central canal of the modiolus. Along its course it 
gives off fibers which radiate outward between the two plates of the lamina spiralis 
ossea, and ramifj^ about the hair cells of the organ of Corti. The ganglion spirale 
is situated in the spiral canal of the modiolus near the fixed border of the lamina 
spiralis. The cochlear nerve mediates the sense of hearing. 



The Common Integument 

The common integxmient (Intcgumentuiii commune) is the protective covering 
of the bod}', and is continuous at the natural openings with the mucous membranes 
of the digestive, respiratory, and urogenital tracts. It consists of the skin (Cutis), 
together with certain appendages or modifications thereof, as hair, horn, feathers, etc. 
It contains peripheral ramifications of the sensory nerves, and is thus an important 
sense organ. It is the principal factor in the regulati(jn of the temperature of the 
body, and by means of its glands it plays an important part in secretion and ex- 
cretion. Some of its special hornj' motlifications or appendages are used as organs 
of prehension or as weapons. 

The thickness of the skin varies in the different species, on different parts of 
the body of the same animal, and also with the breed, sex, and age. The color 
also varies greatly, but this is masked in most places by the covering of hair or wool. 
The skin is in general highly elastic and resistant. 

Permanent folds of the skin (Plicae cutis) occur in certain situations, and in 
some places there are cutaneous pouches or diverticula (Sinus cutis) . 

The skin is attached to the underlying parts by the subcutaneous tissue or 
subcutis (Tela subcutanea). This consists of connective tissue containing elastic 
fibers and fat. AVhen the fat forms a layer of considerable thickness, it is termed 
the panniculus adiposus. Over a considerable part of the body the subcutis con- 
tains striped muscle, the m. cutaneus or panniculus carnosus ; in some regions the 
fibers of the muscle are inserted into the skin, and their contraction twitches the 
skin or produces temporary folds.' The amount of subcutaneous tissue varies 
widely; in some places it is abundant, so that the skin can be raised considerably; 
in other situations it is practically absent and the skin is closely adherent to the 
subjacent structures. Subcutaneous bursas often develop over prominent parts 
of the skeleton where there is much pressure or friction, e. g., at the olecranon, 
tuber coxae, tuber calcis. 

Structure. — The skin consists of two distinct strata, viz., a superficial epithelial 
layer, the epidermis, and a deep connective-tissue layer, the corium. The epi- 
dermis is a non-vascular, stratified epithelium of varying thickness. It presents 

' This muscle has been described in the Myology. 



THE COMMON INTEGUMENT 885 

the openings of the cutaneous glands and the hair-follicles, and its deep surface is 
adapted to the corium.^ It is divisible into a superficial, harder, drier part, the 
stratum comeum, and a deeper, softer, moister part, the stratum germinativum. 
The cells of the latter contain pigment, and by their proliferation compensate the 
loss by desquamation of the superficial part of the stratum corneum. In many 
places further subdivision into strata is evident on properly prepared cross-sections. 
The cerium consists essentially of a feltwork of white and elastic fibers. It is well 
supplied with vessels and nerves, and contain the cutaneous glands, the hair-fol- 
licles, and unstriped muscle. The deeper part of the corium, the tunica propria, 
consists of a relatively loose network of coarse bundles of fibers, and in most places 
there is no clear line of demarcation between it and the subcutis. The superficial 
part, the corpus papillare, is of finer texture and is free from fat. Its superficial 
face is thickly beset with blunt conical prominences, the papillae, which are received 
into corresponding depressions of the epidermis. They contain vascular loops and 
nerves, or, in certain situations, special nerve-endings. - 

The glands of the skin (Cllanduhe cutis) are chiefly of two kinds, sudoriferous 
and sebaceous. The sudoriferous or sweat glands (Glandulse sudoriferse) consist 
of a tube, the lower, secretory part of which is coiled in the deep part of the corium 
or in the subcutis to form a round or oval ball (Corpus glandulse sudoriferae). The 
excretory duct (Ductus sudoriferus) passes almost straight up through the corium, 
but pursues a more or less flexuous course through the epidermis, and opens into a 
hair-follicle or by a funnel-shaped pore (Porus sudoriferus) on the surface of the 
skin. The sebaceous glands (GlanduliE sebaceae) are in great part associated with 
the hairs, into the follicles of which they open. Their size varies widely, and is 
in general in inverse ratio to that of the hair. The larger ones are easily seen with 
the naked eye, and appear as small, pale yellow or browmish bodies. In certain 
situations (e. g., the labia, vulvae, anus, prepuce) they are independent of the hairs 
and are well developed. In form they may be branched alveolar, simple alveolar, 
or even tubular in type. They secrete a fatty substance, the sebum cutaneum, 
which serves as a protective against moisture, and may also (by its aromatic con- 
stituents) play an important part in the sexual life of animals. 

The two kinds of glands described above are those which are most widely distributed, but 
many special types occur. Some of these are to be regarded as modified sweat glands, e.g., the 
naso-Iabial glands of the ox, the glands of the snout of the pig, and the glands of the digital 
cushion of the horse. Others, e. g., the tarsal glands of the eyelids, are modified sebaceous. Still 
others are not yet classified satisfactorily. Some of these s|iccial types have been referredto in 
previous chapters, and others will receive attention in the .s)irii:il .Irsniptions which follow. The 
mammary glands are highly modified cutaneous glands, wliicli are intimately associated in func- 
tion with the genital organs, and have been described with the latter. 

Vessels and Nerves. — The arteries of the skin enter from the subcutis, where 
they communicate freely. In the deeper part of the corium they form a plexus, 
and another network is formed under the papillae. Small vessels from the deep 
plexus go to the fat and sweat glands, and the subpapillary plexus sends fine 
branches to the papillae, hair-follicles, and sebaceous glands. The veins form two 
plexuses, one beneath the papillte, and another at the junction of the corium and 
subcutis. The lymph vessels form subpapillary and subcutaneous plexuses. 

The nerves varj- widely in number in different parts of the skin. The terminal 
fibers either end free in the epidermis and in certain parts of the corium, or form 
special microscopic corpuscles of several kinds. 

' To prevent a possible misapprehension, it may be stated that the epidermis primarily 
molds the corium, and that the glands and hair-follicles are invaginations of the epidermis. 

- The papillse are best developed where the epidermis is thick and hairs are small or absent. 
On thickly haired regions they are small or even absent. On certain parts of the body (anus, 
vulva, prepuce, scrotum, eyeUds, etc.) the corium contiiins pigment in its connective-tissue cells. 



THE SENSE ORGANS AND SKIN OF THE HORSE 



THE APPENDAGES OF THE SKIN 

The appendages of the skin are modifications of the epidermis, and comprise 
the hairs, hoofs, claws, horns, etc. 

The hairs (Pih) cover ahnost the entire surface of the body in the domesticated 
mammals, and some parts which appear at first sight to be bare are found on close 
inspection to be provided with sparse and very fine hair. The hairs are constantly 
being shed and replaced, but at certain periods in the horse, for example, they fall 
out in great numbers, constituting the shedding of the coat. It is customary to 
distinguish the ordinary hairs (the coat), which determine the color of the animal, 
from the special varieties found in certain places. Among the latter are the long 




Fig. 709. — Lateral View op Horse to Show Hair-streams and Vortices. (After Ellenberger-Baum, Anat. fur 

Kunstlur.) 



tactile hairs alsout the lips, nostrils, and eyes; the eyelashes or cilia; the tragi of 
the external ear; and the vibrissas of the nostrils. Other special features will be 
noted in the discussion of the skin of the various species. The hairs are directed 
in such a way as to form more or less definite hair-streams (Flumina pilorum), 
and at certain points these converge to form vortices (Vortices pilorum). 

The part of the hair above the surface of the skin is the shaft (Scapus pili), 
while the root (Ratlix pili) is embedded in a depression termed the hair-follicle 
(Folliculus pili). A vascular papilla (Papilla pili) projects up in the fundus of the 
follicle and is capped by the expanded end of the root, the bulb of the hair (Bulbus 
pili). The hair-follicles extend obliquely into the corium to a varying depth; in 
the case of the long tactile hairs they reach to the underlying muscle. Most of the 
follicles have attached to them small unstriped muscles known as the arrectores 
pilortxm; these are attached at an acute angle to the under side of the deep part 



THE SKIN OF THE HORSE — THE HOOF 887 

of the follicle, and their contraction causes erection of the hair and compression of 
the sebaceous glands, one or more of which open into the follicle. 

The hairs are composed of epidermal cells, and consist from without inward of 
three parts. The cuticle is composed of horny, scale-like cells which overlap like 
slates on a roof. The cortex consists of horny fusiform cells which are packed close 
together and contain pigment. The medulla is the central core of softer, cubical 
or polyhedral cells; it contains some pigment and air-spaces. 

The hair-follicles, being invaginations of the skin, are composed of a central 
epidermal part and a peripheral layer which corresponds in structure to the corium. 
The follicles of the tactile hairs have remarkably thick walls which contain blood- 
sinuses between their outer and inner layers; in ungulates the sinuses are crossed 
by trabeculae and assume the character of cavernous or erectile tissue. 

The hoofs, claws, horns, and other horny structures consist of closely packed 
epidermal cells which have undergone cornification. In structure they might be 
compared to hairs matted together by intervening epidermal cells. They cover a 
specialized corium from which the stratum germinativum derives its nutrition. 



THE SKIN OF THE HORSE 

The thickness of the skin of the horse varies from one to five millimeters in 
different regions, and is greatest at the attachment of the mane and on the tail. 

The glands are numerous and are larger than those of the other domesticated 
animals. The sebaceous glands are specially developed on the lips, the prepuce, 
mammary glands, perineum, and labia of the vulva. The sweat glands are yellow 
or bro^vTi in color. They occur in almost all parts of the skin, but are largest and 
most numerous in that of the lateral wing of the nostril, the flank, mammary glands, 
and free part of the penis. 

In addition to the ordinary and tactile hairs certain regions present coarse 
hairs of great length. The mane (Juba) springs from the dorsal border of the neck 
and the adjacent part of the withers; its anterior part, which covers the forehead 
to a variable extent, is termed the foretop (Cirrus capitis). The tail, with the 
exception of its ventral surface, bears very large and long hairs (Cirrus caudse). 
The tuft of long hairs on the flexion surface of the fetlock (Cirrus pedis) gave rise to 
the popular name of this region. 

The development of these special hairs varies widely, and is in general much greater in the 
draft breeds than in others. In Sliire and Clydesdale horses, for instance, the hair on the poste- 
rior aspect of the metacarpus and metatarsus and fetlock is often so long and abundant as to ac- 
count for the term "feather," which is commonly applied to it by horsemen. 

Subcutaneous bursas (Bursae subcutaneae) may be present at various prominent 
points, e. g., the olecranon, the tuber coxse, the tuber calcis, the withers, etc. They 
are not present in the young subject and appear to be the result of traumatism. 

THE HOOF 

The hoof (Ungula) is the horny covering of the distal end of the digit. It is 
convenient to divide it for description into three parts, termed the wall, sole, and 
frog. 

1. The wall (Paries ungulse) is defined as the part of the hoof which is visible 
when the foot is placed on the ground.' It covers the front and sides of the foot, 
and is reflected posteriorly at an acute angle to form the bars. The latter (Pars 
inflexa medialis, lateralis)- appear on the ground surface of the hoof as convergent 

' The term foot is used here in the popular sense, i. e., to designate the hoof and the structures 
enclosed witliin it. 

2 The term "pila ungulae" has been suggested by Schmaltz for the part popularly known as 
the "bar." 



THE SENSE ORGANS AND SKIN OF THE HORSE 



ridges, which subside in front and are fused with the sole ; they are united with each 
other Isy the frog. For topographic purposes the wall may be divided into an an- 
terior part or "toe" (Paries ungulte dorsalis), lateral parts or "quarters" (Paries 
ungulae medialis, lateralis), and the angles or "heels" (Paries ungul* volaris s. 
plantaris). It presents two surfaces and two borders. The external surface is con- 
vex from side to side and slopes obliquely from edge to edge. In front the angle of 
inclination on the ground plane is about 50° for the forelimb, 5.5° for the hind limb; 
on the sides the angle gradually increases and is about 100° at the heels. The curve 
of the wall is wider on the lateral than on the medial side, and the slope of the medial 
quarter is steeper than that of the lateral one.' The surface is smooth and is crossed 
by more or less distinct ridges, which are parallel with the coronary border and 
indicate variations in the activity of the growth of the hoof. It is also marked by 

fine parallel striae, which extend from border to 
border in an almost rectilinear maimer and in- 
dicate the direction of the horn tubes. 

The internal surface is concave from side to 
side, and bears about six hundred thin primary 
laminae, which extend from the coronary groove 
to the basal border of the wall. Each bears a 
hundred or more secondary laminae on its sur- 
faces, so that the arrangement is pennate on 
cross-section. These horny laminse are continued 
on the inner surface of the bars, and dovetail with 
corresponding laminsB of the the corium. The cor- 
onary border (Margo coronarius) is thin. Its outer 
aspect is covered by a layer of soft horn known 
as the periople (Limbus corneus) ; this appears as 
a ring-like prominence above and gradually fades 
out below; at the angle it forms a wide cap or 
bulb and blends centrally with the frog. The 
inner aspect of the border is excavated to form 
tlie coronary groove (Sulcus coronarius ungula"), 
which contains the thick coronary corium. The 
groove is deepest in front, narrows on the sides, 
and is Avide and shallow at the heels." It is per- 
forated by innumerable small, funnel-like openings 
which are occupied by the papillae of the coronary 
corium in the natural state. Between the border 
of the wall proper and the periople there is a small 
groove which contains the corium of the periople. 
At the heel this groove is merged with the coronary 
groove. The basal or groimd border (Margo basi- 
laris) of the unshod-hoof comes in contact with the ground. Its thickness is greatest 
in front and decreases considerably from before backward on the sides, but there is 
a slight increase at the angles. Its inner face is united with the periphery of the 




Fig. 710. — Digit of Horse, Showing 
Surface Relations of Boxes and 
Joints. The Cartilage is Largely 
Exposed. 

a, First phalanx; 6, second phalanx; 
c, third phalanx; d, cartilage; f, distal sesa- 
moid or navicular bone; /, pastern joint; 
g, coffin joint; h', cut edge of wall of hoof 
(/i) : i, laminar corium. (After Ellenberger, 
in Leisering's Atlas.) 



^ The slope of the wall varies considerably in apparently normal hoofs. Lungwit^ foand 
by careful measurements of 56 fore and 3G hind feet the following average angles; 

Fore Foot Hind Foot 

Toe 47.26° 54.1° 

Medial angle 101.57° 96.5° 

Lateral angle 101.37° 96.1° 

The wall of the fore foot may even be more upright than that of the hind, and may have an 
angle of 60°. The length of the wall at the toe, quarters, and heels is in the ratio of aboiit 3:2:1 
in the fore foot and about 2 : l^/^: 1 in the hind hoof. 

^ The wide groove at the heels, however, contains cliiefly the corium of the periople. 



THE HOOF 



889 



sole by horn of lighter color and softer texture, which appears on the ground surface 
of the hoof as the so-called white line (Zona lamellata). 



Wall 
Lamina: of imll 

Laminar corium 

Third phabinx 

Digital cushion 

Bar 

Frog 

Space between 
bar and frog 

A ngle of wall 
Periople of heel 




Fig. 711. — Cross-section of Foot of Horse, Cut P.\k.\ll 
The wall appears much thicker at the angles than it actually 



'HE CORONART BORDER. 

; it is cut very obliquely. 



In tlie case of unshod horses at liberty the wall is usually worn off to the level of the adjacent 
sole, but if the ground is too soft the wall is likely to become unduly long and spht or break or 
undergo deformation. On very hard or rough ground, on the other hand, the wear may be in ex- 



Periopk 
Coronary 




Ridge farmed 
White line Sole by bar and frog 

Fig. 712. — H.\lf of Hoof of Horse; Internal Surface 



Periople of heel 



cess of the growth. In the case of shod horses it is necessary to remove the excess of growth of the 
wall at each shoeing. The thickness of the wall at the toe, quarters, and heels is about in the 
ratio of 4 : 3 : 2 for the fore foot and about 3 : 2J^ : 2 for the liind foot. 

2. The sole (Basis s. solea ungulse) forms the greater part of the ground sur- 



890 THE SENSE ORGANS AND SKIN OF THE HORSE 

face of the hoof. It is somewhat cresoentic in outline, and presents two surfaces 
and two borders. The internal surface is convex, and slopes with a varying 
degree of obliquity downward to the convex border. It presents numerous small 
funnel-like openings which contain the papillae of the sole corium in the natural 
state. The external or ground surface is the converse of the preceding. It is nor- 
mally arched — and more strongly in the hind than in the fore foot — but the curvature 
is subject to wide variation; in heavy' draft horses the sole is commonly less curved 
than in the lighter breeds and may even be fiat. The surface is usually rough, since 
the horn exfoliates here in irregular flakes. The convex border is joined to the wall by 
relatively soft horn, previously referred to as forming the white line on the ground 
surface of the hoof. The angle of junction is roundeil internally and presents a 




Fig. Tl.*?. — Right Fore Hoof of Horse; Ghouxd Stthface. 
;,' Basal or ground border of wall; 2, lamiuK of wall; S, angle of wall; 4. bar; 5, sole; B'. angle of sole; «, white 
line (junction of wall and sole) ; 7. apex of frog; 8, central sulcus of frog; 9, 9, collateral sulci between frog and bars; 
10, 10, bulbs of hoof. 

number of low ridges and specially large openings for the i^apilhc of the corium. 
There is frequently a ridge of larger size at the toe. The concave border has the 
form of a deep angle which is occupied by the bars and frog. It concurs in part 
with these in forming two pronounced ridges in the interior of the foot. The 
parts of the sole between the wall and bars may be termed its angles. 

3. The frog (Cuneus unguL-e) is a wedge-shaped mass which occupies the angle 
bounded by the bars and sole, and extends considerably below these on the ground 
surface of the foot. It may be described as having four surfaces, a base, and an 
apex. The internal surface bears a central ridge, the spine (jr " frog-stay" (Spina 
cunei ungulte), which is high posteriorly and subsides abruptly in frt)nt. On either 
side of this there is a deep depression, which is bounded outwardly by the romided 



THE HOOF 



891 




ridge formed by the junction of the frog with the bar and sole. This surface 
presents fine strise and openings for tlie papihae of the corium. The external or 
ground surface presents a central 
sulcus (Sulcus cunei), which is 
bounded by two ridges or crura 
(Crura cunei) . The medial and lat- 
eral surfaces (Facies medialis et lat- 
eralis) are united at the upper part 
with the liars and sole, but are free 
below and form the central wall of 
the deep collateral sulci (Sulci para- 
cuneati), which are bountled out- 
wardly by the bars. The base (Basis 
cunei) is depressed centrally ami 
prominent at the sides, where it 
unites with the angles of the wall; 
the junction here is covered by the 
expanded periople and constitutes 
the bulb of the hoof (Pulvinus digi- 
talis). The apex (Apex cunei) oc- 
cupies the central angle of the con- 
cave border of the sole, and forms a 
blunt, round prominence a little in 
front of the middle of the ground sur- 
face of the hoof. 

Structure of the Hoof. — The hoof 
is composed of epithelial cells which 
are more or less completely keratin- 
ized except in its deepest part, the 
stratum germinativimi ; here the cells 
have not undergone cornification, and 

by their proliferation maintain the growth of the hoof. The cells are in part 
arranged to form tubes (Cylindri cornel) which are united by intertubular epi- 
thelium, and enclose medullary 
cells and air-spaces. The wall 
may be regarded as consisting of 
three layers. The external layer 
consists of the periople and the 
stratum tectorium. The periople 
is composed of soft, non-pig- 
mented, tubular horn, and be- 
comes white when the hoof is 
soaked in water. It is contin- 
uous with the epidermis of the 
skin above, and extends do^vn- 
ward a variable distance. Usually 
it forms a distinct band somewhat 
less than an inch wide, except at 
the heels, where it is much wider, 
and caps the angle of inflection of 
the wall. The stratum tectorium 
is a thin layer of lun-ny scales 
which gives the outer surface of the wall below the periople its smooth, glossy ap- 
pearance. The middle layer (Stratum coronarium) forms the bulk of the wall, and 



Fig. 714. — Section of Hoof of Hor.se. 

The section is cut just above the ridges of the frog and 

bars and parallel with the ground surface. 1, Wall; 3, sole; 

5, spine of frog or "frog-stay": 4. ridge formed by junction 

of frog and bar; o, central furrow over apex of frug; 6, 

of bar. 




Fig. 



Posterior 



-Frontal .Section of Hoof of 

P.\RT Viewed from in Front. 
1, Wall; 3^ sole; 3, bar; 4. frog; 5, central ridge of frog; 6, 
lateral ridge formed by junction of frog and bar; 7, lamina? of 
bar; 5, laniinse of wall; 9, coronary groove; 10. periople of heel. 



892 THE SENSE ORGANS AND SKIN OF THE HORSE 

is the densest part of the hoof. Its horn tubes run in a straight direction from the 
coronarj' to the basal border. In dark hoofs it is pigmented except in its deep part. 
The laminar layer (Stratum lamellatinn) is internal; it consists of the homy 
laminae (Lamellae corneae), and is non-pigmented. The primary laminae are narrow 
antl thin at their origin at the lower margin of the coronary groove, but become wider 
and thicker distally. At the junction of the wall and sole they are united by inter- 
laminar horn to form the white line. Only the central part of the laminae becomes 
fully keratinized. They are composed of non-tubular horn in the normal state. 

The sole consists of tubular antl intertubular horn. The tubes run parallel 
with those of the wall and vary much in size. 

The frog is composed of relatively soft horn, which is much more elastic than 
that of the wall or sole, and is not fully keratinized. The horn tubes in it are slightly 
flexuous. 

The hoof is non-vascular and receives its nutrition from the corium. It is 
also destitute of nerves. 

THE CORIUM OF THE HOOF 
The corium of the hoof or pododerm (Corium ungulae) is the specially modified 
and highly vascular part of the curium of the common integument which furnishes 
nutrition to the hoof. It is convenient to divide it into five parts which nourish 
corresponding parts of the hoof.' 

1. The perioplic corium or ring (Margo corii ungulae) is a band 5 to 6 mm. 
in width which lies in a groove between the periople and the coronary border of 
the wall. It is continuous above Avith the corium of the skin, and is marked off by 
a groove from the coronary corium. At the heels it widens and blends with the 
corium of the frog. It bears very fine, short papillae which curve do'wnward and 
are received in depressions of the periople, to which it supplies nutrition. 

2. The coronary corium (Corium coronarium) is the thick part of the corium 
which occupies the coronary groove, and fiu-nishos nutrition to the bulk of the wall. 
It diminishes in width and thickness posteriorly, and along the upper border of the 
bar it is not clearly defined from the corium of the frog. The convex superficial 
surface is thickly covered with filiform papillae 4 to 6 ram. in length, which are re- 
ceived into the funnel-like openings of the coronary groove. At the heels and along 
the bars the papillae are arranged in rows, separated by fine furrows. The deep 
surface is attached to the extensor tentlon and the cartilages of the third phalanx 
by an abundant subcutis which contains many elastic fibers and a rich venous 
plexus. 

3. The laminar corium (Corium laraellatum) ])ears primary and secondary 
laminae which are interleaved with the horny laminae of the wall and bars in the 
natural state." It is attached to the dorsal surface of the third phalanx by a modi- 
fied periosteum (Stratum periosteale) which contains a close-meshed network of 
vessels, and to the lower part of the cartilages by a subcutis which contains a rich 
venous plexus. The laminae are small at their origin above, become wider below, 
and end in several papillae 4 to 5 mm. in length. They supply nutrition to the horny 
laminae and to the interlaminar horn of the white line. 

4. The corimn of the sole (Corium basilare) — also termed the sensitive sole — 
corresponds to the horny sole, to which it supplies nutrition. It is often more or 
less pigmented and bears long papillae, which are specially large along the convex 

' In some veterinary works the statement is made that the various parts of the corium "se- 
crete" corresponding parts of the hoof. The statement is, of course, ludicrous, as the relationship 
here, both anatomically and physiologically, is the same as in the case of the corium and epidermis 
of the skin. Hence the terms " keratogenous rnembrane" and "matrix" should be dropped. 

'The laminae of the corium are commonly termed "sensitive" laminae to distinguish them 
from the "horny" laminae, which are, of course, insensitive. 



THE CORIUM OF THE HOOF 



893 



border and at the angles. Centrally it is continuous with the corium of the frog 
and bars. The deep surface is attached to the sole surface of the third phalanx 
by a modified and highly vascular periosteum. 



Cut edge of skin 

Corium of periople 

Coronary corium 

Laminar corium 




Cartilage of third 
phalni.x 
P.,siti„n of 
iiiiriciilnr bursa 
Position of 
navicular bone 



Outline of hoof 



Fig. 716. — Lateral View or Foot of Horse After Rejioval of Hoof and Part of Skin-, (.\fter Schmaltz, Atlas 

d. Anat. d. Pferdes.) 
Dotted lines in front of navicular bone indicate position of coffin joint. 

5. The corium of the frog (Corium cuneatum) — also called the sensitive frog — 
is moulded on the deep surface of the frog and bears small papillae. Its deep face is 



Perioplic corium 
Coronary corium 

Laminar corium 

Corium of frog 
Position of navicular bone 

Corium of sole 



Position of insertion of 
deep flexor tendon 



White line 
Basal border of wall 



Fig. 717.— Ground Su 




Periople of heel or bulb 

Angle of ivall 
Angle of sole 



Foot of Horse After Re.moval of Half of Hoof to Show Corium. (After 
Schmaltz, Atlas d. Anat. d. Pferdes.) 



blended with the digital cushion. The germinal cells of the frog derive their 
nutrition from this part of the corium. 



894 



THE SENSE ORGANS AND SKIN OF THE HORSE 



The digital cushion (Torus digitalis) is a wedge-shaped mass whicn overlies the 
frog. It presents for description four surfaces, a base, and an apex.' Its deep 
surface faces upward and forward and is connected with the distal fibrous sheath of 
the deep flexor tendon. The superficial surface, covered by the corium of the frog, 
is moulded on the upper face of the frog. The sides are related chiefly to the 
cartilages of the third phalanx; distally the cushion is closely attached to the 
cartilages, but higher up a rich venous plexus intervenes. The base, situated 
posteriorly, is partly subcutaneous, and is divided by a central depression into two 
rounded prominences termed the bulbs of the cushion. The apex lies below and 
is adherent to the terminal part of the deep flexor tendon. The cushion is poorly 
supplied with vessels. It consists of a feltwork of fibrous trabecule and elastic 
fibers, in the meshes of which are masses of fat. The bulbs are soft and loose ia 



Extensor tendon 




Collateral ligament 



Fia. 718. — Section of Digit of H'jhse at Coronari 
1, Extensor process of third phalanx; 2, distal end of second phalanx; 
deep flexor tendon; 5, digital cushion; 6, cartilage of third phalanx; 7, 7, 
navicular bursa; 9, digital vessels; 10, digital nerve. 



Border op Hoof. 

3, distal sesamoid or navicular boue; 4, 
avity of coffin joint; podotrochlear or 



texture and contain a relatively large amount of fat, but toward the apex the cushion 
becomes denser and more purely white fibrous in structure. Branched coil glands 
occur chiefly in the part of the cushion which overlies the central ridge of the frog. 
Their ducts pursue a slightly flexuous course through the corium and pass in a spiral 
manner through the frog. Their secretion contains fat. 

Vessels and Nerves. — The corium is richly supplied with blood by the digital 
arteries. The veins are valveless, and form remarkable plexuses which communi- 
cate freely with each other and are drained by the digital veins. The lymph vessels 
form subpapillary plexuses in the porium of the sole and frog, and a wider-meshed 
plexus at the base of the digital cushion. A lymph vessel lies in the attached edge 
of each of the laminae. The nerves arc branches of the digital nerves; some fibers 
end in lamellar corpuscles and end-bullis. 

' The cushion is to be regarded as a special modification of the subcutaneous tissue, bearing 
on its superficial face the corium of the frog. It is an important factor in diminishing concussion. 



THE ERGOT AND CHESTNUT THE ORGAN OF TASTE 895 

The Ergot and Chestnut 

The ergot is a small mass of horn which is situated in the tuft of hair at the 
flexion surface of the fetlock. It is commonly regarded as the vestige of the second 
and fourth digits of extinct equidae, and hence is absent in cases in which these 
digits are developed. A small fibrous band, 3 to 5 mm. in width, extends downward 
and slightly forward from the fibrous basis of the ergot on each side, crosses over the 
digital vessels and nerves very obliquely, and blends below %vith the digital fascia 
and the digital cushion. It is known as the ligament or tendon of the ergot (Fig. 
572). 

The term chestnut is applietl to the masses of horn which occur on the medial 
surface of the forearm, about a handbreadth above the carpus, and on the distal 
part of the medial face of the tarsus. They have an elongated oval form and are 
flattened. They are regarded usually as vestiges of the first digit. That of the 
hind limb is absent in the donkey and very small in the mule. 

These horny vestiges are quite variable in form and size and are correlated with the fineness 
or coarseness of the integument in general. The supracarpal chestnut is about II2 to 232 inches 
long, oval in outline, the proximal end being pointed; it overlies the flexor carpi radiaUs at a 
quite variable distance above the carpus, and hence should not be used as a surgical landmark. 
The tarsal chestnut lies at a point behind the lower part of the medial ligament of the hock. When 
well developed it is about 2 to 2J2 inches long, broad below and produced above to form a long 
pointed end, with a short blunt anterior process. They are composed of horn somewhat like that 
of the frog. 



Organ of Smell 

The peripheral part of the olfactory apparatus or organ of smell (Organon 
olfactus) is that part of the nasal mucous membrane which was referred to in the 
description of the nasal cavit,y as the olfactory region; this (Regio olfactoria) is 
limited to the ethmoturbinates antl the atljaccnt part of the dorsal turbinate and 
the septum nasi, in which the fibers of the olfactory nerve ramify. It is distin- 
guished by its yellow-bro^\'n color, thickness, and softness. It contains character- 
istic tubular olfactory glands, which are lined by a single layer of pigmented cells, 
and a neuro-epitheliuni, tlie olfactory cells, the central processes of which extend 
as non-meduUated fibers to the olfactory bulb. 

The epithelium is non-ciliated and is covered by a structureless hmiting layer. It consists 
essentially of three kinds of cells, supporting, basal, and olfactory. The supporting cells are of 
long columnar form above and contain pigment granules; below they taper and often branch, 
and their central processes unite with those of adjacent cells to form a protoplasmic network. 
The basal cells are branched and lie on a basement membrane. The olfactory cells ai'e situated 
between the supporting cells; they have the form of long narrow rods, with an enlarged lower 
part which is occupied by the nucleus. The peripheral end pierces the limiting membrane and 
bears a tuft of fine, hair-like cilia (olfactory hairs). A central process extends from the nucleated 
pole of the cell to the olfactory bulb as a non-meduUated olfactory nerve-fiber. 

The vomero-nasal organ (Fig. 452) lies along each side of the anterior part 
of the lower border of the septum nasi. It communicates with the nasal cavity 
through the naso-palatine canal. It con.sists of a tube of hyaline cartilage lined 
with mucous membrane; a small part of the latter along the medial side is olfactory 
in character. 



The Organ of Taste 

The peripheral part, of the gustatory apparatus (Organon gustus) is formed by 
the microscopic taste buds (Calyculi gustatorii), which occur especially in the foliate, 
fungiform, and vallate" papillse, in the free edge and anterior pillars of the soft 
palate, and the oral surface of the epiglottis. The taste buds are ovoid masses, 



896 



THE SENSE ORGANS AND COMMON INTEGUMENT OF THE OX 



which occupy corresponding recesses in the ordinary epithelium; each presents a 
minute opening, the gustatory pore. The l)uds consist of fusiform supporting cells 
grouped around central gustatory cells. The latter are long and narrow; the 
peripheral end of each bears a small filament, the gustatory hair, which projects at 
the gustatory pore ; the central eml is produced to form a fine process which is often 
branched. The taste buds are innervated by fibers of the glosso-pharyngeal nerve 
and the lingual branch of the trigeminus. 



Upper eyelid 



THE SENSE ORGANS AND COMMON INTEGUMENT OF THE OX 

THE EYE 

The eyelids are thick, prominent, and less pliable than those of the horse. 

The lower liil bears a considerable number of cilia, which are, however, finer than 

those of the upper lid. The tarsal 
glantls are more deeply embedded 
^g».: and therefore not so evident. The 

conjunctiva of the lower lid presents 
folds or ridges, and one or two promi- 
nences which contain numerous leuko- 
cytes; the conjunctival epithelium is 
transitional in type. The superficial 
part of the cartilage of the third eye- 
lid is leaf or shovel-shaped antl thicker 
than in the horse; the edge bears a 
narrower process, on which there is a 
transverse bar, giving the arrange- 
ment some resemblance to an anchor. 
The gland of the thinl eyelid is very 
large — an inch or more in length — 
and maj' be divided into two parts. 
The deep part is pink and consists of 
loose lobules, but the much larger 
superficial part is more compact. 
There are two large and several 

smaller excretory ducts. The subconjunctival tissue of the third eyelid contains 

lymph nodules, which are specially 

Conjunctiva 




Lower eyelid 



(After Ellenberger-Bai 
Kunsller.) 



bulbi 



Sclera 



Third eyelid 



Cornea 



numerous on the bulbar side 

The lacrimal gland is thick and 
distinctly lobulated. It is more or less 
clearly dividetl into a thick upper and 
a thinner lower part (Glandula lacri- 
malis dorsalis, ventralis). There are 
six to eight larger excretory ducts and 
several smaller ones. The naso-lacri- 
mal duct is shorter than in the horse, 
and is almost straight. Its terminal 
part is enclosed lietween two plates 
of cartilage, and it opens near the 
nostril on the lateral wall of the vesti- 
bule of the nasal cavity; the orifice is 

placed on the medial side of the alar fold of the ventral turbinate, and is therefore 
not easih' found. 




Pupil 



Fig. 
19, Orbital I 



'20. — Left Eyeball of Ox i 
It. (After Ellenberger-Bai 



The eyeball resembles that of the horse in shape, but is consitlerably smaller. ^ 
The sclera is often more or less pigmented; where non-pigmented, it may have 
a bluish tinge. The point of entrance of the optic nerve is about 2 mm. lateral 
to the vertical meridian, and about 7 mm. below the horizontal meridian.- The 
cornea is thicker than that of the horse. The tapetum of the chorioid is extensive 
at the outer side, but is a narrow strip medially. It has a metallic luster, shading 
from a brilliant green to a deep blue; centrally it has a reddish sheen. The iris is 
usually verj' dark colored. The granula form a continuous series of small nodules 
along the upper margin of the pupil and are most prominent centrally; they are 
very small on the lower margin. The optic papilla is much smaller and is not so 
sharjjly defined on oi)hthalmoscopic examination as that of the horse. Several 
relativclj^ large retinal arteries radiate from the center of the papilla to the periphery 
of the retina. They may be seen to wind spirall.y around the veins, which are very 
large. The vitreous body is less fluid than that of the horse. 

The arteria centralis retinse arises from a posterior ciliary artery and divides close to the 
optic papilla into three branches usually ; the upper one is larger than the two lateral branches. 
The retina is more vascular than that of the horse; it has a round area centraUs at the medial side, 
which is continued outward by a narrow strip of a similar histological structure. 

THE EAR 
The external ear is inclined outward. The middle part is much wider and less 
curved than in the horse. The apex is also wide and does not curve forward. 
The lower part of the anterior border is bent backward and bears long hairs. The 
posterior border is thin and is regularly convex, except below, where it is intlented. 
The oiJening is wide and the concave surface presents four ridges; the convex 
surface presents correspontling depressions. The styloid process of the conchal 
cartilage is short and blunt. The edges of the annular cartilage are in contact at 
the medial side and the upper border is notched laterally. The scutiform cartilage 
is a very irregular quadrilateral plate; it is situated on the lateral aspect of the 
cranium, with its concave surface in contact with the fat and temporalis muscle. 
The osseous external acoustic meatus is directed practically straight inward; it is 
about twee as long as that of the horse, and tapers very gradually from without 
inward. The chief special characters of the auricular muscles are as follows: 
(1) The scutularis blends with the frontalis muscle. The interscutularis arises 
from the base of the processus cornus (or the corresponding area in polled cattle) 
and from the frontal crest. (2) The cervico-scutularis arises from the posterior 
surface of the cranium below the frontal eminence, and receives slips from the 
parieto-auricularis and cervico-auricularis superficialis. (3) The zygomatico- 
auricularis and scutulo-auricularis superficialis ventralis are fused. (4) The scutulo- 
auricularis superficialis dorsalis is distinct from the interscutularis; it arises from 
the superficial face of the scutiform cartilage. (5) The cervico-auricularis super- 
ficialis arises from the ligamentum nuchee and ends on the convex surface of the 
conchal cartilage. (6) The parieto-auricularis arises from the nuchal surface of 
the frontal bone, the adjacent part of the parietal bone, and the ligamentum nuchse; 
it is inserted below the preceding muscle. (7) The scutulo-auricularis superficialis 
accessorius arises from the superficial face of the scutiform cartilage and is inserted 
by a round tendon into the anterior part of the convex surface of the conchal car- 
tilage. (8) The cervico-auricularis profundus minor consists of two fasciculi: the 
medial, narrow part is deep red in color, and arises from the fascia of the cervical 
muscles lateral to the occipital attachment of the ligament nuchse; the lateral 

' The average transverse diameter is about 42 mm., the vertical diameter, 41 mm., and the 
axis, 36 mm. The angle between the optic axes is about 119°. 

- The tliiclvness of the sclera is about 2 mm. at the Dosterior pole, 1 mm. at the equator, and 
1.2 to 1.5 mm. near the cornea. 
57 



898 



THE SENSE ORGANS AND COMMON INTEGUMENT OF THE OX 



witler part, is pale, and arises beneath tlie cervico-auricularis superficialis indirectly 
from the sciitiform cartilage. The two unite and are inserted into the lower aspect 
of the base of the conchal cartilage. (9) The scutulo-auricularis profundus minor 
arises from the temporal crest above the external acoustic meatus and is inserted 
into the anterior part of the deep face of the scutiform cartilage. 

The cavum tjrmpani is small; it communicates ventrally with the air-cells of 
the bulla ossea. The tympanic membrane is nearly circular and is not so oblique 
as in the horse. The auditory ossicles are smaller than those of the horse; the 
malleus is more curved, the body of the incus is longer, and there is a small promi- 
nence on the front of the head of the stapes for the attachment of the stapedius 
muscle. 

The auditive or Eustachian tube is small and is only about two inches long. 

The pharyngeal opening is small and is situated on the side of the fornix of the 

pharynx close to the base of the cranium. There is no flap-like expansion of the 

cartilage, but the medial border of the orifice is formed by 

a fold of mucous membrane (Fig. 476). 

The internal ear has essentially the same arrangement 
as in the horse. 



COMMON INTEGUMENT 
The thickness of the skin of the ox is greater than 
that of any of the other domesticated animals; in general 
it is about three or four millimeters, but at the root of 
the tail and the point of the hock it is about five milli- 
meters and on the brisket six or seven millimeters. The 
variably developed prominence at the anterior part of the 
pectoral region kno^\^l as the brisket consists of a fold of 
skin (Plica colli ventralis longitudinalis), which contains 
posteriorly a mass composed of coarse fibrous trabeculse 
and fat. 

The cutaneous glands are fewer and less developed 
than in the horse. Except about the natural openings, at 
the point of the hock, and the flexion surface of the fet- 
lock, the sweat glands do not form a coil, but are enlarged 
at the deep end and are variably flexuous. The sebaceous 
glands are best developed about the natural openings and on the udder, but there 
are none on the teats. The naso-labial glands form a thick layer under the bare 
skin of the muzzle. They are compound tubular glands and are lined with cubical 
epithelium. The openings of their excretory ducts are easily seen. 

The hairs are extremely variable in color and size in the different breeds and 
in different individuals. The hair of the frontal region is often curly, especially 
in the bull. There is no mane, and the long hairs of the tail occur only at the end, 
where they form the "brush" (Cirrus caudse). 

The claws, four in number on each limb, cover the ends of the digits. Those 
of the chief digits conform in a general way to the shape of tlie third phalanges, 
and each may be regarded as having three surfaces. The abaxial surface is convex 
from side to side, and is marked by ridges parallel with the coronary border. Its 
anterior part is concave from edge to edge, and the angle which it forms with the 
ground is about 30°. The intertiigital surface is concave and grooved; it touches 
the opposite claw only at its ends. The basal or ground surface consists of two 
parts, viz., a slightly concave sole, which is pointed in front and widens behind, and 
a prominent Ijulb of soft thin horn, which is continuous aliove with the skin. The 
claw may be regarded as consisting of three parts — periople, wall, and sole. The 




Fig. 721. — Claws of O: 
Volar Aspect. (Afti 

Ellenberger-Baum, Ana 
fiir Kiiiistler.) 



COMMON INTEGUMENT 899 

periople surrounds the coronary border in the form of a flat band, which is about 
half an inch wide, except at the heels, where it widens to cover the entire surface. 
The wall forms most of the abaxial part of the claw and is reflected in front upon the 
interdigital surface. It thins out toward the bulb or heel, which appears, as stated 
above, to consist of the thin expansion of the periople. The sole occupies the angle 
of inflection of the wall ; it is continuous without demarcation with the periople of 
the bulb. The perioplic corium bears relatively long papillae. The coronary corium 
is much less developed than in the horse and its papillae are short. The laminae are 
much narrower' and are more numerous than in the horse; secondary laminae are 
not present. The corium of the sole is not marked off behind from that of the 
periople; its papillae are very small and close together. The corium of the bulbs 




Lateral extensor tendon 
Metacarpal bone 



M etacar po-phalangeal articulation 
First phalanx 
Lateral extensor tendon 
Common extensor tendon 
Proximal interphalangeal joint 
Second phalanx 

Periople 
Coronary corium 
Third phalanx 
Wall of hoof 



Upper pouch 
of metacarpo- 
'phalangeal 
joint capsule 
Superficial 

xor tendon 
Suspensory 
"(/(iment 
Deep flexor 
Undon 
Supi rticial 
jUxor tendon 
Annular 
liyament 
Proximal 
''sesainoid 
Cruciate 
ligament 
Small claw 
Annular ligament 
Diyilal cushion 
V pjiir pouch of capsule 
(if ilislal interphalangeal 

•it 
jJisliil sesamoid bone 



Sagittal Section of Distal Part of Forelimb of Ox. 



is separated from the flexor tendon by a mass of elastic, fatty tissue, which is 
analogous with the digital cushion of the horse. The papillae here are long and 
often compound. 

The accessory digits bear short conical horn capsules which resemble in a 
general way those of the chief digits, and have a similar corium, which covers one 
or two nodular vestigial phalanges. From these a fibrous band descends obliquely 
on the volar aspect of each chief digit and is attached below to the distal phalanx 
and sesamoid bones, sending fibers also to the elastic pad of the heel. 

The horns (Cornua) enclose the horn processes of the frontal bones (except in 
the polled breeds). They vary very greatly in size, form, and curvature. The root 
or base of the horn (Radix cornus) has a thin edge which is continuous with the 



900 THE SENSE ORGANS AND COMMON INTEGUMENT OF THE PIG 

ordinary epidermis. It is covered by a thin layer of soft horn similar to the periople 
of the hoof of the horse. Near the root the horn is encircled by variable rings. 
Toward the apex (Apex cornus) the thickness of the horn increases till it becomes 
practically a solid mass. The horn consists mainly of tubes which are very close 
together, except at the rings, where there is moi'e intertubular horn. The corium 
of the horn (Corium cornus) is united to the horn process by periosteum which is 
traversed by numerous Ijlood-vessels. The corium at the root of the horn is thick 
and bears long, slender papillae; in the body of the horn it becomes thin and the 
papillse are smaller, but increase in size apically. Rudimentary papillated laminae 
also occur. 

The skin of the sheep varies in thickness from 0.5 to 3 mm., but differs greatly 
in fineness and in other respects in various breeds. In Merinos lai'ge folds 
occur on the neck. Cutaneous pouches (Sinus cutis) are constantly present 
in certain situations. The infraorbital or lacrimal pouch (Sinus cutaneus infra- 
orbitalis) is an invagination about half an inch in dejith, which is situated in front 
of the medial angle of the eye. It bears scattered fine hairs, into the follicles of 
which large compound sebaceous glands open; coil glands are also present. The 
secretion of the glands is fatty and forms a yellow, sticky covering on the skin when 
dry. The inguinal (or mammary) pouch (Sinus cutaneus inguinalis) is much more 
extensive, and is situated in the inguinal region in both sexes. The skin of the 
pouch bears scattered fine hairs and contains well-developed sebaceous glands and 
exceedingly large coil glands. The interdigital pouch (Sinus cutaneus interdigi- 
talis) is a peculiar tubular invagination of the integ:ument which opens at the 
anterior part of the interdigital cleft. On sagittal section it appears as a bent tube, 
an inch or more (ca. 2.5-3 cm.) in length, and about a fourth of an inch (ca. 6- 
7 mm.) in diameter. The pouch extends downward and backward, and then 
curves sharply upward between the distal ends of the first phalanges. Its 
deep blind end is somewhat ampullate. The subcutis forms a capsule around it. 
The skin of the pouch is thin and pale; it bears fine colorless hairs, the follicles of 
which receive the secretion of several sebaceous glands. The coil glands here are 
compound and very large ; they open into the hair-follicles or directly into the pouch. 
The secretion of the glands is a colorless fatty substance. The skin is covered in 
great part by wool, which is similar in structure to hair, but is finer, curly, and 
usually contains no medullary cells. The follicles of the wool are curved, and are 
arranged more or less distinctly in groups of ten or a dozen, several of which open 
in common on the surface. A considerable part of the face and the limbs is covered 
with short, stiff hair, and long hairs occur more or less interspersed among the wool. 
The claws resemble those of the ox. The horns, when present, are more or le.ss 
prismatic, distinctly ringed, and varj^ in length and curvature in different breeds. 
Their structure is similar to those of the ox. 

The olfactory and gustatory organs resemble in general those of the horse. 



THE SENSE ORGANS AND COMMON INTEGUMENT OF THE PIG 

THE EYE 

The posterior jjart of the orbital margin is formed chiefly by the orbital liga- 
ment, which extends from the extremely short supraorbital process to the small 
eminence at the junction of the malar and the zygomatic process of the temporal. 

Cilia occur only on the upper eyelid. The medial canthus is prolonged by a 
groove on the infraorbital region. The tarsal glands are very short and curved. 
The conjunctival epithelium is of the transitional type, with many goblet cells. 



THE EAR — THE SKIN AND APPENDAGES 901 

The deep part of the cartilage of the third eyelid is broad and spoon-like, the 
superficial part somewhat anchor-shaped. In addition to the gland which sur- 
rounds the deep part of the cartilage, there is a deeper one, often termed the gland 
of Harder (Glandula palpebrae tertise profunda), which is surrounded by a distinct 
capsule and a blood-sinus. This gland is brownish or yellowish-gray in color, 
elliptical in outline, and about an inch (2-3 cm.) in length. It is situated deeply 
below the attachment of the ventral oblique muscle. 

The caruncula lacrimalis has the form of a riilge; it divides into two branches 
which join the skin at the metlial commissure. It is red in color and contains 
numerous large coil glands. 

The lacrimal gland is mucous in type. There is no lacrimal sac, and the two 
lacrimal ducts pass through separate openings at the infraorbital margin. The 
naso-lacrimal duct is usually short and opens into the ventral nasal meatus at the 
posterior end of the ventral turbinate.^ The eyeball appears small, partly on 
account of the narrowness of the palpebral opening; it closelj^ approaches the spheri- 
cal form. The cornea, although in reality almost circular, appears oval when viewed 
from the front, the medial end being much the broader. The chorioid has no 
tapetum. The iris is usually dark grayish-brown or yellowish-brown, but sometimes 
has a blue tinge. The pupil is a transverse oval in ordinary light, but almost 
circular when dilated; granula are not present. The optic papilla is nearer the 
posterior pole than in the horse and ox, and has a distinct central artery and vein. 



THE EAR 
The external ear differs considerably in size, thickness, and position. It may 
be carried vertically, inclined inward, or hang tlownward. It is relatively wide and 
is little curved except at the base. The concave surface presents several cutaneous 
ridges which correspond approximately with the long axis of the ear. The anterior 
border of the concha is strongly recurved in its lower part, and divides into two 
branches, one of which passes almost horizontally backward in the cavum conchae, 
while the other continues the general direction of the border. The posterior border 
is slightly concave above, strongly convex below, forming a prominence someM'hat 
analogous to the lobule of the human ear. The osseous external acoustic meatus 
is very long and is directed ventro-medially. The tympanic membrane is almost 
circular. The tympanic cavity proper is small, but it is continuous with the numer- 
ous cells of the large bulla ossea. The auditive or Eustachian tube is short; its 
pharyngeal opening is situated in the upper part of the wall of the pharynx, imme- 
diately behind the posterior nares. It is somewhat infundibular, and is bounded 
medially by a thick fold of mucous membrane (Torus tubarius). 



THE SKIN AND APPENDAGES 
The thickness of the skin in improved breeds is 1 to 2 mm. Fat usually' accu- 
mulates in the subcutis and forms a distinct and often extremely thick panniculus 
adiposus over the greater part of the body. The sebaceous glands are in general 
small and much fewer than in the other animals. The sweat glands, on the other 
hand, are large, yellow or broAvnish in color, and are in many places visible to the 
naked eye. At the medial side of the carpus there are small cutaneous diverticula, 
the so-called carpal glands, into which numerous compound coil glands open. Large 
glands also occur in the skin of the digits and interdigital space. Compound 
tubular glands are present in the skin of the snout. Large sebaceous and sweat 

' The lower punctum lacrimale is frequently absent and tlie corresponding duct therefore 
blind. There is often a duct or its remnant which opens below the ventral turbinate fold, but is 
not connected behind with the functional duct. 



902 THE SENSE ORGANS AND COMMON INTEGUMENT OF THE DOG 

glands are found at the entrance to the preputial diverticulum. The hairs are 
sparsely scattered in improved breeds — indeed, in some cases the skin is almost 
bare. The long hairs or bristles are arranged usually in groups of three. They 
are most developed on the neck and back. The bristles about the snout anil the 
chin are sinus hairs. 

The claws and their corium resemble those of the ox, but the bulbs are more 
prominent and form a greater part of the ground surface; they are also better 
defined from the sole, which is small. The claws of the accessory digits are more 
developed and their parts better differentiated than those of the ox. 

The olfactory region is extensive in correlation with the large size of the 
olfactory bulbs; the mucous membrane here is brown in color. 



THE SENSE ORGANS AND COMMON INTEGUMENT OF THE DOG 

THE EYE 

The posterior margin of the orbit is formed by the orbital ligament, as in the 
pig. The orbital axes if produced backward would include an angle of about 79°, 
the optic axes an angle of about 92.5° (Koschel). The lower eyelid has no distinct 
cilia. The medial angle is wide, the lacus lacrimalis shallow, and the caruncula 
lacrimalis small and yellowish-brown. The conjunctival epithelium is cylindrical, 
with many goblet cells. The gland which surrounds the deep end of the cartilage 
of the third eyelid is large and pink; it is a mixed gland. 

The lacrimal glantl is flat and lies chiefly under the orbital ligament. It is 
pink in color antl mixetl in structure. The naso-lacrimal duct is variable in arrange- 
ment and may differ on the two sides. It may open into the ventral meatus im- 
mediately after its emergence from the osseous lacrimal canal; thence it continues 
forward and opens on the lateral wall of the nostril below the ventral turbinate fold. 

The eyeball is almost spherical and is relatively large, especially in the small 
breeds. The sclera is thick in the ciliary region, where it contains a well-developed 
venous plexus; in the vicinity of the equator it is thin, and the chorioid shows 
through it. The cornea is almost circular. The chorioid is richly pigmented, 
and presents a well-defined tapetum cellulosum; this is somewhat triangular in 
outline and has a metallic luster. Its color is often golden green, shading to blue 
peripherally, but the blue tone may predominate, and in other cases it is mainly 
golden yellow or reddish-yellow. The appearance is due to several layers of peculiar 
flattened polygonal cells. The ciliary muscle is more developed than in the other 
species. The iris is commonly light or yellow brown, but not rarely has a blue 
tinge; the color often differs in the two eyes. The pupil is round; its edge is 
either smooth or bears minute round prominences. The retina presents a round 
area centralis lateral to the optic pajjilla. The latter is variable in outline; com- 
monly it has the form of a triangle with the angles rounded off, but is often round 
or oval. Branches of the central vessels of the retina radiate from the middle of 
the papilla. The surfaces of the lens are not so strongly curved as in the other 
domestic animals, and there is little difference in the radius of curvature of the two 
surfaces. 

THE EAR 

The external ear differs greatly in size and form in the various breeds; in most 
it is relatively wide antl thin and the greater part of it hangs down over the opening. 



THE SKIN AND APPENDAGES 903 

The anterior border has a prominence (Spina helicis) at its lower part, and below 
this it divides into two branches (Crura helicis). One of these continues down to a 
blunt point, while the other turns into the cavity of the concha. The posterior 
border forms a pouch below its middle, and is thick and rounded in its basal part. 
Here the conchal cartilage bears a pointed process (Processus uncinatus), which pro- 
jects upward and backward. The outer wall of the cavuni conchse is supported 
by a quadrilateral plate (Tragus) above and a semi-annular cartilage below. The 
concave surface presents several cutaneous folds, and in the cavum conchae there 
are ridges and irregular prominences. There are long hairs on the borders, apex, 
and the folds of the concave surface, but the skin of the cavum conchse is bare. 
The annular cartilage is a complete ring. The osseous external acoustic meatus 
is wide and extremely short. 

The auricular muscles are thin. The scutularis is extensive anti is divisible 
into interscutularis and fronto-scutularis. It partly covers the occipitalis muscle, 
which is oval and unpaired and ends in the fascia of the frontal region. The 
scutulo-auriculares superficiales, ventralis et accessorius, and the cervico-scutularis 
are not differentiated as separate muscles. The cervico-auricularis superficialis 
and the parieto-auricularis both bifurcate and are inserted into the base of the 
concha and the scutiform cartilage. The parotido-auricularis is narrow and almost 
long enough to meet the opposite muscle. The tragicus consists of two parts; of 
these, the lateral one is long and arises fron the border of the mandible above the 
angular process. The helicis and the verticalis auriculae are well developed. 

The tympanic cavity is very roomy, extending ventrally into the large but 
simple cavity of the bulla ossea. The tympanic membrane is extensive and oval. 
The promontory is very pronounced. The auditory ossicles are large. The 
auditive or Eustachian tube is short, and has a fibrous lateral lamina. Its pharyngeal 
opening is an oblique slit situated on the lateral wall of the naso-pharyngeal meatus, 
and is margined medially by a thick mucous fold. The cochlea has three and a 
half turns and is more sharply pointed than in the ungulates. 



THE SKIN AND APPENDAGES 

The skin varies greatly in thickness in different breeds. It is remarkably 
loose on the dorsal aspect of the neck and trunk, where it can be raised in extensive 
folds. The coat is also subject to extreme variation in length, thickness, color, etc. 
The hairs are arranged in groups of three to a large extent. The sebaceous glands 
are best developed in the short and rough haired breeds. They are largest and 
most numerous at the lips, anus, dorsal surface of the trunk, and sternal region. 
The sweat glands are relatively better developed in the long and fine haired breeds. 
The largest are found in the digital pads. Coil glands occur in the skin of the 
perineimi and the paranal pouches. In the muzzle glands are absent or very 
scanty. 

On the flexion surface of the carpus and digit there are hairless, cushion-like 
pads. The carpal pad (Torus carpalis) is situated medial and distal to the accessory 
carpal bone. The metacarpal and metatarsal pads (Torus metaearpalis, meta- 
tarsalis) are the largest and are situated behind the distal ends of the metacarpal 
or metatarsal bones and the greater part of the first phalanges. They are somewhat 
heart-shaped, with two unequal lateral lobes, and the apex distal. The metajxjdio- 
phalangeal joints rest on them when the paw supports the weight. The digital 
pads (Toruli digitales) are oval and are much smaller; they similarly support the 
second digital joints. That of the first digit is small on the forelimb, and usually 
absent from the hind limb. Each receives two suspensory bands from the tubercles 

' Trautmarm has sliown that the secretion wtiich appears on the muzzle comes from the 
lateral nasal gland, which is well developed. 



904 



THE SENSE ORGANS AND COMMON INTEGUMENT OF THE DOG 



at the distal end of the corresponding second phalanx. The pads have a basis of 
fibro-elastic tissue and fat, which is intimately adherent to the skin and is connected 
by trabeculse with the bones and tendons. The epidermis is thick and largely 
keratinized, and is studded with numerous rounded papillae which are readily seen 





Fig. 723. — Pads < 



UiHT FoHE r.\w OF Dog. Fig. 724. — Pads op Right Hind Paw of Do 

1-5, Digital pads; 6, 6, metacarpal and metatarsal pads; 7, carpal pad. 



with the naked eye. The corium has large papillse, and contains sweat glands and 
lamellar corpuscles. 

The claws (Ungues) correspond in form to the ungual ]5art of the distal pha- 
langes, which they enclose. The horn of the claw consists of a body or wall and a 
sole. The former is strongly curved in both directions, and is compressetl laterally. 




Fig. 725. — Half of Claw of Dog; Inner Surface. 
Coronary part; 6. volar part of wall; c. sole; d, section of c; e, section of wall 
3, dorsal surface. (From Leisering's Atlas.) 



.f, coronary border; ;3, apex; 



Its coronary border fits into the depression under the bony collar or ungual crest 
of the third phalanx and is covered by skin. The lateral borders converge and 
enclose the sole anteriorly. The corium presents a coronary part which bears 
papillse only near the coronary Ijorder. On the dorsal surface it is thickened to 
form a ridge, and the corresponding part of the horny covering is thick and main- 



OLFACTORY AND GUSTATORY ORGANS 905 

tains the pointed character of the claw. The cerium of the sides of the wall bears 
small laminae which converge to the corium of the sole. The latter is papillated. 
When the flexor muscles are inactive, the distal phalanges and the claws are main- 
tained in dorsal flexion by two elastic ligaments. These arise from the tubercles 
at the proximal end of the second phalanx and converge to the dorsal aspect of the 
ungual crest of the third phalanx. 



OLFACTORY AND GUSTATORY ORGANS 

The olfactory region lies above the lamina transversa, which separates it from 
the naso-pharyngeal meatus. The mucous membrane is distinguished bj' its 
thickness and yellow color, and is very extensive. It covers about half of the large 
ethmoturbinates, and one-third to one-half of the septum nasi. The ethmotur- 
binate which projects into the frontal sinus and the adjacent inner wall of the sinus 
is olfactory in character. Olfactory nerve-fibers ramify in the vomero-nasal organ. 

The gustatory apparatus presents no special features of importance. 



NDEX 



Abdomen, lymph vessels of, 

701 
Abdominal aortio plexus, 833 
cavity, 410, 452 
inguinal ring, 290, 292 
part of sympathetic system, 

832 
plexuses, 832 
tunic, 288, 361 
Abomasum, 453, 456, 474 
Accessory organs, 385 
pancreatic duct, 434 
parotid glands, 482 
spleens, 441 
thyroids, 536, 553 
Acetabular angle, 106, 109 

fossa, 109 
Acoustic meatus, external, 
61, 870, 871 
internal, 62, 882 
process, external, 61, 74 
Aditus larjTigis, 406, 407, 521 

oesophagi, 407 
Adrenal bodies, 563, 566, 567, 
569, 570 
plexuses, 834 
Adventitia of ductus deferens, 
575 
of Fallopian tubes, 599 
of seminal vesicles, 578 
jEsthesiology, 857 
Aggregated nodules of large 
intestine, 431 
of small intestine, 442, 
487, 501 
Alee nasi, 508 
Alar canal, 54, 75, 78 
cartilages, 509, 537 
fold, 509 
notch, 184 
Alimentary canal, 385 
Alveolar border of premaxillK, 
65 
ducts of lungs, 534 
periosteum of teeth, 395 
tuberosity, 64, 78 
Alveoli, 71 
dental, 64 

of mammary glands, 605 
of thyroid gland, 536 
Alveus, 787 

Amphiarthroses, 210, 211 
Ampulla ductus deferentis, 
575 
of semicircular canals, 881 
of uterus, 613 
recti, 429 
Amygdaloid nucleus, 792 
Anal sacs, 502 
Anastomosis of arteries, 614 
Anatomy, 17 
comparative, 17 



Anatomy, gross, 17 

macroscopic, 17 

microscopic, 17 

philosophical, 17 

special, 17 

systematic, 17, 18 

topographic, 17, 18 

veterinary, 17 
Angiology, 614 
Angle, acetabular, 106, 109 

duodenal, 433 

of mandible, 70, 71 

of rib, 27 

splenic, 433 
Angular process of mandible, 

195 
Annular cartilage of ear, 871 
Ansate fissure, 849 
Antrum pyloricum, 416 
Anus, 432 

Aortic plexTis, abdominal, 833 
thoracic, 831 

orifice of heart, 626 

valve, 626 
Aperture, posterior, of pelvis, 

111 
Apex of hoof, 891 
Apical lobe of hmg, 540, 547, 

548, 551, 553 
Aponeurosis, 253 

of obliquus abdominis ex- 
temus muscle, 288 

of transversus abdominis 
muscle, 291 

pharyngeal, 407 
Appendages of skin, 886, 901, 

903 
Appendix epididymidis, 573 

testis, 571 

ventriculi laryngis, 522 
Aquaeductus cochlea?, 882 

vestibuli, 881 
Aqueduct of cerebrum, 780 
Aqueous humor, 869 
Arachnoid granulations, 763 
Arachnoidea, 762 

cerebral, 762 

spinal, 763 
Arbor medullaris, 777 
Arch, distal volar, 657 

hemal, 188 

lumbo-costal, 287 

of aorta, 629 

of cricoid cartilage, 515 
plantar, deep, 697, 721 
distal, 678, 697, 719 
proximal, 678, 679, 719 

subcarpal, 657 
venous, 692 
zygomatic, 60, 73 
Aroiate fibers, external, 773, 
774 

907 



Arcuate fibers, internal, 774 

of cerebellum, 777 
Area acustica, 779 
centralis retina?, 868 
cribrosa, 558 
parolfactoria, 788 
Arteria profunda penis, 673 
Arteries or artery, 614, 629, 

706, 736, 744 
abdominal, anterior, 635 

posterior, 675, 752 

subcutaneous, 675 
adrenal, 563, 666 
adventitia of, 615 
alveolar, inferior, 647, 737, 

747 
anastomosis of, 614 
angular, 709 

of eye, 644, 710 
antibrachial, volar, 749 
aorta, 629, 736, 744 

abdominal, 630, 661, 713, 
750 

ascending, 629 

brachiocephaUc, trunk, 
631 

thoracic, 630, 660, 713, 750 
asternal, 635 

auricular, anterior, 646, 709, 
747 

great, 747 

posterior, 644, 709, 736 
basUar, 640 
bicipital, 749 

brachial, 650, 707, 710, 736, 
738, 744, 747 

deep, 651, 710, 749 

left, 632 

right, 631 
brachiocephalic, 631, 736, 

744 
bronchial, 534, 535, 660, 713, 

737 
broncho-ocsophageal, 535, 

660, 750 
buccinator, 649, 710, 737 
cacal, 737, 751 

lateral, 665 

medial, 665 
carotid, common, 635, 707, 
736, 744, 746 
left, 637 
right, 636 

external, 641, 709, 736, 
747 

internal, 640, 736, 747 
central, of retina, 649 
cerebral, anterior, 641, 747 

deep, 641 

middle, 641 

posterior, 640 
cerebrospinal, 640, 747 



908 



Arteries, cervical, deep, ' 633, 
707, 736, 745 
dorsal, 745 

inferior, 635, 707, 736, 746 
chorioid, anterior, 641 
ciliarj', 649 

circulus arteriosus, 641 
major, 867 
minor, 867 
circumflex, anterior, 748, 
749 
of humerus, 651 
external, 718 
lateral, 752 

of thigh, 673 
of coronary cushion, 660 
of scapula, 651 
posterior, 710, 749 
of humerus, 651 
clitoridis, 717 
coats of, 615 

coccygeal, lateral, 672, 717 
middle, 672, 717 
superficial lateral, 754 
coeliac, 662, 713, 737, 750 
colic, 751 
dorsal, 666 
. middle, 666, 715, 737, 751 
right, 737, 751 
ventral, 665 
communicating, posterior, 

640 
condvloid, 639, 708, 747 
coronary, 628, 630, 631, 707, 

744 
costo-cervical. 632 
cremasteric, 674 
digital, 659, 681, 739, 740, 
894 
common, 659, 739, 749 
dorsal, 712, 719 
plantar, 719 
volar, 712 
lateral, 719 

volar, 712 

medial, 719 

volar, 712 

plantar, 754 

• proper, 739, 749 

volar, 712 
dorsal, 632, 707, 736, 745 
dorsalis penis, 717 
end, 614 
ethmoidal, 649 
external coat, 615 
facial, 642 

transverse, 646, 673, 674, 
709, 747 
femoral, 717, 740, 752 
anterior, 675, 718, 752 
deep, 675, 718, 739, 752 
posterior, 676, 754 
first, of small colon, 666 
frontal, 710 
gastric, 535, 662, 750 
gastro-duodenal, 662, 750 
gastro-epiploic, 750, 751 
left, 663 
right, 662 
gastro-hepatic, 737 
gastro-splenie, 751 
gluteal, anterior, 672, 717, 
754 
posterior, 672, 717 



Arteries, hEemorrhoidal, ante- 
rior, 666 

middle, 670, 754 
hepatic, 438, 662, 713, 750 
hypogastric, 669 
ileal, 665, 737, 751 
ileo-cfeco-colic, 716, 737 
iliac, circumflex, 673, 752 

external, 673, 717, 752 

internal, 669, 717, 754 
iliaco-femoral, 673, 717 
ilio-lumbar, 672, 717, 739, 

754 
incisor, 647 
infraorbital, 649, 710, 737, 

747 
intercarotid, 640 
intercostal, 660, 713, 737, 
750 

aortic, 660 
internal coat, 615 
interosseous, common, 654, 
711, 749 

dorsal, 656, 711 

recurrent, 656, 711 

volar, 655, 749 
intima of, 615 
labial, inferior, 643, 709 

superior, 643, 709 
lacrimal, 649 
laryngeal, 637, 707, 746 
lingual, 642, 70S, 736, 747 
lumbar, 668, 669, 717, 738, 

750 
malar, 650, 7_10 ^ 
mammary, 675, 718 
masseteric, 641, 709 
maxillary, external, 642, 70S, 
736, 747 

internal, 646, 710, 736, 747 
median, 654, 711, 738, 748 
medullary, 22 
meningeal, anterior, 641 

middle, 648, 710, 737, 747 

posterior, 639, 709, 747 
mental, 647 

mesenteric, anterior, 665, ' 
715, 737, 751 

posterior, 666, 716, 737, 
752 
metacarpal, 711, 712, 739, 
749 

dorsal, 657, 712 

lateral volar, 657 

medial volar, 657 
metatarsal, 67S, 719, 740, 
753, 754 

dorsal, 680 

great, 681 

plantar, deep, 753 
superficial, 753 
middle coat, 615 
musculo-phrenic, 635 
nasal, 709 

dorsal, 644, 710 

lateral, 643, 710 
nutrient, of femur, 676 

of humerus, 654 

of tibia, 676 
obturator, 673, 717, 718 
occipital, 660, 662, 713, 737, 

750 
a'sophageal, 660, 662, 713, 

737, 750 



Arteries of bladder, 562 
of bone, 22 
of brain, 792 
of bulb, 670, 754 
of clitoris, 670 
of corpus callosum, 641 
of digital cushion, 659 
of ductus deferens, 575 
of external ear, 875 
of eye, S59 

of P^allopian tubes, 599 
of first phalanx, 659 
of internal ear, 884 
of pelvic limb, 673, 717 
of penis, 582, 754 

anterior dorsal, 675 

deep, 754 

dorsal, 754 
of rete carpi volare, 657 
of retina, 869 

central, 649 
of second phalanx, 659, 660 
of skin, 885 
of small intestine, 665 
of third phalanx, 660 
of thoracic limb, 650, 710 
of tympanum, 878 
of uterus, 601 
of vagina, 602 

of vascular tunic of eye, 867 
omaso-abomasal, 713 
ophthalmic, 710 

external, 649, 747 

internal, 747 
ovarian, 598, 668 
palatine, 737 

greater, 650, 710 

lesser, 650 
pancreatic, 662 
pancreatico-duodenal, 662, 

750 
parotid, 637, 736 

inferior, 707 

superior, 709 
pericardiaco-phrenic, 635 
perineal, 670, 754 
periosteal, 22 
peroneal, 678 
pharyngeal, 642, 708, 709, 

746 
phrenic, 661, 713 
phrenico-abdominal, 737, 

751 
plantar, 678, 753 

lateral, 719 

medial, 719 
popliteal, 673, 676, 717, 740, 

754 
prepubic, 675 
profunda penis, 717 
pterygoid, 647 
pudic, external, 575, 675, 
717, 740, 752 

internal, 669, 717, 754 
pulmonary, 534, 614, 629, 

736 
pyloric, 662 
radial, 712, 738, 749 

anterior, 654 

collateral, 710 

distal collateral, 749 

posterior, 654 

proximal collateral, 749 
ramus oollateralis, 716 



INDEX 



909 



Arteries, renal, 560, 666, 717, 
737, 751 
ruminal, 713 
sacral, lateral, 670, 717 
middle, 629, 717, 750 
saphenous, 675, 718, 740, 

753 
spermatic, 573, 575, 717, 
737, 751 
external, 674 
internal, 666 
spinal, ventral, 640 
splenic, 662, 715, 737, 751 
structure of, 615 
stylomastoid, 645 
subcostal, 633, 707, 736, 745 
sublingual, 642, 709 
submental, 642 
subscapular, 651, 710, 748 
supraorbital, 649 
suprascapular, 651 
systemic, 614, 629 
tarsal, lateral, 677, 718, 753 
medial, 678, 718 
perforating, 678, 719, 740 
recurrent, 677 
temporal, deep, 747 
anterior, 648, 710 
posterior, 648 
superficial, 646, 709, 737, 
747 
terminal, 614 

thoracic, external, 635, 707, 
736, 746 
internal, 634, 707, 736, 
746 
thoraoico-dorsal, 651, 710 
thoraco-acromial, 746 
thymic, 635 
thyroid, 707 

anterior, 637, 746 
posterior, 638, 736, 746 
thyro-laryngeal, 637 
tibial, anterior, 678, 719, 
740, 754 
posterior, 676, 719, 740, 

754 
recurrent, 678 
tracheal, 746 
tympanic, 648 
ulnar, 654, 712, 738, 749 
proximal collateral, 710, 
749 
umbilical, 670, 704, 717, 

754 
uterine, 754 
anterior, 668 
middle, 674, 717 
posterior, 670, 717 
utero-ovarian, 668, 717. 751 
vena cava, anterior, 755 
vertebral, 634, 707, 736, 

745 
vesical, 670 
vesico-prostatic, .670 
Arthrodia, 210 
Arthrology, 207 

comparative, 244 
Articular cartilages, 208 
Articulations, 207. See also 

Joints. 
Arytenoid cartilages of larynx, 

517, .538, 546, .5.50 
Atlantal bursa, 213 



Atlanto-occipital membrane, 
dorsal, 215 
ventral, 215 
Atrio-ventricular bundle, 628 
orifice, left, 625, 626 
right, 621, 623 
Atrium of heart, left, 625 
right, 620 

openings in, 620 
ventricuU, 453, 458 
Auditive tube, 878, 898 
Auditory ossicles, 877 

tube, osseous, 63 
Auricle, 620, 870 
Auricular cartilage, 871 
plexus, anterior, 803 
Axis of lens, 869 
of orbit, 74 
of pelvis. 111 
optic, external, 863 



Bands, longitudinal, of caecum, 
424 
of great colon, 428 
of small colon, 429 
moderator, of right ventri- 
cle, 625 
recto-coccvgeus, 431 
Bars of hoof, 887 
Basal border of hoof, 888 
Basilar plexus, 689 

tubercles of occipital bone, 
51 
Basis pedunculi, 780 
Bicipital groove of humerus, 89 
Bicuspid valve, 626 
Bifurcation of trachea, 525 
Bile duct, 463, 468, 487, 490, 
501 
common, 476 
Bladder, 415, 554, 561, 566, 
569. 570 
fixation of, 561 
lateral ligament of, 414 
middle ligament of, 414 
structure of, 562 
Blind sacs of rumen, 454 
Blood-vascular system, 614, 

617, 705 
Blood-vessels, 614 
Body, ciliary, 865 

geniculate, medial, 781, 835, 

847 
mammillary, 769, 782, 847 
pineal, 781, 835 
pituitary, 769, 780, 782, 835, 

847 
restiform, 773 
vitreous, 869, 897 
Bone or Ijones, acetabulum, 
109, 152, 181, 202 
acromion, 146, 197 
arteries, 22 
atlas, 35, 162, 184 
auditory, 877 
axis, 36, 163, 184 
basihyoid, 72 
breast-, 28 

carpal, 29, 93, 98, 148, 160, 
179, 200 
accessory, 94 
first, 95 



Bone, carpal, fourth, 96 

intermediate, 94 

radial, 94 

second, 95 

third, 96 

ulnar, 94 
carpus, 29 
cartilage, 23 

chemical composition, 24 
chevron, 188 
clavicle, 29, 197 
collar-, 29 

compact substance, 21 
condyle, of mandible, 71 
coracoid, 29 

cranial, 28, 49, 131, 166, 188 
descriptive terms, 25 
development and growth, 23 
digital, 29, 30, 31, 161 
digits, 29, 30, 31, 149, 180, 

201 
diploe, 21 
endosteum, 22 
endoturbinates, 56 
epihyoids, 73 
ethmoid, 54, 134, 1.57, 170, 

191 
ethmo-turbinates, 55 
facial, 28, 63, 170, 191 
femur, 31, 112, 152, 160, 

182, 203 
fibula, 31, 117, 1,54, 160, 183, 

204 
fibular tarsal, 120, 155 
flat, 20 
frontal, 59, 135, 157, 168, 

189 
gelatinous marrow, 22 
hip, 31 
hock, 118 
humerus, 29, 88, 146, 176, 

198 
hyoid. 72, 140, 173, 195 
Oium, 31, 105, 151, 160, 180, 

200 
incus, 877 
innominate, 30, 105, 160, 

180 
interparietal, 56, 134, 167, 

189 
irregular, 20 
ischium, 31, 107, 151, 160, 

181, 202 
keratohyoid, 72 
knee, 29 
knee-cap, 31 
lacrimal, 68, 139, 1.59, 172, 

194 
lenticulare, 877 
long, 20 

lymph-vessels, 22 
malar. 68, 139, 194, 159, 172 
malleus, 877 
mandible, 70, 139, 1.59, 172, 

194 
marrow, 21, 22 

spaces, 21 
maxilla, 63, 137, 158, 170, 
191 

inferior, 70 
maxillo-turbinal, 69 
medullarv arteries, 22 

cavity," 20, 21 
membrane, 23 



910 




INDEX 


Bone, mesosternum, 28 




Bone, ribs, floating, 27 


metacarpal, 29, 30, 98, 


149, 


head, 27 


180, 200 




intercostal spaces, 27 


large, 98, 160 




lateral surface, 27 


small, 99, 160 




medial surface, 27 


third, 98 




neck, 27 


metastemum, 28 




posterior borders, 27 


metatarsal, 31, 123, 


161, 


shaft, 27 


184, 205 




sternal, 27, 45 


fourth, 124 




extremity, 27 


large, 123, 155 




tubercle, 27 


lateral, 124 




vertebral extremity, 27 


medial, 124 




sacrum, 41, 129, 156, 164, 


second, 124 




187 


small, 124, 155 




scapula, 29, 86, 145, 176, 


third, 123 




160, 197 


nasal, 67, 139, 171, 194 




sesamoid, 30, 104, 125, 151, 


naso-turbinal, 69 




156, 160, 180, 201, 203, 


navicular, 105 




204 


nerves, 21, 22 




distal, 30 


number, 20 




proximal, 30 


occipital, 49, 131, 157, 


166, 


short, 20 


188 




shoulder-blade, 29 


condyle, 50, 78, 79 




smuses, 21 


development, 52 




sphenoid, 52, 132, 157, 170, 


of arm, 29 




190 


of cranium, 131 




spongy substance, 21 


of forearm, 29, 63, 137 


158 


stapes", 877, 878 


of leg, 31 




sternum, 28, 48, 131, 157, 


of manus, 29 




166, 188 


of pelvic limb, 30, 105, 


151, 


structure, 21 


160, 180, 202 




stylohyoids, 73 


of skull, 28, 49, 73, 173, 


188, 


tarsal,31, 118, 155, 161, 183, 


195 




205 


of thoracic limb, 29, 86, 


145, 


central, 121, 155 


160, 176, 197 




fibular, 120, 155 


of thorax, 28, 49 




first, 122, 155 


ossa cordis, 705 




fourth, 123, 155 


palatine, 66, 138, 159, 


171, 


second, 122, 1.55 


193 




third, 122, 1.55 


parietal, 57, 134, 157, 


167, 


tibial, 120, 155 


189 




temporal, 60, 137, 158, 169, 


patella, 31, 118, 155, 


161, 


189 


183, 204 




condyle of, 60 


pelvis, 110 




thigh, 31 


periosteal arteries, 22 




thorax, 49, 131, 166, 188 


periosteum, 21 




thyrohyoids, 72 


phalanges, 30, 100, 125 


149, 


tibia, 31, 114, 153, 160, 182, 


1.50, 156, 160, 180, 


184, 


203 


200 




condyles of, 1 16 


first, 100 




tibial tarsal, 120, 155 


second, 30, 102 




tissue, 21 


third, 30, 102 




turbinate, 68, 139, 1.59, 172, 


physical properties, 24 




545 


pneumatic, 21 




dorsal, 194 


premaxilla, 65, 138, 


159, 


ventral, 194 


170, 193 




ulna, 29, 92, 148, 177, 199 


prenasal, 172 




veins of, 22 


presternum, 28 




vertebra?, 25, 33, 125, 156, 


pterygoid, 67, 139, 159 


171, 


161, 184 


193 




accessory processes, 26 


pubic, 31, 109, 151, 160 


181, 


anticlinal, 44 


202 




arch, 26 


radius, 29, 90, 147, 160 


177, 


articular processes, 26 


198 




body, 26 


red marrow, 22 




cervical, 25, 34, 1.56, 161, 


ribs, 27, 45, 130, 1.56, 


165, 


184 


188 




coccygeal, 25, 43, 129, 156, 


angle, 27 




164, 187 


anterior borders, 27 




diaphragmatic, 44 


asternal, 27, 45 




false, 25 


costal groove, 27 




fixed, 25 


development, 27 




foramen, 26 


extremities, 27 




htemal arch of, 26 



Bone, vertebrae, joints of, 244 
ligaments of, 211, 244 
lumbar, 25, 39, 128, 156, 

164, 187 
mammillary processes, 26 
movable, 25 
notches, 26 
ossification of, 26 
sacral, 25, 41, 1.56 
spinous process, 26 
thoracic, 25, 37-39, 127, 

1.56, 163, 186 
transverse processes, 26 
true, 25 

ventral spine, 26 
vessels, 21, 22 
vomer, 70, 139, 159, 172, 

194 
yellow marrow, 22 
zygomatic, 68 
Brachial plexus, 814, 840, 846, 

8.53 
Brachycephalic skull, 195 
Brain, 768, 834, 843, 847 

blood-vessels of, 792 
Bronchi, 525, 534, 540, 546, 
550 
interlobular, 534 
structure of, 534 
Bronchial branches of lungs, 

534 
Bronchioles, lobular, 534 

respiratory, 534 
Buds, taste, 895 
Bulb of hair, 886 

of urethra, 581, 585, 593, 

595 
olfactory, 769, 771, 787, 838, 
844, 850 
Bulbar conjunctiva, 859 
Bulbus aorta>, 629 
glandis of penis, 594 
vestibuli, 603 
Bulla, lacrimal, 139 

ossea, 63 
Bundle, atrio-ventricular, 628 
Bur.sa, atlantal, 213 
bicipital, 302 
intertuberal, of biceps bra- 

chii, 302 
navicular, of deep digital 

flexor, 316 
of biceps femoris, 323 
of common digital extensor, 

307 
of gastrocnemius, 338 
of lateral digital extensor, 

309 
of obturator internus, 329 
of rectus femoris, 329 
of semimembranosus muscle, 

325 
of semitendiBosus muscle, 

323 
of tibialis anterior, 337 
of triceps brachii muscle, 

303 
ovarica, 599 
ovarii, 612 
podotrochlearis, 316 
subcutaneous, 254, 884, 887 
of superficial digital flexor, 
339 
subfascial, 254 



INDEX 



911 



Bursa, supraspinous, 213 
synovial, 253 

of infraspinatus muscle, 

299 
of superficial digital flexor, 

339 
of teres minor muscle, 299 
trochanteric, 322 



Cecal impression of liver, 435 
Cseco-colic fold, 424, 428 

orifice, 424 
Cfficum, 422, 465, 475, 487, 502 
Calcarine fissure, 850 
Caliber of great colon, 427 
Callosal sulcus, 786 
Calloso-raarginal fissure, 785, 

837, 844, 850 
Calyces majores, 565 

minores, 565 
Canal, alar, 54, 75, 78 

alimentary, 385 

carotid, 190 

carpal, 306 

central, of spinal cord, 766 

cervical, 607 

condyloid, 131 

dental, superior, 65 

facial, 62 

femoral, 326 

infraorbital, 65 

inguinal, 292 

lacrimal, 82 
osseous, 68 

mandibular, 71 

of Gartner, 607 

of tarsus, 123 

palatine, 64 

parieto-temporal, 63 

petro-basilar, 190 

pterygoid, 54, 67 

sacral, 43 

semicircular, osseous, 881 

semilunar, of third phalanx, 
103 

spiral, of cochlea, 882 

subsphenoidal, 54 

supraorbital, 137 

temporal, 63, 81 

vertebral, 44 

vidian, 54 
Canine teeth, 394, 398, 448, 
479, 493 
deciduous, 403 
Canthi of eye, 857 
Capillaries, 614 
Capsula adiposa, 557 
Capsule, external, 792 

fibrous, of adrenal bodies, 
563 
of kidnev, 558 
of Uver, 438 

internal, 781, 792 

of kidnev, 559 

of lens, 870 

of lymph nodule, 616 

of prostate, 579 

of spleen, 441 
Cardia of rumen, 458 

of stomach, 472, 498 
Cardiac impression of lung, 

531 



Cardiac lobe of lung, 540, 547, 
548, 551, 553 

notch of lung, 533 

opening of stomach, 416 

plexus, 831 

sphincter, 417 
Cariniform cartilage, 48 
Carnassial teeth, 494 
Carotid canal, 190 

foramen, 190 

notch, 54 

plexus, 804 
external, 830 
internal, 830 
Carpal articular surface, 92 

canal, 306 

sheath of deep digital flexor, 
315 
of superficial digital flexor, 
313 
Carpo-metacarpal sac, 222 
Cartilage, alar, 509, 537, 538 

annular, of ear, 871 

articular, 208 

arytenoid, of larynx, 517, 
538, 546, 550 

auricular, 871 

bones, 23 

cariniform, 48 

conchal, 871 

costal, 27, 47 

cricoid, 515, 5.50 
of larynx, 538, 546 

cuneiform, of larynx, 550 

epiglottic, 516 

epiphyseal, 24 

interarytenoid, of larynx, 
546, 550 

marginal, 209 

of larynx, 515 

of septum nasi, 510 

of third phalanx, 104 

parietal, of nasal cavity, 
510, 537 

scutiform, 871 

thyroid, 515, 538, 546, 550 

xiphoid, 28, 49 
Caruncle, lacrimal, 8,58 
Caruncvila sublingualis, 390, 

405 
Cauda equina, 764 
Caudal part of sympathetic 

system, 832, 856 
Caudate lobe of liver, 434, 468, 
488, 503 

nucleus, 792 

process of liver, 434 
Cavernous plexus, 830, 834 

sinuses, 688 
Cavity, abdominal, 410, 452 

articular, 209 

costal, of sternum, 48 

cranial, 81, 142, 1.59, 175, 
197 

glenoid, 60, 73, 78, 87 

nasal, 82, 143, 159, 175, 197, 
.508, 537, 545, 548 

of larvnx, 521 

of mouth, 385, 444 

of rumen, 456 

of tunica vaginalis, 576 

of uterus, 601 

omental, 442 

pelvic, 152, 412, 453 



Cavity, peritoneal, 411 

pleural, 526 

pulp, of teeth, 395 

thoracic, 525, 540 

tympanic, 875 
Cavum tympani, 898 
Cecum, 422, 465, 475, 487, 502 
Cell, nerve-, 760 

ethmoid, 55 

gustatory, 896 

olfactory, 895 
Cement of teeth, 395 
Center, tendinous, of dia^ 

phragm, 287 
Central canal of spinal cord, 

766 
Cephalic part of sympathetic 

system, 829 
Cerebellar peduncles, 777 
anterior, 776 
middle, 776 

tract, direct, 777 
Cerebello-olivary fasciculus, 

774 ^ 

Cerebellospinal fasciculus, 775, 
777 
descending, 777 
Cerebellum, 771, 776, 835, 843, 

847 
Cerebral arachnoidea, 762 

dura mater, 761 

hemispheres, 771, 783, 836, 
843, 849 

peduncles, 769, 780, 835, 843 

pia mater, 763 
Cerebrospinal fasciculus, 776 
Cerebrum, 843 
Cervical canal, 607 

enlargement, 764 

ganglion, anterior, 830, 842, 
846, 856 
middle, 847 
posterior, 830, 842 

part of sympathetic system, 
830, 842, 847, 858 

plexus, dorsal, 812 

ventral, 812 
CervLx uteri, 601, 606 
Chambers of eye, 869 
Cheek teeth, 394, 399, 400, 

401, 448, 471, 480, 494 
Cheeks, 444, 471, 477, 492 
Chemical composition of bone, 

24 
Chestnut, 895 
Chiasm, optic, 769, 783 
Choanse, 78, 512 

posterior, 406 
Chordae tendinese, 624 
Chorioid, 865 

plex-uses, 763, 780, 783, 787, 
792 
of fourth ventricle, 773 
Chyle, 615 

vessels, 615 
Cilia, 858, 886 
Ciliary body, 865 

border of iris, 866 

ganglia, 829 

ganglion, 796, 838 

processes, 866 

ring, 866 
Circle, coronary, 660 
Circulation, fcetal, 704 



912 



INDEX 



Circulation, pulmonary, 704 
Circulatory system, 734, 742 
Circulus arteriosus, 641 
Cisterna chyli, 697, 722, 756 
Cisterns, subarachnoid, 762 
Claustrum, 792 
Claws, 902, 904 
Cleft, vulvar, 603 
Clinoid processes, anterior, 
190 
posterior, 170, 190 
Clitoris, 604, 60S, 610, 611, 613 

prepuce of, 604 
Coccygeal ganglia, 832 

ganglion, 832 
Cochlea, 881, 882 
Cochlear duct, 883 
Cocliac ganglia, 856 

ganglion, 842 

plexus, 832, 843, 856 
Coeliaco-mesenteric ganglia, 

833 
Colic impression of liver, 435 

mesentery, 412, 429 

plexus, 856 
Collateral fissure, 849 

sulci of hoof, 891 

vessel, 614 
CoUiculus facialis, 779 

seminalis, 585, 590 
CoUum glandis of penis, 581 
Colon, 465. 475, 488, 502 

great, 425 

small, 429 
Color of skin, 884 
Columns, gray, of spinal cord, 
767 

of fornix, 790 

renal, 558 

white, of spinal cord, 767, 
768 
Commissure, anterior, of cere- 
brum, 783 

gray, of spinal cord, 766 

hippocampal, 787 

of nostrils, 508 

of vulva, 603 

optic, 769 

posterior, of cerebrum, 782, 
783 

white, of spinal cord, 766 
Compact substance of bone, 

21 
Comparative anatomy, 17 
Concave border of hoof, 890 
Conchal cartilage, 871 
Condyloid canal, 131 

crest, 90 

fossa, 50, 78 
Conical papilte of mouth, 444 

of tongue, 447 
Conjugate diameter of pelvis, 

liO, 112, 1.52 
Conjunctiva, 859, 896 

bulbar, 859 

palpebral, 859 
Conjunctival sac, 859 
Conus arteriosus, 623 

medullaris, 764, 765 
Convex border of hoof, 890 
Coracoid process, 88 
Core, horn, 136 
Corium, 884, 885 

coronary, 892 



Corium, laminar, 892 

of hoof, 892 

of sole, 892 

perioplic, 892 
Cornea, 864, 897 
Cornu, anterior, of thyroid 
cartilage, 515 

of nostrils, 509 

posterior, of thyroid carti- 
lage, 516 
Cornua, great, of horse, 73 

middle, 73 

of uterus, 600, 606 

small, 72 

thyroid, 72 
Corona glandis of penis, 580 

radiata, 792 
Coronal fissure. 837, 844, 849 
Coronary border of hoof, 888 

circle, 660 

corium, 892 

groove of heart, 619 
of hoof, 888 

pillars of rumen, 4.57 

plexus, 692j_831 

sinus, 681, 754 
opening of, 621 
Coronoid fossa of humerus, 90 

process of mandible, 71 
Corpora quadrigemina, 780, 

847 
Corpus albicans s. fibrosum, 
.598 

callosum, 784, 785, 789, 836 

cavemosum, 615 
of penis, .581 
urethra?, .581 

clitoridis. 604 

luteum. 598 

papillare, 885 

rubrum, 598 

striatum, 792 

trapezoideum, 773, 847 
Corpuscle, renal, 558, 559 
Cortex of thymus gland, 536 
Cortical substance, 777 

of lymph nodule, 616 
Corticopontile fibers, 776 
Costal arch, 28 

cartilages, 27, 47 

cavities of sternum, 48 

facets of thoracic vertebrae, 
37, 38 

groove, 27 

pleura, 526 
Cotyledons, uterine, 607 
Cranial cavity, 81, 142, 1.59, 
17.5, 197 

region, 73, 78 

sutures, 217 
Crest, condyloid, 90 

facial. 64; 68, 77 

frontal, 73 
external, 59 

intervenous, 622 

nasal, 65, 66, 82 

nuchal, 51, 79 

occipital, 51 

parietal, 135 

external, 51, 57, 73 
internal. 58, 81 

petrosal, 62, 81 

ptervgoid, 54 

renal, 558, 559 



Crest, sacral, lateral, 129 
median, 129 
semilunar, of third phalanx, 

103 
spheno-occipital, 53 
supracondyloid, lateral, of 
femur, 112 
medial, of femur, 112 
temporal, 137 
tibial, 116 
turbinate, dorsal, 67 

ventral, 64 
urethral, 585 
Cribriform plate of ethmoid, 

54 
Cricoid cartilage, 515, 550 

of larynx, 538, 546 
Crico-thyroid membrane, 518 
Crico-tracheal membrane, 518 
Crista acustica, 884 
galli, 55, 56, 82 
terminalis, 622 
vestibuli, 881 
Crown of tooth, 395 
Cruciate fissure^ 837, 844, 850 
Crura foniicis, 790 

of clitoris, 604 
Crus laterale dextrum, 287 
sinistrum, 287 
mediale dextrum, 287 

siiiistrura, 287 
of fornix, 792 
penis, .581 
Cryptorchism, 577 
Crystalline lens, 869 
Cuneiform cartilages of larjTix, 
550 
processes, 517 
Cupola, 882 
Cushion, digital, 894 
Cuticle, 887 
Cystic duct, 468 



Dartos of scrotum, 574 
Deciduous teeth, 394, 403 
Decussation of anterior pe- 
duncles, 778 

of fillet, 774 

pyramidal, 773, 774 
Deferential fold of testicles, 

577 
Deltoid tuberosity, 88 
Dental alveoli, 64 

canal, superior, 65 

plexus, maxillary, 798 
Dentine, 395 
Descent of testicles, 577 
Descriptive terms, 18 
Diagonal fissure, 837, 844 
Diameter, conjugate, of pel- 
vis, 110, 112, 152 

transverse, of pelvis, 110, 
112, 152 
Diaphragma sellae, 762 
Diaphragmatic flexure, 425 

line of pleural reflection, 530 

lobe of lung, .540, 547, 551, 
553 

pleura, 526 
Diarthroses, 208 
Diencephalon, 781 
Digestive system 385, 444, 

470, 477, 491 



INDEX 



913 



Digital cushion, 894 

synovial sheatli of deep 
digital flexor, 316 
of superficial digital 
flexor, 314 
Dilatator pupillee, 867 
Diploe, 21 

Diverticulum, cutaneous, 884 
duodeni, 421 
nasi, 508 
pharyngeum, 482 
preputial, 593 
suburethral, 607 
ventriculi of stomach, 483 
Dolichocephalic skull, 195 
Dorsum linguae, 390 
Duct or ducts, alveolar, of 
lungs, 534 
bile, 463, 468^ 487, 490, 501 

common, 476 
cochlear, 883 
cystic, 468 
excretory, 383, 578 

of bulbo-urethral glands, 
580 
hepatic, 438 
lacrimal, 860 
lactiferous, 605, 609 
lymphatic, 725 
right, 615, 698 
tracheal, 725, 756 
mandibular, 405, 496 
naso-lacrimal, 509, 860, 896 
of bulbo-urethral glands, 

585 
of epididymis, 573 
of mammary glands, 605 
of testicles, 573 
pancreatic, 434, 463, 487, 
491, 501, 506 
accessory, 434 
parotid, 404, 477, 482, 492, 

495 
prostatic, 579, 585, 589 
semicircular, membranous, 

883 
sublingual, 405, 496 
submaxillary, 405 
thoracic, 615, 697, 722, 740, 

756 
tracheal, 700 
Ductuli aberrantes, 573 
Ductus arteriosus, 629, 704 
deferens, 575, 587 
deferentes, 571 
endolymphaticus, 883 
incisivus, 387, 445, 514 -■ 
reuniens, 883 
sublinguales minores, 482 
sublingualis major, 482 
utriculo-saccularis, 882 
venosus, 468, 704 
Duodenal angle, 433 

impression of liver, 435 
Duodeno-colic fold, 429 
Duodenum, 419, 463, 486, 500 
Dura mater, 761 
cerebral, 761 
sinuses of, 687 
spinal, 762 



Ear, 870, 901, 902 
external, 870, 897 
58 



Ear, internal, 881, 898 

middle, 875 
Ectolateral fissure, 849 
Ectomarginal fissure, 785, 837, 

844, 849 
Ectosylvian fissure, 849 
Ejaculatory orifice, 575 
Elastic membrane of trachea, 

525 
Embryology, 17 
Eminence, frontal, 136 

ilio-pectineal, 109 

intercondyloid, of tibia, 116 
Eminentia concha;, 871 

medialis, 779 
Enamel of teeth, 395 
Enarthrosis, 210 
Encephalon, 768 
End-lirain, 783 
Endocardium, 621, 628 
Endolymph, 881 
Endoskcleton, 20 
Endosteum, 22 
Endothelium of eye, 865 
Entomarginal fissure. 785, 837, 

844, 849 
Epicardium, 617, 627 
Epicondyle, lateral, of femur, 
114 
of humerus, 90 

medial, of femur, 114 
of humerus, 90 
Epidermis, 884 
Epididymis, 571, 573, 586 

structure of, 572 
Epidural space, 762 
Epigastric zone, 411 
Epiglottic cartilage, 516 
Epiglottis, 538, 546, 550 
Epiphyseal cartilage, 24 
Epiphysis cerebri, 781 
Epiploic foramen, 442, 461 
Epithelium, 383 

cornea>, 864 

of lens, 870 
Equator of eve, 863 

of lens, 869 
Erectile tissue of urethra, 

585 
Ergot, 895 

tendon of, 306 
Eruption of teeth, 403, 450, 

471, 481, 495 
Esophagus, 409, 451, 472, 483, 

497 
Ethmoid cell, 55 
Ethmoidal foramen, 53, 55, 75, 
82 

fossa, 55, 82 

meatuses, 55, 512 

sinus, 86 
Eustachian tube, 878, 898 
osseous, 63 

pharyngeal orifices of, 
406 
Excretory duct, 383, 578 

of bulbo-urethral glands, 
580 
Extensor fossa of femur, 114 
Eye, 857, 896, 900, 902 
Eyeball, 862, 897 
Eyelashes, 886 
Eyelids, 857, 896 

third, 859, 896 



Facet, anterior, of larynx, 515 
costal, of thoracic vertebrae, 

37, 38 
of tibia, 116 
posterior, of larynx, 515 
Facial canal. 62 
crest, 64, 68, 77 
nucleus, 801 
tuberosity, 137 
Fallopian tubes, 596, 599, 606, 

609, 610, 612 
False nostril, 260, 508 

vocal cords, 522 550 
Falx cerebri, 761 
Fascia, 254 

abdominal, 287 
buccal, 255 
bulbi, 861 
carpal, 305 
coccygeal, 279 
common, of leg, 318 
cruris, 318 
deep, 254 

of abdomen, 288 

of forearm, 305 

of head, 255 

of neck, 266 

of shoulder and arm, 298 

of metacarpus and digit, 
306 

of thigh, 317 
digital, 318 
endothoracic, 530 
femoral, medial, 318 
gluteal, 317 
iliac, 317 

lata of gluteal region, 318 
lumbo-dorsal, 276 
metatarsal, 318 
of back, 276 
of forearm, 305 
of head, 255 
of loins, 276 

of mammary glands, 604 
of manus, 305 
of neck, 266 
of pelvic limb, 317 
of tail, 279 
orbital, 861 
pectoral, 295 
pelyic, 317, 413 
perineal, 413 
pharyngeal, 255 
propria of neck, 266 
scrotal, 574 
superficial, 254 

of abdomen, 287 

of forearm, 305 

of gluteal region, 317 

of head, 255 

of metacarpus and digit, 
306 

of neck, 266 

of shoulder and arm, 298 

of thigh, 317 
tarsal, 318 
temporal, 255 
transversalis of transversus 

abdominis muscle, 291 
Fasciculus, cerebello-olivarj', 

774 
cerebellospinal, 775, 777 

descending, 777 
cerebrospinal, 776 



914 



INDEX 



Fasciculus cuneatus, 768 
dorsal longitudinal, 776 
nucleo-cerebellar, 777 
pyramidal, 776 
Femoral canal, 326 

lamina of external oblique 

abdominal muscle, 290 
Fenestra cochlea", 876 

vestibuli, 876, 881 
Fibers, corticopontile, 776 
of heart, 628 
of stomach, 417 
Fibro-cartilages, interverte- 
bral, 211 
of patella, 118 
Fibrous capsule of adrenal 
bodies, 563 

of kidney, 558 

of liver, 438 
coat of kidney, 559 

of ureters, 561 

of viscera, 384 
layer of pericardium, 617 
membranes, 384 
rings of heart, 628 

of intervert-eliral fibro- 
cartilage, 211 
sheath of tendon, 254 
tunic of eye, 863 
Filiform papilla of tongue, 391 
Fillet. 774 
lateral, 776 
medial, 776 
Filum tcrminale, 764, 765 
Fimbria of brain, 787, 791, 792 
of Fallopian tubes, 599 
of ovary, 599 
Fissure, 837 
ansate, 849 
calcarine, 850 
calloso-marginal, 785, 837, 

844, 850 
collateral, 849 
coronal, 837, 844, 849 
cruciate, 837, 844, 850 
diagonal, 837, 844 
ectolateral, 849 
ectomarginal, 785, 837, 844, 

849 
ectosylvian, 849 
entomarginal, 785, 837, 844, 

849 
genual, 837, 844. 8.50 
hippoeampal, 850 
interlobar, of lung, 540 
lateral, 785, 837, 843, 849 

of cerebrum, 478 
longitudinal, of brain, 769, 
771 

of cerebrum, 784 
marginal, 785, 837, 844 
medilateral, 849 
naso-maxillary, 85 
occipito-temporal. 850 
p.alatine. 66. 78, 82, 
p.-illH •brill, .s.-,7 
jictnil viii|i:uiic, 63 
p.irlal. -i:;4, 168 
prrsvlviiiii, 7S5. 844, 849 
.spli-nial, S44, 8.50 
s\il)]iMibir, 7S6 
suprasplenial, 850 
suprasylvian, 785, 837, 844, 



Fissure, transverse, 786. 837 

of bram, 771 

of cerebrum, 784 
umbilical, 435 
ventral median, 765, 766 
Flexure, diaphragmatic, 425 
sigmoid, 589 
sternal, 425 
Floccular fossa, 190 
Floor of mouth, 390 
Foetal circulation, 704 

lung. 531 
Fold, alar, .509 

ca'co-colic, 424, 428 

deferential, of testicles, 577 

duodeno-colic, 429 

gastro-pancreatic, 417 

genital, 414 

glosso-epiglottic, 391 

ileo-csecal, 421 

of mucous membrane, 383 

of skin, 884 

of vena cava, 526 

rumino-reticular, 457 

serous, 384 

spiral, of abomasum, 460 

sublingual, 390 

turbinate, dorsal, 513 

ventral, 513 
umbilical, lateral, 414 

median, 414 
valvular, of ca>cum, 424 
Foliate papilla of tongue, 391 
Follicle, hair-, 886 
lingual, 392 
lymph, 616 
of thyroid gland, 536 
Follicuii oophori, .598 
Foramen alare parvum, 54, 75 
cECCum, 847 
carotid, 190 
epiploic, 442, 461 
ethmoidal, .53, 55, 75, 82 
hypoglossal, 50, 78, 82 
incisivum, 65, 73, J8 , 
infraorbital, 64, 77 
intervertebral, 26, 125, 128, 

703, 791 
lacerum, 51, 63, 78, 82 
lacrimal, 172 
magnum, 50, 78, 79 
mandibular, 71 
mastoid, 62 
maxillary, 65, 76 
mental, 70 
nutrient, 22 

of femur, 112 

of humerus, 88 

of ilium, 106 

of metacarpus, 99 

of tibia, 116 
obturator, 109, 112, 152, 202 
optic, 53, 75, 82 
orbital, 53, 75 
orbito-rotundum, 134 
ovale, 134, 622, 704 
palatine, 76 

anterior, 66 

posterior, 65 
postglenoid, 60 
pterygoid, 54 
rotundum, 53, 75 
sacral, 41 

ventral, 129 



Foramen, sciatic, greater, 231 
lesser, 231 

spheno-palatine, 65, 67, 76, 
82 

stylo-mastoid, 62 

supraorbital, 59, 73 

supratrochlear, 198 

temporal, 54 

trochlear, 54, 75 

venas cavae, 287 

vertebral, 26 

volar, of third phalanx, 103 
Fore-foot, 29 
Formatio reticularis, 767 
Fornix, 785, 790 

conjunctivae, 859 

vaginae, 602 
Fossa, acetabular, 109 

anterior, of skull, 82 

clitoridis, 603 

condyloid, 50, 78 

coronoid, of humerus, 90 

ethmoidal, 55, 82 

extensor, of femur, 114 

floccular, 190 

glandis of penis, 581 

hv:di)i<lca, S69 

hypophyseal. .53 

infratein]ioral, 7.8 

intercondyloid, of femur, 
114 
of tibia, 116 

interpeduncular, 769, 780 

lacrimal, external, 159 

lateral, 769 

of cerebrum, 784 

masseteric, 19.5 

middle, of .skull, 82 

olecranon, 90 

ovalis, 622, 704 

ovulation, 597 

pituitary, 53 

])osterior, of skull, 82 

pterygoid, 170 

pterygo-palatine, 67, 76 

rhomboidea, 778 

supraoondyloid, of femur, 
112 

synovial, 208 

temporal, 73 

trochanteric, of fenmr, 113 
Fourth ventricle, 778 
Fovea, anterior, of fourth ven- 
tricle, 779 

capitis of femur, 113 

dentis, 36 
Frsnula labii, 387 
Frenum Unguae, 390, 391 

preputial, 583 
Frog of hoof, 890, 892 
Frog-stay, 890 
Frontal crest, 73 
external, 59 

eminence, 136 

process, 191 

region of skull, 73 

sinus, .59, 85, 143, 175, 197 

suture, 60 
Front o-lacrimal sutures, 60 
Fronto-maxillary opening, 86 

suture, 60 
Fronto-palatine suture, 60 
Fronto-turbinate sinus, 85 
Fundus reticuli, 456 



915 



Fundus uteri, 601 
Fungiform papilla of tongue, 
391 



Gall-bladder, 468, 490, 505 
Ganglia, 760, S29 

ciliary, 829 

coccygeal, 832 

coeliac, 856 

cceUaco-mesenteric, 833 

lumbar, 832 

mesenteric, anterior, 856 

of sympathetic trunk, 829 

otic, 829 

peripheral, 829 

sacral, 832 

sphenopalatine, 797, 829 

thoracic, 831, 842 
Ganglion, cervical, anterior, 
830, 842, 846, 856 
middle, 847 
posterior, 830, 842, 856 

ciliary, 796, 838 

coccygeal, 832 

coeliac, 842 

geniculate, 801 

intercaroticum, 804 

jugular, 805, 839, 845, 851 

mesenteric, anterior, 842 
posterior, 833 

nodosum, 805, 839, 845, 851 

otic, 799, 838 

petrous, 804 

semilunar, 795 

spinal, 811 

spirale, 884 

splanchnic, 832 

stellatum, 830 

vestibular, 803 
Gartner, canals of, 607 
Gastric impression of liver, 434 

plexus, 833 
anterior, 852 
posterior, 852 
Gastro-pancreatic fold, 417 
Gastro-splenic omentum, 412, 

417, 441 
Gelatinous marrow of bone, 22 
Geniculate body, medial, 781, 
S35, 847 

ganglion, 801 
Genital fold, 414 

organs, 554 

female, 596, 605, 609, 610, 

612 
male, 571, 586, 591, 593 
Genu of corpus callosum, 789 
Genual fissm-e, 837, 844, 850 
Ginglymus, 210 
Girdle, pelvic, 30, 105 

shoulder, 29 
Glands or gland, 382 

adrenal, 563, 566, 567, 569, 
570 

alveolar, 383 

alveolo-tubular, 383 

anal, 502 

buccal, 387, 445, 477 

bulbo-urethral, 571, 579, 
589, 592, 594 
dvicts of, 585 

cardiac, of stomach, 419 

cermninous, 872 



Glands, circumanal, 502 
coil, of digital cushion, 894 
compound, 383 
cutaneous, 898 
duct of, 383 
ductless, 439 
duodenal, 501 
fundus, 383 

of stomach, 419 
gastric, 418 
haemolymph, 616 
labial, 387, 444 
lacrimal, 860, 896 
laryngeal, 523 
lingual, 392 
Hver, 434, 465, 475, 488, 503 

structure of, 438 
lobules of, 385 
l>anph, 616, 722, 733 
abomasal, 731 
anal, 703, 742 
atlantal, 724, 733 
atrial, 730 

aallarv, 703, 728, 741, 757 
bronchial, 700, 727, 741, 

757 
cajcal, 702, 731, 742 
cervical, anterior, 699, 
724, 756 
middle, 699, 724, 741, 

756 
posterior, 699, 724, 725, 

741, 756 
superficial, 699, 756 
coehac, 728 

colic, 702, 731, 742, 759 
costo-cervical, 725 
coxal, 733 
cubital, 703, 757 
duodenal, 731 
epigastric, 729 
gastric, 702, 730, 742 
hepatic, 702, 732, 742 
hyoid, 724 
iliac, external, 701, 729, 

742, 758 
infraspinatus, 728 
inguinal deep, 703 
iliac, internal, 701, 728, 

742, 758 
inguinal, superficial, 701, 

729, 734, 742, 759 __ 
intercostal, 700, 725, 757 
ischiatic, 701, 730, 742 
jejuno-ileal, 731 
lumbar, 701, 728, 742, 758 
mammarv, 701, 734 
mandibular, 698, 722,733, 

740, 756 
merliastinal, 741, 757 
anterior, 700, 726 
diajihragmatic, 726 
dorsal, 726 
posterior, 700, 726 
ventral, 726 
mesenteric, 702, 731, 733, 

742, 759 
of abdomen, 701 
of head, 698 
of pelvic limb, 703 
of pelvis, 701 
of thoracic limb, 703 
of thorax, 700 
of neck, 698 



Glands, lymph, omasal, 731 

pancreatic, 702 

pancreatico-intestinal, 732 

paralumbar, 729 

parapharyngeal, 699, 724 

parietal, 701 

parotid, 723, 733, 740, 756 

]iericardiac, 727 

pharyngeal, 699 

popliteal, 703, 733, 742, 
759 

portal, 758 

prefemoral, 703, 732, 733, 
742 

prepectoral, 699, 741 

prescapular, 699, 725, 741, 
756 

pterygoid, 724 

pulmonary, 727, 757 

rectal, 702, 732 

renal, 701, 728, 759 

reticular, 731 

rhomboid, 728 

ruminal, 730, 731 

sacral, 701, 730, 758 
external, 730 
internal, 730 

splenic, 702, 742 

sternal, 727, 733, 741, 757 
anterior, 727 

subiliac, 703, 732 

submaxillary, 698 

supramammary, 729, 759 

suprapharvngeal,699, 722, 
733, 740, 756 

tarsal, 742 

thoracic, 741 

visceral, 701, 702 
mammarv, 596, 604, 609, 

610, 611, 613 
mandibular, 404, 451, 482, 

496 
mucous, of pharynx, 408 
nasal, 514 
naso-labial, 444, 898 

of duodenum, 421 
of kidneys, 559 
of large intestine, 431 
of skin, 885, 887 
of small intestine, 421 
of third eyelid, 896 
olfactory, 514, 895 
palatine, 389 
pancreas, 432, 468, 470, 476, 

491, 505 
parathyroids, 536, 544, 553 
parotid, 404, 451, 482, 495 

accessory, 482 
preputial, 583 
prostate, 571, 578, 589, 592, 

593 
pyloric, of stomach, 419 
renal, 742 

salivary, 404, 451, 471, 495 
sebaceous, 885, 898 
simple, 383 

spleen, 439, 476, 491, 506 
sublingual, 405, 451, 482, 496 
submaxillary, 404, 482 
sudoriferous, 885 
~ sweat, 885, 898 
tarsal, 859 
thyroid, 535, 536, 544, 548, 

553 



916 



Glands, thjToid, accessory, 
536, 544, 553 

tracheal, 525 

tubular, 383 

tubulo-alveolar, 383 

urethral, 585 
lateral, 585 

uterine, 607 

zygomatic, 496 
Glandula; vestibulares ma- 
jores, 603, 608 
minores, 603, 608 
Clans clitoridis, 603, 604 

penis, 580, 589, 594 
Glenoid cavity, 60, 73, 78, 87 

notch, 87 
Glomerulus of kidney, 559 
Glosso-epiglottic fold, 391 
Glottis, 522 
Gluteal line, 105 
Gomphosis, 208 
Granula iridis, 867 
Granulations, arachnoid, 763 
Gray columns of spinal cord, 
"767 

commissure of spinal cord, 
766 

matter of nervous system, 
760 
of spinal cord, 766 

rami, 829 
Great colon, 425 
Greater omentum, 442, 461, 

499 
Groove, bicipital, of humerus, 
89 

coronary, of heart, 619 
of hoof, 888 

dorsal intermediate, 766 
median, 765 

dorso-lateral, 765 

intertuberal, of humerus, 89 

lacrimal, 64 

longitudinal, of heart, 619 

musculo-spiral, 88 

oesophageal, 458, 473 

of rumen, 454, 455 

of tibia, ll6 

optic, 53 

rumino-reticular, 454 

supraorbital, 137 

palatine, 65, 78 

pubic, 109 
Gross anatomy, 17 
Gromid border of hoof, 888 
Gubernaculum testis, 577 
Gums, 387 
Gustatory cells, 896 

organs, 905 
Guttural pouches, 879 

region, 78 
Gyri, 837 

cerebellar, 777 

cerebri, 771, 785 
Gyrus dentatus, 786 

subcallosal, 788 



HEMORRHOIDAL plexus, 834 

anterior, 856 
Hair-follicle, 886 
Hairs, 886, 887, 898 

tactile, 886 
Hair-streams, 886 



Hamulus pterygoideus, 67 
Hard palate, 78, 387, 445, 470, 

477, 492 
Head, lymph vessels of, 698 
Heart, 614, 617, 705, 734, 735, 
742, 743 

structure of, 627 
Hemal arches, 188 
Hemispheres, cerebral, 771, 
783, 836, 843, 849 

of cerebellum, 771, 776 

of urethra, 595 
Hepatic duct, 438 

plexus, 439, 833 
Hiatus aorticus, 287 

cesophageus, 287 
Hilus of lung, 531 

of ovary, 597 

of spleen, 440, 470, 477 

renal, 555 
Hippocampal commissure, 787 

fissure, 850 
Hippocampus, 786, 792 
Histology, 17 
Hock, 31 
Hoof, 887 
Horns, 899 

core, 136 

of female uterus, 610 

of lateral ventricle, 791 

of spinal cord, 767 

of uterus, 600 
Homy lamina of hoof, 892 
Humeral articular surface, 92 
Humor, aqueous, 869 

vitreous, 869 
Hyaloid membrane, 869 
Hydatides terminales, 599 
Hymen, 602 
Hyoid process, 62 
Hypogastric zone, 411 
Hypoglossal foramen, 50, 78, 

82 
Hypophyseal fossa, 53 
Hypophysis, 769, 780, 782, 

835, 847 
Hypothalamic nucleus, 781 

tegmental region, 781 



Ileo-c,ec.\l fold, 421 

orifice, 424 

valve, 421 
Ileo-colic orifice, 501 

valve, 501 
Ileum, 420 

Iliac lamina of external ob- 
lique abdominal muscle, 290 
Ilio-pectineal eminence, 109 

line, 105 
Impression, csccal, of liver, 435 

cardiac, of lung, 531 

colic, of liver, 435 

duodenal, of liver, 435 

gastric, of liver, 434 
Incisive foramen, 65, 73, 78 
Incisor teeth, 394, 397, 448, 
471, 479, 493 
deciduous, 403, 448 
Infraorbital canal, 65 

foramen, 64, 77 

pouch, 900 
Infratemporal fossa, 78 
Infmidibular recess, 783 



Infundibulum, 769, 780, 782, 
836 
of incisor teeth, 397 
tuhx uterina, 599 
Inguinal canal, 292 
pouch, 900 

ring, abdominal, 290, 292 
external, 288, 292 
internal, 290, 292 
subcutaneous, 288, 292 
Inlet of orbital cavity, 76 
of thoracic cavity, 525 
pelvic, 152, 160, 181, 202 
Inscriptiones tendinea> of rec- 
tus abdominis muscle, 291 
Interalveolar septa, 64 
space, 64, 65, 71, 78 
Interarytenoid cartilage of 

larynx, 546, 550 
Inter-brain, 781 
Intercarpal sac, 222 
Intercavernous sinus, 688 
Intercondyloid eminence of 
tibia, 116 
fossa of femur, 114 

of tibia, 116 
spaces, 27 
Interdental space, 64 
Interdigital pouch, 900 
Interlobar fissures of lung, 540 
Interlobular bronchi, 534 

tissue, 383 
Intermediate zone of kidney, 

550 
Intermuscular septa, 254 
of forearm, 305 
of gluteal region, 317, 318 
of leg, 318 
of shoulder, 298 
Interosseous membrane of 
tibio-fibular articulation, 
239 
space of leg, 31, 116 

of radius, 91 
tendon, 225 
Interpeduncular fossa, 769, 

780 
Intertarsal sac, 240 
Intertuberal groove of hum- 
erus, 89 
Interventricular foramen, 783, 
791 
septum, 627 
Intervertebral fibro-cartilages, 
211 

foramen, 26, 125, 128 

Intestine, 463, 475, 486, 500 

large, 422, 465, 487, 502 

structure of, 430 
small, 419, 463, 475, 486, 
500 
Intraosseous plexus, 692 
Iris, 866, 897 
Ischiatic spine, 106, 107 
Isthmus f auciuni, 390, 406, 446 
oesophagi, 497 
of male urethra, 585 
of prostate, 579 
of thyroid gland, 535, 553 
pharyngeal, 408 



Jejuno-ilbum, 420, 486 
Joints, 207, 211 



INDEX 



917 



Joints, abduction of, 210 
adduction of, 210 
angular movements, 209 
antibrachio-carpal, 221 
arteries of, 209 
atlanto-axial, 214 
atlanto-occipital, 214 
basi-coniual, 218 
capsule of, 208 
carpal, 221, 246 
carpo-metacarpal, 221 
cartilages of, 208 
cavity, 209 
chondro-sternal, 216 
circumduction of, 210 
coccygeal, 213 
coffin, 228 
costo-central, 215 
costo-chondral, 216 
costo-transverse, 216 
costo-vertebral, 215 
crico-arytenoid, 517 
crico-thyroid, 517 
discs of, 209 
elbow, 219, 246 
extension of, 209 
femoro-patellar, 232 
femoro-tibial, 235 
fetlock, 224 
fibrous layer, 208 
flexion of, 209, 210 
folds of, 208 
gliding movements, 209 
hip, 231, 250 
hock, 239, 251 
hyoidean, 218 
intercarpal, 221 
intercentral, 211 
intercornual, 218 
intermetacarpal, 223, 247 
intemeural, 212 
interphalangeal, 248 

distal, 228 

proximal, 228 
interstemal, 245 
intertransverse, 213 
knee, 221 

lym]5h-V(-ssels of, 209 
mandil)ular, 217 
metacarpo-phalangeal, 224, 

247 
movements of, 209 
nerves of, 209 
of auditory ossicles, 878 
of larjnix, 517 
of pelvic limb, 229, 250 
of skull, 217 

of thoracic limb, 218, 245 
of thorax, 215, 245 
of vertebrse, 244 
pastern, 228 
radio-carpal, 221 
radio-uhiar, 221, 246 
rotation of, 210 
sacral, 213 
sacro-iliac, 229, 250 
shoulder, 218, 245 
sternal, 217 
stifle, 232, 250 
surfaces of, 208 
synovial layer, 208 
temporo-hyoid, 218 
temporo-mandibular, 245 
thyro-hyoid, 518 



Joints, tibio-fibular, 239, 251 

tibio-tarsal, 239 

veins of, 209 

villi of, 208 
Jugular ganglion, 805, 839, 

845, 851 



Kidneys, 554, 564, 566, 567, 
569 
capsule of, 559 
cortical substance of, 558 
fibrous capsule of, 558 

coat of, 559 
fixation of, 557 
glomerulus of, 559 
intermediate zone of, 558 
left, 555, 565, 569 
lobules of, 559 
lymph-vessels of, 560 
medullary substance, 558 
mucous coat of, 559 
muscular coat of. 559 
right, 554, 564, 569 
stroma of, 559 
structure of, 558 
vessels and nerves, 560 
weight and size of, 557 

Knee, 29 



Labia vulvre, 603 
Labyrinth, membranous, 881, 
882 

of ethmoid bone, 55 

osseous, 881 
Labjrrinthine wall, 876 
Lacrimal apparatus, 860 

bulla, 139 

canal, 82 
osseous, 68 

caruncle, 858 

ducts, 860 

foramen, 172 

fossa, external, 159 

groove, 64 

lake, 858 

pouch, 900 

process, 194 

sac, 860 

tubercle, 68 
Lacteals, 615 
Lactiferous ducts, 605, 609 

sinus, 605, 609 
Lake, lacrimal, 858 
Lamina basalis, 865 

choriocapillaris, 865 

cribrosa sclerae, 863 

elastica posterior, 864 

externa, 21 

fusca, 863 

homy, of hoof, 892 

interna, 21 

lateralis of ethmoid bone, 
55 

layer of hoof, 892 

Umitans anterior, 864 

medullary, 777 

of cricoid cartilage, 515 

of hoof, 888 

of nostrils, 509 

of thyroid cartilage, 515 

omasi, 460 

propria, 383 



Lamina spiralis ossea, 882 
suprachorioidea, 865 
terminalis, 783 
transversalis of ethmoid 
bone, 170, 191 

of palatine bone, 171 
vaseulosa, 865 
Laminar corium, 892 
Laryngeal saccule, 522, 550 
Larynx, 514, 538, 546, 550 
arytenoid cartilages, 517, 

538, 546, 550 
cartilages of, 515 
cavity of, 521 
cricoid cartilage of, 515, 538, 

546, 550 
cuneiform cartilages, 550 
facets, 515 
interarytenoid cartilage of, 

546, 550 
lateral ventricle, 522, 539, 

550 
membranes of, 517 
middle ventricle, 522 
mucous membrane, 523 
posterior compartment, 523 
vessels and nerves, 523 
vestibule of, 522 
Layer, fibrous, of pericardium, 

617 
laminar, of hoof, 892 
parietal, 384, 412 
serous, of pericardium, 617 
visceral, 384, 412 

of pericardium, 617 
Lemniscus, 774 
Lens, crystalline, 869 

fibers, 870 
Lenticular nucleus, 792 
papillae of tongue, 447 
Ligament or ligaments, 209 
accessory, of hip joint, 232 

of prepubic tendon, 292 
alar, 244 
annular, 254 

digital, distal, 306 
proximal, 306 

dorsal, of carpus, 305 

of leg, 318 

of radius, 246 

volar, of carpus, 306 
of fetlock, 306 
arytenoid, transverse, 518 
atlantal, lateral, 215 
atlanto-axial, dorsal, 214 

ventral, 214 
broad, of uterus, 415, 601, 

607, 612 
carpal, dorsal, 222 

volar, 222 
caudate, of liver, 437 
check, 240 

inferior, 222, 315 

of deep digital flexor, 341 

subcarpal, 315 

superior, 313 
collateral, 209 

of coffin joint, 228 

of fetlock joint, 224 

of metacarpo-phalangeal 
joints, 247 

of pastern joint, 228 
conjugal, 215 
coronary, 437, 488 



918 



INDEX 



Ligament, costo-sternal, radi- 
ate, 216 
costo-transverse, dorsal, 216 
cruciate, of stifle joint, 238 
dorsal, of hock joint, 241 

of interphalangeal joints, 
250 
dorso-scapular, 276 
falciform, 437, 488 
femoro-patellar, 233 
gastro-phrenic, 416 
hepato-renal, 437 
ilio-lumbar, 231 
inferior check, 315 
inguinal, 288 
intcirliondral, 216 
intcrdigital, 248 

cruciate, 249 

distal, 249 
interosseous, 209 

of forearm, 221 

of tiliial and fibular tar- 
sal bones, 242 
intersesamoidean, 224 
interspinous, 214 
intra-articular, 209 
lateral, left, of liver, 437 

of bladder, 414, 562 

of carpal joints, 222 

of elbow joint, 221 

of hock joint, 240 

of stifle joint, 238 

right, of liver, 437 
longitudinal, dorsal, 211 

ventral, 211 
medial, of carpal joints, 222 

of elbow joint, 221 

of hock joint, 241 

of stifle joint, 237 
metacarpal, interosseous, 

223 
middle, of bladder, 414, 562 
navicular, distal, 229 

suspensory, 229 
odontoid, 214 
of auditory ossicles, 878 
of cartilages of third pha- 
lanx, 229 
of coffin joint, 228 
of dens, 214 
of ergot, 306 

of fibular tarsal bone, 242 
of hock joint, 240, 242 
of larynx, 517 
of liver, 437, 488 
of neck, 215 
of ovary, 597, 612 
of pelvic girdle, 230 
of peritoneum, 412 
of stifle joint, 233, 237 
of tibial tarsal bone, 242 
of vertebrse, 211, 244 
)iali)('bral, 858 
IK.i.'llar, 233, 234 
pcriarlicular, 209 
pi'i icardiaco-phrenic, 742 
lilialango-sesamoidean, 229 
plaiiiar, of hock joint, 241 
pulmonary, 526 
radial, 313 
radiate, 215 

costo-sternal, 216 
round, of bladder, 414, 562 

of hip joint, 231 



Ligament, round, of liver, 437, 
490 

of uterus, 601, 607, 612 
sacro-iliac, dorsal, 230 

lateral, 230 

ventral, 230 
sacro-sciatic, 230 
scrotal, 574 
serous, 384 
sesamoidean, 224 

collateral, 224, 229 

cruciate, 227 

deep, 227 

distal, 226 

middle, 226 

short, 227 

straight, 226 

superficial, 226 

suspensory, 317 
sternal, internal, 217 
sterno-pericardiac, 705 
subcarpal, 222 

check, 315 
subtarsal, 240 
superior check, 313 
supraspinous, 212 
suspensory, 225 

navicular, 229 

of anus, 432 

of penis, 580 

of spleen, 441 

sesamoidean, 317 
thyro-epiglottic, 518 
tracheal annular, 525 
transverse, of atlas, 245 

of carpus, 306 

of radio-ulnar articula- 
tion, 221 
vaginal, 254 
ventricular, 518 
vocal, 518 

volar, of pastern joint, 228 
Ligamenta flava, 212 
Ligamentum arteriosum, 629, 

704 
denticulatum, 764 
nucha), 213 

pectinatum iridis, 865, 866 
spirale cochleae, 883 
Line, diaphragmatic, of pleu- 
ral reflection, 530 
gluteal, 105 
ilio-pectincal, 105 
nivld-hvoid, 70 
of pleural reflection, 530 
I)()|ilUeal, uf tibia, 115 
sternal, of pleural reflection, 

530 
terminal, 110, 410 
vertebral, of pleural reflec- 
tion, 530 
white, of hoof, 889 
Linea alba, 288 
Lingual follicles, 392 

process, 72 
Lingula, 776 

Lips, 385, 444, 470, 477, 491 
Liquor foUiculi, 598 
pericardii, 617 
pleura>, 530 
Lobe or lobes, apical, of limg, 

540, 547, 548, 551, 553 
cardiac, of lung, 540, 547, 

548, 551, 553 



Lobe, caudate, of liver, 434, 

468, 488, 503 
cerebellar, 777 
diaphragmatic, of lung, 540, 

547, 551, 553 
intermediate, of lung, 540, 

534, 547, 551 
of li\-er, 438, 488, 490, 503 
of lung, 540, 547, 551 
of mammary glands, 605 
of prostate, 579 
of thymus gland, 536 
of thyroid gland, 535, 536, 

553 
of urethra, 595 
piriform, 784, 788, 850 

of brain, 769 
Lobular bronchioles, 534 
Lobulation of lungs, 534, 544 
Lobules of kidney, 559 
of li\er, 438 
pulmonary, 534 
Lumbar enlargement, 765 
ganglia, 832 
part of sympathetic system, 

856 
Lumbo-costal arch, 287 
Lumbo-sacral plexus, 824, 841, 

846, 855 
Limg, 530, 540, 544, 547, 

551 
alveolar ducts of, 534 
apex of, 533, 534 
apical lobe of, 540, 547, 548, 

551, 553 
basal border of, 533 
base of, 533 
body of, 534 

bronchial branches of, 534 " 
cardiac impression of, 531 

lobe of, 540, 547, 548, 551, 
553 

notch of, 533 
color of, 531 
costal surface of, 531 
diaphragmatic lobe of, 540, 

547, 551, 553 
dorsal border of, 532 
ftrtal, 531 
form of, 531 
hilus of, 531 

interlobar fissures of, 540 
intermediate lobe of, 534, 

540, 547, 551 
lobes of, 540, 547, 551 
lobulation of, 534, 544 
lymph-vessels of, 534, 535 
mediastinal surface of, 531 
root of, 534 
\-entral border of, 533 
vessels and nerves of, 534 
Lymph, 616 
ducts, tracheal, 725, 756 
follicles, 616 
nodes, 616 
nodules, 616 
sinus, central, 616 

peripheral, 616 
spaces, 616 
vessels, 615 

of abdomen, 701 

of adrenal bodies, 564 

of bladder, 562 

of bone, 22 



INDEX 



919 



Lymph vessels of corium of 
lioof, 894 

of Fallopian tubes, 599 

of head and neck, 698 

of heart, 628 

of kidneys, 560 

of lung, 534, 535 

of ovary, 599 

of pelvic limb, 703 

of pelvis, 701 

of penis, 582 

of skin, 885 

of spermatic cord, 576 

of testicles, 574 

of thoracic limb, 703 

of thorax, 700 

of uterus, 602 

of vagina, 602 
Lymphatic duct, 725 

right, 615, 698 
system, 615, 697, 722, 740, 

756 
Lymphocytes, 616 
Lyssa, 493 



Macroscopic anatomy, 17 
Maculae acusticge, 883 
Malleolus, lateral, of tibia, 117 
medial, of tibia, 117 
of tibia, 117 
Mammillarv body, 769, 782, 
847 
processes, 26, 45, 163 
Mandibular canal, 71 
duct, 405, 496 
foramen, 71 
notch, 71 
space, 70 
teeth, 401 
Manulirium sterni, 28, 48 
Marginal cartilage, 209 
fissure, 785, 837, 844 
pole, 836 
Margo plicatus, 418 
Marrow of bone, 21, 22 

spaces, 21 
Masseteric fossa of mandilile, 

195 
Mastoid liorder of occipital 
bone, 52 
foramen, 62 
process, 61, 74 
Maxillary dental plexus, 798 
foramen, 65, 76 
process, 194 
region, 76 

siilus, 84, 144, 175, 197 
interior, 84 
superior, 85 
teeth, 400 
tuberosity, 65 
Meatus, acoustic, external, 61, 
870, 871 
internal, 62, 882 
common, of nose, 69 
dorsal, of nasal cavity, 545 

of nose, 69, 83 
ethmoidal, 55, 512 
middle, of nasal cavity, 545, 

550 
nasal, common, 511 
dorsal, 511 
middle, 69, 83, 511 



Meatus, nasal, ventral, 69, 83, 
511 
ventral, of nasal cavity, 546, 
550 
Medial epicondvle of femur, 
114 
malleohis of tibia, 117 
supracondyloid crest of fe- 
mur, 112 
Mediastinal pleura, 526 
Mediastinum thoracis, 525 
Medihitcral fissure, 849 
Medulla oblongata, 769, 771, 
773, 834, 843, 847 
of thvmus gland, 536 
cavity, 20, 21 
Medullary cords, 616 
lamina, 777 
substance, 777 

of adrenal bodies, 563 
velum, 776 
anterior, 779 
posterior, 779 
Membrana basilaris, 883 
nictitans, 859 

propria of middle ear, 876 
tympani, 876 
vestibularis, 883 
Meml^rane, at lanto-oecipit al , 
dorsal, 215 
atlanto-occipital, ventral, 

215 
crico-thyroid, 518 
crico-tracheal, 518 
elastic, of trachea, 525 
fibrous, 384 
hyaloid, 869 
interosseous, of tibio-fil)ular 

articulation, 239 
obturator, 231 
of larynx, 517 
serous, 384 

synovial, of carpal joints, 
222 
of elbow joint, 219 
of hip joint, 232 
thyro-hyoid, 518 
Membranous labvrinth, 881, 

882 
Meninges, 761 
Meniscus, 209, 235 
Mental foramen, 70 
Meridians of eye, 863 
Mesaticephalic skull, 195 
Mesencephalon, 780 
Mesenteric ganglion, anterior, 
842, 856 
posterior, 833, 843 
plexus, anterior, 833, 856 
posterior, 833, 856 
Mesenterv, 412 
colic, 412. 420 
great, 412, 420 
Mesocolon, 502 
Mesoduodenum, 419, 500 
Mesogastric zone, 411 
Mesorchium, 576, 577 
Mesorectum, 413, 429 
Mesosalpinx, 599, 612 
Mesotendon, 253 
Mesothelium, 384 
Mesovarium, 597 
Microscopic anatomy, 17 
Mid-brain, 780 



Moderator bands of right 

ventricle, 625 
Modiolus, 882 
Molar teeth, 394, 399 
Morphology, 17 
Motor fibers, 80S 
nucleus, dorsal, 808 
of fifth nerve, 776 
ventral, 808 
root of fifth nerve, 776 
Mouth, 385, 444, 477, 491 
cavity of, 385, 444 
floor of, 390 

mucous membrane of, 385 
Mucous coat of bladder, 562 
of Fallopian tubes, 599 
of kidney, 559 
of small intestine, 421 
of stomach, 418 
of vagina, 602 
membranes, 383 
of aliomasum, 462 
of ductus deferens, 575 
of large intestine, 431 
of larynx, 523 
of mouth, 385 
of nose, 512 
of crsophagus, 410 
of omasum, 462 
of pharynx, 407 
of reticulum of stomach, 

462 
of nmien, 458 
of seminal vesicles, 578 
of small intestine, 421 
of tongue, 390 
of trachea, 525 
of vu'eters, 561 
of urethra, 585, 604 
of uterus, 601, 607 
of vulva, 603 
tympanic, 878 
Mucus, 383 

Muscle or muscles, 252, 254 
abdominal, 287, 349, 361, 

377 
abductor cniris posterior, 
378 
digit i fiuinti, 381 
halhicis, :iS2 

piillicis brevis et opponens 
poUicis, 375 
longus, 373 
accessory structures, 253 
action of, 253 
adductor, 326, 356, 365 
digiti quinti, 375 

secundi, 375 
femoris, 380 
hallucis, 382 
of second and fifth digits, 

381 
pollicis, 375 
anconeus, 304, 363 
antitragicus, 874 
arrectores pilorum, 886 
articularis genu, 355 
arvtenoideus transversus, 

520 
attachments of, 252 
auricular, 872, 897 
anterior, 872 
deep, 873 
dorsal, 872 



920 



Muscle, auricular, posterior, 
873 
belly of, 253 
biceps, 351 

brachii, 302, 363, 372 
femoris, 322, 355, 365, 378 
bipennate, 253 
biventer cervicis, 376 
blood supply of, 253 
brachialis, 302, 363, 373 
braehiocephalious, 294, 351, 

360, 362, 371 
brachioradialis, 308, 373 
buccinator, 258, 345, 368 
bulbo-cavemosus, 586, 589, 

595 
capsularis, 301, 333, 351, 

355, 363, 365, 380 
cervical cutaneous, 347, 376 
cervicalis ascendens, 269 
cervico-auricularis profun- 
dus major, 873 
minor, 873 

superficialis, 873 
cervico-scutularis, 872 
chondro-pharyngeus, 407 
ciliary, 866 
cleido-cervicalis, 371 
cleido-mastoideus, 351, 362, 

371 
cleido-occipitalis, 351, 362 
coccyseus, 279, 377 
compicxus, 273, 361, 376 

major, 376 
constrictor vestibuli, 603 

vulva;, 603 
coraco-brachialis, 300, 351, 

363, 371 
corrugator supercilii, 260 
creraaster, external, 291, 

361, 576, 587, 591 
crico-arytenoideus dorsalis, 

519 
lateralis, 519 
crico-pharj'ngeus, 407 
crico-thyroideus, 519 
cutaneous, 252, 254, 343, 
360, 368, 884 
colli, 254 
faciei, 254 
labiorum, 254 
omo-brachialis, 254 
trunci, 254 
deltoid, 351, 362, 371 
deltoideus, 298 
depressor labii inferioris, 
258, 344, 359, 368 
superioris, 344 
rostri, 359 
diaphragm, 285, 349, 361 
digastric, 253 
digastricus, 264, 346, 359, 

370 
digital extensor, common, 
307, 352, 363, 373 
lateral, 308, 335, 352, 
356, 363, 367, 373, 
380 
long, 333, 356, 366, 380 
medial, 352, 356 
of second digit, 363 
short, 356 
flexor, deep, 315, 339, 354, 
364, 367, 374, 381 



Muscle, digital flexor, long, 340 
superficial, 313, 339, 
353,364,367,374,381 
dilatator naris apicalis, 345 
lateralis, 258, 345, 359 
extensor carpi obliquus, 310, 
352, 363, 373 
radialis, 306, 352, 363, 
373 
brevis, 373 
longus, 373 
ulnaris, 374 
digitalis brevis, 343, 367, 

380 
hallucis longus, 367, 380 
of fifth digit, 374 
of first and second digits, 

373 
of third and fourth digits, 
373 
facial cutaneous, 359 
flexor carpi radialis, 310, 
364, 374 
uhiaris, 310, 364, 374 
deep, 359 

digitalis longus, 368 
pedis longus, 381 
hallucis, 341, 368 
brevis, 382 
longus, 381 
pollicis brevis, 375 
superficial, 359 
frontalis, 343 
fronto-scutularis, 872 
gastrocnemius, 338, 359, 

367, 381 

gemellus, 329, 356, 365, 378 
genio-glossus, 394 
genio-hyoideus, 265, 347 
gluteus accessorius, 322 

medius, 321, 355, 365, 378 

profundus, 322, 355, 365, 
378 

superficialis, 321, 365, 378 
graciUs, 325, 356, 365, 380 
head of, 253 
helicis, 874 
hyo-epiglotticus, 519 
hyo-glossus, 392 
hyoid, 264, 347, 359, 370 
hyoideus transversus, 265, 

347, 359 
hyo-pharyngeus, 407 
iliacus, 320, 354, 378 
ilio-psoas, 319, 378 
incisivus inferior, 257, 344 

superior, 257 
infraspinatus, 299, 351, 362, 

371 
insertion of, 252 
intercostal, external, 283, 
349, 361, 376 

internal, 283, 349, 361 
interosseous, 317, 343, 365, 

368, 375, 381 
interosseus medius, 354 
interscutularis, 872 
interspinales, 349, 362, 376, 

377 
intertransversales, 347, 349, 
361, 362, 376, 377 
caudffi, 281 
coUi, 270 
lumborum, 279 



Muscle, ischio-cavernosus, 582, 
589, 604 
ischio-urethral, 586, 595 
kerato-hyoideus, 265, 347, 

359 
kerato-pharyngeus, 407 
lateralis nasi, 259 
dorsal part, 345 
ventral part, 345 
latissimus dorsi, 295, 351, 

362 
levator labii superioris pro- 
prius, 256, 344, 359, 368 
nasolabialis, 255, 258, 

343, 359, 368 
palati, 389 
palpebrse superioris, 260, 

861 
rostri, 359 
levatores costarum, 281, 

349, 361, 376 
lingual^ 392 

longissfmus atlantis, 376 
capitis, 376 

et atlantis, 271, 361, 
376 
costarum, 277, 349, 362, 

377 
dorsi, 278, 349, 371, 377 
longus com, 270, 347, 360, 

376 
lumbricales, 317, 343, 354, 

365, 368, 375, 381 
malaris, 260, 345 
mandibular, 260, 346, 359, 

370 
masseter, 261, 346, 359, 370 
mentalis, 258 
multifidus, 362 
cer\'icis, 273 
dorsi, 279 
multipennate, 253 
mylo-hyoideus, 264, 347, 

359, 370 
nasal, 368 

nerve supply of, 253 
non-striated, 252 
obliquus abdominis exter- 
nus, 288, 349, 361, 
377 
internus, 290, 350, 361, 
377 
capitis anterior, 275 
posterior, 273, 361 
dorsalis s. superior, 861 
ventralis s. inferior, 861 
obturator, 378 

externus, 328, 356, 365 

internus, 328, 356, 365 

occipito-hyoideus, 265, 347, 

359 
occipito-mandibularis, 262, 

346, 370 
ocular, 861 
of abdomen, 287, 349, 361, 

377 
of anus, 432 
of arm, 302, 351, 363 
of auditory ossicles, 878 
of back, 349, 361, 376, 377 
of cheeks, 256 
of digit, 343 
of eyeball, 861 
of eyelids, 260 



921 



Muscle of face, 343, 359, 368 
of foot, 333, 356 
of forearm, 305, 352, 363 
of head, 255 

ventral, 360 
of hip, 365 

lateral, 320, 355 
of larynx, 518 

extrinsic, 518 

intrinsic, 519 
of leg, 333, 356, 366 
of hps, 255 

of loins, 276, 349, 361, 377 
of nianus, 305, 352, 363 
of metatarsus, 343 
of neck, 266, 347, 360, 376 

lateral, 271 

ventral, 266 
of nostrils, 258 
of pelvic Umb, 319, 354, 365, 

378 
of penis, 582 
of pharynx, 407 
of shoulder, 298, 351, 362 

girdle, 293, 350, 362 
of soft palate, 389 
of tail, 279, 349, 362, 377 
of thigh, 365 

anterior, 329, 355 

lateral, 320, 355, 356 

medial, 325 
of thoracic limb, 293, 350, 

362, 370 
of thorax, 281,349, 361, 376 
of tongue, 392 
omo-hyoideus, 268, 347, 359, 

360 
omo-transversarius, 360,351, 

362, 370 
orbicularis oculi, 260, 345 

oris, 255, 343, 359, 368 
origin of, 252 
palatinus, 389 
palato-pharyngeus, 407 
palmaris brevis, 375 

longus, 374 
palpebral, 368 
panniculus carnosus, 254, 

884 
parieto-auricularis, 872 
parotido-auricularis, 873 
pectineus, 326, 356, 365, 380 
pectoral, 295 

deep, 296, 351, 371 
anterior, 296, 362 
posterior, 296, 362 

superficial, 295, 351, 371 
anterior, 295, 362 
posterior, 296, 362 
peroneus brevis, 380 

longus, 356, 366, 380 

tertius, 335, 356, 366, 386 
piriformis, 378 
popUteus, 343, 367, 381 
preputial, anterior, 590 

posterior, 590 
pronator quadratus, 375 

teres, 354, 364, 374 
protractors, 590 
psoas major, 319, 354, 365, 
378 
minor, 319, 354, 365, 378 
pterygoideus lateralis, 262, 
346, 359, 370 



Muscle, pterygoideus medi- 
aUs, 261, 346, 359 
pterygo-pharyngeus, 407 
quadratus femoris, 328, 356, 
365, 378 
lumborum, 320, 354, 365, 

378 
plants', 381 
quadricejjs femoris, 329, 355, 

365, 379 
recti capitis dorsales, 361 
rectus abdominis, 290, 350, 
361, 379 
capitis dorsalis major, 275 
minor, 276 
lateralis, 270, 347, 376 
ventrahs major, 269, 
347, 376 
minor, 269, 347, 376 
dorsalis s. superior, 861 
femoris, 329, 379 
lateralis, 861 
medialis, 861 
thoracis, 283, 361 
ventralis s. inferior, 861 
relations, 253 
retractor, 590 
ani, 432, .502 
costae, 283, 361 
oculi, 861 
penis, 582, 589 
rhomboideus, 293, 351, 371, 
362 
cervicalis, 293, 371 
thoracalis, 293, 371 
rotator, 873 

sacro-coccygeus, 362, 377 
accessory, 377 
dorsalis, 280 
lateralis, 280 
ventralis, 281 
sartorius, 325, 356, 365, 380 
scalenus, 268 

dorsaUs, 347, 360, 376 
ventralis, 347, 360, 376 
scutularis, 872 
scutulo-auricularis pro- 
fundus major, 873 
minor, 874 
superficialis accessorius, 
872 
inferior, 872 
niedius, 872 
superior, 872 
semimembranosus, 324, 365, 

355, 379 
semitendinosus, 323, 355, 

365, 379 
serratus cervicis, 297 

dorsalis anterior, 277, 349, 
361, 377 
posterior, 277, 349, 361, 
377 
thoracis, 297 

ventralis, 297, 351, 362, 
371 
shape of, 252 
skeletal, 252 
soleus, 359, 339, 367 
sphincter, 252 
ani externus, 432 

internus, 432 
vesicae, 562 
spinalis, 273 



Muscle, spinalis et semispi- 

nalis, 362 
splenius, 271, 347, 361, 37G 
stapedius, 878 
sterno-cephalicus, 266, 347, 

360, 376 
sterno-hyoideus, 359, 370 
sterno-mandibularis, 347 
sterno-raastoideus, 347 
sterno-thyro-hyoideus, 268, 

347, 360, 370 
sterno-thvroideus, 370 
striated, 252 
structure of, 253 
stylo-glossus, 392 
stylo-hyoideus, 265, 347, 

370 
stylo-pharyngeus, 407 
sublumbar, 319, 354, 365 
submultifidus, 376 
subscapularis, 300, 351, 363, 

371 
supinator, 364, 374 
supraspinatus, 298, 351, 362, 

371 
synovial membranes of, 253 
temporalis, 261, 346, 370 
tendinous inscriptions, 253 

intersections, 253 
tensor fascia; antibrachii, 
303, 352, 363, 373 
laU-e, 320, 355, 365, 378 

palati, 390 

tympani, 878 
teres major, 300, 351, 363, 
371 

minor, 299, 351, 362, 371 
thjTo-arytenoideus exter- 
nus, 521 
thyro-hyoideus, 518 
thyro-pharyngeus, 407 
tibialis anterior, 336, 357, 
366, 380 

posterior, 340, 367, 381 
trachealis, 525 
tragicus, 874 

transversus abdominis, 291, 
350, 361, 378 

nasi, 259, 359 

thoracis, 285, 361 
trapezius, 293, 350, 362, 370 

cervicalis, 293 

thoracalis, 293 
triceps, 352, 363, 373 

brachii, 303, 304 
ulnaris lateralis, 313, 364, 

374 
unipennate, 253 
urethral, 586, 590, 593, 595, 

604 
vastus intermedins, 333, 379 

lateralis, 330, 379 

mediaUs, 331, 379 
ventricularis, 520 
verticalis auricula^, 875 
visceral, 252 
vocalis, 520 

zvgomatico-auric.ularis, 872 
zygomaticus, 257, 344, 359, 

368 
Muscular coat of abomasum, 
462 

of bladder, 562 

of ductus deferens, 575 



922 



Muscular coat of Fallopian 
tubes, 599 

of kidney, 559 

of large intestine, 430 

of cesophagus, 409 

of omasum, 462 

of reticulum of stomach, 
462 

of rumen, 461 

of seminal vesicles, 578 

of small intestine, 421 

of stomach, 417 

of ureters, 561 

of urethra, 604 

of uterus, 601, 607 

of vagina, 602 

of viscera, 384 
process of temporal bone, 

63 
tissue, 384 
Muscularis mucosae, 383 

of small intestine, 421 
Musculi papillares of left ven- 
tricle, 627 

of right ventricle, 624, 625 
pectinati of right atrium, 

621 
Musculi)-s])iral gi-oove, 88 
Myenteric jilcxus, 833 
Mylo-liyoiil line, 70 
Myocardium, 628 
Myology, 252 



Nares, posterior, 78, 406, 512 
Nasal cavity, 82, 143, 159, 175, 
197, 508, 537, 538, 545, 
548 
common meatus, 511 
dorsal meatus, 511, 545 
ethmoidal meatuses, 512 
meatuses, 511 
middle meatus, 511, 545, 

550 
parietal cartilage, 510 
ventral meatus, 511, 546, 

550 
vessels and nerves, 510 
crest, 65, 66, 82 
process, 65 
region, 73 
septum, 82, 84 
spine, posterior, 193 
Naso-frontal suture, 60, 67 
Naso-lacrimal duct, 509, 860, 
896 
gi'oove for, 82 
orifice, 508 
suture, 67 
Naso-maxillary fissure, 85 
notch, 67 
opening, 511 
suture, 67 
Neck, lymph vessels of, 698 

of tooth, 395 
Nerve or nerves, 760 
abdurcnt, 770, 801 
acdustic, 770, 803 
alveolar, inferior, 851 
mandibular, 800 
maxillarv, 798 
middle, 798 
posterior, 798 
articular, 761 



Nerve, auricular, 805 

anterior, 803 

internal, 802 

posterior, 802, 812 
auriculo-palpebral, 802, 839, 

851 
axillary, 815, 816 
bronchial, 808 
buccal, 803, 839, 845, 851 
buccinator, 799 
cardiac, 808, 831, 856 
cerebral, 793 
cervical, 803, 812, 851 

eighth, 813 

fifth, 813 

first, 812 

fourth, 813 

second, 812 

seventh, 813 

sixth, 813 

third, 813 
chorda tympani, 801, 802 
ciUary, long, 850 

short, 796 
coccygeal, 829 
cochlear, 803, 884 
cranial, 793, 838, 844, 850 
cutaneous, lateral, of leg, 
826 

of neck, 813 

of thigh, 823 

posterior, of leg, 826 
of thigh, 825 
dental, 798 
depressor, 807, 853 
digastric, 802 

digital, 819, 841, 846, 853, 
854, 855, 856 

lateral volar, of fifth digit, 
854 
dorsalis penis, 828 
eighth, 770 
eleventh, 771 
ethmoidal, 796, 850 
facial, 770, 801, 839, 850 
femoral, 824 
fifth, 770 
fourth, 770 

frontal, 796, 838, 845, 85j)_ 
glosso-pharyngeal, 771, 773, 

804 
gluteal, anterior, 824 

posterior, 824 
hsemorrhoidal, posterior, 

828 
hypoglossal, 771, 773, 810, 

840, 845, 853 
ilio-hypogastric, 822 
ilio-inguinal, 822 
infraorbital, 798, 845, 850 
infratrochlear, 796, 850 
intercostal, 820 
interosseous, 819 
labial, 850 

su])('i-ior, 798 
lacrimal, 795, 83S, 845, 850 
laryngeal, 852 
anterior, 807 
lingual, 800, 805, 851 
lumbar, 822 
fifth, 823 
first, 822 
fourth, 823 
second, 822 



Nerve, lumbar, sixth, 823 

third, 823 
mandibular, 798, 800, 838, 

845, 850 
mas.seteric, 799 
maxillary, 796, 845, 850 

incisor, 798 
median, 814, 818, 841, 846, 

854 
metacarpal, 819 

volar, 854 
metatarsal, dorsal, 856 
musculo-cutaneous, 814,815, 

819, 853 
mylo-hyoid, 800, 850 
nasal, anterior, 798 

external, 798, 850 

posterior, 797, 850 
naso-eiliary, 796, 838, 845 
ninth, 771 
obturator, 824 
oculomotor, 769, 773, 780, 

794, 806, 808, 838 
oesophageal, dorsal, 839 

ventral, 840 
of adrenal bodies, 564 
of corium of hoof, 894 
of cornea, 865 
of ductus deferens, 575 
of external ear, 875 
of eye, 859, 860 
of Fallopian tubes, 599 
of heart, 629 
of kidneys, 560 
of penis, 582 
of pterygoid canal, 798 
of skin, 885 
of spermatic cord, 576 
of testicles, 574 
of uterus, 602 
of vagina, 602 
of vascular tunic of eye, 867 
of veins, 615 
olfactoiy, 793 
ophthalmic, 795, 850 
optic, 769, 793 
palatine, 850 

anterior, 798 

greater, 798 

lesser, 798 

posterior, 798 
pectoral, 814, 815 
peroneal, 826 

common, 855 

deep, 826, 841, 846, 855 

superficial, 826, 841, 846, 
855 
petrosal, 802 
pharyngeal, 804, 807, 839, 

852 
phrenic, 813 
plantar, 828, 846 

digital, 841 
lateral, 841, 856 
medial, 841, 856 
metatarsal, 856 
pterygoid, 799 
pudic, 828 

pulmonary, 534, 535 
radial, 815, 816, 841, 846, 

853 
recurrent, 807, 853 
sacral, 828 
saphenous, 824, 855 



INDEX 



923 



Nerve, sciatic, great, 825 
second, 769 
seventh, 770 
sixth, 770 
spermatic, external, 823 

internal, 833 
sphenopalatine, 797, 850 
spinal, 810, 840, 845, 853 
accessory, 771.808, 840 
splanchnic, great, 831, 842 
gi'eater, 856 
lesser, 856 
small, 832, 842 
stapedial, 802 
subscapular, 814 
suprascapular, 814, 815 
sympathetic, 629 
temporal, 803 
deep, 799 

superficial, 800, 838, 845, 
850 
tenth, 771 
third, 769 
thoracic, 820 
anterior, 814 
external, 815 
long, 815 
posterior, 815 
thoraco-dorsal, 815 
tibial, 827, 841, 846, 856 
tracheal, 808 
trigeminal, 770, 795, 838 
trochlear, 777, 780, 794 
twelfth, 771 
tympanic, 804 
uhiar, 814, 817, 841, 846, 

853 
vagus, 629, 771, 773, 805, 
839, 845, 851 
left, 806 
right, 805 
vestibular, 803, 884 
volar, 819, 841 
lateral, 819 
medial, 819 
zygomatic, 796, 850 
Nerve-cell, 760 
Nerve-fibers, olfactory, 769 
Nerve-plexus, 761 
Nervous system, 760, 764, 834, 
843, 847 
sympathetic, 829, 842, 
846, 856 
Ner\'-us dorsahs penis, 828 

transversarius, 830 
Neuroglia, 760 
Neurology, 760 
Neurone, 760, 829 
Nippers, 395 
Nodes, lymph, 616 
Nodules, aggregated, of large 
intestine, 43 
of small intestine, 422, 
487, 501 
lymph, 616 
of thyroid tissue, 536 
solitary, of large intestine, 
431 
of small intestine, 422, 
487 
splenic, 441 
Nodulus, 776 

Nostrils, 508, 537, 545, 548 
false, 260, 508 



Nostrils, true, 508 
Notch, alar, 184 

cardiac, of lung, 533 
carotid, 54 
mandibular, 71 
naso-maxillary, 67 
tt'sophageal, 435 
oval, 54 

popliteal, of tibia, 116 
sciatic, greater, 106 

lesser, 108 
semilunar, of ulna, 93 
sphenoidal, 60 
spinous, 54 
Nuchal crest, 79 

of skuU, 51 
Nucleo-cerebellar fasciculus, 

777 
Nucleus ambiguus, 808 
amygdaloid, 792 
caudate, 792 
cuneatus, 774 
dorsalis, 767 
facial, 801 
gracilis, 774 
hypothalamic, 781 
lenticular, 792 
motor, dorsal, 80S 

of fifth nerve, 776 

ventral, 808 
of lens, 870 

of origin of nerves, 760, 774 
of solitary tract, 808 
olivary, anterior, 776 

posterior, 774 
pulpy, of intervertebral 

fibro-cartilage, 211 
red, 781 

sensory, dorsal, 808 
terminal, of nerves, 760, 774 
Nutrient foramen, 22 

of femur, 112 

of humerus, 88 

of ilium, 106 

of metacarpus, 99 

of tibia. 116 



Obex, 779 

Obturator foramen, 109, 112, 
152, 202 

membrane, 231 
Occipital condyles, .50 

crest, 51 

protuberance, external, 51, 
79 
internal, 57 

sinuses, 688 
Occipito-mastoid suture, 52 
Occipito-temporal fissure, 850 
(Esophageal groove, 458, 473 

notch, 435 

plexus, 808, 831, 8.53 
(Esophagus, 409, 451, 472, 483, 

497 
Olecranon fossa, 90 
Olfactory bulb, 769, 771, 787, 
838, 844, 850 

cells, 895 

nerve-fibers, 769 

organs, 905 

stria;, 769, 788 

tract, 769, 788, 844 



Olivary nucleus, anterior, 776 

posterior, 774 
Olivo-cerebellar fibers, 777 
Omaso-abomasal orifice, 460 
Omasum, 453, 456, 474 
Omental cavity, 442 
Omentum, 412 

gastro-splenic, 412, 417, 441 

greater, 412, 417, 442, 461, 
499 

lesser, 412, 417, 456, 460, 
499 
Ontogeny, 17 
Optic axis, external, 863 

chiasm, 769, 783 

commissure, 769 

foramen, .53, 75, 82 

groove, 53 

papilla, 868 

recess, 783 

tract, 769, 780, 783, 835 
Ora ciliaris retinse, 868 
Orbit, 74 

Orbital foramen, .53, 75 
internal, 53 

region, 74 

wings, 53 
Organ, spiral, of Corti, 884 

vomero-nasal, 514, 895 
Organs of senses, 857, 896, 900, 

902 
Orifice, aortic, of horse, 626 

atrio-ventricular, left, 625, 
626 
right, 621, 623 

caeco-colic, 424 

ejaculatory, 575 

ileo-caecal, 424 

ileo-colic, 501 

naso-lacrimal, 508 

omaso-abomasal, 460 

preputial, 583 

pulmonary, of right ventri- 
cle, 624 

reticulo-omasal, 459 

rumino-reticular, 458 

ureteral, 562 
internal, 562 

urethral, external, female, 
603, 607 
male, 585, 589 
internal, male, 585 
Orificium externum uteri, 601 

internum uteri, 601 
Os acetabuU, 110 

penis, 594 

rostri, 545 
Osseous lab}T-inth, 881 
Ossicles, auditory, 877 
Ossification, 23 

center of, 23 

endochondral, 23 

intramembranous, 23 
Osteoblasts, 23 
Osteoclasts, 23 
Osteogenesis, 23 
Osteology, 20 
Ostium abdominale tuba;, 599 

uterinum tubs, 599 
Otic ganglia, 829 

ganglion, 799, 838 

papilla, 897 
Outlet of pelvis. 111, 112, 413 
Ova, 598 



924 



Oval notch, 54 

Ovaries, 596, 605, 609, 610, 

612 
Ovisacs, 59S 
Ovulation, 598 

fossa, 597 



Palate, hard, 78, 387, 445, 
470, 477, 492 

soft, 388, 446, 477, 492 
Palatine canal, 64 

fissure, 66, 78, 82 

foramen, anterior, 66 
posterior, 65, 76 

groove, 65, 78 

process of inaxilla>, 04, 65 
of premaxilla?, 66 

region, 78 

sinus, 137, 145 

suture, median, 78 
transverse, 79 
Pallium, 785 
Palpebral conjunctiva, 859 

fissure, 857 

sebum, 859 
Pampiniform plexus, 693 

of testicles, 574 
Pancreatic duct, 434, 463, 487, 
491, 501, 506 
accessory, 434 
Panniculus adiposus, 884 
Papilla, 383 

filiform, of tongue, 391 

foliate, of tongue, 391 

fungiform, of tongue, 391 

hair, 886 

incisiva, 387 

of hard palate, 445 

of cheeks, 445 

of Ups, 444 

of mammary gland, 604 

of skin, 885 

of tongue, 391, 447 

optic, 868 

otic, 897 

renal, 565 

vallate, of tongue, 391 
Paradidymis, 573 
Paramastoid process, 50, 78, 

79 
Paranasal sinuses, 84 
Parenchyma of adrenal bodies, 
563 

of hver, 438 

of mammary glands, 604 

testis, 572 
Parietal border of occipital 
bone, 52 

cartilage of nasal ca\'ity, 
510, 537 

crest, 135 

ex-ternal, 51, 57, 73 
internal, 58, 81 

layer, 384, 412 

pleura, 526 

radicles, 693 

region of skull, 73 

suture, 57 
Parieto-frontal suture, 57, 60 
Parieto-occipital suture, 52, 57 
Parieto-temporal canal, 63 
Paroophoron, 599 



Parotid duct, 404, 477, 482, 
492, 495 

plexus, 803 
Pars ciliaris retina;, 868 

disseminata, 589, 592 

iridica retina;, 868 

longa glandis, 594 

optica retinje, 868 
Patches, Peyer's, 422, 487, 501 
Pecten ossis pubis, 109 
Peduncles, anterior, decussa- 
tion of, 778 

cerebellar, 777 
anterior, 776 
middle, 776 

cerebral, 769, 780, 835, 843 

middle cerebellar, 776 
Pelvic cavity, 152, 412, 453 

girdle, 30, 105 

inlet, 152, 160, 181, 202 

limb, lymph vessels of, 703 

outlet," 413 

part of sympathetic system, 
832 

peritoneum, 413 

plexus, 832, 834, 856 
Pelvis, lymph vessels of, 701 

renal, 559 

symphysis, 231 
Penis, 580, 589, 592, 594 

coUum glandis of, 581 

corona glandis, 580 

corpus cavernosum, 581 

fossa glandis of, 581 

glans, 580, 589, 594 

structure of, 581 

suspensory ligaments, 580 

trabeculse of, 581 

tunica albuginea, 581 

vessels and nerves of, 582 
Pericardiac pleura, 526 
Pericardium, 617, 705, 734, 

742 
Perilymph, 881 
Perilymphatic space, 881 
Perimysium, 252 
Periople, 888, 891 
Perioplic corium, 892 
Periorbita, 860 
Periosteum, 21 

alveolar, of teeth, 395 
Peripheral ganglia, 829 
Peritoneal cavity, 411 
Peritoneum, 411, 441 

pelvic, 413 
Permanent teeth, 394, 396 
Petro-basilar canal, 190 
Petrosal crest, 62, 81 

sinuses, dorsal, 688 
ventral, 688 
Petrotympanic fissure, 63 
Petrous ganglion, 804 
Peyer's patches, 422, 487, 501 
Pharyngeal aponeurosis, 407 

isthmus, 408 

opening of Eustachian tube, 
878 

orifices of Eustachian tubes, 
406 

plexus, 807, 852 

recess, 407 
Pharynx, 405, 451, 472, 482, 

497 
Philosophical anatomy, 17 



Phrenico-costal sinus, 530 
Phylogeny, 17 
Pia mater, 763 
cerebral, 763 
spinal, 763 
Pillar, posterior, of soft palate, 

408 
Pillars of rumen, 457 
Pilomotor fibers, 829 
Pinchers, 395 
Pineal body, 781, 835 

recess, 783 
Piriform lobe, 784, 788, 850 
of brain, 769 
recess, 408 
Pituitary body, 769, 780, 782, 
835, 847 
fossa, 53 
Plantar arch, deep, 697, 721 
distal, 678, 697, 719 
proximal, 678, 679, 719 
Plate, cribriform, of ethmoid, 

54 
Pleura, 526, 540, 547 
costal, 526 
tliaphragmatic, 526 
mediastinal, 526 
parietal, 526 
pericardiac, 526 
pulmonary, 526 
visceral, 526 
Pleural ca\'ity, 526 

reflection, diaphragmatic 
line of, 530 
fines of, 530 

sternal reflection of, 530 
vertebral fine of, 530 
Plexus, abdominal, 832 
adrenal, 834 
aortic, abdominal, 833 

thoracic, 831 
auricular, anterior, 803 
basilar, 689 

brachial, 814, 840, 846, 853 
cardiac, 831 
carotid, 804 
external, 830 
internal, 830 
cavernous, 830, 834 
cervical, dorsal, 812 

ventral, 812 
chorioid, 763, 780, 783, 787, 
792 
of fourth ventricle, 773 
coehac, 832, 843, 856 
coUc, 856 
coronary, 692, 831 
dental, maxillary, 798 
dorsal, 692 
gastric, 833 
anterior, 852 
posterior, 852 
ha-morrhoidal, 834 

anterior, 856 
hepatic, 439, 833 
intraosseous, 692 
lumbosacral, 824, 841, 846, 

855 
mesenteric, anterior, 833, 
856 
posterior, 833, 856 
myenteric, 833 
nerve-, 761 
oesophageal, 808, 831, 853 



INDEX 



925 



Plexus, pampiniform, 693 
of testicles, 57-1 

parotid, 803 

pelvic, 832, 834, 856 

pharyngeal, 807, 852 

prostatic, 834 

pulmonary, 808, 831, 853 

renal, 834 

s. sinus venosus scleras, 863 

spermatic, 574, 834, 856 

splenic, 833 

submucous, 833 

subsidiary, 856 

tracheal, 808 

tympanic, 804 

utero-ovarian, 834 

utero-vaginal, 834 

vascular, 614 

venous, 614 

vesical, 834 

volar, 692 
Plica pterygomandibularis, 

390 
Pododerm, 892 
Pons, 769, 775, 835, 843, 847 
Popliteal line of tibia, 115 

notch of tibia, 116 
Portal fissure, 434, 468 

ring, 433 

system, 614 
Post glenoid foramen, 60 

process, 60, 73 
Pouch, cutaneous, 884 

guttural, 879 

infraorbital, 900 

inguinal, 900 

interdigital, 900 

lacrimal, 900 

recto-genital, 415 

recto-vesical, 414 

vesico-genital, 415 
Premaxillary region, 73 
Premolar teeth, 394, 399 

deciduous, 403 
Preorbital region of horse, 76 
Prppubic tendon, 292 
Prepuce, 582, 590, 593, 595 

of chtoris, 604 
Preputial diverticulum, 593 

frenum, 583 

orifice, 583 

ring, 583 
Presylvian fissure, 785, 844, 

849 
Process, acoustic, external, 61, 
74 

angular, of mandible, 195 

caudate, of liver, 434 

ciliary, 866 

clinoid, anterior, 190 
posterior, 170, 190 

coronoid, of mandible, 71 

cuneiform, 517 

frontal, 191 

hyoid, 62 

lacrimal, 194 

lingual, 72 

mammiUary, 45, 163 

mastoid, 61, 74 

maxillary, 194 

muscular, of temporal bone, 
63 

nasal, 65 

palatine, of maxillae, 64, 65 



Process, palatine, of pre- 
maxillae, 66 
paramastoid, 50, 78, 79 
postglenoid, 60, 73 
pterygoid, 54, 171 
spinous, of lumbar vertebrae, 
129 
of thoracic vertebrae, 128 
of vertebrae, 44 
styloid, 63, 871 
of radius, 199 
of ulna, 148 
supraorbital, 59, 73 
urethral, 581 
vocal, 517 

zygomatic, of frontal bone, 
59 
of malar bone, 68 
of maxillary bone, 65 
of temporal bone, 60 
Processus anconaeus, 93 
cornus, 136 
urethra?, 585 
vaginalis, 577 
Projection fibers, 792 
Promontory, 876 
Prostatic ducts, 579, 585, 589 

plexus, 834 
Protuberance, occipital, ex- 
ternal, 51, 79 
internal, 57 
Proventriculi of stomach, 453 
Psoas tubercle, 106 
Pterygoid canal, 54, 67 
crest, 54 
foramen, 54 
fossa, 170 
process, 54, 171 
Pterygo-palatine fossa, 67, 76 
Pubic groove, 109 
Pulmonary circulation, 704 
lobule, 534 

orifice of right ventricle, 624 
pleura, 526 
plexuses, 808, 831,853 
valve, 625 
Pulp cavity of teeth, 395 
of tooth, 395 
spleen, 441 
Pulpy nucleus of interverte- 
bral fibro-cartilage, 211 
Puncta lacrimalia, 860 
Punctum lacrimale, 858 
Pupil, 866 

Pupillary border of iris, 866 
Pvloric opening of stomach, 
"416 

sphincter, 417 
valve of stomach, 419 
Pyramid of medulla oblongata, 
773 
renal, 558, 565 
Pyramidal decussation, -773, 
774 
fasciculus, 776 
tracts of oblongata, 774 



Radiation of corpus callosum, 

790 
Radicles, parietal, 693 

visceral, 693 
Radii lentis, 870 
Radio-carpal sac, 222 



Rami communicantes, 829 

of lower jaw, 70 
Ramus communicans, 811 

gray, 829 
Raphe of oblongata, 774 

pharyngis, 407 

prseputii, 583 

scroti, 574 
Recess, infundibular, 783 

optic, 783 

pharyngeal, 407 

pineal, 783 

piriform, 408 
Recessus cochlearis, 881 

ellipticus, 881 

sphaericus, SSI 
Recto-coccygeus band, 431 
Recto-genital pouch, 415 
Recto-vesical pouch, 41-i 
Rectum, 429, 488, 465, 502 
Red nucleus, 781 
Refractive media of cyebaU, 

869 
Region, cranial, 73, 78 

frontal, of skull, 73 

guttural, 78 

maxillary, of horse, 76 

nasal, 73 

orbital, 74 

palatine, 78 

parietal, of skull, 73 

premaxillary, 73 

preorbital, 76 
Renal columns, 558 

corpuscles, 558, 559 

crest, 558, 559 

hilus, 555 

papilla, 565 

pelvis, 559 

plexuses, 834 

pyramids, 558, 565 

sinus, 555 

tubules, 559 
Respiratory broncliioles, 534 

system, 508, 537, 545, 548 
Restiform bodies, 773 
Rete carpi dorsale, 657 

mirabile, 614, 707 
cerebrale, 710 

testis, 586 
Retia vasculosa, 614 
Reticulo-omasal orifice, 459 
Reticulum of lymph nodule, 
616 

of stomach, 453, 455, 473 
Retina, S68 
Retractor ani, 432 
Rhombencephalon, 773, 785, 

787 , 
Rhomboideus capitis, 371 
Ridge, trochanteric, of femur, 

113 
Rima glottidis, 522, 539, 546 

oris, 477, 491 
Ring, ciliary, 866 

fibrous, of heart, 628 

of intervertebral fibro- 
cartilage, 211 

inguinal, abdominal, 290, 
292 
external, 288, 292 
internal, 290, 292 
subcutaneous, 288, 292 

portal, 433 



926 



INDEX 



Ring, preputial, 583 

of trachea, 525 

vaginal, 290, 576, 587 
Root of hair, 886 

of tongue, 390 

of tooth, 395 
Rostrum of corpus callosum, 
789 

suis, 545 
Rubro-spinal tract, 778 
Rumen, 453, 472 

blind sacs of, 4M 

cardia of, 458 

cavity of, 456 

dorsal curvature of, 454 

grooves of, 454, 455 

longitudinal grooves of, 454 

mucous membrane of, 458 

muscular coat of, 461 

pillars of, 457 

serous coat of, 460 

ventral curvatitfe of, 454 
Rumino-rcticular fold, 457 

groo^•e, 454 

orifice, 458 



Sao, anal, 502 

blind, (if nimon, 454 

(•ani"-mc1acarpal, 222 

(•c,ii,juiicli\:d, S,59 

intercarpal, 222 

intertarsal, 240 

lacrimal, 860 

radio-carpal, 222 

synovial, of hock-joint, 240 

tarso-metatarsal, 240 

tibio-tarsal, 240 
Sacculations of ca>cum, 424 
Saccule, 883 

laryngeal, 522, 550 
Saccus cEecus, 416 
Sacral canal, 43 

crest, lateral, 129 
median, 129 

foramen, 41 
ventral, 129 

ganglia, 832 

part, of sympathetic system, 
S50 
Sagittal pole, 836 

sinus, 687, 688 
Scala tympani, 882 

vestibuli, 882 
Sciatic foramen, greater, 231 
lesser, 231 

notch, greater, 106 
lesser, 108 
Sclera, 863, 897 
Scrotum, -574, 586, 591, 593 
Scutiform cartilage, 871 
Sebum cutaneum, 885 

palpebral, 859 
Secretory fibers, 829 
Sectorial teeth, 494 
Semicircular canals, osseous, 
881 

ducts, membranous, 883 
Semilunar canal of third pha- 
lanx, 103 

crest of third phalanx, 103 

ganglion, 795 

notch of ulna, 93 



Seminal vesicles, 571, 578, 587, 

591, 593 
Seminiferous tubules of testi- 
cles, 572 
Sense organs, 857, 896, 900, 

902 
Sensory fibers, 808 
nucleus, dorsal, 808 
root of fifth nerve, 776 
Septum, dorsal, median, 766 
interalveolar, 64 
intermuscular, 2.54 
of forearm, 305 
of gluteal region, 317, 318 
of leg, 318 
of shoulder, 298 
interventricular, 627 
nasi, S2, 84, 510 

cartilage of, 510 
pellucidum, 791 
penis, 589, 594 
scroti, 574 
Serous coat of bladder, 562 
of Fallopian tubes, 599 
of large intestine, 430, 465 
of hver, 438 
of rumen, 460 
of smaU intestine, 421 
of spleen, 441 
of stomach, 417, 499 
of uterus, 601 
folds, 384 

layer of pericardium, 617 
membranes, 384 
Shaft of hair, 886 
Sheath, carpal, of deep digital 
flexor, 315 
of superficial digital 
flexor, 313 
fibrous, of tendon, 254 
synovial, 253 

digital, of deep digital 
flexor, 316 
of superficial digital 
flexor, 314 
of common digital ex- 
tensor, 307 
of coraco-brachialis mus- 
cle, 300 
of extensor carpi ob- 
liquus, 310 
radialis, 306 
of flexor carpi radialis, 310 
of lateral digital extensor, 

309, 335 
of long digital extensor, 
335 
flexor, 340 
of tibiaUs anterior, 337 
of ulnaris lateralis, 313 
tarsal, of deep digital flexor, 
342 
Shoulder girdle, 29 
Sidebqne, 104 
Sigmoid flexure, 589 
Sinus, cavernous, 688 
communicans, 688 
coronary, 681, 754 
opening of, 621 
ethmoidal, S() 

frontal, 5!), S5, 143, 175, 197 
front u-turljinate, 85 
intercavernous, 688 
lactiferous, 605, 609 



Sinus, longitudinal, dorsal, 687 

ventral, 688 

lymph, central, 616 
peripheral, 616 

maxillary, 84, 144, 175, 197 
inferior, 84 
superior, 85 

occipital, 688 

of aorta, 630 

of bone, 21 

of dura mater, 687 

of lymph nodule, 616 

of pulmonary artery, 629 

palatine, 137, 145 

paranasal, 84 

petrosal, dorsal, 688 
ventral, 688 

phrenico-costal, 530 

renal, 555 

sagittal, 687, 688 

sphenoidal, 53, 145, 175 

sphenopalatine, 53, 67, 86 

straight, 688 

tarsi, 120 

tonsillar, 446 

transverse, 688 

of pericardium, 617 

urethral, 581 

urogenital, 603 

venarum of right atrium of 
heart, 620 

venous, 615 

vertebral, longitudinal, 689 
Skeleton, 20, 32, 125, 156, 161, 
184 

appendicular, 20 

axial, 20 

flat bones, 20 

irregular bones, 20 

long bones, 20 

meduUaiy cavity, 20 

number of bones, 20 

short bones, 20 

splanchnic, 20 

visceral, 20 
Skin, 884, 887, 898, 900, 901, 
903 

appendages of, 886, 901, 903 

of concha, 871 

of eyelids, 858 

of mammary glands, 604 

of nostrils, 509 
Skull, brachycephahc, 195 

dolichocephalic, 195 

mesaticephalic, 195 

synarthroses of, 217 

synchondroses of, 218 
Smegma praeputii, 583 
Smell, organ of, 895 
Snout, 545 

Soft palate, 387, 446, 477, 402 
Sole, 889, 892 

Solitary nodules of large in- 
testine, 431 
of small intestine, 422, 
487 
Space, epidural, 762 

interalveolar, 64, 65, 71, 78 

interdental, 64 

interosseous, of leg, 116 
of radius, 91 

mandibular, 70 

perilymphatic, 881 

subarachnoid, 762 



INDEX 



927 



Space, subdural, 762 

submaxillary, 70 
Special anatomy, 17 
Spermatic cord, 575, 586, 591, 
593 

plexus, 574, 834, 856 
Spheno-frontal suture, 60 
Sphenoidal notch, 60 

sinus, 53, 145, 175 
Spheno-occipital crest, 53 
Sphenopalatine foramen, 65, 
67, 76, 82 

ganglia, 797, 829 

sinus, 53, 67, 86 
Spheno-squamous suture, 61 
Sphincter ani externus, 432 
internus, 432 

cardiac, 417 

ilei, 424 

of mammary gland, 605 

papillae, 867 

pyloric, 416, 417 

vesicae, 562 
Spinal arachnoidea, 763 

cord, 764, 834, 843, 847 

dura mater, 762 

ganglion, 811 

pia mater, 763 

root of fifth nerve, 775 
Spine, ischiatic, 106, 107 

nasal, posterior, 193 

of hoof, 890 

of tibia, 116 

ventral, 26 

of cervical vertebra:', 125 
Spinous notch, 54 

process of cervical vertebra^, 
125 
of lumbar vertebrae, 129 
of thoracic vertebrce, 128 
of vertebrae, 44 
Spiral canal of cochlea, 882 

folds of abomasum, 460 

organ of Corti, 884 
Splanchnic fibers, afferent, 829 
efferent, 829 

ganglion, 832 
Splenial fissure, 844, 850 
Splenic angle, 433 

nodules, 441 

plexus, 833 
Splenium, 789 

Spongy substance of bone, 2 1 
Squamous suture, 58, 60, 61 

temporal bone, 60 
Sternal flexure, 425 

line of pleural reflection, 530 
Stomach, 415, 453, 472, 483, 
497 

cardiac opening of, 416, 472, 
498 

fibers of, 417 

greater curvature of, 416 

lesser curvature of, 416 

mucous coat of, 418 

pyloric extremity, 416 
opening, 416 

serous coat of, 417, 499 

structure of, 417 
Stop of face, 196 
Straight sinus, 688 
Stratum eorneum, 885 

germinativuni, 885 
of hoof, 891 



Stratum granulosum, 598 

tectorium of hoof, 891 
Stria, lateral, 769, 788 

medial, 769, 7S.S 

medullaris, 7M 

olfactory, 7(j9, 788 

terminalis, 781, 792 
Stroma iridis, 867 

of kidney, 559 

of ovary, 598 

of thyroid gland, 536 

vitreous, 869 
Styloid process, 63, 871 
of radius, 19» 
of ulna, 148 
Stylo-mastoid foramen, 62 
Subarachnoid cisterns, 762 

s|)ace, 762 
Siilicallosal gyrus, 788 
Siihcatpal arch, 6,S7 
Sul)cutan('ous inguinal ring, 
288, 292 

tissue, 884 
Subcutis, 884 
Subdural space, 762 
Sublimbic fissure, 786 
Sublingual duct, 405, 496 

fold, 390 
Submaxillary duct, 405 

space, 70 
Submucous plexus, 833 

tissue, 383 
Subserous tissue, 384 
Suhsidiiii-^- iiii'xus, S56 
Sul.splinioidal i-:iiud, 54 
Sulistaiilia uclatinosa of spinal 
cord, 767 

jierforata posterior, 769, 780 

nigra, 780 

propria, 864 
Suburethral diverticulum, 607 
Succus entericus, 421 
Sulcus, callosal, 786 

central, of hoof, 891 

cerebellar, 777 

collateral, of hoof, 891 

intertubercularis, 89 

limiting, of fourth ventricle, 
779 

median, of fourth ventricle, 
779 

muscularis of tibia, 117 

of brain, 771 

omasi, 460 

rhinahs, 785, 837, 844, 850 

sclera-, 863 
Supracondyloid crest, lateral, 
of femur, 112 
medial, of f cmin', 1 1 2 

fossa of femur, 112 
Supraoccipital part of skull, 51 
Supraorbital canal, 137 

foramen, 59, 73 

groove, 137 

process, 59, 73 
Supraspinous bursa, 213 
Suprasplenial fissure, 850 
Suprasvlvian fissure, 785, 837, 

844, 849 
Supratrochlear foramen, 198 
Suspensory ligaments of penis, 

580 
Su.stentaculum tali of fibular 

tarsal bone, 121 



Sutura harmonia, 207 
serrata, 207 
squamosa, 207 
Suture, 207 
cranial, 217 
frontal, 60 
fronto-lacrimal, 60 
fronto-maxillary, 60 
fronto-palatine, 60 
naso-frontal, 60, 67 
naso-lacrimal, 67 
naso-maxiUary, 67 
occipito- mastoid, 52 
palatine, median, 78 

transverse, 79 
parietal, 57 
parieto-frontal, 57, 60 
parieto-occipital, 52, 57 
spheno-frontal, 60 
spheno-squamous, 61 
squamous, 58, 60, 61 
Sympathetic nervous system, 
829, 842, 846, 856 
trunk, 829 
Symphysis, 207 

mandibulae, 72, 218 
pelvis, 231 
Synarthroses, 207 

"of skull, 217 
Synchondrosis, 207 

'of skuU, 218 
Syndesmosis, 207 
Synovial bursa, 253 
" fossa\ 208 
membrane of carpal joints, 
222 
of elbow joint, 219 
of hip joint, 232 
sacs of hock joint, 240 
sheath, 253 

digital, of deep digital 
flexor, 316 
of superficial digital 
flexor, 314 
of common digital ex- 
tensor, 307 
of coraco-brachialis mus- 
cle, 300 
of extensor carpi ob- 
Uquus, 310 
radialis, 306 
of flexor carpi radialis, 

310 
of lateral digital extensor, 

309, 335 
of long digital extensor, 
335 
flexor, 340 
of tibiafis anterior, 337 
of ulnaris lateralis, 313 
Systematic anatomy, 17, 18 



Tabula vitrea, 21 
Tactile hairs, 886 
Ta-nia thalami, 783 
Tapetum, 897 

cellulosum, 902 

fibrosum, 865 

of chorioid, 865 
Tarsal sheath of deep digital 

flexor, 342 
Tarso-metatarsal sac, 240 



928 



INDEX 



Tarsus of eye, 859 
Taste buds, 895 

organ of, 895 
Teat of mammary glands, 604, 

609, 613 
Teeth, 394, 396, 448, 471, 478, 
479, 493 _ 

alveolar periosteum of, 395 

canine, 394, 398, 448, 479, 
493 
deciduous, 403 

carnassial, 494 

cement of, 395 

cheek, 394, 399, 448, 471, 
480, 494 
lower, 401 
upper, 400 

crown of, 395 

deciduous, 394, 403 

enamel of, 395 

eruption of, 403, 450, 471, 
481, 495 

incisor, 394, 397, 448, 471, 
479, 493 
deciduous, 403, 448 

mandibular, 401 

maxillary, 400 

molar, 394, 399 

neck of, 395 

nippers, 395 

permanent, 394, 396 

pinchers, 395 

premolar, 394, 399 
deciduous, 403 

pulp of, 395 
cavity of, 395 

root of, 395 

sectorial, 494 

structure of, 395 

temporary, 394 

wolf, 64, 71, 395, 400 
Tegmentum, 780 
Tela chorioidea, 763, 773, 779, 

783, 787 
Telencephalon, 783 
Temporal canal, 63, 81 

crest, 137 

foramen, 54 

fossa, 73 

wings of horse, 53 
Temporary teeth, 394 
Tendinous center of dia- 
phragm, 287 
Tendo Achillis, 338 

calcaneus, 338 
Tendon, 252 

interosseous, 225 

of ergot, 306 

prepubic, 292 
Tentorium cerebelli, 762 

osseum, 81 
Teres tuberosity, 88 
Terminal line, 110, 410 

nuclei of nerves, 760, 775 
Testicles, 571, 586, 591, 593 

deferential fold of, 577 

descent of, 577 

ducts of, 573 

lymph-vessels of, 574 

pampiniform plexus of, 574 

parenchyma of, 572 

seminiferous tubules, 572 

structure of, 572 

tunica albuginea of, 572 



Testicles, tunica vaginalis 
propria of, 572 

vessels of, 573 
Thalamo-cortical fibers, 778 
Thalamus, 781 
Theca foUiculi, 598 
Thickness of skin, 887 
Third eyelid, 859, 896 

ventricle, 783 
Thoracic aortic plexus, 831 

cavity, 28, 525, 540 

duct, 615, 697, 722, 740, 756 

ganglia, 831, 842 

limb, lymph vessels of, 703 

part of sympath'.'tic system, 
831 
Thorax, 547 

lymph vessels of, 700 
Thyro-hyoid membrane, 518 
Thyroid cartilage, 538, 546, 
515, 550 

cornua, 72 
Tibial crest, 116 
Tibio-tarsal sac, 240 
Tissue, interlobular, 383 

muscular, 384 

subserous, 384 
Tongue, 390, 447, 471, 478, 

493 
Tonsil, 388, 471, 478, 493 
Tonsillar sinus, 446 
Topogi-aphic anatomy, 17, IS 
Torus pyloricus, 485 
Trabecula; carnea> of right 
ventricle, 625 

of lymph nodule, 616 

of penis, 581 

splenic, 441 
Trachea, 523, 540, 546, 550 
Tracheal ducts, 700 

lymph ducts, 725, 756 

plex-us, 808 
Tract, olfactory, 769, 788, 844 

optic, 780, 783, 835 

pyramidal, 774 

rubro-spinal, 778 
Tractus centralis of thymus 

gland, 536 
Tragus, 886 
Tricuspid valve, 624 
Trigonum olfactorium, 769, 
784, 788 

vesicae, 562 
Trochanter major of femur, 
113 

minor of femur, 112 

tertius, 112 
Trochanteric fossa of femur, 
113 

ridge of femur, 113 
Trochlea of femur, 113 

of tibial tarsal bono, 120 
Trochlear foramen, 54, 75 
Trochoid, 210 
True nostril, 508 

vocal cords, 522, 550 
Truncus bicaroticus, 635 

intestinalis, 737 

of corpus callosum, 789 
Tuber calcis of fibular tarsal 
bone, 121 

cinereum, 769, 782, 847 

cox£e, 106 

ischii, 108 



Tuber sacrale, 106 
scapula>, 87 
spinse, 86 
Tubercle, anterior, of tha- 
lamus, 781 
lacrimal, 68 
psoas, l06 
Tuberculum cinereum, 773 
faciale, 773 
olfactorium, 844 
pubicum, 109 
Tuberosity, alveolar, 64, 78 
deltoid, 88 
facial, 137 
maxillary, 65 
of tibia, 116 
Tubules of mammary glands, 
605 
renal, 559 
seminiferous, of testicles, 

572 
uriniferous, 559 
Tunic, abdominal, 288, 361 
fibrous, of eye, 863 
vascular, of eye, 865 
Tunica albuginea, 572, 589 
of penis, 581 
propria of skin, 885 
vaginalis, 576, 586, 593 
communis, 576 
parietal layer of, 574, 576 
propria, 572 
visceral layer of, 576 
Turbinate crest, dorsal, 67 
ventral, 64 
fold, dorsal, 513 
ventral, 513 
Tusks, 479 

Tympanic cavity, 875 
mucous membrane, 878 
opening of Eustachian tube, 

878 
plexTjs, 804 



Umbilical fissure, 435 
fold, lateral, 414 
median, 414 
Ureteral orifice, 562 

internal, 562 
Ureters, 554, 561, 566, 569, 570 
Urethra, 554 
bulb of, 581 
female, 604, 609, 611 
male, 571, 584, 590, 593, 595 
Urethral crest, 585 

orifice, external, female, 603, 
607 
male, 585, 589 
internal, male, 585 
process, 581 
sinus, 581 
Urinary bladder. vSee Bladder 

organs, 554, 564, 567, 569 
Uriniferous tubules, 559 
Urogenital sinus, 603 

system, 554 
Uterine cotyledons, 607 
tubes, 596, 599, 606, 609, 
610, 612 
Utero-ovarian plexuses, 834 
Utero-vagina! plexus, 834 
Uterus, broad ligament of, 415 



INDEX 



929 



Uterus, female, 596, 599, 606, 

609, 610, 612 
masculinus, 579, 589, 592, 

593, 594 
Utricle, SS2 
Uvula, 478 



Vagina, 596, 602, 607, 610, 

613 
Vaginal ring, 290, 576, 587 
Vallate papilla of tongue, 391 
Valve, aortic, 626 
bicuspid, 626 
ileo-ca>cal, 421 
ileo-colic, 501 
pulmonary, 625 
pyloric, of stomach, 419 
tricuspid, 624 
Valvular fold of caecum, 424 
Vas deferens, 575, 576, 591 
Vasa vasorum, 615 
Vascular plexus, 614 

tunic of eye, 865 
Vasomotor fibers, 829 
Vein or veins, 614, 681, 719, 

740, 754 
abdominal, posterior, 696 

subcutaneous, 696, 721 
adrenal, 563, 693 
alveolar, inferior, 684 
auricular, gi-eat, 685 
brachiocephalic, 755 
bronchial, 683, 690, 755 
buccinator, 686, 740 
cardiac, 681 

great, 681, 755 

lesser, 755 

middlo, 681 

small, 682 
central, of adrenal bodies, 

563 
cephalic, 687, 690, 755 

accessory, 690, 720, 755 
cerebellar, dorsal, 689 

ventral, 689 
cerebral, 687, 689 

ascending; 689 

basal, 689 

deep, 689 

descending, 689 

dorsal, 685 

great, 689 

internal, 689 

ventral, 685, 720 
cervical, deep, 682 

inferior, 687 
circumflex, lateral, 695 
coats of, 615 
condyloid, 685 
coronary, 628 

left, 681 

right, 681 
dental, 684 
digital, 692, 721, 756 

common, 692 

dorsal, 720, 755 

lateral, 720 

medial, 720 

volar, 720, 755 
common, 720 
diploic, 687, 689 
dorsal, 682 
59 



Vein or veins, emissarium, 615 
emissary, 687 

facial, anterior amicular, 
684 

transverse, 685, 686 
femoral, 695, 756 

anterior, 696 

deep, 695 

posterior, 696 
frontal, 720 
gastric, anterior, 695 

posterior, 695 
gastro-duodenal, 695 
gastro-epiploic, right, 695 
hepatic, 439, 693 
hypogastric, 695 
iUac, circumflex, 695 

common, 695 

external, 695, 756 

internal, 695, 756 
iliaco-femoral, 695 
iho-lumbar, 695 
infraorbital, 686 
intercostal, dorsal, 683 

ventral, 682 
internal coat, 615 
interosseous, common, 692 
jugular, 683, 719, 755 

external, 720, 755 

internal, 719, 755 
labial, 685 

common, 685 

superior, 720 
lingual, 686 

dorsal, 683 
lumbar, 693, 695 
masseteric, 685 
maxillary, external, 685, 740 

internal, 683, 755 
median, 691 
meningeal, 687, 689 

middle, 684 
mesenteric, 693 

anterior, 694 

posterior, 694 
metacarpal, 692, 720, 755 
metatarsal, 697, 721, 756 
middle coat, 615 
nasal, dorsal, 720, 740 
obturator, 695 
occipital, 685 
oesophageal, 683, 687 
of bladder, 562 
of bone, 22 
of brain, 793 
of corium of hoof, 894 
of cranium, 689 
of ductus deferens, 575 
of external ear, 875 
of Fallopian tubes, 599 
of head, 683 
of internal ear, 884 
of mammary glands, 721 
of neck, 683 
of ovary, 598 
of pelvic limb, 695 
of penis, 582 
of retina, 869 
of skin. 8,85 

of thoracic limb. 690, 720 
of utei'us, 602 
of vagina, 602 
of vascular tunic of eye, 867 
ophthalmic, 686 



Vein or veins, orbital, 720 
palatine, great, 686 
pancreatic, 695 
pancreatico-duodenal, 695 
parotid, 687 
perineal, 721 
phrenic, 693 
plantar, 697 
popliteal, 696, 756 
portal, 438, 693, 722, 755 
pterygoid, 684 
pudic, external, 696, 721 

internal, 57.5 
pulmonary, 534, 535, 614, 

625, 681 
radial, 755 

anterior, 692 
renal, 560, 693 
sacral, middle, 721 
saphenous. 696, 721, 756 
satellite, 614 
spermatic, 574, 576 

internal, 693 
sphenopalatine, 686 
spinal, 689 
splenic, 693, 694 
structure of, 615 
sublingual, tiN7, 720 
subniriital, liSo 
tarsal, jicrforating, 697, 721 

recurrent, 696, 721, 756 
temporal, posterior, deep, 
684 

superficial, 684 
thoracic, external, 690 

internal, 682 
thoraco-dorsal, 690 
thyroid, 687 
tibial, anterior, 696, 756 

posterior, 697, 756 

recurrent, 696 
tracheal, 687 
ulnar, 692, 755 
umbilical, 704 
utero-ovarian, 693 
valves of, 615 
vena azygos, 621, 682, 755 

cava, 614 
anterior, 682 

opening of, 620 
posterior, 692, 720, 755 
opening of, 620 

hemiazygos, 683, 719, 755 

reflexa,"686, 720, 740 

rhinalis posterior, 689 
vertebral, 682, 689 
Velum, medullary, 776 

anterior, 779 

posterior, 779 
Vena comitans, 614 
Venae vorticosae, 867 
Venous arch, 692 
plexuses, 614 
sinuses, 615 
Ventricle, fourth, 778 
lateral, 785, 791 

of larynx, 522, 539, 550 
middle, of larynx. 522 
of heart, left, 625 

right, 623 
of olfactory bulb, 787 
third, 783 
Vermis cerebelli, 771, 776 
Vertebral canal, 26, 44 



930 



Vertebral column, 25, 125, 
156, 161, 184 

curves, 129, 165 

foramen, 26 

formula, 25 

line of pleural reflection, 530 

notches, 26 

sinuses, longitudinal, 689 
Vertex cornete, 864 
Verticalis auriculae, 875 
Vesical plexus, 834 
Vesicles, seminal, 571, 578, 

587, 591, 593 
Vesico-genital pouch, 415 
Vesiculse seminales, 571, 578, 

5S7, 591, 593 
Vestibular ganglion, 803 
Vestibule of ear, 881 

of larynx, 522 

of omental cavity, 442 
Veterinary anatomy, 17 
Vibrissse, 886 



Vidian canal of horse, 54 
Visceral layer, 384, 412 
of pericardium, 617 

pleura, 526 

radicles, 693 
Vitreous body, 869, 897 

humor, 869 

stroma, 869 
Vocal cords. 521, 539, 546, 550 
false, 522, 550 
true, 522 

process, 517 
Vomero-nasal organ, 514, 895 
Vortex cordis, 628 
Vulva, 596, 603, 607, 610, 611, 

613 
Vulvar cleft, 603 



Wall of hoof, 887, 891 
White columns of spinal cord, 
767, 768 



White commissure of spinal 
cord, 766 
line of hoof, 889 
matter of nervous system, 
760 
of spinal cord, 767 
Wolf tooth, 64, 71, 395, 400 



Xiphoid cartilage, 28, 49 



Zone, epigastric, 411 
hypogastric, 411 
intermediate, of kidney, 558 
mesogastric, 411 
Zonula ciliaris, 870 
Zygomatic arch, 60, 73 
process of frontal bone, 59 
of malar bones, 68 
of maxillary bone, 65 
of temporal bone, 60 



-^^0^ 



4 O 



o V 



iO-7- 



c 








